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Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.

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“Step Out From the Old to the New”

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“The Right to Information, The Right to Live”

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“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

IS 6287 (1985): Methods of Sampling and Analysis for SugarConfectionery [FAD 16: Foodgrains, Starches and Ready toEat Foods]

Gr 10

IS: 6287 - 1985(Reaffirmed 1999)

Indian Standard

METHODS OFSAMPLING AND ANALYSIS FOR

SUGAR CONFECTIONERY

( First Revision)

First Reprint OcrOBER 2000

UDe 664.144/.149: 543.05: 620.113

© Copyright 1986

BUREAU OF INDIAN STANDARDSMANAK BHAVAN. 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

April 1986

IS 16287 -1985

Indian StandardMETHODS OF

SAMPLING AND ANALYSIS FORSUGAR CONFECTIONERY

( First Revision)

Bakery and Confectione ry Industry Sectional Committee, AFDC ,I

Chairman

SHKI R. B. RAGRep"Jtnll'l~

Utrarn Brscuu Company Ltd, Hydr-rabad

Directorate General of Technical Development,New Delhi

Odence rood Research Laboratory (Ministry ofDefence ), M} sore

Srrn i T. K. CHAKRABARTY (Alternate)SHRI G. S, BAINS Punjab Agr icultur.i l Uruversrty, Ludh ianaSURI N. B CHaUDHARY Brady & Morns Engineering Company Ltd, BombaySHRIl M DATIA Britannia Industri.-, L«I, Ilomhay

SHRI RAVI KRISHNA (Alternate)BRIG S. K. DEW AN Technical Standarrhzanon Committee ( Foodstuffs ).

Armv Purr.havo Orgaruvat ion ( MIn.,tI} of Foodand CIVil Supphes ), New Delhi

SlIftI K. S. KUISHNAMUIlTlIY ( Alternate }SHm R N. GHATAK Indian Yeast Company Ltd, Calcutta

DR T GUllA ( Altemat« )SHBI R. C, GuprA

MembersSlUU S. S. ARVA

SHI

IS : 6287 • 1985

( C.nlltlU4d from /Jag. I )

School of Baking, Gujarar Agricultural University,Anand

Indian Confectionery Manufacturers' Association,New Delhi

Warner Hmdusran Ltd, H yderabad

Members

SHUI K. K. MERRA

R'/Jres.nllng

Federation of Hotel & Restaurant Association ofIndia. New Delhi

Dlt V. B. MITUANOKR Modern Food Industries ( India) Ltd, New Delhin» M. M KIU'HINA (Alternale)

SHltI (. K. !'I,JON Royal Taney ')w.:-etmeat Saloon, BombaySu ur A. A. FIUVI ( Alternat« )

SHIU M. M. PATEL

SURI N. RAMAMUIlTIlY

DR T. BRAnDI\ U. Rxv r RAO ( AII'NUlt.)

SHRI M. G. SATHE Federanon of Biscuit Manufacturers' of India, DelhiSHiU M. N. KRANN\ ( AII.rnal.)

SII:OItI TARY Central Commun-e for Food Standards ( Ministry ofHealth and Family welfare ), New Delhi

SMT D. MUldlEltJI'E ( Allernal.)SHRI J. C. SIIAH Moruta Bakmg Corporation, Bombay

SHItI PANKAJ V. Sn x u ( Alternal.)SHRI K K. SIIAIlMA Daurala Sugar Worh, Daurala; and Indian Sugar

Mill, Assocrat ion, New DelhtSHRI S. R. SJllJRPAL!'lKAU Central Food Tel hnological Research Institute

( CSIR ), MysoreSURI S. B. SINI,)[ Publtc Analyst, (;OVl'rnment of Uttar Pradesh,

LucknowBRIG R. N. VmtMA Food Inspection Organization, Quartermaster

General's Branch (Ann) Headquarters), NewDeihl

LT·COL K. N. ACHAIlYA ( Allernal.)SHRI T. PUIlN\'i"\NI)\II, Director General, lSI (Ex-oiJicloMember)

DIrector \ A~n & r'ood )Secrelary

SIlIlIMA'I1 SUA'Inl SARI lo.NDeputy Director ( Agri & Food), IS I

Confectionery Subcommittee, AFDC 31 : 2

P.lrry'~ Confecnonery Ltd, Madras

Food Inspection Orgamzanon, QMC's Branch( Army Headquarters), Nt'w Delhi

Ravalgaon Sugar Farm Ltd, RavalgaonCentral Food Research and Standardization

Laborator y, GhazlabadNanonal Products, BangaloreDalima Biscuirr Ltd, RajpuraWarner Hindustan Ltd, Hyderabad

Convener

SHIll H. R. S. In NOAltMembers

Ll-COL K. N A( IlARYA

Slim B. S. GANGllLISHin S. S KATAltIASuar T. B. RAO

DR U. R~v[ RAO (Alternate)SnRI R. D. SHtNOY Hindustan Cocoa Froducts Ltd, Bombay

Suar S. J. KEKoR \D ( Altemat« )SHRI S. R. SHURPALI "AR Central Food Technological Research Institute

( CSIR ), My.ore

2

CJlIY.~· {'PI JlNIV,II, Anvrsa«Snur P. K. DHINOIt \

AMENDMENT NO. 1 MAY 2002TO

IS 6287: 1985 METHODS OF SAMPLING ANDANALYSIS FOR SUGAR CONFECTIONERY

( First Revision)

(Page 13. clause 8.3.1. line 6) - Substitute 'm' for 'M·.

( Page 13. clause 8.3.2 ) - Insert '(R)' after 'Reducing sugars. percent bymass'.

( Page 15.clause 9.3 ) - Substitute the following for the existing:

'9.3 Calculation

9.3.1 See 8.3.1 anti8.3.1.1.

m,9.3.2 Reducing Sugar (R,) '" - x 10

M,

where

ml =milligrams of anhydrous dextrose in 1 ml of solution (see 9.3.1). andM I = mass in g of the prepared sample used for making 100 ml of final

solution (see 9.2).

9.3.3 Sucrose. percent by mass =(R, - R ) x 0.95where

Rl = reducing sugar obtained after inversion. and

R =reducing sugar originally present (see 8.3.2).

(FAD 15)Reprography Unit. B'5. New Delhi. Indta

IS I 6287 • 1115

Indian StandardMETHODS OF

SAMPLING AND ANALYSIS FORSUGAR CONFECTIONERY

(First Revision)

n, FOR E W 0 R D0.1 This Indian Standard ( First Revision) was adopted by the IndianStandards Institution on 31 May 1985, after 'the draft finalized by theBakery and Confectionery Industry Sectional Committee had beenapproved by the Agricultural and Food Products Division Council.

0.2 Confectionery products are consumed by children in large quantities.It is, therefore, necessary that strict quality control measures are adoptedin their production. This standard was prepared with a view to provid-ing authentic methods of sampling and analysis, and facilitating theinterpretation of results on a uniform basis.

0.3 This standard was first published in 1971. It is being revised totake into account the new developments in test methods. For the deter-mination of trace metals the atomic absorption spectrophotometricmethods have also been introduced. The method for determination offat has also been replaced as the earlier one was not suitable forconfectionery products.

0.4 In reporting the results of a test or analysis made in accordance withthis standard, if the final value, observed or calculated, is to be roundedoff, it shall be done in accordance with IS : 2·1960·.

1. SCOPE

1.1 This standard prescribes the methods of sampling and analysis forsugar confectionery.

2. Q.UALITY OF REAGENTS

2.1 Unless specified otherwise, analytical grade reagents and distilledwater (lei IS : I070-1977t ) shall be employed in tests.

'Rules for rounding off numerical values ( reliiseJ ).tSpecification for water for general laboratory use ( uto"J r,vis;o" ).

3

IS 1 &287• 1985

3. SAMPLING

3.1 Geaeral Reqlllremeat8 of Sampling

3.1.0 In drawing, preparing, storing and handling samples, the follow-ing precautions and directions shall be observed.

3.1.1 Samples shall be taken in a protected place not exposed to dampair, dust or soot.

3.1.2 The sampling instruments shall be clean and dry when used.

3.1.3 Precautions shall be taken to protect the samples, the materialbeing sampled, the sampling instrument and the containers of samplesfrom adventitious contamination.

3.1.4 The samples shall be placed in clean and dry glass containers.The sample containers shall be of such a size that they are almostcompletely filled by the sample. The samples shall be filled loose andnot pressed in the container.

3.1.5 Each container shall be sealed air-tight after filling and markedwith full details of sampling, date of sampling, batch or code number,name of the manufacturer and other important particulars of theconsignment.

3.1.6 Samples shall be stored in such a manner that the temperatureof the material does not vary unduly from the normal temperature.

3.2 Scale of Sampling

3.2.1 Lot - All the containers in a lingle consignment of the materialdrawn from a single batch of manufacture shall constitute a lot. If theconsignment is declared to consist of different batches of manufacture,the batches shall be marked separately and the groups of containers ineach shall constitute separate lots.

