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Operating instructions

METTLERDL21 TitratorDL25 Titrator

. " • _ £ • • •

METRE

Directions and warning noticesfor DL21 and DL25 in compliance with IEC-348

This instrument of protection class 1 has been constructed and tested in compliance withIEC publication 348, Safety Regulations for Electronic Measuring Instruments, and has leftthe factory in faultless condition in regard to safety. To maintain this condition and ensureoperation free from hazards the user must observe the directions and warning notices inthese operating instructions.

The instrument is intended for indoor use. Occasional exposure to temperatures between+5°C and -10°C has no adverse effect on its reliability.

Before switching on, ensure that the operating voltage set on the instrument matches thepower supply voltage.

If this instrument is to be operated via an autotransformer connected to a power supply ofhigher voltage it must be ensured that the base of the transformer is connected to theneutral wire of the power supply.

The power plug may be inserted only in a socket with ground contact. The protectiveaction must not be nullified by an extension lead without an equipment groundingconductor.

When covers are opened or parts removed, except when this is possible by hand, liveparts can be exposed. Connection points may also be live.

Before adjustment, maintenance work, repair work or replacement of parts the instrumentmust be disconnected from all voltage sources if it has to be opened.

It must be ensured that only fuses of the specified type and the specified rated amperageare used as replacement. The use of repaired fuses or shorting of the fuse holder is strictlyforbidden.

If it appears that hazard-free operation is no longer possible, the instrument must be shutdown and secured against inadvertent usage.

't may be assumed that hazard-free operation is no longer possible- when the instrument is visibly damaged-when the instrument no longer operates- after a lengthy storage period under adverse conditions- after severe transport stress.

Table of contents

1.1.11.21.31.41.51.61.71.81.9

2.2.12.22.32.4

PreliminariesIndroductionInstallation procedureSwitching on the instrumentEntering the dateGeneral informationSwitching on the stirrer in the standby modeDisplaying the measuring signalBlocking and unblocking critical key functionsMaintenance

Titrant preparation and dispensingTitrant concentration CONCHow to use the interchangeable burettesFilling the buretteDisDensina

-

6677788899

1010111112

3. Titration 133.1 How to perform a titration 133.2 Printing out additional information 14

4. Titration methods 174.1 How to select, display, change and store methods 174.2 Printing out methods and list of methods 18

5. Adapting the parameters to the titration 205.1 Configuration 205.2 System configuration (configuration parameter 8) 215.3 Configuration parameters 1 through 7 22

6. Result calculation 306.1 Entering and checking the calculation constant CONST 306.2 Special calculations 31

7. The titrant concentration CONC 327.1 Entering CONST REAG 347.2 Performing a CONC determination 34

8. Calibration of the pH electrode 358.1 Performing a calibration 358.2 Manual entry and checking of the electrode parameters 36

9. Dispensing and measurement as a method 379.1 Dispensing 379.2 Measurement 37

METTLER DL21/DL25

10. End point titration 3810.1 Two end points 39

11. p-and m-values 41

12. Acid and base number TAN/TBN 4312.1 Titration according to ASTM D664/D4739 4512.2 Equilibrium titration according to ASTM D2896 46

13. pH stating 4713.1 Data storage and printout 4913.2 Time window 4913.3 Entering the time window 4913.4 How to perform a pH stat titration 50

14. Special evaluation procedures 5314.1 Determination of the minimum/maximum 53

of a titration curve14.2 Titration curves with linear sections 54

(segmented curves)

15. Back titration ^ 5515.1 How to determine the excess 5615.2 How to perform a back titration 56

16. Blank 5816.1 How to determine the blank 59

17. Series titration 6117.1 Sample entry 6117.2 How to perform a series titration 6217.3 Statistical evaluation 6317.4 Checking and alteration of series sample data 6517.5 Series titration without sample entry 6617.6 Rinsing, dosing, titration and conditioning with the 66

ST20 Sample Changer (config. parameters 9, A, B, C)17.7 Manual operation of the ST20 Sample Changer 70

18. Remote control 71

METTLER DL21/DL25

Appendix A: Technical specifications 75

Appendix B: Standard equipment and optional accessories 78Standard equipment 78Optional accessories 79

Appendix C: Installation procedure 86Checking the operating voltage 86Changing the operating voltage 86Setting up the titration system 87Installation and maintenance of the 89interchangeable burettesPeripherial instruments 93Switching on 94

Appendix D: Errors and malfunctions 95Error messages 95Faults, possible causes, remedial action 98

Appendix E: Glossary (Technical terms) 100General terms 100Units 102

Appendix F: Applications and standard method 0 103

Appendix G: Index 104

Appendix H: Configuration data 106

METTLER DL21/DL25

Preliminaries

1.1 Introduction

The METTLER DL25 and DL21 Trtrators are complete analysis stationsfor titrimetric analyses. They enable a titration to be performed andevaluated automatically. Consideration of the sample weight in the resultcalculation allows the analysis to be reported in the desired unit.

A particular feature of the METTLER DL25/21 Trtrators is their simple,easy-to-understand operation. The setup procedure for a particularanalysis avoids the use of technical instrument parameters, which wouldbe unfamiliar to a chemist. In very many cases, a titration can be carriedout with optimum accuracy using just the standard configuration.

Before the start of a titration, a request is made for sample weight andsample identification number. The rest of the procedure is automatic. Abalance and a printer for the result record can be directly connected andno additional equipment is required. Special auxiliary functions supportthe determination of the titrant concentration (titer determination) as wellas determination of the blank value required for certain analyses.

The DL25 Titrator allows storage of 50 complete methods. It is thusespecially suitable for use in situations where a workstation has to be setup for several analyses. The less expensive METTLER DL21 with nomethod storage is particularly well suited to dedicated (single-method)workstations.The DL40GP MemoTitrator has been optimized for certain more complextitrations (method combination). For the determination of water by theKarl Fischer method, the METTLER DL18 Karl Fischer Titrator or theDL40GP MemoTitrator should be used.

When the METTLER ST20 Sample Changer is connected, the DL25/DL21 Titrator becomes a titration station for the automatic analyses of aseries of samples. Up to 20 samples in the standard beaker (100 ml) orup to 14 samples in the larger beaker (250 ml) can be titrated. In additionto rinsing of the titration head inserts after every titration, the ST20Sample Changer also allows versatile sample preparation: dilution,dosing of an auxiliary solution and adjustment of a pH value. Beakers withwash or conditioning solution can be inserted between samples; this-isespecially important in the acid and base number determination ofpetroleum products.The DL25 Titrator allows remote control of a second DL25, and a specialfeature of the instrument is the extremely simple connection to a computer(LIMS, robot,...)

METTLER DL21/DL25

8.8.8.8.8.

d.At 0

1

BE3S

WKKESk\ a |

0

0

6•9

I

7 I

RUN

RUN }

RUN

RESET

or

or

1

Standby

0 MODE

With the exception of a few points in Section 4, these operating instructionsapply to both the DL25 and DL21 Titrator.

1.2 Installation procedure

To install the instrument, please refer to the instructions given inAppendix C.

1.3 Switching on the instrument

As a test, all display elements light up briefly when the instrument isswitched on.

1.4 Entering the date

This can be effected directly after the instrument has been switched on:

The date can be entered directly after the instrument has been switchedon:Entry of day, month and year (3 values) for printout of the date with theresult record:Key in three sets of numbers and confirm each set with [RUN].

[RESET], if the entered values do not have to be changed.

All the indicator lamps of the display column from"WEIGHT"to "BUFFER B"are off.

Entry when on standby without switching the instrument off. The year canbe entered and printed out as a 2- or4-digit number, but appears only asa 2-digit number in the display.

METTLER DL21/DL25

1.5 Genera! information

•*• • • • n't - - " - $ • • n — -

RESET- *,

Standby \

CE

Standby

PARAMETER

StandbyPARAMETER

3

AbortAll operations can be aborted by pressing this key. The burette is filled,if necessary.Any error message must be cancelled by pressing [RESET] to continueworking.

The display is set to zero, orthe last result is displayed again if the titrationdata are still in storage.

Clear entryPress this key to clear incorrectly entered numbers.

Entering a numeric value (CONC, CONST REAG, BLANK, BACK,CONST, METHOD)Type in the= value and press the corresponding parameter key, e.g.[CONC].

Checking the stored value of a parameter (CONC, CONST REAG,BLANK, BACK, CONST, METHOD).By pressing the corresponding parameter key, the stored value isdisplayed until the key is released.

1.6 Switching on the stirrer in the standbymode

SfaRdby

2 RUN4

Standby

This function is used to recheck and adjust the stirring intensity with acontrol knob at the right side of the housing.

Stirrer is switched on.

1.7 Displaying the measuring signal

2

3

Calib

pH £Calib E

Measurement and display of the potential in mV.

or Measurement and display of the potential in pH units.

The stirrer is switched on automatically

METTLER DL21/DL25

. . - V , , • ' • ' I '"**.-«. ' '

A pH electrode must be attached to the DL25/DL21 forthis and calibratedin the manner described on Page 35 (measurement as a method, seeSection 9.2).

Abort by [RESET].

The measuring signal is transferred at rate of 5 values per second to theRS232C interface concurrent with the signal display in mV or pH.

1.8 Blocking and unblocking critical keyfunctions

Standby

1 9 i MODE;

Standby

If the titrations to be performed are always the same, the instrument canbe protected against any accidental change in the methods.

BlockingThe following functions are blocked:

Writing over of CONC, CONST, CONST REAG, BLANK, BACKDetermination of CONC, BLANK and BACKChanging the configuration datapH calibration and writing over of electrode parametersChanging the sample data of the series

8 MODE!UnblockingThe above functions can now be used again.

1.9 Maintenance

ElectrodesThe combination glass electrodes (DG111, DG112) should be cleanedoccasionally first in moderately concentratedacid and then, afterthoroughrinsing, in an ultrasonic bath. See also the Maintenance Instructionspacked with the electrode.

BurettesPeriodic cleaning of the burette cylinder, piston and stopcock and tubingwith ethanol is recommended. Make sure the cleaning solution is neverwarmer than 40°C. Do not dry the parts in an oven! Never place O-ringsor rubber washers in organic solvents. Before immersing a burettecylinder in a liquid, remove the label plate. To clean the tubes, simply runa cleaning solution through them.

METTLER DL21/DL25

The piston head is subject to wear and tear and must be replaced if thepiston seal is no longer tight.To achieve a better seal, the stopcock can be lubricated with siliconegrease. (See Page 79.)Lightly coat the piston rod with the same grease as a protection againstrust.

The assembly of the burette parts is described on Page 90.

2. Titrant preparation and dispensing

2.1 Titrant concentration CONC

Sfandby0

0

CONC

9 8

Sfandby

The titrant concentration (see also definition in the Glossary, 0)is stored in the DL25 Titrator as the CONC parameter in mole per liter(equivalent to mmol/mL). For very accurate titrations, it should bedetermined periodically using a calibration sample (standard solution,primary standard), (see Section 7). If very stable titrants are used, a singledetermination ora manual entry is sufficient. The titrant, its concentrationand the date are inscribed on the label plate of the burette.

Manual entry of the CONC valueEnter the titrant concentration (in mol/L) and press the[CONC] key.

To enter the known titrant concentration, the value normally specified inequivalent /liter (normality) multiplied by the liter should be keyed in.

Example:Normality 0.1 mol/LTiter 0.98

CONC = 0.1 • 0.98 = 0.098 mol/L

Checking the stored CONC valueThe stored value is displayed as long as the [CONC] key is pressed.

10 METTLER DL21/DL25

2.2 How to use the interchangeableburettes

Slide the required interchangeable burette on the holder rack of theTitrator DL25/DL21 and, with the knurled screw turned to the right,position it above the drive. When it is evident that the burette has snappedin, turn knurled screw to the left and tighten slightly in orderto take up theslack between the holder rack and the burette.

For the maintenance of the burette, see Page 9 and Appendix C,Page 86.

After every reagent change, the titrant concentration specified on thelabel plate of the burette must be inputted as CONC value (DL21) orthemethod changed to one with the correct CONC value (DL25).

2.3 Filling the burette

The burette is filled by pressing the [BURET/mL] key. To eliminate airbubbles from the burette, carry out a least three burette strokes (10 mL-burette).

For filling the burette and, in particular, for removal of air bubbles, thefunction [BURET/mL] must be used without input of a quantity. (This is theonly way in which the burette can be zeroed with the stopcock positionedfor delivery.)

If after several burette strokes there are still some air bubbles in thesystem, they can be eliminated by alternately pressing the [BURET/mL]and [RESET] keys and by gently tapping the tubes. If an ultrasonic bathis available, degassing of the solution before use is recommended.

It is often not possible to eliminate small air bubbles directly. Theprocedure outlined below is based on the fact that small bubbles areabsorbed by larger bubbles:

METTLER DL21/DL25 11

Unscrew suction tube of burette and wait until titrant has completelyflowed back into the bottle.

Reconnect tube to the burette.

Rinse burette once as described above (press [BURET/mL] key). Thecontent of the burette is dispensed and the burette refilled. This proceduresucks air out of the tube.

Slide burette out of the burette holder and place it upside down. Shakeit gently until all existing small airbubbles have been completely absorbedby the large bubble. Again install burette.

Again rinse burette 1 or 2 times (press [BURET/mL] and [RESET] keys).

2.4 Dispensing

Standby5

BURET

A reagent can be dispensed rapidly and accurately with the help of the[BURET/mL] function. The burette volume is defined with parameter 4(see Page 28).

Key in the volume to be dispensed in miililiter (mL) (• •decimal point)If no entry, the entire burette contents are dispensed.

' 5 digits plus

The selected 2.5 mL is dispensed. The burette is then filledautomatically.(dispensing as a method, see Section 9.1).


3, Titration

Standby

RUN

HEIGHT-blinking

RUN

RUN

blinking

RUNI

"BUSY"

"RESULT-

TITBATION

METHODWEIGHT B.IDENT

corxc moX/L.conat

RESULT onmoly

RESULT mmoXx

2

251

3559

.1005020.000

' L6.1301

' L6.0950

operator

3 1 01-11-1988

remarks

Appropriate configuration data are necessary for a successful titration.The adaptation of these parameters to the titration problem is describedin Section 5. It should be noted, however, that a major portion of alltitrations can be carried out with standard values.

3.1 How to perform a titration

Entering a weight value: Type in sample weight in g (or volume in ml if notalready taken into account in the calculation constant CONC) and press[RUN]. If a balance is connected, the sample weight is displayed as asuggested value, but you can write over it with the keyboard.