3.2.1.1 Samples shall be tested for each lot for ascertaining itsconformity to the requirements of the corresponding specification.

3.2.2 The number of containers to be sampled from each lot shalldepend on the size of the lot and it shall be done according to Table 1.

3.2.3 The containers shall be selected at random from the lot and forthis purpose a random number table· as agreed to between the purchaserand the supplier shall be used. If such a table is not available, thefollowing procedure shall be adopted:

Starting from any container in the lot count them as 1, 2, 3, ......

. . h' he i I fN' Nup to , 10 a systematic manner, w ere, IS t e integra part 0 -./I

·S" IS : 4905·1968 Methods for random sampling.4

IS I 6287 - 1985

being the total number of containers in the lot, n the number ofcontainers to be selected (see Table I). Everv rth container thuscounted shall be separated until the requisite number n container isobtained from the lot to give the sample for the test.

TABLE 1 NUMBER OF CONTAINERS TO BE SELECTEDFOR SAMPLING

( Clause 3.2.2 )

NIJKBFR O} CON'lAI1'oFHS TOilE Str.EI Ttl>

(n) t OH SIZL 01' TilE C'ON1 ...I1'FR'

3.4 Nurnbes- of 'I'es t s and Criteria for Conformity

3.1.1 1\\1 th.- rr-q nu ements of the c.or respondrng ~rf'('Jfi( at io n ,Ii ill hI't(',ted on the (OIJ1po

18 I 6287 - 1985

4. PREPARATION OF SAMPLE4.1 Mince as quickly as possible with a sharp-edged knife or grind in adry pestle and moi tar, I 'i0 g of the sample on a clean porcelain slab.Mince rhorouuhly to secure a uniform sample. Store the minced sampleimmediately in an air-tight glass container and use this wherever the useof prepared sample i~ indicated.

5. DETERMINATION OF MOISTURE CONTENT ( VACUUMDRYING METHOD)

5.1 Procedure - Weigh accurately about 5 g of the prepared sample(see 4.1) in a tared aluminium flat divh with tight-fit cover having adiameter of about Ti mm and a heig-ht of about 25 mrn. Distribute themater-ial a~ evenly as practicab!e over the bot torn of the dish by gentlesidewise move ments. Place the dish in a vacuum oven, remove the coverof the dish and dry the man-rial for two hours .u 65 ± I''C at a pressurenot exceeding ')0 rn rn of mere ury. Run a current of dry air through thearea cluring dryrng. Remove the dish from oven, cover, dry in a desic-cator and wci~h Rerh y for aile hour and repeat the process till thedifference between t he two succevsive weighing~ is le~~ than 2 mg. Allowthe dish to rool to room temperatur e and weigh.

5.2 Calculations

5.2.1 Moivt iu P, percent by mass -

whore

M ~ lllass in g of the prepared sample taken for the experi-mr-nr , and

M 1 ~ 1ll,I~S in g of the material after drying.

NUTJ. I - 'iul"t.ll\ce' coru.urnru; no fruc tose or orhi r decomposable substance mayb~ dr red ftlr 3 hours .u 1,)(1 Cat uorma l pr..ssure,

N0111l'l - In t hv L\,,' 114111d Of ,em]-}JlluJl) subst ance-, prel immary drying wrt hquartz 'and Of purrucv ,10fH' sho ul.I be mad.. tin ,1 vtr-arn b.rth.

Drying ll/nJn PI/mice Stolle - ( Applicable to massecuitcs, molasses, andother liquid .md sorn iliq uid products) - Pr e par e pumice stone of 2gradl·g of fine nevs, one [0 pasv through l-rnrn sieve, other throuqh fi-rnmbut not I-111m SIC\'e. Dlt;"('sr path for 8 hours with hydrochloric acid( I : .~ ) on ,I srr-.rm b.u h, 'V,I,h ar-icl-fi eo and hc.u to 52')oC. Makedeterminanon JlI Il.i: metal dish of 50-Will dJamett'l. Place 3 m m layerof the fin« pu m ir (' stone on bottom of drsh, then 6 to 10 mm layer ofcoarse pumice stone, d I Y and weigh. Dilute sample with weighedportion of w.uvr so that the diluted material contains about 20 to 30pe-rcent of solid matter. Weigh into prepared dish an amount of dilutedsample to yield nbout 1 ~ of dry matter. If t his weighing cannot bemade rapidly, use a weighing bottle provided with a cork throughwhich ,\ pipette passes. Dry at 70°C under pressure of not greater than

6

IS I 6287 • 1985

50 mm mercury ( 6·7 kPa ) bleeding with dry air. Make trial weighingsat 2 hours intervals towards end of drying period until change in mass isnot more than 2 mg. Report loss in mass as water. Substances contain-ing little or no fructose or other readily decomposable substance may bedried in an oven at 1000e.

Drying on Quartz Sand - ( Applicable to massecuites, molasses, andother liquid and semiliquid products) - Digest pure quartz sand thatpasses through 425-rnicron but not through 250-micron sieve withhydrochloric acid, wash acid-free, dry and ignite. Preserve in a stopperedbottle. Place 20 to 30 g prepared sand and short stirring rod in dishabout 55 mm diameter and 40 rnrn deep and fitted with a cover. Drythoroughly, cover dish, cool in a desiccator and weigh immediately. Addenough diluted sample of known JTIa~s to yield about I g of dry matterand mix thoroughly with sand. Hnat on a steam bath for 15 to 20minutes stirring at 2 to 3 minutes intervals, or until mass become, toostiff to manipulate readily. Dry at less than 70°C (preferably 60°C)under pressure not more than 50 mrn mercury ( 6'7 kPa ) bleeding withdry air. Make trial weighings at 2 hours intervals towards end of dry-ing period ( about 18 hours) until change in mass is not more than 2 mg.For materials containing no fructose or other readily decomposablesubstances dry for 8 to 10 hours at atmospheric pressurp in an ovenmaintained at \OO°C. Cool in a des icca tor , and weigh, repeatingheating and weighing until loss in I hour heating is not greater than2 mg. Report loss in mass as Water. (As dry sand, and dried sampleabsorbs appreciable moisture on standing over most desiccating agents,make all weighings as quickly as possible after cool ing in a desiccator. )

6. DETERMINATION OF SULPHATED ASH

6.1 Reasent6.1.1 Sulphuric Acid - 10 percent ( mim ).

6.2 Procedure - Accurately weigh about 5 g of the prepared sample( see 4.1.1 ) into a 9-cm diameter platinum basin. Add 5 ml of sulphuricacid to the material in the dish. Gently heat the dish OIl a hot plateuntil the material is well carbonized, and then increase the heat until theevolution of sulphuric acid fumes ceases. Ash the carbonized matterin a muffle furnace at 550 ± 25"C. Cool the ash and moisten it with2-3 ml of sulphuric acid ( see 6.1.1). Heat strongly on a hot plate untilsulphuric acid fumes cease to be evolved and finally ash in t hr- mufflefurnace at 550 :i: 25°C for about 'L hours. Cool in a deviccator andweigh. Heat again in the muffle Furnace for 30 minutes at 550 :i: 25°C.Cool in a desiccator and weigh. Repeat the process of heating in themuffle furnace for 30 minutes, cooling and wei~hmg till the differencebetween two successive weighings is less than I mg. Record the lowestmass.

7

IS : 6287 • 1985

6.3 Calculation

100 u,6.3.1 Ash, sulphated, percent by mass =- M2

where

M1 - mass in g of the ash, andM 2 c= mass in g of the prepared sample taken for the test.

7. DETERMINATION OF ACID INSOLUBLE ASH

7.1 Reagent

7.1.1 Dilute Hydrochloric Acid - Approximately 5 N (prepared fromconcentrated hydrochloric acid ).

7.2 Procedure - Weigh accurately about 5 g of the prepared sample( see 4.1 ) in a tared, clean and dry platinum basin of 100 ml capacity.Carbonize the material in the dish with the flame of a burner. Completethe ignition by keeping in a muffle furnace at 550 ± 25°C until grey ashresults. Cool in a desiccator. To the ash, add 25 ml of the dilutehydrochloric acid, cover with ,1 watch glass and heat on a small flame ofa burner to near boiling. Allow to cool and filter the contents of dishthrough Whatman filter paper No. 42 or its equivalent. Wash thefilter with hot water until the washings are free frorn chlorides. Returnthe filter and the residue to the dish. Keep it in an air-oven maintainedat 105 ± 2"C for about :I hOUI~ Icnitc in the muffie furr.,. I' at550 ± 2')'C for one houi , Cool the d ish m a desiccator ark' we,,;h.Heat again for 10 minutes in the muflle fur n.« e , cool and weigL. j '('[''23(this proccs~ of heating fOI 10 minu u.v, coolill~ and weighi!,,;. u: ;.,'dlfrclcnc(' between two surccsvivc wei'4hlll~~ i., less than one milligram.Note the lowest mass.

7.3 Calculation

7.3.1 Acid insoluble ash, percent by mass

where

M 1 "'" mass in ~ of the acid insoluble ash, and

M 2 :2 m.1SS in g of the pr epared sample taken for the test.

8. DETERMINATION OF REDUCING SUGARS

8.1 Reagents

8.1.1 Stock Solution of Dextrose -- \Vcigh accurately 10 go of anhydrousdext rose mto a l-Iitr e gr.iduated Ilask and dissol ve it in water Add tothi s solution 2'5 g of benzoic acid, sh ake to dissolve the benzoic acid andm.ike up the volume to the mark With water. (This solution vliall notbe used after 48 hours ).

8

IS t 6287 • 1985

8.1.2 Standard Dextrose Solution - Dilute a known aliquot of the stocksolution of dextrose (see 8.1.1 ) with water to such a concentration thatmore than 15 ml but less than 50 ml of it will be required to reduce allthe copper in the Fehling's solution taken for titration. Note the concen-tration of anhydrous dextrose in this solution as milligrams per 100 ml( see Note ), prepare this solution fresh every day.

NaTE - When 10 ml (see 8.3.1) of Fehling's -olution arc taken far titration, astandard dextrose solution conrainmg 0'11 to 0'30 percent (mjv) of anhydrousdextrose is convenient for use.

8.1.3 Methylene Blue Indicator Solution - Dissolve 0'2 g of methyleneblue in water and dilute to 100 ml.

8.1.4 Petroleum Ether - Re-distilled below 60°C.

8.1.5 Fehling's Solution (Soxhlet Modification) - Prepared by mixingimmediately before use, equal volumes of solution A and solution B.

8.1.5.1 Solution A - Dissolve 34'639 g of copper sulphate (CUS045H20 ) in water, add 0'5 ml of concentrated sulphuric acid of sp gr1'84 and dilute to 500 ml in a graduated flask. Filter the solutionthrough prepared asbestos.

8.1.5.2 Solution B - Dissolve 173 g of potassium sodium tartrate( KNaC4H 40 a, 4H20 ) ( Rochelle salt) and 50 g' of sodium hydroxide,analytical reagent in water, dilute to 500 ml in a graduated flask andallow the solution to stand for two days. Filter the solution throughprepared asbestos or filter paper ( Whatman No.4).

8.1.5.3 Standardization of Fehling's solution - Pour standard dextrosesolution ( see 8.1.2 ) into a 50-ml burette ( see Note 3 under 8.2.3). Findthe titre ( that is the volume of standard dextrose solution required toreduce all the copper in 10 ml or Fehling's solution ) corresponding tothe concentration of standard dextrose solution from Table 2. (If, forexample, the standard dextrose solution contains 167'0 mg of anhydrousdextrose per 100 rnl, the corresponding titre would be 30 ml ). Pipette10 ml (see 8.3.1.1 ) of Fehling's solution into a 300-ml conical flask andrun in from the burette almost the whole of the standard dextrosesolution required to effect reduction of all the copper, so that not morethan one rnillilitre will be required later to complete the titration. Heatthe flask containing the mixture over a wire gauze. Gently borl thecontents or the flask for 2 minutes. At the end of 2 minutes of boiling,add without inter-rupting borling , one millilitre of methylene blueindicator solution. While the contents of the flask continue to boil,begin to add standard dextrose solution ( one or two drops at a t irne )from the burette till the blue colour or the indicator just disappears.[The titration should be completed within one minute so that thecontents of the flask boil together for 3 minutes without interruption(see Note 2 under 8.7.3) J. Note the titre ( that is the total volume in

= 30'1

- 167'0

= Titre in ml X numberof mg of anhydrous dex-trose in one miIlilitre ofstandard dextrose solu-tion

IS I 6287 • 1985

rnillilitres of standard dextrose solution used for the reduction of all thecopper in 10 ml of Fehling's solution). Multiply the titre ( obtained bydirect titration) by the number of milligrams of anhydrous dextrose inone millilitre of the standard dextrose solution to obtain the dextrosefactor. Compare this factor with the dextrose factor given in Table 2and determine correction, if any, to be applied to the dextrose factorderived from Table 2.

Example:

Concentration in mg/IOO ml ofanhydrous dextrose in standarddextrose solution

Titre in ml obtained by directtitration

Dextrose factor for 30'1 ml ofstandard dextrose solution

Dextrose factor for 30'1 ml ofstandard dextrose solutionfrom Table 2( calculated by interpolation)

Correction to be applied to thedextrose factor derived fromTable 2

=a 30'1 X 1'670= 50'2670

= 50'11

- 50'2670 - 50'11= + 0'1570

8.1.6 Zinc Acetat» Solution - Dissolve 21 9 g of zinc acetate[ Zn ( C2H302 l2. 2H20] and 3 ml of glacial acetic acid in water.Dilute to 100 ml.

8.1.7 Potassium Ferrocyanide Solution - A 10'6 percent aqueous solution.

8.2 Procedure

8.2.1 Preparation of Solution - Wei~h accurately about ') ~ of samplein a beaker and transfer into a '200-ml volumetric flask quantitativelywith the aid of warm water Dilute to about ISO mi. In case thesolution is not sufficiently clear, ad I with gently m ixing 5 ml zinc acetatesolution, and rrux , followed by ;) 101 of potassium ferrocyamIe solutionin the same manner. Make the volume up to the 200-ml rnu-k Filterthrough a Whatm"1n filter paper No. 40 or its equivalent. Collect thefiltrate for titration

10

IS I 6281 • 1985

TABLE 2 DEXTROSE FACTORS FOR 10 ml or FEHLING'S SOLUTION( CltJum 8.1.5.3 and 8,3.1 )

TITRE DEXTROS.~ DEXTROSF' CONTE!'>1'FAl 'ron" PP'R 100 ml fH

SOLIJTION

(I) (2) (3)

ml mg

15 49 I 32716 49'2 30717 49':5 28918 49'3 27419 49'4 26020 49'5 247421 49-5 235822 49'!> 225523 49-7 21b-12~ 498 207'425 49-B 199326 49'9 191821 49-9 \S4928 50'0 178-529 50'0 172'530 50'1 167031 50-2 161'832 50'2 IS!> 933 503 151.'434- 503 146 ()35 50'4 148 'J36 50'4 \40'037 50'S 136-438 505 1~2'939 50-6 129'(,.f{) 50-6 126-541 507 123_642 507 120 B43 508 118'1H 50'8 115'545 509 113'04tJ 509 110'647 51 0 lOB 44-8 510 105249 51 0 104-1'}O '>1 I 102'2

• Mrlhgams of anhydrous dextrose corre-pondmg to III ml of I ehhng\ soluuon,

11

I.:6287· )9858.2.2 Incremental Method of Titration - Pour the prepared solution

( so 8.2.1 ) into a 'lO·ml burette ( se« Note 3 under 8.2.3). PIpette 10 mlof Fehling's solution into a 300-ml conical flask and run in from theburette 15 ml of the prepared solution Without further dilution, heatthe content, of the fta ..k over d wire gauze, and boll. (After the liquidhas been boilmg for about 15 seconds it will be possible to judge ifalmost all the copper IS reuuced by the brrght led colour imparted tothe boihng hqurd :Jy the suspended cuprous oxide ). When it is judgedthat nearly all the copper is reduced. add one rmlhbtre of methyleneblue rndicator solution ( see Note I). Conunue boiling the contents ofthe flask fOI one to two minutes from the commencement of ebulhuon,and then add the prepared solution 10 small quantities ( one millihtre orless at a time) allowing the liquid to bot! for about 10 seconds betweensuccessive addrnons, till the blue colour of the indicator just disappears( see Note 2 under 8.2.3) In case there still appears 10 be much unre-duce d lopper after the mixture of Fehlmg's solution with 15 ml of theprepared solution has been hading for 15 seconds, add the preparedsolution from the burette in larger increments ( more than one millilitrcat a time according to judgeme-nt ) and allow the mixture to boil for15 seconds after each addruon. Repeat the addition of the preparedsolution at intervals of 15 seconds until It IS consrdered unsafe to add alarge increment of the prepared solution. At this stage, continue theboiling' for an additional one to two minutes, add one rnrllrlitre ofmethylene blue indicator solution and complete the ntrauon by addingthe prepared solution in small quannties ( less than one millilitre at atime) ( see also Note 2 ).

NL.CI;. r It." aJ\ b.luI .. net tv al:d dole ul(~i\..dtor unt.l tht. c nd pc.n, has ~,-~llnearly reached because the mdicator retarns ItS full colour until the end POint ISalmost rl'lIched and thus gives no warning to the operator t" go slowly,

NOTE 2 - Whl'n t he operator has had a fair amount of experience with themethod, a -ufficient ly accur.ite result may oflen be obtained b) a .mgle est imat ronby the mer- mental mel hod of urrauon For the ut most degree of accuracy of whrchthe method IS capable, a second t n r u ion should be carr-red out by the standardmethod of turanon ( st' 8.:1.3).