Sample identification. (No request, if no printer, matrixprinter or labinformation system is configured.)

As soon as the titration vessel containing the sample is attached to thetitration head, the titration is started with [RUN].Warning: If the titration vessel is missing, splashing may occur!

The titration is running. The stirrer is switched on automatically. Stirringspeed is adjusted with the control knob at the right side of the housing.During the titration, the signal is displayed according to configurationparameter 1 in mV or pH.

The result is calculated as described in Section 6 and displayed.

ExamplerTitration of 50 mL of a mixture of hydrochloric acid and aceticacid with NaOH, c = 0.1 mol/L, indication: DG111 glass electrode

Titration number (set to 1 every time theinstrument is switched on)

^ 2 0 (seePage31)

1st result: hydrochloric acid content in mmolL

2nd result: acetic acid content in mmol/L

With each titration the DL25/DL21 prints, next to the methods number,parameters 1 and 2, namely type (3) and control (1) and the date of thelast modification (22-07-87). See also Pages 18 and 19.


f^iP$

J RUN

TITRATION

METHODWEIGHT SIDENTo d 11 o in o IL / LJ

START mVRESULT m LE Q . F O T . mVHNV mV

RESULT mmo

RESULT mL'E Q . F O T . mVHNV m V

R E S O L T m m o

2

251

3559.1005020.000

259.93.0498

191.7245.1

1/L.6.1301

3.0323-58 .8124.2

1/L6.0950

3.2 Printing out additional information

Additional information can also be printed out after the titration iscompleted. However, this information can also be included in the auto-matic result record by appropriate selection of configuration parameters1 and 7 (see Page 29). The possibility of subsequent printout is lost if theweight requestfora new titration is initiated with [RUN], the configurationdata are changed with [1] [MODE], or a new method is called up.

Initial signal, consumption, equivalence point potential and halfneutralization value

Result of the last titration is displayed.

Same example as on Page 13.

Titration number

Method numberWeightIdentificationTitrant concentrationCalculation constant

Initial potential of sample solution in millivolt (or pH)1st reagent consumption in mL (without blank correction)Equivalence point potential in millivolt (or pH)Half neutralization value in millivolt (or pH)

1st Result: HCI in mmol/L

2nd Reagent consumptionEquivalence potentialHalf neutralization value

2nd Result: Acetic acid in mmol/L

Titration curve and 1st derivativeThe titration curve and first derivative can be printed with the matrix printer(but not with the printer GA44). The curves shown on Page 15 werereduced in size by 60%. The titration header (from titration number toCONST) which is also printed with every curve has been omitted.


Standby .' ;

5 RUN

6 i RUN

Titration curveResult of last titration is displayed.

Same example

-400

V

2

4

8

10

as

i

ii

i

1

on Page 13

-200 0 200

Ij

//

/

, . • • • • " '

400 nV

First derivative of the titration curveResult of last titration is displayed.

Same example as on Page 13

-1000 -100 0 mV/mL

0

2

4

6

8

10

/

j

• • .

1

The derivative is shown on a logarithmic scale to allow even smallinflections in the flat part of the titration curve to be seen. (Exception:segmented curves, see Section 14.2).


RUN

Table of measured values of the titration curveResult of the last titration is displayed.

Same example as on Page 13.

Volume

VOLUME

mL

.28560•43860

.50060

.64060

4 .1400

4 .20504 OfiSfl^ a .*_ W ••* r—1

4 .32504 • •pTf i

4 ..J/564 .4200

4 .46504 .5100

4 .55504 A4RPi" « '_* ~ v —

4 .71604 .7550

4 .8058

4 .85504 .9058

4 .95585 . Pi Pi 5 0

Fl .P i55Pi

c i --i M ATj . 1 j i ri £1

5 .2358

A. ,3258A..4908

£ p " p fS

7 ,828@

y • J JL y y

3 .3286

9 .3268

GA44 record

1st Derivative

DERIU.

mU/mL

-3 .9366-5 .4348— ̂ 0171

-4 .6450

-125 .72

-127 .27_ 1 O 1 '• -•

-142 .38* .- . * ~

— * 7 7 A 7

i •-' *. . '-• J.

-198 .84

-146 .22-117 7 1

-197 .13_ =: -i =. -?=.

-1942 ,4— I i^, M -? . ^

_=;;-;=: ̂ 77

~ O ̂ 1 '-1 = :"' ~̂

— • • 7 5 = 3 1

- r '- ' ~" ~ "-'

t , -~ i < ^L :• .' f

— 1 . /':-^ ̂ , 'A

— ' . y :~* A!~;

Volume

VOLUMEmL

. 0 0 0 0 01.25001.75002.00002.34002.57002.74002.87002.98503.09003.19503.31503.45003.61503.80504.03004.28004.52004.77005.01005.21505.40505.55005.67505.77005.85005.91005.97006.03006.09006.15006.21006.27006.33506.40006.46506.53006.60506.69006.81007.00007.20507.60508.05508.55509.05509.5550

Dot matrix

Increment

INCREMENTmL

.000001.2500.50000.25000.34000.23000.17000.13000.11500.10500.10500.12000.13500.16500. 19000.22500.25000.24000.25000.24000.20500.19000.14500.12500.09500.08000.06000.06000.06000.06000.06000.06000.06000.06500.06500.06500.06500.07500.08500.12000.19000.20500.40000.45000.50000.50000.50000

printer record

Signal

SIGNALmV

259.9249.1241.8237.0228.3220.0211.8204.1196.3188.8181.6173.9166.4158.3150.3142. 1133.6125.7117.6109.2101.392. 885.076.568.559.751.038.615.8

-70 . 1-125 .3-147.9-164. 4-179 .0-191.4-201 .9-210.5-218.8-226 .3-234. 1-243.4-250 .5-260 .3-268 .3-274.7-279 .5-283.6

Signal change

S.CHANGEmV

- 1 0 . 8- 7 . 3- 4 . 8- 8 . 7- 8 . 3- 8 . 2- 7 . 7- 7 . 8- 7 . 5- 7 . 3- 7 . 6- 7 . 5- 8 . 1- 8 . 0- 8 . 2- 8 . 5- 7 . 9- 8 . 2- 8 . 4- 7 . 9- 8 . 5- 7 . 8- 8 . 4- 8 . 0- 8 . 8- 8 . 7

- 1 2 . 4- 2 2 . 8- 8 5 . 9- 5 5 . 2- 2 2 . 6- 1 6 . 5- 1 4 . 6- 1 2 . 5- 1 0 . 5

- 8 . 6- 8 . 3- 7 . 5- 7 . 8- 9 . 3- 7 . 1- 9 . 8 *- 8 . 0- 6 . 4- 4 . 9- 4 . 1

1st Derivative

DERIVATIVEmV/mL

- 8 . 6 2 1 8-14.695-19.146-25.666-35.913-43.189-59.511-67.668-71.173-69.131-63.733-55.780-48.970-42.141-36.568-33.870-32.828-32.636-34.864-38.428-44.823-54.062-67.452-84.119-110.50-144.95-206.93-379.23-1431.7-920.45-376.81-274.68-224.30-191.61-161.81-131.56-110.26-88.346-65.212-49.206-34.567-24.501-17.687-12.724-9.7144-8.2330


4. Titfation methods

This Section does only partly apply to the DL21 Titrator, which has no me-thod storage facilities, except for one method.

The M ETTLER DL25 Titrator allows storage of 50 different methods. Theterm "method" is defined in these Operating Instructions as follows:

A method comprises all the information necessary forthe performanceand evaluation of a titration.

Such information includes the complete configuration list (see Page 18),the titrant concentration CONC (Page 10), the associated constantforthestandardization CONST REAG (Page 32), the calculation constantCONST (Page 30), the blank value BLANK (Page 58), and for backtitrations the excess BACK (Page 55). These parameters, in particularCONC, are components of the method. If the same titrant is used inseveral methods, CONC must be inputted separately in all these methods.The calibration data of the electrode (or buffer values with TAN/TBN) arevalid for all methods. In other words, when the electrode data arechanged, they are altered automatically in all relevant methods.

A method with optimized parameters forthe relevant titration is set up forevery analytical procedure in an appropriate manner. This can beeffected by changing the standard parameters (method 0) or by changinga similar method.

The DL25 stores 15 standard methods. They are described in detail in theApplication Brochure DL25. See page 78.

When the instrument is switched on, the method last used is active. Thisalso applies to a provisional method.

4.1 How to select, display, change andstore methods

Standby ,n |.

METHOD• • •METHOD

•

Method n (0...50) is selected and can be used forthe analysis. It can nowalso be displayed or altered. The instrument is in the standby mode.

The current method number is displayed for as long as the [METHOD] keyis pressed.

Method 12 is active.


n I SAVE

SAVE

By changing a configuration parameteror another critical parameter, e.g.CONC, the method becomes provisional. If an attempt is made to displaythe method number, the display shows:

Provisional method

The method is stored underthis number (n = 1 ...50). Successful storageis acknowledged by an audio signal.

The number is occupied (occ = occupied)

The old method is overwritten. If the current method should not beoverwritten, abort with [RESET] and enter a new number.

4.2 Printing out methods and list ofmethods

The current method is printed out.

METHOD

d<=a-fce? O 1 — 11 —

cz o n a m o l / Lc o n s t r~ «= 3L CJto «si c: l< m m a 1b 1 a n k mmcslconst

CO MR" I <3LJF?«T I ON

1 TYPE2 CONTROL-3 PREDOSING^ BUR/MAXVOL

6=, S T IF? T I ME~7 O U T P U TS S V S T E MS> S T 2 O COND^ RINSE TIMEO F? I MSE DOSC DOS T I M E

pHO pMSLOPE mV/pM

25

S S

.10050

.20420

.00000

.0000020.000

V2.0

3

12

10

05

800101

05

15

0

7.000-59.2

Method number

Date of last change

Titrant concentration in mol/LConstant for CONC determinationExcess for back titrationBlank valueCalculation constant

Software version

Titration typeControl and measured value acquisitionPredispensing (or duration for pH-stat)Burette + maximum volumeEnd point, threshold, dispensing or inactiveStirring timeResult calculation + representationSystem + peripheral unitsSample changer + conditioningRinsing timeDisp. time 1 for pump RINSE (or pH-stat time interval)Dispensing time 2 for pump DOSE

Zero point of electrode assembly pH0

Slope


MODE]

neiTMOD n o .

X

2 53<i>

3 7

3 S3 S >

^ - O

4 1

^ - 2

^ 3

^ 5

-̂<£=,

4 7

^ - O

5 O

type

1 0 1

33 3

90307014

1

40111001300310011001100110052001

1

14

1

control

315011

2

1 0 2

2

2

12312347111110221011

3 1

20111104

21

date

14-10-8801-11-B800 00 0001-11-8800 -OQ. 0000 00 00

00 00 00

0&-09-8B

00 00 00

29-10-38

00 00 00

00 00 00

00 00 00

00 00 00

00 00 00

00 00 00

00 00 00

inactive configuration methods are characterized by the absence of textin the method printout. The numeric value is then meaningless (e.g.configuration parameter 5 in the above example).

The list of stored methods is printed out (with the exception of thestandard method 0 and any provisional method). In addition to themethod number, parameter 1 for the titration type (type), parameter 2 forthe control (control), and the date of the last change are printed out.

Methods36...50areMETTLER standardmethods (date 00 00 00), which can atany time be deleted or modified, such asmethods 46 and 47.

0

25

METHOD

SAVE

occ | 25

Clearing methodsA method is cleared by loading method 0 (standard parameters) andstoring it in place of the method to be cleared. To clear method 25, forexample:

Call up method 0.

Method number 25 is occupied.

Method 25 is cleared (comprises standard parameters only).

SAVE


5. Adapting the parameters to the titration

5.1 Configuration

RUN

A series of operating data must be entered in the DL25/DL21 for eachtitration. Those configuration parameters (1...7) which allow adaptationof the instrument to a titration problem as well as definition of the resultrepresentation are described in detail on Page 22. The parameters (9...C)needed for operation with the sample changer are described on Page 66.The present Section describes the configuration parameters associatedwith the manner in which the system is set up. A listing is tabulated inAppendix H or on the memo card.

Entering the configurationIndicator lamps "WEIGHT" to "BUFFER B" are off.

Recalling the configuration dialog.

The first number indicates the configuration parameter we are dealingwith (1: titration type etc.). The last four digits represent the current data.These data can now be simply confirmed or overwritten. The descriptionof the configuration data is summarized in Appendix H, Page 106.

After an entry or to confirm an old value, press the [RUN] key.

RESETS

The next parameter appears in the display.The entire set of parameters can be run through several times.

The configuration dialog is concluded by pressing the [RESET] key.

Please note: If the instrument cannot be configured in "Standby" with keysequence [1 ] [MODE], the critical functions are blocked. These must firstbe unblocked with key sequence [8] [MODE] (see Section "Blocking andunblocking critical key functions", Page 8).


mm

5.2 System configuration(configuration parameter 8)

Configuration parameters contains details of the peripheral instruments(except balance and recorder) connected to the Titrator DL25/DL21 :

Output devices:

P8: • • • 0 No output device

P8: • • • 1 Matrix printer (EPSON or compatible) to CL serial interface, 2400 baud,

8 bit, without parity check, at least 2K data buffer

P8: • • • 2 Lab data system to RS232C interface*, 2400 baud, 7 bit, even parity

P8: • • • 3 Matrix printer to CL serial interface and lab data system to RS232Cinterface, as above

P8: • • • 4 Printer to CL serial interface METTLER GA44, 2400 baud, 7 bit, evenparity

P8: • • • 5 Printer to CL serial interface and lab data system to RS232C interface,as above

Active peripheral units to RS232C interface:(In these system configurations, a lab data system can be connected tothe CL serial interface and configured in the same manner as a printer.)

No sample changer

ST20 Sample Changer is attached. If an error appears, the series isaborted and an error message outputted (ERRORS 30-33).

T20 Sample Changer is attached. If an error appears (ERRORS 30-33)the result is set to zero and the series run to completion.

P8: • 3 • • The same as • 2 • • but with errors 30-34 the table of measured valuesis printed out to provide a clue to the cause of the error.

P8: A • 0 • Titrator DL25/DL21 to be configured (master) is connected to a second,subordinate Titrator DL25/DL21 (slave)Device code A = 2, 3 or 4 (same code as for configuration of thesubordinate instrument)

P8:0 0 A • Titrator DL25/DL21 is subordinate to other active instrument (slave).Device code A = 2,3 or 4

P8:«

P8:«

P8:«

1 • •

2 "


* If the request-to-send line is not active, the data to be transferred arestored in the internal buffer storage (ca. 180 characters) of the DL25/DL21. If this is overloaded, the last string is replaced by CR/LF.