8.2.3 Standard Me/hod of T'itrntum - Prpeuc 10 ml of Fehling's solutioninto a 100-rnl conical flask and run in fi orn the burette almost the"hole of rhr- prepare-d

IS I 6287· 1985

In case of doubt, the flame may be removed from the wire gauzefor one or two seconds and the flask held against a sheet of while paper.(A holder of paper, suitably fixeu around the neck of the flask IS veryconvenient for this purpose as it can be left round the neck of the flaskwithout risk of overbalanrmg it.) The top lodge of the lrquirl wouldappear bluish If the indicator is not r o mplere ly dec olour ize d. It isinadvisable to interrupt the boding 1'01 ITIOI e t han a few seconds as theindicator undergoes back oxidation rather r a prdly when air IS allowedfree access into the flask, but then' i s no danger of t hiv as long as acontinuous stream of steam is issuing from the mouth of the flask.

NOTE 1 - The mdicator 1\ so seusrrive that It IS possible to den rrmne the endpoint within one drop of the prf'pared solut ion in rnanv C.. 'N. 1 he completedecolourauon of the mcrhvlene hl ur "U'uall) indrcared by the whole reactIon liquid,In which tbe cuprous OXIde 1\ con nnuously churned up, becormng bnght red ororange in colour.

NOTE 2 - It should be obse-rved that with both incremental and standard methodsof titration, the flask conrammg the re vctron mixture I~ left on the wire gauze overthe flame throughout the titration, except when It may be removed for a few secondsto ascertain If the end point IS rear h- d.

NOTE 3 - In adding sugar volut ion to the r eact ron mixture, th.. burette may beheld in hand over the flask. 1 h,' burette mav he filll'd with a small outlet tube benttwice at rrghr angles, so t hat the bod) oj t he bur(,lt<

IS I 6287 - 1985

M' =- mass in g of the prepared sample used for making100 ml of solution ( see 8.2.1 ).

TABLE 3 DEXTROSE FACTORS FOR 25 ID.I OF FEHLING'S SOLUTION( Claus»8 3 1.1 )

TITll~ DEXTRON!': DEXTllOSl'; CONTENTFACTOR· P~R lOa ml OF

"iOT,UTJONml mg

(I) (2) (3)

15 120'2 80116 120'2 75117 120'2 70718 120-2 66819 120'3 b3820 1203 GOI521 120'3 572'922 120'3 547'323 IlO·of. 523624 120'5 501925 120'5 48202b 120'6 463727 120'h 446'828 1207 431 I29 120'7 416'430 120 II 402731 120'8 389732 1201\ 377 633 120-'l 3b6334 120'9 355'635 121'0 345'63(, 121'0 33(>'337 121'1 327438 121'2 318839 121'l 310 740 121'2 303'141 121'3 295942 121 4- 289043 121'4- 2824-44- 121'5 271'I45 121 5 270 I46 12\ fi 2fi4- 347 121 fi 258 e48 121'7 253 ~49 III 7 248450 121 8 2436

NUTI': - Tables 2 and 3 vhow, for the stand ird method of ntranon, the valuescorrepondong to ontpgnl mdhhtres of the sugar soiut ron, mterrned rare values beingobtained by Inteq!OJallon,

*MIIIIgram! of an hvdrouv dext ro-» corr... pondmg to 25 ml of F, hl'ng', so lutron,

14

IS: 6287 • 1985

9. DETERMINAnON OF SUCROSE

9.1 Reagents

9.1.1 Concentrated Hydrochloric A, id - sp ~r 1'16, analytical reagentgrade.

9.1.2 Fehling's Solution (Soxhlet Modification) -- Prepared by mixingimmediately before use, equal volumes of Solution A and Solution B.

9.1.2.1 Solution A - Dissolve 34 639 g of copper sulphate ( CUS04'5H20) in water, add 0':> ml of concentrated sulphuric acid of sp gr1'84 and dilute to 500 ml in a graduated flask. Filter the solutionthrough prepared asbestos.

9.1.2.2 Solution B - Dissolve 173 g of potassium sodium tartrate( KNaC4H40e, 4H20) Rochelle salt and 50 g of sodium hydroxide,analytical reagent, in water. Dilute to 500 rnl in a graduated flask andallow the solution to stand for two days. Filter this solution throughprepared asbestos.

9.2 Procedure - Take 10 ml of the prepared solution ( set! 8.2.1 ) in aconical flask and add 1'5 ml of the concentrated hydrochloric acid andabout 10 ml of water. Heat the flask at 60 to 70'C for 10 minutes in awater-bath Cool immediately and neutralize with 30 percent sodiumhydroxide ( mtu ) and transfer quanntauvcly the neutralized invertedsolution to a graduated flask and make lip the volume to 100 mJ.

Determine the reducing sugars in the inverted solution as describedin 8.

9.3 CalcnladOD

9.3.1 Sur rose, percent by mass ( a - R M ) 6'95M

where

a = the value in col 3 of Table 3 corresponding to the titre;R - reducing sugars, percent by mass ( see 8 ); andM -- mass in g of the original material taken for the test

( see 8.2.1 ).

10. DETERMINATION OF FAT

10.0 Two methods for the determination of fat are given. Any of thesemay be used. If the confectionery is known to contain milk, methodNo.2 (Roese-Gottlieb Method) wherein ammonia is used to dissolvethe milk protein before fat extraction may be used,

13

IS : 6287 - 1985

10.1 SiDlple EstractioD Method

10.1.1 Apparatus

10.1.1.1 Mojonnier fat extraction tube or any other similar apparatus.

10.1.1.2 Flasks

10.1.2 Reagents

10.1.2.1 Diethyl ether - peroxide free.

10.1.2.2 Petroleum ether - boiling range 40 to 60°C.

10.1.3 Procedure - Dissolve 10 g sample in 10 mJ of warm water andintroduce Into Moj »nnier fat extraction tube or similar apparatus. Add25 ml peroxide free diethyl ether. Cork the tube and shake vigorouslyfor I minute. Add 25 ml of petroleum ether and shake vigorously for30 seconds. Let it stand for 30 minutes or until separation is complete.Draw off the fat solution into a suitable flask ( previously dried at 100DC,cooled and weighed). Repeat the extraction and subsequent operationstwice more. Evaporate the ether and dry the fats for I hour at IOODC.Cool and weigh.

10.1.4 Calculations

10.1.4.1 Fat, percent by mass ( on dry basis)

when>

M 1 - mass in g of extracted fat,

M 2 mass in g of the prepared sample taken, and

AI = percentage of moisture in the material.

10.2 Roese-Gottlieb Method

10.2.1 A/JParalus

10.2.1.1 Mnjonl'lier fat extraction tube or similar apparatus

10.2.2 Reagents

10.2.2.1 Concentrated alnmall1a solution - \ P gr 0'88.

10.2.2.2 Ethyl alcohol W) to (\6 pel cent ( u'u ).

10.2.2.3 Diethyl ethrr - ~p 0;1' 0'720 ( peroxide free ).

10.21.4 Petroleum ether -- boilin\.{ range 40 to 60°C, recently distilled

16

IS I 6287 • 1985

10.2.' Method

10.2.3.1 Introduce 4 g sample or amount of uniform solventequivalent to this weight of dry substance into a Mojonnier fatextraction tube or similar apparatus. Dilute to 10 rnl with water. Add1'2 ml ammonia solution and nux thoroughly. Add \0 ml alcohol andmix; then add 25 cui ether and shake vigorously for about 30 secondsand finally add 25 ml petroleum ether and shake again for about30 seconds. Let stand for ~O minutes or until separation of liquids iscomplete.

10.2.3.2 Draw off as much as possible of ether-fat solution (usually0'5 to 0'8 ml is left) into a weighed flask through a small rapid filter.Weigh flask with a similar one as counterpoise. Again extract liquidremaining in tube, t his time with IS ml each of ether and petroleumether; shake vigorously for about 30 seconds with each solvent and letsettle. Proceed as above, washing mouth of tube and filter with a fewrnillilitres of mixture of equal parts of the two solvents ( previouslymixed and freed from deposited water ).

10.2.3.3 For greater degree of accuracy, repeat extraction. Ifpreviously solvent-fat solutions have been drawn off closely, third extrac-tion usually yields approximately up to I mg fat or about 002 percentwith 4 g sample. Slowly evaporate solvent on steam bath and then dryfat in an oven maintained at 100°C to constant mass. Test purity of fat bydissolving in a little petroleum ether. If residue remains, wash out fatcompletely with petroleum ether, dry the residue, weigh and calculatethe mass of the fat.

n. DETERMINATiON OF PROTEIN11.1 Apparatus

lI.I.l A recommended apparatus, as assembled, is shown in Fig. I.

11.1.1.1 Description - The assembly consists of a round bottom flaskA of I 000 ml capacity fitted with a rubber stopper through whichpasses one end of the connecting bulb tube B. The other end of thebulb B is connected to the condenser C which i~ attached, by means of arubber tube, to a dip tube D which dips into a known quantity ofstandard sulphuric acid contained in a beaker E of 250 ml capacity.