In addition to the reagent concentration CONC (see Page 10) andcalculation constant CONST (see Section 6, Page 30), the properselection of configuration data 1 through 7 is important forthe achievementof correct results. Below you will find a detailed description of thepossibilities provided by the METTLER Titrator DL25/DL21.

With the configuration parameters 3,5, A, B and C the numberfor a singlepositive value is with or without decimal point. These parameters aremarked in what follows with XXX.X.

In certain parameters, each digit has its own particular significance. If inwhat follows only one digit is addressed, the other possible digits aremarked with a •.

Example: P1: • • 1 •. Of the four possible digits, the 2nd digit from the rightof the parameter 1 is addressed.

5.3 Configuration parameters 1 through 7

(Configuration parameter 1) Titration type

P1: • • • 1 Titration to the first equivalence pointIn by far the majority of cases, universal titration mode 1 can be used toachieve yourobjectfve. The titrant is added in variable increments whosesize depends on the dynamics of the signal change (dynamic titration).At the same time, the data of this titration curve are checked for thepresence of an equivalence point. If an equivalence point is found, thetitration is stopped and the result is calculated. Only equivalence pointswith a 1st derivative greater than 20 mV/mL are detected.

P1: • • • 2 Determination of the steepest jump *Titration mode 2 is used if the titration curve exhibits weaker inflectionspriorto the actual equivalence point, and determination of these inflectionsis not required, orif the whole titration curve isto be recorded. The tit rationis stopped when reaching the maximum volume (see Page 28).

P1: • • • 3 Determination of all equivalence points *Titration mode 3 allow the determination and evaluation of all reco-gnizable steps of a titration curve up to the maximum volume.Caution: In this case, it is recommended to do a plausibility check bymeans of the titration curve or the table of values!


P1:

P1:P1:

P1:

P1:

2«1 •

• •

• •

•7• 7

• 8

• 9

P 1 : • -1 •

For the determination of the end point an iterative evaluation procedureis employed that utilizes the theoretical profile of the titration of a strongacid with a strong base as a model. If the titration curve shows majordeviations from the typical S-shape, the iterative procedure can fail. Insuch cases the inflection point of the curve is determined by cubicinterpolation. This is indicated in the result printout by the text"interpolation". The procedure also fails if the sign of the first derivativechanges immediately before or after the volume increment with thegreatest slope. In this case the warning «deriv. sign change»is outputtedin the result printout.

End point titration: positive end point (generally in pH)!negative end point(possible onlywith mV unit ofmeasurement)

If the end point of a titration is prescribed by a standard method orfor otherreasons, titration mode 4 or 5 is selected, depending on the sign of theend point. The titration runs in a manner similar to the titration to anequivalence point but the size of the increments in the vicinity of the endpoint (end point ± 1 -5°AE8J (see P2: • X • •) is reduced to single pulsesof the burette. The end point is entered as configuration parameter 5(Page 28).

Dispensing in mmol, when P7: • 9 • • dispensing in ml (Page 12)

Determination of minimumDetermination of maximum. The minimum/maximum determination is anequivalence point titration with the special abort criterion of an absoluteminimum or maximum (see Page 53)

Evaluation of segmented titration curves (Page 54)

Measurement:The signal is measured and recorded in mV or with P1 :• • 19 in pH. Seriescan also be measured and statistical evaluations performed.

* The data storage can accommodate information for maximum 120dosed increments. Equivalence points can therefore only be recognizedand evaluated if they lie within the last 120 increments.

Measured variable millivolt

Measured variable pH:There are various reasons for converting the measuring signal to pH: theinitial pH may be of interest as analytical information and a printout isrequired (see Page 29); or, for a given titration, the end point ispredetermined in pH. In all cases, it is prerequisite that the calibration dataof the electrode are determined automatically or inputted correctly (seeSection 8, Page 35). The titration curve should be scaled in pH units.


P1: • • 2 • Measured variable millivolt and determination of the half neutralizationvalue (HNV).

P1: • • 3 • Measured variable pH and determination of the half neutralization value(HNV).

P1: • 1 • • High resolutionIn a titration to the equivalence point, it is possible to have the incre-mentin the steep region of the titration curve reduced to 1/1000 of the burettevolume (1/2000 in an end point titration). Under standard conditions(• 0 • •). the increment does not fall below 1% of the volume alreadydispensed. With 5 mL, not below 0.05 mL; with 20 mL, not below 0.2 mL.Thanks to the evaluation logarithm, the time saving in the majority ofcases is considerable yet a very precise result is still obtained.

P1:0 • • • Standard parameter:The value of the threshold which must be exceeded before an equivalencepoint is recognized is 20 mV/ml. If the value of the first derivativeincreases twice and then decreases twice and if the maximum is greaterthan the threshold value, an equivalence point is recognized.

P1:1 • • • or 2 • • • Tendency and thresholdIn most titrations the equivalence point is clearly defined. Specification ofthe tendency (direction of the potential change in the region of theequivalence point = sign of the derivative) is unnecessary. With certaintitrations, the direction can change during the titration and the tendencyneeds to be specified. Probably a more common reason for indicating thetendency is that a value different from the standard value is required forthe threshold (see below). When the tendency and threshold are specifiedthe measuring signal unit (mV or pH) must be noted. Tendency andthreshold should be set only in awkward situations since the conditionsforthe equivalence point recognition are less strict than with the standardparameter. An equivalence point is recognized when the tendency iscorrect, the value of the first derivative is greater than the threshold andthe subsequent value of the first derivative is smaller.

P1:1 • • • Positive tendency:Titrations with acids (mV), bases (pH), silver nitrate, oxidizing agents

P1:2 • • • Negative tendency:Titration with bases (mV), acids, reducing agents


J «,,„, J^ /•

When specifying the tendency, it is mandatory to also define the thresholdin parameter 5. The threshold is used principally to prevent relativelysmall disturbances in the curve being mistaken for an equivalence point.The first derivative must be Iargerthan the threshold to ensure recognitionof an equivalence point. Typically, half of the greatest value of the firstderivative is advisable for the value of the threshold, (see table ofmeasured values and 1st derivative of the titration curve).

P5: XXX.X Threshold in mV/mL or pH/mL (parameter 5)

Special titration modes

P1:X- -« (X-3. . .9) see sections 13,12,15and 11.

(Configuration parameter 2) Measured value acquisition, time response and control

In the standard case, regulation of the titrant addition by the Titrator DL25/DL21 is dynamic and equilibrium controlled. This means that the titrantcan be added in variable increments (volume steps). A constant potentialchange AEset, defined in parameter 2: • X • • is aimed for. This is achievedby varying the increment size. The minimum increment (AV^) is definedby parameter 1 (• 0 • • or • 1 • •); the maximum increment ftV^J byparameter 2 (X • • • ) .With large volumes the minimum increment could be greater than themaximum increment. The maximum increment has priority. Before anincrement is added, the measuring signal must have stabilized (showminimal drift, have attained equilibrium), parameter 2: (• • • X). However,the next increment is added at the earliest after a minimum time ( t^) andat the latest after a maximum time ( t ^ ) . The time window is defined inparameter2 (• • X •). The increments can, however, also be added at fixedtime interval (parameter 2: • • X •) if need be.

P2:1 StandardIn the standard case, it is assumed that both the response of the electrodeand the reaction under study are sufficiently rapid.

P2: • • • X Equilibrium (Drift)The equilibrium conditions must be adapted to the reaction type. Withlarge jumps (100...500 mV), an equilibrium of 1 mV/s or 0.5 mV/sgenerally suffices.With small jumps, the drift should be limited to 0.25 or 0.1 mV/s.


Parameter 2 Drift

1234567

1 mV/s0.5 mV/s0.25 mV/s0.1 mV/s0.25 mV/s0.1 mV/s0.5 mV/6 s (oil)

1.5 s1.5 s3S4.5 s6s7.5 s18 s

P2: • • X • Time conditionThis parameter is used to define a time window (tmfct...tm-x). The minimumtime (t^J is as well determined by the equilibrium condition selected (seePage 25). Proper choice of the time window not only prevents anincrement being added too early (after only apparent attainment of theequilibrium) but also means that an unnecessarily long waiting time canbe avoided. Virtually without exception, times longer than the standardtimes are needed only in redox titrations.For optimum selection of the two parameters equilibrium and timecondition, please see Appendix F.For optimum determinaton of these parameters for an unknown andsensitive titration, it is advisable to connect a line recorder to the analogoutput and to observe the course of the signal as a function of time in apreliminary experiment with stricter parameters.

Parameter 2

• • 0 •• • 1 •• • 2 •• • 3 *• • 4 •

1.5/3/4.5 S6S12s8S3S.

tmax

20 s60s120 s24 s90s

*tmjn from the equilibrium condition is used if it is greater.

In certain cases a fixed time interval is specified or recommended forother reasons. The equilibrium condition is naturally ignored in this caseand can be set to zero (e.g. P2..50). A timed increment titration isperformed.

Parameter

. - 5 -• • 6 •. . 7 .• • 8 •«• 9 •

Time increment

3s10s20 s30 s90 s (oil titration)


.£a&sJtkj&riiiiirJ£tsAH&e&*J!

P2: • X • •

P2: X • • •

If a fixed time increment is specified, the equilibrium condition (P2.. .X) ismeaningless. It can be setted to zero e.g. (P2.-...10).In the standard case, the DL25/DL21 Titrator controls the titrant additiondynamically to a set potential change AE^, (also called anticipation) of 8mV. In the case of a small, steep jump better control is achieved bylowering AE^, to 4 mV. An acceleration can be achieved by raising AE^to i6mV.

Parameter 2 AE•sal

•0'1•2•3

8mV4mV16 mV30 mV

standardslowerfasteroil titration

(8 mV with blank determination)(8 mV with blank determination)

Maximum increment(X = 0 • • • to 3 • • •)The standard value of the maximum increment ( A V ^ = 5% of the burettevolume) assures optimum, rapid control in most applications, especiallywith sigmoidal curve profiles. With titration curves which begin flat andthen exhibit a large, steep jump, there exists a danger of overshooting.As a precaution, the maximum increment in this case is reduced to 2%of the burette volume or even less.

Parameter

0 • • •1 . . .2 . . .3 - - «

5 %2 %1 %0.5 %

standardsteep curve

Fixed increment(X = 4 • • • to 9 • • •)Fixed volume increments are specified in various standards andapplications.

of the burette volume

(0.5% in blank determination)(0.5% in blank determination)(0.5% in blank determination)

Parameter

Af • • •

5 — «6 • • •7 . . .8 . . .9 . . .

AV

0.1 %0.2 %0.5 %1 %2 %5%


(configuration parameter 3)

P3: XXX.X


P4:X

P4: • X X X

(configuration parameters)

P5: X X X.X

Predispensing

Before the controlled titration, the tit rant volume inputted in ml is dispensedin 3 increments. This allows a reduction in the titration time. In general,a small predispensing is advisable (standard value 0.5 ml) since theelectrode potential at the start of the titration often changes drastically oris poorly defined. This in turn could cause detection of a false equivalencepoint at the start of the titration.The equilibrium conditions also apply to the predispensing, which occursin three steps.P3 has a different meaning with pH stat (see page 47).

Burette volume and maximum volume

This is the abort criterion for titration types 2 and 3 as well as theemergency termination for titration types 1, 4 and 5 with error mes-sage 31.

Input of the burette volume:

10 mL20 mL5mL1 mL

(DV910)(DV920)(DV905)(DV401)

0123 '

standard

input of the maximum volume

P4: 10 10 mL standardExample: 1010 (20 ml burette)

Maximum volume of 1...999 mL (whole mL only)

End point (P1: • • • 4 or • • • 5)

The end point potential is indicated in mV orpH. (The sign is defined bythe titration mode, configuration parameter 1.)

Dispensing (P1:6 or 16)

Dispensed amount in mmol or ml (P7: • 9 • •)

Threshold (P1:1 • • •, 2 • • • and 3 • • •)

With special modes 1,2 and 3: threshold in the derivative in mV/ml or inpH/ml



P6: X X X X

Stirring time

Before measurement of the initial potential and before the start of thetitration a stirring time in seconds can be selected. The stirring time allowshomogenization and dissolution of the sample.


P7: • • X X

P7: 0 • • •

P7:1 • • •

P7: 2 • • •

P7: 3 • • • to 9 • • •

Representation of the results

No curveTitration curve (pH stat: volume against time)1st derivative of titration curveTitration curve and derivativepH stat: signal against timepH stat: volume, derivativeand signal against time

No additional dataInitial signal (unit pH or mV according toP1: • • X •), consumption in mlTable of measured values + IS + V

•0• 1• 2• 3

' 4

12

The table of measured values of the titration curve is printed out innumeric form. The raw result in milliliter and the equivalence pointpotential in mV or pH are also printed out.The records generated using these possibilities correspond to theexamples shown on Pages 14 to 16.All the information, except the curves, specified here is also available atthe RS232C data interface if a lab information system has been configured(see Page 21).Each protocol 2 ends with ASCII character CTRL Z (ASCII hex 1 A).

Audio signal (beep)

Keying, result, errors and inadmissible entries are signalled audibly.

Only the result, errors and inadmissible entries are signalled audibly.

No audio signal.

Complex calculations. Audio signal as 0 • • •.

System configuration (configuration parameter 8)(See Page 21)Series titration (configuration parameter 9, A-C)(See Section "Series titration", Page 66)


In the standard case, the result is calculated according to the folio1

formula:

RESULT= CONST- 1 • V • CONCWEIGHT

V = titrant consumption up to the equivalence point in milliliter (mL;V • CONC = raw result in millimoleCONST = calculation constant to convert the raw result into the des:unit. It can be determined in accordance with the Table on Page 31Weight = weight (or volume) of the sample.

For more complex calculations, see Page 31 ; for the calculation of btitrations, see Page 55. The blank correction is described on Page £

CONST

Standby

6.1 Entering and checking the calculationconstant CONST

Type in the value of the calculation constant and press [CONST] ke

Without entry the stored value is displayed as long as the key is press

The parameters for the result calculation and forthe units (P7: • X • •)described on Page 31.

For determination of the calculation constant CONST the approprieformula for the desired result unit can be found in the following table


Definition of the result unitSuitable selection of parameter 7: -unit with the result.