11.1.2 Kjeldahl Flask - Capacity 500 ml.

11.2 Reagents

11.2.1 Anhydrous Sodium Sulphate

11.2.2 Copper Sulphate

11.2.3 Concentrated Sulphuric Acid - sp gr 1°8417

S : 6287 • 1985

FlO. 1 DISTILLATION ASSEMBLY

11.2.4 Sodium Hydroxide Solution - Dissolve about 225 g of sodiumydroxide in 500 ml of water.

11.2.5 Standard Sulphuric Acid - 0'1 N.

11.2.6 Methyl Red Indicator Solution - Dissolve one gram of methyl red1 200 ml of rectified sp irit ( 95 percent lI/O )

11.2.7 Standard Sodium Hydroxide Solution - 0'1 N.

18

IS I 6287 - 1,.5

11.3 Procedure

11.3.1 Transfer carefully about one to two grams of the materialaccurately weighed, to the Kjeldahl flask, taking precaution to see thatparticles of the material do not stick to the neck of the flask. Add about10 g of anhydrous sodium sulphate, about 0'2 to 0'3 g of copper sulphateand 20 mI of concentrated sulphuric acid. Place the flask in an inclinedposition. Heat below the boiling pomt of the acid until frothing (eases.Increase heat until the acid boils vigorously and digest for 30 minutesafter the mixture becomes clear and pale green or colourless. Cool thecontents of the Hask. Transfer quantitatively to the round bottom flaskwith water, the total quantity of water used being about 200 ml Addwith shaking a few pieces of pumice stone to prevent bumping Addabout 50 ml of the sodium hydroxide solution (which is sufficient tomake the solution alkaline') carefully through the side of the flask sothat it does not mix at once with the acid solution but forms a layerbelow the acid layer. Assemble the apparatus as shown in Fig. Itaking care that the dip tube extends below the surface of the standardsulphuric acid contained in the beaker. Mix the contents of the flaskby shaking and distil until all ammonia has passed over into thestandard sulphuric acid. Shut off the burner and immediately detachthe flask from the condenser. Rime the condenser thoroughly withwater into the beaker. Wash the clip tube carefully so that all tracesof the condensate are transferred to t he beaker When all the washingshave been drained into the beaker, add two or three drops of methylred indicator solution and titrate with the standard sodium hydroxidesolution.

11.3.2 Carry out a blank cletcr minat ron IISll1£; all rl'at~pnt~ ill t ho qlll('q uantities but without the rnater i.il to hr- H>'ted

11.4 Calculation

Il.4.1 Total protein ( }If (,25 )percent by mass

where

B 7:'1 (Ii - ,1 ) N111

B =- volume in m] of tile vtan.Ia r d so diu m hydlo'\.idl'

18 f 6287 • 1985

12. DETERMINATION OF SULPHUR. DIOXIDE

12.1 Apparatu.

12.1.0 The apparatus. as assembled, is shown in Fig. 2.

SODIUMC.ARBONAlE.SOLUTION

(ARBONDIOXIDE----B

7~Oml

100ml

COLDWATER

H

L

HYDROGEN PEROXIDEsorur ION

['10. 2 ASSEMBLY OF ApPARATU~ FUR TH£ DETERMlNA1'lON 01'SULPHUR DIOXIDE

12.1.1 The apparatus consists of the round bottom flask C of capacity750 ml lit ted with the three-hole ~toppel' D. The rubber stopper D isfitted with the delivery tube B, the dropping funnel E. and the sloping,water-cooled, reflux condenser F, the lower end of which is cut off atan angle. The free end of delivery tube B is connected to the washbottle A contaming sodium carbonate solution. The upper end of thereflux condenser F is connected to the deliver y tube }-{ by the rubberstopper G. The free eml of the delivery tube II nearly reaches thebottom of the 100 ml Erienrneyr-r flack J containing 25 ml of hydrogenperoxide solution I'he Erlenmeyer flask] is provided with a two-holerubber stopper; I hrouuh one hole passes the delivery tube 1/ and throughthe other tube K. The fief' end of the tube K IS connected to the Peligottube L containing 5 ml of hydrogen peroxide solution.

12.2 Reagent

12.2.1 Sodium Carbonate Solution - 10 pel cent ( mtn ), aqueous.

20

IS : 6287 - 1985

12.2.2 Bromophenol Blue Indicator Solution - DIssolve 0 I g ofbromophenolblue in 3'0 rnl of 0 05 N sodium hydroxide solution and 5 rnl of ethylalcohol (90 percent by volume) by gently wdrlllmg Make up thevolume of the solution with ethyl alcohol ( 20 percent vllJ ) to 250 mlma volumetric flask.

12.2.3 Hydrogen Peroxide Solutum - Dilute ,) 30 pel cent ( mi» ) hydlOgenperoxide solution with about twice Its volume of water and neutralizethe free sulphurrc acid that may be present J1I the hy dr ogen peroxidesolution wrth barrum hydroxide -o lut ion, USing bromophenol bluemdrcator solution. Allow the prer ipuate of barium sulphate to SI ttle,and filter. Determme the concentratron of hydi ogen peroxide In thofiltrate by ntraung with standard patas'JUIII pei ma nganate solutronDIlute the filtrate with cold warei so as to obtain a 3 percent ( mIl)solution 01 hydrogen peroxide.

12.2.4 Concentrated Hydrochloric ACId - ~p gr I 16.12.2.5 Carbon Dioxide Gas - fi orn a cy lmdr.r12.2.6 Standard Sodium Hydroxide SOLutiOTl - Appi oxnnate Iy 0 I 1\"

standard ized at the tJ me of the expct iruent 1ISlIl!; brornoplu nol blur-indicator solution.

12.3 Procedure12.3.1 Assemble the appar.ltu~ as shown In Fig 2 Introcluc e Into t he

fl ask C, 300 ml of \\ arer and 20 1111 of r oncent rated hy.lro. Idol II' acidthrough the dr oppmg funnc I E Run a steady CUrI'lIt of coldVI ater through the con ck nser /. Bod the JIllxtUIC com ainc d III theflask G fOI a short tune 10 ox pe l all flam t he ~y"[( III III c.urr enr of c.u bo ndroxu!e gas previou-Iy passed tluough th. w.ish bott lr- A \\'''I~haccur ately about 100 g of the m.uer ial and rmx wu h the nnrn m u ruquantity of water so as to make rhe .hluted ma ter ia l ea,ily now down 10the dropping funnel Inn ocluce the di lutcr] m ater rul i nt o the Ila-k Crhrou ah the dropping funnel Z' Wa,h t lu- (iJopplllg fu nru I with d vnr.i l]quantIty of water and run the' w.islung 1Il10 t he flask C Ag.lIll hod rhemixture contained JI1 the Ilask C lJl a vlow CUI rent of cal bon dIOXide gas(lMssed previously thro uvh the wash bottle A) fOl 01H' hom [ustbefore the end of the drsnllauon, stop the flow 01 w.uer HI the colldlll,el( 1 hrs causes the condenser to become hot and (II IVP~ 0\ e r rr ~Illu.dtraces of sulphur dioxrde I f'lamed In the condenser ) When th- clch verytube H, just above the Erlenmeyer fla'J.,.]. beco mc- hot to touch, removethe stopper] rm med rate ly Wa"h the dclrvcry tube II .wl! lIlt' r ontr Ills01 the Pelrgot tube L wit h w arr-. into the Er Ieruueyer flask Copj thecontents of the Er k-mneyer Ilask to loom ternperatu n-, add a few dropsof bi omophenol blue mdrcator solunon and t nr.ue w ith ~t arid arrl sodiumhydroxide solunon (Bromopllf'nol hlue IS u naffec tecl by cal bon choxrdeand !.;Ives a disunct change of colour in cold hydrogen peroxidesoluuon ).

21

32 030 ( V - v ) NM

IS I 6287 - 1985

17.3.2 Carry out a blank determination using 20 mJhydrochloric acid diluted with 300 ml of water.

12.4 Calculation12.4.1 Sulphur dioxide,

mg/kg

where

of concentrated

V volume in ml of standard sodium hydroxide solutionrequii ed for the test with the material;

II volume in ml of standard sodium hydroxide solutionrequired for the blank determination;

N normality of standard sodium hydroxide solution; andM mass in g of the material taken for the test.

13. DETERMINATION OF ARSENIC

13.0 Two methods for the determination of arsenic have been prescribed,n .rnely, the visual comparison method and the silver diethyldithiocarba-mate method. Any of the two methods may be used, however for refereepurposes the silver dicthylditbiocarbamatc method shall be used. Thismethod is however applicable for quantities of arsenic (as As) in therange I to 20 ",g.