X • • allows printout of the associated

il

Parameter 7

• 0 • ••1 ••.2"• 3 "• £^ • •

• 5 - »> 6 • •• 7 "• 8 • •• 9 • •

Result unit

nonemmol%ppmmg/gmg/Lg/Lg/100mLmmol/LmL

CONST

freely selectable1M/(10«z)M-1000/ZM/zM-1000/(z«U)M/(z • U)M/(10«z»U)1000/(z«U)1

M: molar mass of sample (g/mol)Z: valence of sample (relative to titrant)U: volume of sample solution (mL). This quantity can also be inputted

in place of the weight: V = U.U does not then appear in the formulafor CONST!

6.2 Special calculations

As a supplement to the standard content calculation, there is a possibilityto calculate additional results automatically. They always follow thestandard result, are characterized by a special name and are printed outwithout unit. The nature of the special calculation is defined in parameter7. Reciprocal values, ratios of and differences between the last tworesults and actual value minus set value can be determined. Thesespecial calculations take results which are generated in a slave DL25/DL21 also into account.

Equation and meaning Parameter 7

1 / result = reciprocal value 3 • • •last result / penultimate result 4 • • •penultimate result / last result 5 • • •last result - penultimate result 6 • • •penultimate result - last result 7 • • •resuit - set value 8 • • •penultimate result + last result 9 • • •

Designationin printout

reciprocallast R/prev Rprev R/last Rlast R - prev Rprev R - last RR - set Rprev R + last R


feu.

Note: The penultimate result must originate from the same determinateas the last result. If it is generated by the "slave" it must be ensured ththe "slave" uses the same constant and result unit as the "master". If tfpenultimate result is missing, neither a special calculation is performenor a special result printed out.In the "actual-set" determination (8 • • •) the back titration is not possibsince the set value must be defined in the BACK memory.These special calculations are not possible in the determination of theand m value (see Section 11) or in the determination of the acid and basnumber (see Section 12).

The titrant concentration CONC

The titranteoncentration is stored in the DL25/DL21 Titratoras parameteCONC in mole per liter (mol/L). A CONC determination automatical!overwritesthe old value.(Formanual entry of CONC, see Page 10.) Whethe burette is changed, a method with the correct value must btemployed.

The titrant concentration is determined by a special titration of a standardsubstance (primary standard). To obtain the automatic conversion of thtitrant consumption to the desired concentration, a special calculationconstant CONST REAG is used:

CONC = - 1 .WEIGHT

CONST REAG =

CONST REAG V

V = titrant consumption up to the equivalence point in milliliter (mL)

The calculation constant is determined according to the following formu la

With pure primary standard. Q. ~ ^ A" ^M1000'Z

1c*z

1U*cz

With a standard solution of known concentration c, thevolume U used is entered as WEIGHT.

With a standard solution of known concentration cWEIGHT = 1 .

M: molar mass of sample (g/mol)z: valence of sample (relative to titrant)c: concentration of standard solution (mol/L)U: volume of standard solution used (mL)


• * -

Of,

£ I« |i I

i

The titration is influenced by the same configuration parameters as thestandard titration. However, in the CONC determination, the back titrationmethod is not allowed: a value stored in the BACK register is ignored.Moreover, the blank value stored in BLANK is not incorporated in thecalculation. Furthermore, in place of the determination of all equivalencepoints (P1: • • • 3 ) , a titration to the first equivalence point (P1: • • -1) isperformed. The control parameters as well as threshold and tendencyare, however, taken into account. In the majority of cases, this allows aCONC determination to be performed without changing the conf iguration.

If these restrictions are not acceptable, CONC can be carried out with astandard titration. The special calculation (parameter 7:3 • • •) likewisegenerates a reciprocal result (set CONC = 1).It is also possible to perform the CONC determination as a series titration;the value of the last determination is entered in the memory each time.If, however, a subsequent statistical evaluation is performed using[9] [RUN], the calculated mean value is entered in the memory andprinted out.


REAG

7.1 Entering CONST REAG

Type in value and press [CONST REAG] key. Entered value is checkecby pressing the same key without an entry.

7.2 Performing a CONC determination

Standby

MODE'

RUN

"WEIGHT* blinking

I1DENT* blinking

RUN

i

RUN

"BUSY"

CONC-DETEBM.

METHODWEIGHT &I DENT

o o in et "t. IT* <i €1 &

CONG mol/n.

7

prov.1017

204.23

.20420

.09635

The lamp above CONC indicates that the user has selected the automaticdetermination of CONC.

Here, the weight of the primary standard, the volume of the standarcsolution or 1 (in accord with the formula for CONST REAG) is entered

Sample identification. (No request is made, if no printer, matrix printer orlab information system is configured.)

Attach titration beaker with sample to titration head.Warning: If the titration beaker is missing, splashing can occur!

The titration is running.

The concentration is calculated according to the formula on the precedinpage, displayed and simultaneously stored in the parameter storagCONC.

Example: CONC determination of sodium hydroxide with potassiurhydrogen phthalate (M = 204.2 g/mol)

Configuration: 3 , 1 , 0.5,10 (first 4 configuration parameter values)

Indication: DG111 glass electrode

CONSTREAG=• M

1000-=0.2042 (see Page 32)

CONC in mole per liter (mol/L) is stored immediately.

In all other methods with the same titrant, CONC must be entermanually.


Standby

k Calibration of the pH electrode

The following standard values for the electrode parameters are stored inthe DL25/DL21 Titrator:

Zero point of electrode assembly pHopH 7.0 at 0 mV-59.16 mV/pHElectrode slope (at 25°C)

These values can be corrected by calibrating the electrode with two buffersolutions or by manual entry. For configured TAN/TBN determination,see Section 12!

8.1 Performing a calibration

Standby; pH

Calib

I

4 Calib

7 I pHCalib

"BUFFERS linkingRUN

i

"BUFFER 0"

RUN

The pH electrode is calibrated with the help of two of the following buffersolutions. The order of the two buffer solutions in the measurement isimmaterial.

Buffer solutions pH 4 and pH 7



The first buffer solution is secured to the titration head.. Make sure thatboth, the glass membrane and the contact point of the reference electrode(frit, taper) are immersed.

The measurement is made with the stirrer switched on after attainmentof a stable measuring signal. If the signal remains unstable, e.g. becausethe electrode is not properly immersed, the errormessage 34, is displayed.

The second buffer solution is secured to the titration head.

The measurement is made as before. If the buffer solution has not beenchanged, the "BUFFER B" lamp blinks again to indicate that both buffersolutions are required for the calibration.

The electrode parameters are calculated automatically stored, andprinted.


Printout of the electrode parameters determined by the calibration

When working with the ST20 Sample Changer, two buffer solutionsintroduced into the sample tray (if necessary, they can be separate;a washing solution). In that case, the entire calibration sequence isried out automatically after "BUFFER A" is blinking. Washingconditioning solutions and conditioning can be carried out before, betwand afterthe two buffer solutions (not normally necessary in pH calibrawith aqueous buffer solutions). If configured, rinsing will be perform

StandbyPH [

Calib j

7

RUN

ii~~^~JtjL~~^•IBttiiitiiiB

RESET

Standby

8.2 Manual entry and checking of theelectrode parameters

Parameter number is displayed for one second: 1 -»pH0.

Stored pH0 value is displayed.

Corrected value is entered or

Displayed value is confirmed with [RUN].

Parameter number is displayed for one second: 2 -»slope.

Stored slope is displayed.

Entry or confirmation. The entered value is automatically set negative-

Parameter number.

Conclude with [RESET] key.


. * . . •• J —

I!The electrode may be calibrated manually with other buffer solutions. Inthis case, pH. and the slope have to be calculated from the measuredpotentials of these buffer solutions using the following formulas:

p H 0 = p H Buffer-

Steigung*

Steigung

For the potential measurement, see page 8.

A temperature correction is also performed manually.

Dispensing and measurement as amethod

These functions can be configured as a method so that they can berecorded on an attached printer/lab data system and automated with theST20 Sample Changer.

9.1 Dispensing

Configuration parameter 1 6 or 16Configuration parameter 5 dispensed amount in mmol orml (P7: • 9 • •)Configuration parameter 7: 10

9.2 Measurement

Configuration parameter 1: 9 or 19

It is possible to measure the initial signal in mV or pH, exactly as in atitration. A pH electrode must be attached to the DL25/DL21 for this andcalibrated in the manner described on Page 35.

A statistical evaluation of the measured potentials can be printed out with[9][RUN] if [SERIES][RUN] has been used.


to. End point titration

TITRATIOfM

METHOD

UJE I GMT <g

I DENT

c o n c mo 1 /I

c: con s t

e n d p o i n t P>M

(=>MO p>H

SLOPE m'v'/pM

FtESCJI_T g / i O O n

4

2 0

1

6 0

.10050

6.0000

9.500

6.9S5

-58.5

5.5551

In addition to its universal method of an equivalence point finding titraticthe DL25/DL21 Titrator also provides the possibility of titrating topreselected end point. This type of titration is used primarily if itspecified by a standard method (DIN, ASTM, etc). In these cases, itfrequently not a genuine equivalence point that is determined, but raththe titration is used to determine a characteristic value that has beedefined by this standard method. (The titration curve does not necessanshow an inflection point in the region of the end point.)

The end point is generally specified as a pH value. To set up the TitrateDL25/DL21 for the end point titration, the configuration list must badjusted as follows (see also Page 22):

Configuration parameter 1Configuration parameter 5

• •14End point in pH

Configuration parameter 1 is set to 4 or 5, depending on whether the en,point has a positive or negative mV value. If necessary, the otheconfiguration parameters must also be adjusted according to Section £

The end point titration is aborted with error message 30 if the signal at thestart of the titration changes by more than 10 mV in the wrong directionThis can be prevented by configuring the tendency P1:1/2 • • •.

An end point titration is performed exactly as the titration described orPage 13, but here the end point is printed out as an additional parameter

Example: Determination of the acid content of vinegar with NaOH,c = 0.1 moI/L by titration to pH 9.5.

Configuration: 4 , 1 , 0.5,10, 9.5 (first 5 configuration parameters)

Titration numberIndication: DG111 glass electrode

= —=6.0010

(see Page 31)

Result: g acetic acid/100 mL vinegar


iMETHOD

c4-«i- OJL- l l -J

cone mol/lcons t i-^&<3t o . 3 i c : * < m m o lo 1 ̂ in l< mmo 1c on ̂ t

CONF I C3CJF=!(=iT I OM

x T Y P E

2 CONTROL3 PREDOSIN6•"* BUR/MAXVOL5<£> S T I R T I ME"7 OUTPUTS SYSTEM

Bc

pHQ p MSLOPE mV^/p,ME P 1 o w p» MEP h i g h p> H

37

.09930

.20420

.00000

.00000200.00

W2.0

903023

IS0

104823

10000

7.000-59.24.6009.200

TITRATION

METHODWEIGHT &IDENT

o o n o moX/Lic o ti e -fcSTART £>H

SLOPE mV/pH

E£=" Xow p HEl? h i g h E>H

RESULT mLHNV E.H

R ESULT mLHNV s>H

9

371

98

.09330200.002.504

6.764-58. 8

4.6009.200

1.74522.795

34.660

1.93046.995

R h i g h :E>H m m o X / L38.339

1.1062

10.1 Two end points

Titration to two preselected end pointsThis mode (P15 • 10 and 9 • 30) allows titration to two preselected endpoints. This titration can be performed only in the pH mode. In contrastto the usual end point titration, the two end points are not defined in theconfiguration but in the electrode data memory following the electrodecalibration. All other possibilities of the titrator remain unchanged.

Definition of the two end pointsThe function [1] [pH-CALIB] is called up in the standby mode. If theelectrode data remain unchanged, they are confirmed by pressing [RUN]twice; the instrument then requests the two end points. The two endpoints are printed out subsequently in the configuration together with theelectrode data.

How to perform a titration to two end points

Example: Titration of phosphoric acid

Titrant: NaOH, 0.1 mol/L

Consumption to pH 4.6 in mmol/L

Consumption from pH 4.6 to pH 9.2 in mmol/l

Ratio of the two results


Automatic printout of titration and 1st derivative by settingparameter 7 to • • • 3.

TITRATION

METHODWEIGHT &IDENTcsono mol/L

2 4

0

1

2

3

•1!

1

\

.1

9

371

98.09930200.00

S 8 10

QlL

0

0

1

2

3

i

4 \

1

\

10 pfi


11 > p*» a n d

The determination of the p- and/or m-value in water and waste-wateranalysis is a special case of an end point titration. Here, the titrantconsumption is determined in mmol/L up to a pH value of 8.2 (p-value)and to a pH value of 4.3 (m-value). In titrations with hydrochloric acid thep-value is also known as the phenolphthalein alkalinity or acid capacityKSB2, whereas the m-value is called the total alkalinity or acid capacityKs^ (DIN38409). Analogously, DIN38409 refers to the m- or p- valueobtained through titration with sodium hydroxide as the base capacityKB4a or Ksa.2' respectively. (Depending on the application and specification,additional, special instructions are given. For example, the standard DIN38409 stipulates addition of a citrate-tartrate solution in the determinationof KB8J,.) Furthermore, there are other standards with slightly different pHvalues.

The Titrator DI25/DL21 determines both values automatically if the initialpH lies outside these limits. For such cases, connection of a printer ormatrix printer is indispensable as only the second result remains in thedisplay.

The Titrator DL25/DL21 is set up for the p- and m-determination in thefollowing manner:

Configuration parameter 1: 4 . . .Switching to pH and specifying the end points to pH 4.3 and pH 8.2 isautomatic. The other configuration parameters may be adjusted ifnecessary as described in Section 5. Parameters in particular has to beset to 8 • • • for the unit mmol/L. In the analysis of water, we recommendthat the predispensing (configuration parameter3) be set to zero. The twoend points can be modified in the way described on Page 39.

In the CONC determination described in Section 7, the initial digit 4 ofconfiguration parameter 1 is ignored. Consequently, forthis purpose, thetitration can be defined with • • • (and the configuration parameters 2 and,if required, 5)! The blank-value correction of the p- and m-values ispossible, as well as the backtitration. No half neutralization values(HNV)are calculated

When the p- and m-values are determined, there is no difference inprocedure from the description on Page 13.


TITHATION

METHODWEIGHTI DENT

oono mo

START ]=>

a

1/L

H

S L O P E mV/]pH

M-POINTP-POINT

RESULT

F>-VALUE

RESULT

M — V A L U E

E>HE>H

m L

mmo X

m L

m m o l

14

401

39

.099SO20.0008.803

/ L

4

/L9

6.764-58.8

4.3008.200

32680

65032

.6249

.2036

Example: Determination of the acid capacity of alkaline effluent.