13.1 Vi.ual Comparison Method

13.1.1 Apparatus

13.1.1.1 Distillation apparatus - Assembled as shown in Fig. 3.

13.1.1.2 Apparatus for the tletermination of arsenic - Assembled asshown in Fig. 4. The apparatus consists of the following parts:

a) Wide-mouth bottle - Capacity 120 ml.b) Glass tube - Made from ordinary glass tubing and having a

total length of 200 mm. It should have an internal diameter ofexactly 6'S mm and an external diameter of about 8 mrn. It isdrawn out at one end to a diameter of about one millimetre anda hole not less than 2 mm in diameter is blown in the side of thetube, near the constricted part The upper end of the tube iscut off square and is either rounded off slightly or groundsmooth.

c) Rubber bungs - Three. One fits exactly into the mouth of inewide-mouth bottle and has a hole bored centralIy to take thelube from lIS constricted end. Each of the other two rubberbtl ngs (abollt 2') X 25 mm) ha-, a hole, exactly 6 5 mrn in dia-rneter , borr-d centrally and are fitted with a rubber band orspring clip for holding them tightly together.

22

IS : 6287 - 1985

d) Preparat~on of the glass tube - MOIsten a small quantity of cottonwool with lead acetate solution and then dry it in a dust freeatmosphere. LIghtly pack the g lass tube with this cotton wool,so that the upper SUI face of the cotton w 001 is not less than1S mrn below the top of the rubr-, Insert the upper end of thetube into the narrow end of one of the p.ur of rubber bungseither to a depth of about IO mm ( when the tu be has roundedoff end) or to vuc h an extent that the ground end of the tube isHush with larger end of the bung. Plate a piece of mercuricchloride paper flat on the top of the bung Place the other bungover this with its larger end In contact with the piece of mercu-ric chloride paper. Fasten the two bungs by means of therubber band DC the spring chp III such a manner that the borrngsof the two bungs (or the upper bung and the glass tube) meetto form a true tube of 6'5 mm diameter Interrupted by adiapharagm of mercuric chloride paper.

Instead of this method of atrachmg the mercuric r hlorrde paper anyother method may be used provided that (a) the whole of the evolvedgas passes through the paper, (b) the pOItion of the paper III contact withthe gas is a circle of 6'S mm diameter. and (c) the paper IS protectedfrom sunlight during the test.

13.1.2 Reagents

13.1.2.1 Dilute nunc acid - 30 percent.

13.1.2.2 Concentfated sulphuric acid - sp gr I 84

13.1.2.3 Concentrated ntlrtc acid - sp gr 1'42.

13.1.2.4 Chloride-hydrazme-bromtde mixture - MIX ') g of sorhu mchloride, 0·5 g of hyclrazrne sulphate and 0'02 g of potassium bromidefollowed rapidly by 10 ml of concentrated hy droch lor ic ar id and storein a tightly stoppered bottle.

13.1.2.5 Lead acetate solution - 10'0 nercent ( mIl' ) in distilled waterrecently boiled.

13.1.2.6 Mercuric chloride paper - Smooth white filtcz paper, not Jessthan 25 mm in WIdth, soaked in a satu rated solution of rnercnr icchloride in warer; pressed to remove superfluous solution, and dried at60°C in the dar k. The grade of the filter paper shall be SUt h that themass in glm2 shall be between 65 and 120; the rh ickness in mm of 400papers shall be approximately equal, numerically, to the mass in gjrn2•Same quality of paper shaIJ be used [OJ the control and experiment.Mercurrc chloride paper should be stored in a stoppered bottle In thedark. Paper w hich has been exposed to mnlight or to the vapour ofammonia should not be used as they give a lighter coloured stain or nostain at aIJ when employed in the quantitative test for arsenic

23

IS : 6287 • 1985

L£NG1H OF NECKOF FLASK = 178 -203mm

L£NGTH OFCONOfNSfR:: 457 - SOBm/!)

FlO. 3 DISTILLATION ApPARAnJ'S

24

25ml

IS I 6287 • 1985

13.1.2.7 Concentrated hydrochloric acid - sp gr 1·16.13.1.2.8 Stannous chloride solutum - Dilute 60 ml of concentrated

hydrochloric acid with 20 ml of water , add to It 20 g of lin, heat gentlyuntil gas ceases 10 be evolved, and add sufficient \\ ater 10 produce 100 m ,allowing the undissolved lin to remain in the solution. Decant theclear solution, add an equal volume of concentrated hydrochloric acid,boil down to the original volume and filter Ihrough a fine-gram fillerpaper.

13.1.2.9 Stannated hydrochlonc acid - Mix together one millilitrc ofstannous chloride solution and 100 ml of concentrated hydrochloric acid.

13.1.2.10 Potassium iodide - Crystals or in the form of pow der.

oo...

,..l_

SPIIING CLI~'

MERCURIC C~LORIDI~APER

• '"... O'A (APPRoXI

- COT TON WOOLWITH LUD AC£TATE

WIDt! MOUTH IOTTUOf I~O ",I c.r.MClTY

FIG. 4- ASSEMBLY OF ApPARATUS FOP.. THE DETE.RMINATION OF ARSENIC25

IS 16287· 1985

I:U.2.11 ~inc - Granulated and complying with the following test:

Take SO ml of water, 10 ml of stannated hydrochloric acid and0'1 ml of dilute solution of arsenic ( Jet 13.1.2.13) in the wide-mouthbottle. Add one gram of pota-siurn iodide and 10 g of zinc.Quirk:;' place the prepared gl:m tube ( see 13.1.1.2) in position.Allow the reaction to continue for one hour. A faint but distinctyellow stain shall be produced on the mercuric chloride paper.

13.1.'2.12 Strong solution of arsenic - Dissolve 0'132 g of arsenictrioxide in SO ml of concentrated hydrochloric acid and add sufficientwater to produce 100 m\.

13.1.2.13 Dilute solution of arsenic - Freshly prepared. Dilute onemillilitre of strong solution of arsenic with water sufficient to produce100 m!. This solution contains 0'01 mg of arsenic per millilitre.

13.1.3 Procedure

13.1.3.1 Preparation of the solution - Weigh 4'5 to 5'5 ~ of theprepared sample (see 4.1) to an accuracy of 0'01 g and place with 10 mlof dilute nitric acid in a 100 or 200 rnl resistance glass or silica Kjeldahlflask, and heat the mixture until any initial vigorous reaction subsidesand ceases, Cool and add gradually 10 ml of concentrated sulphuricacid at such a rate as to present excessive frothing or heating ( 10 minutesare usually required) and continue the heating. Add to the hot solution5 ml of concentrated nitric arid in small portions, and boil until colour-less, If necessary, add concentrated nitric aciel in further small portionsat a t irne Note for the pur pose of the blank dcterrrnnation the totaiamount of concentrated nitric acid added. (The digestion usually takesabout 30 minutes). Cool, dilute with 50 ml of water and transfer to theflask of the dj~tillation apparatus. 130il the solution without inserting thecondensing arm till the bulk i~ re-duced to about 10 ml or until whitefume-s appear; cool, dilute and again boil down to 10 ml; cool and add7'0 ml of water. Cool well the liquid and add 5 R of the chloride·hydrazine-brcmide mixture. Fit the condenser quickly and distil theliquid into a mixture of 10 ml of water and 2 ml of concentrated nitricacid. Then evaporate the distillate to dryness on the water-bath andevapor-ate the residue twice to dryness with 5 ml of water to removenitric acid. Dissolve the final residue by warming in 3 ml of concentra-ted sulphuric acid, cool and dilute with water.

13.1.3.2 Transfer the whole of the prepared solution til the wide-mouth bottle, add 15 ml of stannared hydrochloric acid and one gramof potassium iol ide. Then add 10 g of zinc. Quickly place the prepared~rass tube [ see 13.1.1.2 ( b ) ] in position. Allow the reaction to continuefor 40 minutes. Remove the piece of mercuric chloride paper at the endof this period. If arsenic is present in the material, compare the yellow

26

IS , 6287 • 1985

stain produced on the mercuric chloride paper, b} daylight with thestandard stains prepared a; descrrbed under 13.1.3.4:

a) I f the stain in this test exceeds that produced by 002 mg ofarsenic ( that IS, 2 2 ml of solution ), make the solution to a knownbulk with dilute sulphuric acrd ( I : 8) and lake an aliquot toproduce a stain suitable for matching.

b) The reacnon may be accelerated by placing the apparatus on awarm surface, care being taken that the mercuric chloride paperremains quite dry throughout the test. The most suitabletemperature for carrymg out the test is l{enerally about 40°C, butbecause the rate of evolution of the gas vades somewhat wnhdifferent batches of zinc, the temperature may be adjusted toobtain a regular, but not too vrolent , evolution of gas. The tubeshould be washed with concentrated hydrochloric arid. rinsedwith water, and dried between succesvive tests.

13.1.3.3 Companson of slams - The comparison of the stains is madewith freshly prepared standard stain Immediately at the completion ofthe test,

13.1.3.4 Preparation of standard statns -- Prepare a series of solutionsby mixing to~ether different quantities ( ran~in~ up to 20 ml ) of dilutesolution of arsr-mc with 50 ml of water and 10 ml of stannated hydro-chloric acid. Tr eat each solution in the series separately as describedunder 13.1.3.2 to prepare the series ot standard stains.