Configuration: 4011,2, 0,10 (first 4 values)

Titration numberIndication: DG111 glass electrodeSample: U = 50 mL

Const = 1525L =20 (see Page 31)

p-value or KS8, in mmol/L

m-value or K^ in mmol/L

METHOD

£=t£»tl«= O 1 11

f— i—»n c: fn CD 1 / 1

cons-fc r-^sgb a c k mmcDlb l a n k mmcDlcz on s -t

CONf -XGUR^TIO

^ T V F = J E ;

•2. C O M T F ! O I _3 F>REDOS I MB** BUR/MAXVOLS

<£=, S T I R T I ME"7 OUTPUTS S YSTEt-1<y

, 0 ,

BC

pMO pHSl—OPE mV/p>MM P O I M T p>MP — P O I M T P>M

4O

.099SO

.12110

.00000

.0000020.000

M V2.0

401120

1 0

0

0

8 1 0

1

0

0

0

0

6.764

-58. B4.300B.200

Corresponding method


12, Acid and base number TAN/TBN

BUFFEHlBUFFER2

mVmV

99.8-221.5

Determination of the acid or base number in accordance with the ASTMprocedure D664/D4739 or D2896 is not easy to carry out using thestandard titration. In the Titrator DL25/DL21 therefore, special titrationfunctions are available which allow the analysis of petroleum-basedproducts according to the standard method. The TAN/TBN determinationrequires connection of a printer or matrix printer as several results aredetermined automatically.

Buffer potentialsAccording to the ASTM D664/D4730 standard, if no recognizable inflectionpoint is found the consumption up to the specified potential of two buffersolutions is evaluated.In the TAN/TBN determination with the DL25/DL21 Titrator the function[pH CALIB] thus has a different meaning; instead of the electrodeparameters for a pH measurement the potentials of the two specifiedbuffer solutions are measured in mV and stored. The determination isperformed and checked exactly as described in Section 8.

Concerning acid and base number

acidic buffer potentialbasic buffer potential

Result printout of buffer potential measurementsif the Titrator DL25/DL21 is configured for TAN/TBN determination

If several TAN/TBN - methods are stored, the buffer potentials will be thesame for all these methods (only DL25).

According to the ASTM D2896 standard, only inflection points in thetitration curve are evaluated. To prevent the evaluationto bufferpotentials,the first buffer value is thus set to 0 by manual entry (see Page 36).

Since the Titrator DL25/DL21 switches off the TAN/TBN titration modefora CONC determination automatically, access to the buffer potentials ispossible only aftertitration of a sample or after determination of the bufferpotentials with [1] [pH CALIB].


, .. .̂

Result determinationAll results are printed out in mg KOH per g sample either needed toneutralize acidic components (SAN, TAN, ACID NO.) or equivalent to thebasic components (SBN, TBN, BASE NO.)

Acid number: SAN Strong acid number, determined from the consumption to acidic bufferpotential.

TAN Total acid number, determined from the consumption to basic bufferpotential.

ACID NO. Acid number, determined from the consumption to detected inflectionpoint. Every inflection point found is evaluated.

Base number: SBN Strong base number, determined from the consumption to basic bufferpotential.

TBN Total base number, determined from the consumption to acidic bufferpotential.

BASE NO. Base number, determined from the consumption to detected inflectionpoint. Every inflection point found is evaluated.

SAN, TAN (and SBN, TBN) are results that are determined only atspecified buffer potentials in accordance with ASTM D664/D4739.

Contrary to the other titration modes the titrator calculates in the TAN/TBN mode the consumption from the start of the titration to the potentialor inflection point.Half neutralization values (HNV) are not calculated.Afterthe titration has been evaluated, the TAN orTBN value is displayed.Without buffer potentials, the last acid or base number is displayed.

Blank value determinationThe determination of the blank value of the particular solvent mixture inquestion is performed using the same titration method (sameconfiguration).With buffer potentials not set to 0, the consumption is evaluated up to thebuffer potential designating the total acid number or total base number.Otherwise, consumption to the 1ST equivalence point or the steepestjump is evaluated.


_*SS_ i'-s-i

12.1 Titration according to ASTM D664/D4739

Configuration parameter 1

3 0 0 3


2347

7 0 9 0

Setup

This sets the calculation constant CONST to 56.1 and the signal unit tomV automatically. The buffer potentials must be measured periodicallywith fresh buffer solutions.In the CONC determination, the initial digit 3 of configuration parameter1 is ignored and the final digit 3 automatically set to 1 (titration to firstequivalence point). The configuration must not therefore be changed.

Meaning

Dynamic equilibrium titration with- Maximum increments of 1% of the burette volume {0.1 ml with 10 ml

burette)- potential change anticipation: 30 mV- admissible drift 0.5 mV/6 s- minimum waiting time 18 s- maximum waiting time 90 s

Timed increment titration with-fixed increments of 1% of the burette volume (0.1 ml with 10 ml burette)- time interval between increments: 90 s

ParameterThe above parameters correspond to the conditions required by thestandard. Naturally, they can be adapted for preliminary experiments orspecial applications.

The remaining configuration parameters are adjusted if necessary asdescribed in Section 5. The predispensing (configuration parameter 3) isnormally set to zero.

The titration is stopped if the buffer potential designating the total acid ortotal base number is exceeded and the signal derivative falls below500 mV/mmol (= 50 mV/mL) at CONC = 0.1 mol/L).


Configuration parameter 5 Threshold

The equivalence point recognition can be influenced by a change in thethreshold. The first derivative must be greater than the threshold in theregion of the equivalence point to ensure evaluation of an equivalencepoint.

Blank correctionOnly those results whose consumption is greater than the consumptionup to the total acid ortotal base number are corrected by the stored blank.(SAN or SBN are thus not corrected.)

StatisticsThe TAN or TBN value is used as result for the statistics.

12.2 Equilibrium titration according toASTM D2896


3 0 0 1

Direct titration

The calculation constant CONST is set to 56.1 and mV assigned to thesignal unit automatically.

Thefirstbufferpotential must be settoO to prevent evaluationof the titrantconsumption up to the buffer potentials.The final digit of configuration parameter 1 has the meaning described onPage 22 and occasions the end of the titration afterthe equivalence pointhas been found (1) or when the maximum volume is reached (2,3).In the CONC determination, the initial digit 3 of the configurationparameter 1 is ignored. The configuration must notthereforebechanged.


3 2 7 The recommended equilibriumconditionsfortheTAN/TBN determinationin the case of parameter 327 correspond to the 5 mV/min (0.5 mV/6 s)required by the standard. The potential change aimed for is 30 mV (or16 mV with parameter 2:227).The remaining configuration parameters are adjusted if necessary asdescribed in Section 5. The predispensing (configuration parameter 3) isnormally set to zero.


Configuration parameter 5 Threshold

The equivalence point recognition can be influenced by a change in thethreshold. The first derivative must be greater than the threshold in theregion of the equivalence point to ensure evaluation of the equivalencepoint.

Back titration

The back titration is referred to in the ASTM D2896 standard. The DL25/DL21 Titrator allows back titration with both the equilibrium titration andthe incremental titration. The first buffer potential must, however, alwaysbe set to zero.In a first step, an excess of the 1 st titrant is added as described in Section17. Titration is then carried out with the 2nd titrant to the first detectedinflection point only (Par. 1:3001).

13» ph stating

The pH stat titration or pH stating is used to keep the pH constant.Of prime interest here is the time dependence of the titrant consumption.In addition to measurement of the total consumption of titrant this methodcan be used to determine the mean consumption (ml/min) within aselectable time window. Before the actual pH stating, the pH must inmany cases be adjusted before the sample is added. This can beachieved using a pretitration or by means of a normal end point titration.

In the pretitration of pH stating the end point is reached quicker than in theend point titration since in the vicinity of the end point the decrease in thesize of the volume increment to be dispensed is less. The pretitration isusually controlled with the same parameters as the end point titration.

Pretitration and pH stating employ the same control parameters. Only theequilibrium (drift) and the time condition of configuration parameter 2have an appreciable influence on the control of pH stating. The timecondition must be selected such that tmin of the time window is as smallas possible. The time t^ is the earliest time the next titrant increment canbe added when the signal differs from the end point (set potential) of thepH stating. For pH stating therefore, only the parameter values

P2: • • 01 and P2: • • 02

are appropriate.


Parameter

PL

PL

PL

PL

P3:

P3:

B:>

; 5 . . .

: 7 . -

; 6 • • •

8 • • •

XXXX

0

<xxx

B:0

The set potential change AE^ (P2: • X • •) has no appreciable influenceon the control of the pH stating as long as the deviation from the set valueis less than 1.5'AE^. But with a greater AE^ the pretitration can beaccelerated.

The control of the pH stating can also be adjusted by use of differentburette volumes (e.g. 5 ml) and/or by dilution of the titrant. It must benoted, however, that after the discharge of one complete burette strokesomewhat more than twenty seconds elapse before the burette is refilledand the pH stating can be continued.

Meaning

pH stating with pretitration, positive tendency

pH stating with pretitration, negative tendency. In a first step the pH of thesolution is adjusted. The sample can then be added. Recording of theconsumption-does not begin until after addition of the sample.

pH stating, positive tendency

pH stating, negative tendency

Duration of the pH stating in minutes and seconds. Apredispensing is notpossible in the pH stating.

pH stating with no time limit. Abort effected with [RESET]

Time interval for the storage and printout of the data in seconds. With atime interval < 4 seconds, irregularities may arise since the time for theaddition, measurement and printout of the data is too short.Automatic dispensing with the rinsing pump at the ST20 Sample Changeris thus not possible.

Storage after addition of every increment.


• & , S . . J . . . . * _ : \

13.1 Data storage and printout

Any number of data sets can be printed out online. After 119 data pointsa data reduction is effected in the data memory, i.e. every second entryis cleared.The message «Data Points > 120» appears on the printer.If an interval time has been configured, after every data reduction this isdoubled when entered in the data memory.If no interval time has been configured, each measured value is enteredeven after a data reduction.

The table, which can also be printed out online, i.e. during the pH stating,shows all important values: time, volume and consumption during thetime interval (increment), the signal of the electrode (pH) to check thequality of the pH stating and the derivative of the consumption againsttime as the frequently most important result. The derivative is a directmeasure of the reaction or dissolution kinetics under investigation by pHstating.

13.2 Time window

Many pH stat applications need as result the reaction rate within a certaintime interval. The time window can be defined before or after the titrationwith 1 [pH CALIB]. The time window is thus not part of the method. It mustbe reentered if required when one pH stat method is replaced by another.The values last inputted for a time window remain stored.

13.3 Entering the time window

The zero point of the electrode assembly pH0 is displayed. (Electrodecalibration, see Section 8.)

The electrode slope is displayed.

The start of the time window can be entered in minutes and seconds.

The end of the time window can be entered in minutes and seconds.

The end of the time window can be entered.


Standby

1 Calib

4*

RUN r4,

banking

RUN

I

RUN

13.4 How to perform a pH stat titration

With pretitratlonThe desired method is recalled and in a first step a beaker with solventbut without sample is attached to the titration head. The pretitration (a nor-mal end point titration with the same parameters as the pH stating) isstarted with [RUN]. After attainment of the end point no result appears butthe burette is set to zero and the sample data (WEIGHT and IDENT) arerequested. The "BUSY" lamp begins to flash, indicating that the weighedsample can now be added. The actual pH stating is started with [RUN].The pH-stating with pretitration can only be performed manually and notwith the Sample Changer ST20.

Example: Determination of the enzyme activity of pancreatic lipase at pH8 by pH stating with sodium hydroxide 0.025 mol/l, temperature: 41 °C.

~r I ~rr=tt*~r

METMOOWE I GHTI DEIMT"c o n c m

cz or-t s -t

sr-» d po i

p H O p>M

SLOPE

RESULTRESULT

p>MO p>MSLOPET I {-IE JL

"TIME 2RESULT

I ON

<3

ol /L

n t p>l—1

p H

m^/ /" pH

m l _

1 0

3 4

.994738.126.02500800.008.000

6.9236.739-59.5

6.5500

131.70

6.739-59.5

1.00005.0000

1.163B

Configuration: 5114,1101, 5, (Par 1...3), Par B: 15Titration numberIndication; DG111 combination glass electrodeSample: Enzym suspension (~1 mg Enzym)

CONST = M • 100/5 for a result in activity units/g. Enzym = ml, NaOH(0.025 mol/l) «100/min.

Result: Titrant consumption in ml_ and activity units/g EnzymResult: mean consumption within the specified time window

Time windowResult: mean consumption of NaOH in ml/min.

For the interpretation and evaluation of a pH-stating, data other thanthose provided by a standard titration are of interest. These data can betaken from the table of measured values online (Par 7: • • 3 •) or printedout afterwards with [7] [RUN].

d pain

TIME

m i n

1111

2

"222

3

3

3

s

1

15

3 0

4 5

0

1 5

3 0

4 5

0

15

3 0

4 5

0

15

3 0

t pM

VOLUME

mL

.01000

.85500

1.1750

1.5350

1.8950

2.1900

2.4950

2.B35O

3.1800

3.4900

3.7500

4.0200

4.3100

4.6200

4.9100

8.000

INCREMENT

mL

.01000

.B45O0

.32000

.36000

.36000

.29500

.30500

.34000

.34500

.31000

.26000

.27000

.29000

.31000

.29000

DERIVATIVE

mL/min

3.6214

1.2800

1 .4400

1.4400

1.1800

1.22OO

1.3600

1.3800

1.2400

1.0400

1.0800

1.1600

1.2400

1.1600

SIGNAL

p H

7.235

8.017

7.927

7.953

7.999

7.950

7.937

7.970

7.932

7.996 i

7.998

7.969

7.975 ' •

a. 0098.028


/ - T

Three different curve plots can be configured or subsequently printed outwith [X][RUN]. The consumption is usually shown as a function of time(P7:'---1,«--3or[5]IRUN])

The first derivative of the consumption as a function of time allowsassessment of the reaction or dissolution kinetics (P7: • • • 2, • • • 3 or [6][RUN])

0

2

4

1

\'V

, - • • " •

i

1

1

1

2 J 4 mL/min


For a check on the quality of the control with the selected controlparameters, information is provided by the plot of the signal as a functionof time (Par 7: • • «4 or [8] [RUN]) or online with a line recorder connectedto the analog output.With parameter 7: • • • 5 all curves are printed out.

6 . 5

0

z

4

6

ntin

7 7 . 5

• • • _ . .

g

— ,

\

V

j1\

\

\

a.s pH

1

pH stating without pretitrationIf the pH of the solvent, the medium or the substrate is correct ornoncritical, there is no need to perform a pretitration. For work with thesample changer the pretitration must be switched off. Some other meansmust be used to preadjust the solvent to the correct pH. The same alsoapplies if the sample weight has to be determined by back weighing.


14, Special evaluation procedures


0 « - 7

2 . . 7

1 "7

The evaluation procedure of the DL25/DI21 can no longer be used if noS-shaped curves are obtained. Two additional methods are available insuch cases to calculate the titrant consumption up to the equivalencepoint. These titrations are performed in accordance with the descriptionin Section 3.1.

14.1 Determination of the minimum/maximum of a titration curve

The result of this determination is the minimum (maximum) calculatedfrom the data points of the titration. This titration mode finds principal usein turbidimetric surfactant determinations with photometric indication.

Meaning

Determination of the minimum; standard threshold 20 mV/ml

Determination of the minimum; threshold according to parameter 5

Determination of the maximum; threshold according to parameter 5

The titration is aborted after recognition of the first equivalence point(minimum or maximum).

A minimum (maximum) is recognized as an equivalence point if thefollowing two conditions are fulfilled:

- After a minimum(maximum) the measured potential value must increase(decrease) twice.

- Before the attainment of the minimum (maximum) the value of the firstderivative of the titration curve must be greater than the value of thethreshold at least once. Adaptation of the threshold allows suppressionof small discontinuities in the titration curve that can lead to falseminima (maxima).

All other configuration parameters have their usual meaning (seeSection 5.2). A half neutralization value (HNV) is not calculated.


14.2 Titration curves with linear sections(segmented curves)


0««8

1 ««8

2 - « 8

Various methods of indication (including photometry, conductometry andamperometry) generate titration curves with linear or approximated linearsections (segmented curves). A special evaluation procedure has beendeveloped forthese curves. Foran exact determination of the equivalencepoint it is essential that these curves have not only linear sections but alsoa distinct break in the region of the inflection point.

Meaning

Evaluation segmented curve. No specific tendency, threshold in mV/mlz

or pH/ml2 according to parameter 5

Evaluation segmented curve. Tendency positive, threshold in mV/ml2orpH/ml2 according to parameter 5

Evaluation of segmented curves. Tendency negative, threshold in mV/ml2 or pH/ml2 according to parameter 5

The titration is aborted at maximum volume.

The threshold and tendency have a meaning different from that in othertitration modes.

The tendency (direction of the potential change in the vicinity of theequivalence point) relates not to the titration curve but to the firstderivative. The threshold thus relates to the second and not the firstderivative. The second derivative must be greater than the presetthreshold inthe region ofthe equivalence point inorderthat an equivalencepoint can be recognized. As an aid, for each equivalence point found themaximum value of the second derivative (max deriv2) is printed out in therecord. The printout of the 1 st derivative of the titration curve has a linearscale of the ordinate.

All other parameters have their usual meaning (see Section 5.2).

It is advisable to perform the titration with constant volume increments(P2: X • • -, X = 4, 5, 6, 7, 8, 9).

For S-shaped curves the titration data are evaluated using the standardprocedu re. This does not use the experimental points of the titration cu rvebut ratherthe data of the first derivative calculated from such points. A halfneutralization value (HNV) is not calculated.

E

J

f

_JSchwolle

— V V


, Backtltratton

In a back titration, the first step involves addition of an excess of titrant tothe sample. In the second step,' the unreacted portion of the titrant isdetermined with the aid of a complementary titrant. The content of thesample is given by the difference in the added millimoles of the two titrantsused.

This method is used, for example, if the sample reacts only slowly with thetitrant and this reaction can be accelerated by addition of an excess oftitrant. The extraction of the components to be titrated out of the samplematrix can also be accelerated in some cases. An additional applicationexample is the determination of nitrogen by Kjeldahl's method in whichthe ammonia released is steam distilled into a sulfuric acid trap anddetermined by back titration with sodium hydroxide.

The Titrator DL25/DL21 calculates the result of a back titration (i.e. ifBACK * 0) by the following formula:

RESULT=CONST- 1WEIGHT

(BACK - V • CONC - BLANK)

BACK = Excess in millimoleV «CONC = Raw result in millimoleBLANK = Positive blank value in millimol (see Section 18)

If the result unit ml is configured (P7: • 9 • •) in atitration, this configurationmust also be employed for the blank determination and the entry of theexcess.

Back titration is not possible in the CONC determination (see Page 32).

Use of the titration mode to all equivalence points (configuration P1: • • • 3)is also senseless and can lead to calculation errors.

In the Titrator DL25/DL21 the excess can be added using the dispensingfunction [BURETj. The amount is entered in the parameter storage BACKin miliimol and taken into account automatically in the calculation of thetitration result. A practical approach involves the use of two burettes, thetips of which can both be inserted into the titration head. The change inreagent can then be accomplished simply by sliding the burettes in theholding rack and locking in place by means of the knurled screw.The excess can also be added automatically with a second DL25/DL21(slave) or with a dispenser (only with ST20 Sample Changer).


Jf , ' , ^ . , - . , . , _ >

15.1 How to determine the excess

Standby

MODE

2

BURET

MODE

o i- -

Standby

The amount of excess in millimoles is found from the concentration inmillimole per milliliter and the volume dispensed in milliliters:

BACK(mmol)

CONC(mmol/mL)

Volume(mL)

For value entry, see Page 7.

The excess can also be determined automatically and stored. Thisinvolves dispensing, in a different mode, of the required quantity of the 1 sttitrant with the dispensing function [BURET] after determination of thetitrant concentration by the method described in Section 7:

Correct CONC value of 1st titrant is in the parameter storage.

The lamp above BACK (and BLANK) indicates that the determinationinvolves the excess to be dispensed. (If dispensing is not required at thistime, no burette is placed over the drive.)

Volume to be dispensed is entered in milliliter (= 20 mL).

The required volume is delivered.

BACK m 2.O2OOThe value calculated in mmol (CONC • 20) is printed out and stored in theparameter storage BACK.

15.2 How to perform a back titration

The concentration of the 2nd titrant must now be stored in the parameterstorage CONC. The burette containing the 1st titrant is in the drive. Theexcess is dispensed using the dispensing function [BURET] (see Page 12).Next, the burette above the drive position is changed and the actualtitration performed as described in Section 3, Page 13.

If it is desired to enter the sample weight and identification beforedispensing the excess the entries should be made with [SERIES INPUT],The titration is started with [SERIES RUN] after the excess has beendispensed (see also Series titration, Page 62).


SERIESINPUT

RUN£ • • "

RESET

Standby

2 L 0

BURET

I

Standby

SERIES"*RUN

-BUSY-foiinkifig

RUN

"BUSY* *

4"RESULT"

Standby

The correct amount of excess is stored in BACK, concentration of the 2ndtitrant in CONC.

The sample number is displayed for one second.

The weight is entered or transferred from connected balance.

Sample identification. (No request, if no printer, matrix printer or labinformation system is configured.)

1st titrant in drive position, sample at working place.

The same volume as that in the excess determination is entered for theexcess in terms of burette volume.

The excess is dispensed.

Change to 2nd titrant.

The titration is performed with the data entered as "series sample".


The result of the back titration is calculated using the formula on Page 55and displayed.

Example: Determination of potassium aluminium sulfate contentBack titration of aluminium with EDTA and zinc sulfate, 0.1 mol/L.

Configuration: 1, 3, 0.5,10 (first 4 values)

T I TRAT

METHOD

we IGHTI DENT

c o n e m

cz on s tl

I ON

o 1 • l_

b^c k mmol

RESULT

1 9

14

.8294

1 1 0

.09870

47.439

2.0034

97.A9O

Titration numberIndication: Amalgamized DM141 silver electrode,3 drops Hg-EDTA, 0.05 mol/LBuffer: pH 4

CONST = M/10 = 47.439 (see Page 31)Dispensed excess EDTA for back titration.

Result in %


In certain titrations a small part of the titrant consumption up to theequivalence or end point is not due to the sample component undeinvestigation but to the sample matrix (all othercomponents), the solveror in general to the sample preparation. In such cases, an exact resinrequires correction by the so-called blank. Such a blank correction iscarried out automatically if the blank in millimoles is stored in theparameter storage BLANK. The result calculation described in Section 6is then carried out according to the modified formula:

RESULT=CONST- 1WEIGHT

(V-CONC- BLANK)

V • CONC = Raw result in millimolBLANK = Positive blank in millimol


m

! MODE

j RUN

! RUN

HRRUN

§t MODE

mmmwarn

••Hi

"BUSY*: t"RESULT"

16.1 How to determine the blank

The DL25/DL21 Titratorsupports the blank determination and storage bymeans of a special operating mode. This involves a titration to the firstequivalence point. Any configured predispensing is suppressed. Maximum8 mV is allowed as set potential change. In a titration with fixed volumeincrements work is performed with increments of maximum 0.5% of theburette volume. A sample is titrated that should contain ail samplecomponents except that under investigation. For example, a sample withthe known content zero is prepared in exactly the same manner as thenormal samples.

The blank is equal to the raw result of the blank determination:BLANK = V • CONC.

The lamp above BLANK indicates that a blank determination is beingperformed.

No weight entry.

Insert identification number.

Attach titration beaker with sample for blank determination to titrationhead.


The displayed result is the blank value in millimol or, if configured, inmilliliter, which is simultaneously stored as BLANK.

The blank titration can be performed as a series titration. Here the valueof the last determination is entered each time as BLANK. If a subsequentstatistical evaluation is performed with [9][RUN], the calculated meanvalue is entered and printed out.


- •-.*'^:. £i

BUANK—DETERM.

METHOD

I DENT

c o n c: ma 1 / I—

canst

BLANK <nmo 1

2

1 6

0

.09890

56.100

.00473

Example: Determination of the blank value of 50 ml solvent (ether/ethanoi 1:1) forthe titration of the free fatty acids in sunflower oil with KOHin t-butanol, c = 0.1 mol/l.

Configuration: same as for titration of the sample (see below)

Titration number

Indication: DP550 Phototrode, phenolphthalein

Blank in mmol or ml

TITRATION

METHOD

WE I GHT <3

I DENT

c o n e mol /I—

c: on ̂ t

b l a n k mmCDl

R E S U L T m<3 S <3

4

16

9.9268

1SQ6

.09890

56.100

.004 73

2.197B

Example: Determination of free fatty acids in sunflower oil with KOH int-butanol, c = 0.1 mol/l, taking into account solvent blank.

Configuration: 1, 2, 0.5,1 (first 4 configuration parameter values)

Titration number

Indication: DP550 Phototrode, phenolphtalein

Conversion to mg KOH/g: CONST = M(KOH) = 56.1Blank in mmol

Result: acid number in mg KOH/g sample.


17, Series titratfon

The Titrator DL25/DL21 possesses a memory for 60 series sample data(sample weight, identification number and result). It is thus possible toweigh a series of samples before the first titration is started. This is ofspecial value if all the samples have to undergo analysis pretreatmentsimultaneously.Examples: Solubilization, extraction, saponification by boiling.Using a sample changer and a dot matrix printer, the titration of the wholeseries may be automated.

StandbySERIESINPUT

17.1 Sample entry

"WEIGHT blinking

RUNI

RUN


The weight is entered or transferred from a connected balance.

Sample identification. (No request, if no printer, matrix printer or labidentification system is configured.)

"WEIGHT* blinking

! RESET

Standby

The next sample number is displayed for one second.

The weight of the next sample is entered.

The sample entry is concluded.

UJE I GHTI DEMT

S AMF="l_EIAJE I GHTI DENT

S <=* 1-1 P=» l_ EWE I C3MTI DEMT"

NO .

MO .g

12.30B9

55

22.7415

55

2.1B4255

Entry record for the first 3 samples.

Sample entry is not possible while the series titration is running. But it ispossible, with the key [SERIES INPUT], to cause the Titrator DL25/DL21to interrupt the process at the end of that particulartitration. Then an entrymay be made.


17.2 How to perform a series titration

.Standfey-

SERIESRUN

•SUSY" tanking

RUN

"BUSY* blinking

RUN1

Standby

NOWE I GHT gI DENT

.10O0O5.B44O.00473

12.3089

55

22.7415

55

32.4842

55

When a sample changer is attached processing of the entire series isstarted automatically with [SERIES RUN]. No other manipulations arenecessary.

Without sample changer:The titration is started as soon as the titration beaker containing the firstsample is attached to the titration head.

The titration is running.Warning: If the titration beaker is missing, splashing may occur!The result is printed out.

The next sample is attached to the titration head.

If no printer, matrix printer or lab information system is configured, theinstrument displays the result after the titration in the standby mode. Thenext sample is started by pressing [SERIES RUN] again.The instrument also returns to the standby mode after the final samplehas been titrated.

Example: Determination of the NaCI content of mayonnaise with0.1 AgNO3, c = 0.1 mol/L; Stirring time 60 seconds

Configuration: 1,1,0.5,10, 0,60 (first 6 configuration parameter values

Indication: DM141 silver electrode

CONST = M/10 = 5.844 (see Page 31)

% NaCI in sample 1

% NaCI in sample 2

% NaCI in sample 3


r,.^ js 'V'f^

attoiSB

17.3 Statistical evaluation

SERIES INPUT

METMOD

1 .4869 ^

1 .4409 3

1 . 431 . 4 3

1.46

1 .4S<I , 4 31 .44*

1 .431 . 4 3Et . 4 4

4 4 1

7 5

37

)9 3

1 53 3

3 3

2 S7 3

3 2 .5 2 .3 2 .

0 2 .0 2 .3 2 .

5 2 .3 2 .

5 2 .

5 2 .5 2 .

3 2 .

30B974154642

6SS580037O43

7554

992996O3

6288

24 58

With series titrations, the DL25/DL21 Titrator allows statistical evaluationof the results. A result (the last in the case of several results) is stored forevery series sample. The statistical evaluation is performed over allanalyzed samples of a series (maximum 60). The results remain storedeven after the statistical evaluation. But if the method is modified,replaced by a different method (DL25 only) or if a series blank or CONCdetermination is performed, the results memory is cleared automatically.As a consequence, statistical evaluation of results of different or alteredmethods is not possible.With series without data input, statistical evaluation is performed over anunlimited number of results since the individual results are not stored inthis case, but rather the mean value and standard deviation arecontinuously updated.

Checking the resultsWith [2][SERIES INPUT] all results contained in the series samplestorage can be printed out.