13.1.3.5 Make sure that no solid material comes in contact with theground In poruon of the bottle.

13.1.3.6 A blank cletermmauon shall be carried out under the sameconditions, on the same reagents and by the same person but withoutusing the material. The blank should not produce any visible stain onthe mercurrc chloride paper

13.1.4 Calculauo«

13.1.4.0 Express the arsenic content of the material as milligramsof arsenic ( As ) per kilogram of the material.

13.1.4.1 Calculate the arsenic content by using the formula giveneither in (a) or (b) as appropriate:

. 10 Aa) Arsenic ( As). mg/kg = -M~

27

IS I 6287 • 1985

b) Arsenic ( As ), mg/kg = IOAVDMwhere

A = volume in ml of dilute solution of arsenic used to preparethe standard stain that matches with the stain preparedfrom the material ( set 13.1.3.4 )j

M ..:= mass in g of the • prepared sample' used in the prepara-tion of the solution of the material ( See 13.1.3.1 );

V - total volume in ml of the solution made from the residueof the distillate with dilute sulphuric acid ( 1 : 8 ) [set13.1.3.2 ( a ) ]; and

v

IS : 6287 • 1985

10 TO 12'1>

BALLJOINT __

90 BI

C 165

\...210

FIG. 5 ApPARATUS FOR DETERMINATION 01' ARSENIC ( SILVERDIETHYLDrrHlOCARBAMATE METHOD)

29

IS : 6287 • 1985

14 TO 15 ---+.--

IS : 6287 • 1985

CONNECtING WBE

ABSORBER

RUBBERBUNG

---t---r---1l 10 150

100

II1I

I1

r RUBBE RBUNG

GASDiSTRIBUTION

REACTIONVESSEL

All dimenuon In milh metres.

Flo. 7 ApPARATUS FOR DETERMI:'

IS I 6287 • 1985

13.2.3.5 Silver diethyldithiocarbamate solution - Dissolve I g of silverdiethyldithiocarbamate in water-white pyridine and dilute to 200011 withpyridine, Store the solution in stoppered-glass bottles away from light.

13.2.4 Procedure

13.2.4.1 Preparation of calibration curve - The curve shall be confirmedevery time when a new solution of silver diethyldithiocarbamate isprepared.

13.2.4.2 Evolution of arsenic - Transfer to a series of 100 ml conicalflasks, aliquots of standard arsenic solution corresponding to 0,5, 10, 15,20 and 25 flog of arsenic and proceed as given in (a).

a) Add 10 011 of concentrated hydrochloric acid and dilute to 50 ±5 ml with water. Add 2 ml of potassium iodide and stannouschloride solution respectively. Mix well and let it stand for 15to 20 minutes, Pack lightly the top third of the connecting tubewith impregnated absorbent cotton wool and assemble with theabsorption tube. Transfer 5'0 ml of silver diethyldithiocarbamatesolution to absorption tube C. After 15 to 20 minutes, introduce~ g of zinc granules into the conical flask A and quicklyreassemble the apparatus. Allow the reaction to proceed for45 to 60 minutes at room temperature.

b) Sputrophatometm measurements - Disconnect the absorption tubeand tilt the absorber so that the reagent solution flows balk andforth between the absorber so that the reagent solution flows backand forth between the absorber and bulb to disperse the sol idcontents, if any, and to mix in the solution well. Tramfer thesolution to a photometric cell and measure its absorbance at thewavelength of maximum absorption, 540 nm, using water asreference liquid.

NmE - The colour oftbe dispersion is not very stable for long trrne and henceabvorpriometr ir (n",phelometrIc) measurement should be made wrt hrn 2 hours ofth .. developrnr-nt of colour. Care should also be taken to prevent the evaporationof solution as its volume IS small.

In the case of fritted glass absorber, raise and lower the connectingtube into the absorber several times to allow the solution to pass throughthe frit back and forth effecting the dispersal of the red deposit. Letthe connecting tube finally drain into the absorber.

10 flog standard shall have an absorption of the order of 0'4.

c) Plotting of the calibration curve - Calculate corrected absorbance bysubtracting the reading obtained for the solution containing nostandard arsenic solution from the observed reading. Plot agraph of corrected absorbance of solution against their arseniccontents.

32

IS : 6287 • 1985

13.2.4.3 The test solutions shall be prepared so as to contain 1 to10 ",g of arsenic in a solution of 5 0 ± 0'5 rnl volume. Transfer thesolution to the conical flask, cool to room temperature, if necessary, andproceed as prescribed in 13.2.4.2, 13.2.4.2 ( a ) and 13.2.4.2 ( b ).

13.'2.4.4 Blank test - Carry out a blank test as prescribed in 13.2.4.2,13.2.4.2 ( a ) and 13.2.4.2 ( b ) omitting the sample.

13.2.5 Calculation - Calculate the corrected absorbance by subtractingthe value obtained for the blank solution from that obtained for the testsolution and read from the calibration curve the corresponding mass ofarsenic.

Arsenic content, mgjkg = ~~-

where

M 1 = mass in Itg of arsenic found, andM 2 = mass in g of sample in the solution tested.

14. DETERMINATION OF LEAD

14.0 Two methods for the determination of lead have been prescribed.Any of these may be used for routine purposes. However, for refereepurposes, the atomic absorption spectrophotometric method should beused,

14.1 Atom.ic Absorption Spectrophotollletric Method

H..l.! Pr::.::p!c . Org1r':c p1;)tt~r i~ r1igl'stPrl "lnrl lean rplpa~erl (")-precipitates with strontium sulphate, soluble sulphate salts are decantedand precipitate is converted to carbonate salt, dissolved in acid anddetermined by atomic absorption at 217 or 2B3'3 nm,

14.1.2 Apparatus

14.1.2.1 Atomic absorption spectrophotometer

14.1.2.2 Stimn/{ motor - with eccentric coupling for stirring centri-fuge tubes.

14.1.3 Reagents

14.1.3.1 Strontium solution - 2 percent. Dissolve 6 g strontiumchloride ( SrCJ 2, 6H20 ) in 100 ml water.

14.1.3.2 Ternary acid mixture - Add 20 ml sulphuric acid to 100 mlwatei , mix, add 100 ml nitric acid and 40 ml of 70 percent perchloricacid and mix.

14.1.3.3 Nuric acid - Add 128 ml red ist i lled nitric acid to 500·800 mldistilled or deionized water and dilute to 2 lit res.

33

IS l 6287 • 1985

14.1.3.4 Lead standard solution

a) Stock solutions - 1 000 ",g/rnl Dissolve 1'5985 g lead nitrate[ Pb ( 1\03 )2] recrystallized in about 500 ml 1 N nitric acid in aI lure volumetric flask and dilute to volume with I N nitricacid

b) Workl1lg soluttou - Prepare 100 ",g Pbjrnl by drlutmg 10 ml stocksolution to 100 m l with I N nrtric acid Dilute I, J, 5, 10, 15and ~5 ml alrquots of this solution to 100 rnl with I N ruti IC acid( I, 3, 5, 10, 15 and 25 ",g Ph/IIlI respectively).

14.1.4 SeparatIOn of Lead14.1.4.1 Accurately weigh sample contanung approximately 109

dry matter and up to 3 ",g lead. Place in 500 ml boihng or Kjeldahlflask and add 1 ml of 2 percent strontium solution and several glassbeads. Prepare reagent blank and carry through same operations assample. Add IS ml ternary acid mixture for each gram dry matter andlet stand lor approximately up to 2 hours. Heat under or water vacuummanifold system unul flask contains only sulphuric acid.

NOTJ - I ake care to aVOI(! sample loss from foa mmg when heal IS first apphed,and when [oarrung occurs soon aftr r sample ch.rrs Remove hr a t and SWirl flaskbefore eontmumg dIgestIOn Add nitrrc acid, rf necessary.

14.1.4.2 Cool, digest for a few minutes (dlge~t should be coolenough to add about 15 ml water safely, but hot enough LO boil whenwater is added) Wash while still hot into a 40 to 50 ml tapered bottomcentrifuge tube and SWirl Let cool centr rfuge for 10 mm at 350 g anddecant liquid into water beaker (film-like precipitate may be discarded )Dislodge precipitate by vigorously stirring With cccentrrc-couplcd stirringmotor. To complete transfer, add 20 rnl water and I ml 1 N sulphuricacid to orrgrnal flask and heat Do not ormt this step even though Itappears transfer was complete in first wash. Wash hot contents ofor igmal drgesuon flask into centrrfuge tube conrairnng precipitateSwirl to mix Cool, cenn ifuge and decant Iiquid rnto waste beakers,

14.1.4.3 Dislodue precipitate by snrr ing vigorously, add 25 mlsaturated ammonium carbonate r(1\H4 h C03 J solution (about 20percent) and sur until all the precipitate 1\ dispersed I et stand forI hour Centrifuge and decant liquid mto waste beaker. Repeatammonium carbonate treatment

14.1.4.4 After decanting invert centrifuge tube on paper towel anddrain all liquid. Add 5 rnl I N nitric acid (use larger volume I Nnin ic acid m both sample and blank if more than 25 "'£!; Pb is expected ),stir vigorously to expel carbon dioxide or use ultrasonic bath for 2 to 3minutes, Let stand for 30 minutes and centrifuge if precipitateremains.