Clearing the resultsAll sample data and hence also all results are cleared with [9] [SERIESINPUT]. Selective clearance of all samples with result is performed using[7][SERIES][INPUT]. In the event of a power failure, however, all sampledata are preserved.With [1 ] [SERIES INPUT], a single result, for example a maverick, can becleared selectively by overwriting the result not wanted for the statisticswith [0] (only in series with data input). This is done in the way describedon Page 65. The instrument confirms the deletion by the printout:"Sample deleted".


METHOD

NUMBERM E A N •%.S S-F?SD •/-

SAMPLE NO

1

23

4

5

6

7B9

10

11

12

I CS

RESULT

1.48671.44891.45371.45531.48571.45091.43591.44611.43231.43831.44221.4497

2

121 .4522.017451.2020

IDENT

55

55

55

0

0

55

55

5555555555

WEIGHT

2.308V2.74152.48422.68552.80032.704 52.54992.75542.99292.96032.62882.2458

How to perform a statistical evaluationA series of several titrations is complete, the instrument is in the standbymode. The statistical evaluation is started with [9] [RUN].

Break and errorsIf a series is interrupted during a titration with RESET the result of thissample is set to zero. If an erroroccurs the result is also set to zero. Resultzero (0.000) is ignored in the statistics and the message: "Sampledeleted" appears on the printer.

Method No 2

Number of resultsMean value with unitStandard deviation with unitRelative standard deviation in %

List of results


17.4 Checking and alteration of seriessample data

Standby

1 SERIESINPUT

Sample data already entered can be displayed and written over:


"WEIGHT blinking

RUN I

4"IDENTtt blinking

RUN

t

The sample weight is displayed and can be written over.

A quick press of the [RUN] key causes the sample number to be raiseddirectly.

The identification is displayed and can be written over.

The next sample number is displayed for one second.

"WEIGHT mmmPrinting out the contents of the series sample storageKeying in [2][SERIES INPUT] prints out the series sample storagecontents (see Page 63).

METHOD

SAMPLE NO

1

234

5

6

I NPUT

RESULT

2

I DENT

55

5555

0

0

55

WEIGHT

2.30692.74152.48422.68552.80032.7045

Clearing the data of a sampleIf 0 is entered instead of the sample weight, the data of a sample arecleared. This is possible, however, only at the start and end of a series.

Clearing the contents of the series sample storageEntry of [9][SERIES INPUT] clears the contents of the series samplestorage completely. Note particularly that the stored results of titratedseries samples are also cleared.


17.5 Series titration without sample entry

Configuration parameter 9 Set up:

This further simplifies the series titration if fixed volume samples are usedand if an identification entry is not needed. The sample volume in thiscase is taken into account in the calculation constant (see Page 31). Theresults are numbered consecutively.The series titration is started with [SERIES RUN]. This continues as longas there is no break in the sequence of sample beakers on the sampletransport.It is possible to add additional sample beakers to the end of the series atany time.

17.6 Rinsing, dosing, titration and conditio-ning with the ST20 Sample Changer

Summary of the configuration possibilities with the ST20 SampleChanger

For more details about parameter 8 see also Page 21.

P8: • 1 • • The sample changer is attached. In the event of an error the series isaborted with an error message.

• 2 • • The sample changer is attached. In the event of an error the result is setto zero and a warning appears on the printout. The series is continued.

• 3 • • The sample changer is attached. In the event of an error the result is setto zero and a warning appears. The series is continued. Further, if valuesare available, a table of measured values is printed out.

P9: • • • 0 Series titration with sample data entry (for maximum 60 samples)

1 Series titration without sample data entry, unlimited number of samples..• • • 2 Seriestitrationwithoutsampledataentry,butwithresultstorage(maximum

60 samples)

• • N • Conditioning after N titrations

X X " Conditioning time XX in units of 10 seconds (10...990 s)


fc £ - fUistn •$£S;x£,

PA:PB*PC:

Rinsing time, with pump at connection "RINSE" in secondsDosing time, with pump at connection "RINSE" in secondsDosing time, with pump at connection "DOSE" in seconds

'Parameter B has a different meaning in pH-stating (see Page 47).

RinsingFor accurate work with the sample changer, the carryover of residuesfrom one sample to the next must be prevented. This is achieved byintensive rinsing of burette tips, electrode and stirrer in the titrated samplelowered to the middle position before transport of the next sample. Thetotal rinsing time with the pump connected to the "RINSE" socket isdefined in configuration parameter A in seconds (rinsing time=A seconds).Additional cleaning is possible by use of wash samples as "conditioningsamples" (see Page 68).

DosingThe ST20 Sample Changer allows three independent dosing operationsbefore the actual titration:

Dosing of solventsDosing of solvent to dissolve or dilute the sample.Here, the solvent dispensed through the rinsing channels is the same asthat used for rinsing after the titration. The quantity to be dosed is definedby the dosing time in configuration parameter B* in seconds (dosingtime = B seconds).

Dosing of additional liquidsEither a pump connected to the "DOSE" socket or a dispenser connec-ted to the Dl N socket can be used f orthis dosing operation. (Simultaneousoperation of the two types of connection is also possible.)In the case of the pump (or magnetic valve), the quantity to be dosed isdefined by the dosing time in configuration parameter C in seconds. Theprecise volume is set on the dispenser and the unit simply receives a startsignal.An additional possibility involves use of a second DL25/DL21 for precisedosing, forthe adjustment of a desired pH value (end point titration) orfora first titration. For a description, see Page 12 and 71.

-i', V:


ConditioningThe use of conditioning samples has several purposes:

Conditioning of the electrode at the end of a series.

Conditioning of the electrode after each batch of N samples, e.g. innonaqueous titrations the operational efficiency of the glass electrodeshould be preserved using an aqueous conditioning sample.

Cleaning of electrode, stirrer, etc. in a suitable wash solution.

Conditioning samples are marked by red stoppers on the sample table.Any number of conditioning samples can be distributed. When aconditioning beaker is recognized in place of the next sample, stirring isperformed with this beaker at the titration station during the conditioningtime and rinsing is then carried out as normal.The conditioning time XX is defined in units of 10 s in the two lefthanddigits of configuration parameter 9 (XX • •)• Conditioning time = XX • 10seconds (10...990 s).To save space on the sample changer, configuration parameter9 can bedefined with • • N • such that conditioning must be performed after everybatch of N samples. If now there is no conditioning sample marked witha red stopper in the next position, the sample changer searches back tothe last conditioning sample. It then continues with the next sample. Theonly condition which must be observed is the following: There must be noempty positions between the last titrated sample and the last conditioningsample. If this were the case, the error message "ERROR 41" wouldappear and the sequence be aborted.If the table has to rotate back to a conditioning beaker, no rinsing is carriedout after conditioning since the beaker could be overfilled.

Chronological sequence of all functions of the series titration withthe ST20 Sample ChangerStart of the series titration at the Titrator DL25/DL21 (master).-> Printout of the sample data of the 1st sample.

If conditioning beaker in next position:After rinsing into the last beaker, the sample changer transports theconditioning beaker in which conditioning is carried out during theconfigured stirring time to the titration head.


•il},

. \ «§?i - ' ; '? ' .-'

If sample in next position:After rinsing into the last beaker, the sample changer transports 1stsample to the titration head.

Rinsing agent is dosed during the configured time B.

Stirrer starts.Second DL25/DL21 (slave) performs the configured titration ordosing. Ifthe second DL25/DL21 is configured for a lab data system, ail output data(without curves) are printed out via the master.

Dosing agent is dispensed during the configured time C. Dispenser isstarted.

Master DL25/DL21 performs the configured titration.If conditioning beaker in next position or sample counter indicates thatconditioning is required:Sample changer transports conditioning beaker to the titration head afterrinsing into the titrated sample.

If sample in next position:Sample changertransports next sample to the titration head after rinsing,etc.


i. -. . a-, ^>&JljUji*t£..tlM.2.*41

17.7 Manual operation of the ST20Sample Changer

S&ndfcy

5 !

MODE;

The sample changer functions can be activated individually via thekeyboard of the Titrator DL25/DL21 for setting up and checking pur-poses.The ST20 must be configured in the active method for this.

Operation mode for manual operation of the ST20 Sample Changer.

The function is called up by means of the numeral keys.

The Titrator DL25/DL21 remains in this operating mode until aborted with[RESET].In case of an error press [RESET] twice.

The individual functions

Pump "RINSE" is active as long as this key is pressed.

Pump "DOSE" is active as long as this key is pressed. Further, thedispenser is started.

Functions 1 and 3 serve to fill or rinse the lines.

Pump "RINSE" is activated for A seconds (A = the time selected inconfiguration parameter A).

Pump "RINSE" is activated for B seconds (B = the time in configurationparameter B).

Pump "DOSE" is activated for C seconds (C = the time selected inconfiguration parameter C). Dispenser is started.

Functions 1 ...6 can only be executed if the lift is in the upper or middleposition.

With each press of the key, the lift is moved one position:bottom -> top -> middle -> bottom...

With each press of the key, the turntable is moved forwards one position.

With each press of the key, the turntable is -moved backwards oneposition.

For functions 8 + 9, the lift is moved to the lowest position beforehand.


13, Remote control

Full remote control of the Titrator DL25/DL21 is possible by use of amaster control unit. All key functions are controllable via the RS232Cinterface using the commands shown in the table below. Foroutput of thedot matrix printer record via the RS232C interface (excluding graphicalrepresentation), see System Configuration, Page 21.

Each remote-control command blocks the whole keyboard since noprovision is made for parallel operation. On the other hand, the keyboardcan be freed again by remote control. Remote control commands (exceptstatus request, RESET and, in part, RUN) are accepted by the TitratorDL25/DL21 only in the standby mode (exactly analogous to the keys).

Key -

0to9

CERESETBURST/mLpH-CAUBHUMMODECONSTSERIES INPUTSERIES &UHBLANKBACKCONCOONST REAOSAVEMETHOD

Unblocking keyboardSimulated1 power upStatus request

Command -

0tO9«CLMM0HizjKEZGZX>ZFZPQZ

Y1?

ASCII hex'}

3010 392E434C4D4E4F434&5A*)4A4B455A*}475A2)445A*)4SSAa)50

213F

1) serial 7 bit ASCII2400 baud1 parity bit, not checked1 stop bitOther than the stated characters are ignored

z) 2 characters command


lamp Status

WEK3HTblinking

IDENTblinking

BUSYbanking

BUFFERAblinking

BUFFER Bbiinktng

BUFFER A& 8

Display test

"Not Standby"3}

19

412

1624

3240

48

119

64

The remote control commands occasion no feedback except when aprinter output has been triggered (if so configured).Exception: Status request. The status message reports the status of thecolumn of lamps at the left of the display. It is effected in decimal form asan ASCII string and is closed with CR/LF. Blanks can precede the statusmessage. The status message is, however, suppressed if the DL25/DL21 is outputting a titration curve or its derivative via the CL interface.

3) This status message is always transmitted when the Titrator DL25/DL21 is not in the standby mode, the actual function, is not, however,signaled by a lamp. (For example, the burette is being filled aftercompletion of a titration.)


A ! '<-

Connection of a second DL25/DL21The Titrator DL25/DL21 can be used as master for remote control of asecond DL25/OL21 used for dispensing or to perform another titrationwith the same sample. The function of the second DL25/ DL21 (slave) isperformed before the titration of the master.

Master: Configuration parameter 8 2 • 0 •Slave: Configuration parameter 8 0 • 22 0*23 (if a dot matrix

printer is attachedto the slave)

For manual entry on the second DL25/DL21, the keyboard must be freedwith [RESET] on the master DL21/DL25. If the outputs of the secondDL25/DL21 are to be printed out on the printer or matrix printer connectedto the master DL25/DL21, the RS232C interface and the printer must beentered in configuration parameter 8 of the second DL25/DL21 (25 and21, respectively, see Page 21). The printing of further information (seePage 29 and following) with the second DL25/DL21 is possible only ona printer connected to this instrument.

Remote control of the master DL25 by a master computer is possible. Theadapter cable (order number 23826), for example, can be employed forthe connection. All lines which begin with DCn (n=2,3 or4, correspondingto configuration parameter 8) received by the computer are commandsto the second DL25 and should be ignored.

Connection of a sample transportThe Titrator DL25/DL21 can control a sample transport in addition to asecond DL25/DL21.

Remote control of the master DL25/ DL21 by a master computer ispossible also in this case. If the DL25/DL21 controls a sample changeronly, the adapter cable (order number 23826) can again be used. Forremote control of a master DL25/DL21 wich controls the sample changerand a second DL25/DL21, a special adapter cable must be employed. Alllines beginning with DCn (n = 1,2,3 or 4, corresponding to configurationparameter 8) received by the computer are commands to the samplechanger and the second DL25/DL21. They should be ignored.


Testing of the interfaceFor testing of the interface and a better understanding of the set ofcommands for the remote control of the DL25/0L21 one can use eithera ANSI-terminal or an appropriate terminal program. Example of such aprogram in BASIC on an IBM PC.

SYSTEM

100 CM$-"comln

150 CIiS: PRINT "Terminal Emulator"160 OPEN CM$+":2400 ,e ,7 , l f cs0 ,ds0 ,cd0 ,pe" AS #1170 T$-INKEY$180 IF T$-"" GOTO 210190 IF ASC(T$)-27 THEN PRINT "Good bye":200 PRINT T$;: PRINT #1,T$;205 IF ASC(T$)-13 THEN PRINT CHR$(10) ;210 IF (256-LOF(l))«=0 GOTO 170220 P$-INPUT$(1, #1)230 IF ASC(P$)<>10 THEN PRINT P$;235 IF ASC(P$)«=13 THEN PRINT CHR$ (10) ;240 GOTO 170


Appencffx A: Technical specifications.

Measuring SystemEnd point indication

Amplification range

ResolutionAccuracyMeasuring inputInput resistanceOffset current

Analog output forpotentiometric recorder

DispensingInterchangeableburettesBurette volumesResolution

Accuracy

Delivery timeFilling time

potentiometricvoltametric (with DK102, DM142)colorimetric (with DP550, DP660)

±3000 mV

0.1 mV, 0.001 pH±0.02 pH within the pH range 0-14DIN 19262 jack and 4 mm banana socket>5 «1O1Z Q, protected up to 1000 V<1 pA (20°C)

1:1

equipped with maximum 21,5,10 and 20 mL1/2000 of burette volume= 0.5, 2.5, 5 or 10 uJbetter than 0.3% for consumption greater orequal 30% of burette volumeminimum 20 s for one burette volume-20 s

KeyboardSplashproof

Titration typesTo first equivalence pointEquivalence point corresponding to steepest inflection in titration curveAll equivalence pointsTo preselected end pointTo two preselected end pointspH statingTAN/TBN (acid or base number) according to ASTM D664, D2896p- and m- value

Reagent addition: dynamic or with constant volume stepsMeasured value acquisition: equilibrium controlled or timed increment


Result calculationAutomatic conversion of titrant consumption relative to sample weight toyield the content in the desired unit.Evaluation procedures for S-shaped titration curves (standard), forcurves with minimum/maximum and for curves with several sections.Back titrationBlank correctionReciprocal resultSum of two resultsRatio of two resultsDifference between two resultsResult minus set value

Series sample storageSample weight, sample identification and results for 60 samples

Data storageStorage for 120 points (volume and signal)

Method storage (DL25 only)Storage for 50 methods

Auxiliary functionsDetermination of titrant concentration with automatic evaluationBlank determinationExcess determination for back titrationpH calibration (2 point)DispensingStirringMeasurement

Propeller stirrerAutomatically switched, variable speed adjustment0...-3200 RPM

Connection possibilities for peripheral instruments

Balance

Printer

Dot matrix printer

Bit-serial current loop data interface for allMETTLER balances with CL and 03 dataoutput.

Same interface for alphanumeric METTLERGA44 printer (20 characters per line).

Same interface for Epson-compatible matrixprinter (with graphics facilities) with bufferedRS232C interface (minimum 2K buffer) viaconversion cable.


Laboratory informationsystem (LIMS),Computer

ST20 Sample Changer

Second DL25/DL21

Computer and secondDL25/DL21 and ST20

Optional RS232C (DCE) datainterface, also for remote control.

Connection also via optional RS232C (DCE)data interface.

Connection also via RS232C (DCE) datainterface and adapter cable for remote controlby first DL25/DL21 (master-slave operation).

Connection via special adaptercable.

Additional specifications

Plastic parts Polyester (housing), polypropylene (titrationstand)

Width x depth x height 38 x 35 x 27 cmapprox. 5.5 kg10...35°C100/117/220/240 V (+10%/-15%);50/60 Hz; ca. 45 VA

WeightAmbient temperaturePower supply


Appendix B: Standard equipment andoptional accessories

Standard equipment

Equipment supplied Order No.

1 Basic DL25 or DL21 instrumentincl. spare fuse

Operating instructions

Memo card*

Application brochure

Power cable

Interchangeable burette 10 mlincl. burette piston, piston rodburette holder, tip holder, dispensing andsuction tubes, tube of silicone grease

Propeller stirrer, complete

Titration stand, complete

GermanEnglishFrench

GermanEnglishFrench

GermanEnglish

NeutralFRGUSASwitzerland

see

704093704094704095

704079704080704081

724100724101

87576879258866887920

Accessories

23830

DV702

Coaxial cable for electrodes with plug-in headSC - DIN 50 cm

1 Phillips screwdriver No. 1

89603

73071

* Short-form operating instructions and memo cards in other languagesare in preparation and can be requested from your METTLER agency.


a

Optional accessories

Interchangeable burettes

Interchangeable burette, complete

comprising:

1 i Brown glass bottle

Burette holder

Piston

Piston rod

Stopcock parts (1 of each)

Light protection tube

Dispensing tube with siphon tip

Suction tube

1 ml5 ml

10 ml20 mi

3 pcs

70 cm

83 cm

Order No.

DV401DV905DV910DV920

71296

23645

DV905DV910DV920

for DV905forDV910for DV920

Valve diskRubber washer

Follower camThreaded ring

237102371123712

236362363623636

101003257372571525716

23644

25687

25688


^

Gasket for 11 brown glass bottle

Tip holder for burette tip

Stopper ST 14.5

Set of labels

Order No.

23981

23960

5 pcs 23646

for DV905DV910DV920

257032570425705

NOTE: The 1 ml burette differs from the other three burettes. If you orderthe DV401 you will receive a set of operating instructions with details ofthe appropriate spare parts.

For titrants that have to be protected against moisture or CO2 you canorder a drying tube with holder, for titrations that you have to run undera certain gas atmosphere a gas inlet, and for bottles with a different screwthread the appropriate adapter.

ill


Drying tube

Drying tube holder

Gas inlet

Adapter incl. gasket

Tube of silicone grease

Titration stand, complete, comprising:spacing ringthreaded ringclamping ringknurled screw (for securing the titration arm)

Rinsing unit, complete, withtitration head insert and stoppersfor titration head openings not in use1 Set of stoppers for rinsing unit

Order No.

23961

23915

23721

Bottles ofMerck, D

Fisher, USAFluka, CHFison, GB

Ericsen, USA

2377423787238172378925776

71300

DV70223842234552384523846

23821

101230

Disposable titration beakers, polypropylene, 100 ml(set of 1400)

Titration vessel, glass, 80 ml (set of 16)

101974

101446


Titration vessel, glass, 250 ml(set of 10)

Titration vessel, glass, 20 ml

Heat exchanger for thermostatingparticularly with sample changerincl. adapter with taper joint

Thermostatable titration vessel, glass

Combination universal glass electrodefor acid-base titrations (up to pH 14)in aqueous solution

Combination glass electrode with sleeve diaphragmfor acid-base titrations in nonaqueousmedia (up to pH 14 in water)

Combination platinum ring electrode forredox titrations

Combination silver ring electrode forargentometric and complexo metrictitrations

Cables for electrodes with plug-in head:Coaxial cable with DIN connector SC-DIN50 50 cmCoaxial cable with DIN connector SC-DIN100 100 cm

Double platinum pin electrode for voltametrictitrationsBanana plugs, cable length 50 cmBanana plugs, cable length 100 cm

Order No.

23515

23516

23834

23517

DG111-SC

DG112-SC

DM140-SC

DM141-SC

8960389604

DM142DM142/100


Propeller stirrer complete with 2 stirring rods

Stirring rod

Micro stirring rod

Order No.

23830

101229

25738

Photometric probefor colorimetrlcally indicated titrations

Phototrode, transmission measurement at 555 nmPhototrode, transmission measurement at 660 nmwith mirror cap

Mirror cap

Metal probe (stainless steel) for certainorganic solvents (e.g. tetrahydrofuran)with mirror cap

DP550DP660

22684

999186

Peripheral units

Alphanumeric printer (incl. connection cableNo. 42561, length 1.5 m)

METTLER balances with data output

Sample changer for 20 samples (100 ml) or ST20with a turntable for 14 samples of 250 ml(optional accessory)

GA44

AE, AM, AT, AJPE, PJ, PM


P*T"fc •^i l i"- ilv""" ' V ^ l i n - ™fff*&W/ •«• i —*)*ps*-p s*~-

„ tf J- * A * ' * J i t* J

Miscellaneous

Microfuses, 400 mA, slow-blow for 220/240 V,set of 3Microfuses, 800 mA, slow-blow, for 110/117 V,set of 3

Connection cable for METTLER AE balancesConnection cable for METTLER balancesof type PE, PM, AM, AJ, PJ, AT

Conversion cable dot matrix printer(with RS232C) - DL25 (CL)

Data output RS232C (DCE)

Connection cable for RS232C interfacemale - femalemale - male (enclosed with ST20Sample Changer)male (25-pin) - female (9-pin)

Adapter cable DL25 (RS232C, DCE) - DL25(RS232C, DCE) and ST20 Sample Changer(RS232C, DTE)

Order No.

51367

20182

2377823618

23827

23955

5934259348

59759

23826


it •'it^.i


j*ft&A>».tt

Appendix C: Installation procedure

Checking the operating voltage

Before switching on the system for the first time, make sure the voltacindicated on the yellow label (at the powercable socket) concides with thvoltage of the local power line. The power voltage is also indicated on thmodel plate next to the power cable socket.

Changing the operating voltage

wTo adjust the operating voltage of the instrument, proceed as follows:

Disconnect power cable!Place instrument on table as shown in illustration and loosen the sevescrews (1) with a Phillips screwdriver.Carefully remove bottom from upper housing and place it down on th.-;table.

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The transformer is built into the upper housing.Change brown cable (2) to the pin which is labeled with the local poweline voltage.Before reassembling the instrument, make sure connectors are all weconnected and positioned.When reassembling the instrument, make sure knob (3) used to adjusthe stirrer speed fits into the cutout of the upper housing made for thLpurpose. If an RS232C data output is built in, it must be inserted in the;upper housing with a slight pessure. Screw in the seven screws (1).If incorrect, cover up the voltage indication on the model plate by a labewhith the newly set voltage.Using a screwdriver, pull out the fuse holder (arrow) from between thepower switch and the power socket, and recheck the nominal current cthe microfuse:

100/117 V 800 mA slow-acting Order No. 20182220/240 V 400 mA slow-acting Order No. 51367


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Setting up the titration system

How to equip the titration headLoosely attach the titration Head (4) with the knurled screw (5) to theTitrator DL25/DL21, position it until the torsion-protection cam snaps in,then tighten knurled screw (5).Insert stirrer drive (6) from the top and stirring rod (7) from the bottom intothe center opening of the titration head (4) and attach them to each other.Insert burette tip (8) into one of the small openings and electrode (14) inone of the large openings next to the stirrer (6). Whenever possible, theyshould be placed opposite each other (better control conditions). Closeoff unused openings with stoppers.Place clamping ring (10) on threaded ring (9) and screw onto titrationhead (4) by turning twice. Press titration beaker upwards against theinside of the titration head and secure by screwing threaded ring (9) nottoo tight.Set a relatively high stirring speed, but avoid splashing.

Assembly of rinsing unitRemove sample beaker and stirrer.Unscrew threaded ring (9) completely, pull clamping ring (10) andspacing ring (11) out of the titration head (4).It is imperative that unoccupied openings in the rinsing unit (12) be closedwith stoppers (12b) in accordance with the procedure described below.Place rinsing unit (12) in titration head in a manner such that theconnecting tube (12a) is inserted into the opening with raised edge.Secure connecting tube by means of knurled nut (13).Connect rinsing-water bottle to connecting tube (12a) with tubing. Securetube endings with locking plastic rings.Place clamping ring (10) on threaded ring (9) and screw onto titrationhead.

Unoccupied openings must be closed with stoppers (12b) at all costs!For fitting, place stopper on the forefinger with the edge facing upwards.Position the stopper below the opening to be closed and press against thestopper with the metal rod (12c) (see illustration). Guiding the stopper inthis manner, press it into the opening.For removal, simply press out the stopper (12b) with the metal rod (12c).


Connection of stirrer, electrode and line recorderThe electrode cable plug (15) is plugged into either the DIN jack (16) orthe sockets (17).The stirrer cable plug (18) is plugged into the cinch socket (19). Thebanana plugs of the recorder cable are connected to the banana socketsbelow the power plug.

Attaching the sample beakerTurn threaded ring on bottom of titration head slightly to the left (loosen),and remove beaker with titrated sample. Press titration beaker with nextsample upwards against the inside of the threaded ring and manually turnring to the right until the beaker is attached. Avoid fixing the beaker,especially brown-glass beakers, too tightly as because the clamping ringthen loses its shape. As a consequence, it may then become difficult toremove the beaker. To restore the clamping ring to its original shape,unscrew the threaded ring, remove clamping ring and carefully stretch itby hand.


Installation and maintenance of theinterchangeable burettes

Inserting the piston

a. Piston (1,2 + 3) and piston rod (4) for a 10 ml or 20 ml burette.

Insert O-ring (1) in the groove of the lower part of piston (2) and screwtogether with piston head (3) and piston rod (4).

b. Piston (1,2 + 3) and piston rod (4) for a 5 ml burette:

O-ring (1) does not slot into its final position until piston rod (4) isscrewed into piston head (3).

a. Slide the piston carefully into the burette cylinder so that the broaderpart of piston rod (1) remains visible.

b. Press the burette onto burette holder (2) thus positioning the pistonexactly (3).

Inserting the burette

Slide the burette onto burette drive 3 (1) with the stop of the arrestmentknob (2) facing left. Secure the burette after it has snapped in by turningthe arrestment knob to the right.


Assembling the burette

- Lay gasket (2) on bottle (1) and sc

- Insert either stopper (5) or a dryin

NOTE: If you use a stopper as protection forthe reagentstopperwith the flat sides (seeotherwise an underpressure

rew on burette holder,

tube.

stopperwith the flat sides (see ACCESSORIES.always use the

: OrderNo.26646)will build up in the bottle.

- Push suction tube (5) into the bottle(5a) as kink protection - and screvburette head. Screw dispensing tube (6)place other end in the tip holder (7

- slide the red PE tubing over fittingit into the left connection on the

into the right connection and

- (8) is the burette head that you canto avoid smearing the inscription ontube.

emove when cleaning the cylinderlabel (9). (10) is the light protection

If you replace or clean parts of the stopcock (11threaded ring (11) and remove followevalve disk (14).

thePlace the rubber washer on the fodisk. You can then lightly smearsilicone grease. Press the three par!of the burette with cam (15) pointing outward (centered exactly)the burette, mount the threaded rinfollower cam.

lower cam followed by the valvesurface of the valve disk with

s from below onto the ceramic disk. Invert

and screw it on while holding the

, 12,13 + 14), unscrewcam (12), rubberwasher(13) and


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Cleaning the burette parts

Depending on the titrant, you should clean the burette cylinder, piston,stopcock and tubing relatively often.

- Slide the burette off the titrator, invert it and carefully take out the piston;this causes the burette contents to flow out through the suction tube.Turn the stopcock to the left through 90° and any liquid in the stopcockwill flow away through the dispensing tubing. Then disassemble theburette completely and clean each part:

- Depending on the contamination caused by the titrant, rinse cylinderand tubing with acid or deionized H2O then with ethanol and finally drythe parts with compressed air.

- Never attempt to remove any crystals in the cylinder by scratching witha hard object!

- Never put the parts in a drying oven at a temperature greater than40°C!

- Never place O-rings and rubber washers in organic solvents!

Notes for burette parts

- You can smear the piston rod with grease to protect it against rust.

- You should replace the piston if it leaks.

- You should replace the rubber washer of the stopcock fairly often asit becomes hard and brittle with time.

- With titrants that can crystallize out in the tip of the dispensing tube(KMnO4 or KOH/MeOH) and which you do not intend to use in the nearfuture, it is best to empty and clean the dispensing tubing: Unscrew itat the connection and the titrant flows out automatically. Then alsocheck the threaded connection and wipe off any drops!


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