NOTE - Use same technique for all samples.

34

IS : 6287 • 1985

14.1.5 Determinauon

14.1.5.1 Set instrument to previously established optimum conditions,using air acetylene oxidrzing flame and 217 or 283'3 nm resonantwavelength. Determine absorbance of sample and blank solutions formore than 5 standards, within optimum working range ( 10 to 80 percenttransmittance) before and after sample readmgs Flush burner with1 N mtric acid and check zero point between readings, Dcterrnme leadfrom standard curve of absorbance against /lg Pb ml

14.1.6 Calculations

14.1.6.1 Lead, mgJkg

where

Ml = mass in p.g of lead,VI ... volume in ml of 1 N rutrrc acid used, and

M2 = mass in g of sample taken for test.

14.2 Visual Comparison Method

14.2.1 Apparatus

14.2.1.1 Nessler cylinders - 50 ml capacity.

14.2.2 Reagents

14.2.2.1 AcetIC acid - approximately 33 percent ( uJv ).

14.2.2.2 DIlute ammonium Irydroxlde - approximately 4 N.

14.2.2.3 Potassium cyanide solulum - Dissolve 10 -g of potassiumcyamde in gO ml of water, add 2 ml of hydrogen peroxide ( 20 volumestrength ), allow to stand for 24 hours and make up to 100 ml withwater.

14.2.2.4 Sodium sulphIde solution - Dissolve to g of sodium sulphide( Na2S.9H20 ) in 100 I'll of water.

14.2.2.5 Standard lead solutum - DISSolve 0-160 g of lead nitrate in5 ml of concentrated mtrrc acid (conformm~ to IS : 264-1976* ) anddilute to 100 ml in a graduated flask. Agam dilute 10 ml of thesolution to I 000 m\. One rnilhlitre of the solution finally obtained contains0-0I mg of lead ( as Pb ).

·Specification Cor nitric acid (fint "VlJlDn ).

35

IS z 6287 • 1985

14.2.3 Procedure - Dissolve 5 g of the prepared sample ( see 4 ) in waterin a Nessler cylinder and add 5 ml of acetic acid. Make the mixturealkaline with dilute ammonium hydroxide and add I ml of potassiumcyanide solution If turbid, filter. Add two drops of sodium sulphidesolution and mix well Carry out a control test in another Nesslercylinder in exactly the same manner but using I ml of standard leadsolution In place of the prepared sample. DIlute the solution in boththe cylinders to 50 ml mark. Compare the colour produced in the twocylinders against a white background.

14.2.3.1 The material shall be taken to have not exceeded the limitspecified, If the Intensity of colour obtained with the material is notgreater than that obtained in the control test

15. DETERMINATION OF COPPER

15.0 Methods - Three methods, namely, the spectrophotometric( see 15.1 ) gravimetrrc ( see 15.2) and atomic absorpnon spectrophoto-metric method ( see 15.3 ) are prescribed for the determination of copperin the material. Whereas the spectrophorometrrc method or atomicabsorption spectrophotometric method should be used for refereepllrpm{'~, for routine analysis the gravimetric method may be usedwherever facihties for spectrophotometric analysis are not available.

15.1 Spectrophotometric Method

15.1.1 Apparatus

15.1.1.1 Spectrophotometer - of a suitable type.

15.1.2 Reagents

15.1.2.1 Concentrated sulphur« acid-s- sp gr 1'84.

15.1.2.2 Sodium carbonate - solid.

15.1.2.3 Concentrated hydrochlonc acid - sp gr I 16, diluted WIth anequal volume of water

15.1.2.4 Cttnc acid - solid.

15.1.2.5 Ammonium hydroxide solution - sp gr 0'90.

15.1.2.6 Sodium diethyldithiocarbamate solution - 0'1 percent (m/v)aqueous

15.1.2.7 Carbon tetrachloride - re-distilled.

15.1.2.8 Sodium sulphate - anhydrous.

15.1.2.9 Concentrated nitric acid - sp gr 1'42 diluted with an equalvolume of \\ ater

36

IS =6287 • 1985

15.1.2.10 Standard copper solution - weigh accurately 0'1000 g ofpure copper turning, carefully dissolve In rmmrnurn amount of nitricacid, cool and dilute to one litre. Pipette 101111 of this solution into a130 ml volumetric flask dilute to the mark. This solution contains 10 ~gof copper per rrullihtre,

15.1.3 Procedure

15.1.3.1 Preparation of test solution -- Weigh accurately about 200 gof the prepared sample (see 4.1) in a platinum dish and add to it 2 mlof concentrated sulphurrc acid, Heat the dish gently over a Bunsenburner until charring is complete and ash the residue in a muffle furnaceat 550 to 600°C. Cool the dish, add to the ash about 2 g of sodiumcarbonate and fuse the contents of the dish for IO minutes at 900 0 r:.Cool the dish and drssolve the Iu-ed matter in the minimum amount ofhydrochloric acid, covering the dish With a watch-glass to avoul loss byspattering. Heat the dish until solution IS complete Cool the dishand make up the solution to 100 rnl In a volumetric flask With water.

15.1.3.2 Transfer 10 ml of the test solution to a separating funnel bymeans of a pipette. Add one gram of citric acid to the test solution anddissolve it by shaking. Make the resulting solution alkaline to htmuspaper by adding ammonium hydroxide solution in small quantities. Addto this alkaline solution, 5 ml of sodium diethyldithiocarbamate solution,~hake thoroughly and extract With 5 ml portions of carbon tetrachlorideuntil the final extract is colourless ( about four extracnons are usuallyadequate). Dry the combined extract> by shaking thoroughly withanhydrous sodrurn sulphate. Filter the dry extract and wash the filterpaper with carbon tetrachloride Make up the volume of the filtrate to25 ml with carbon tetrachloride and measure the absorption at 437 mlJ-by means of the spectrophotometer.

15.1.3.3 Prepare a series of standard colour solutions. using differentvolumes of standard copper solution mvtead of 10 rnl of the test solutionand proceeding as descrrbe d under 15.1.3.2. This series should coverthe concentrauon of the colour solutions prepared from the test solution.Measure the absorption of each of the colour solutions in the series.

15.1.3.4 Carry out blank deter minations on the water and thereagents used In the prep vrat ron of the standard colour solutions(sfe 15.1.3.3) an.] colour soluuon from the material (see 15.1.3.1and 15.1.3.2). If the values so abt.rined ale of any vigruficance , correct(he respect! VI' values ob .('1 vNI fOI t he

IS : 6287·1985

15.1.4 Cauulation

Copper ( as Cu ) content of the material,parts per million

10MW

where

M - - mass in ~g of copper present in 10 ml of the test solution( see 15.1.3.5 ), and

W = mass in g of the material taken for the test.15.2 GraviDletric Method

15.2.1 ReagentJ - The following reagents are required. The reagentsshall be free from traces of copper.

15.2.1.1 Concentrated sulphuric acid - sp gr 1'84.

15.2.1.2 Sodium carbonate - solid.

15.2.1.3 Hydrochloric acid - concentrated hydrochloric at id of sp gr1'16 with an equal volume of water.

15.2.1.4 Sodium hydroxide solution - approximately 2 K.

15.2.1.5 Sodium acetate - crystalline.

15.2.1.6 GlaciaL acetic acid

15.2.1.7 Salicylaldoxime solution - Dissolve one gram of salicylal-doxime in 5 ml of rectified spirit without the aid of heat. Gently, pourthis solution into 95 ml of water at 80aC. The oxime partially separatesout in the form of a fine oil suspension, but quickly redissolves. Avoidshaking at this stage as shaking helps the small droplets of the oximegrow. When the solution becomes clear, shake it for some time andfilter. Use the filtrate.

15.2.1.8 Ferrous chloride solution - about 5 percent ( m v ).

15.2.2 Procedure

15.2.2.1 Proceed as desired under 15.1.3.1, but do not make up thevolume to 100 m!.

15.2.2.2 To the whole of the solution so obtained, add sodiumhydroxide solution until a lasting precipitate is for rned, Add one gramof sodium acetate and 10 01) of glacial acetic acid, and stir until theprecipitate redissolves, Dilute the resulting solution to about 100 mlwith water. Add to this dilute solution a bare excess of salicylaldo-xime solution to precipitate all the copper present in the solution.Coagulate the precipitate by stirring with a glass rod and allow to settle.

38

IS : 6287 - 1985

Test the supernatant liquid for completeness of precipitation by addingseveral drops of salicylaldoxime solution. (A considerable excess ofsalicylaldoxime should be avoided, as the precipitate has to be washedfree from it before drying, Otherwise the precipitate would be visiblydecomposed during drying. ) Filter the precipitate through a tared No.3Gooch crucible and wash it with cold water until the filtrate ceases togive any colour with ferrous chloride solution. During washing, takecare that the precipitate always remains moist. Finally, wash theprecipitate twice again with water, and then dry it as far as possible bysuction. Dry the crucible with contents to constant weight at 105 to110°C. Cool in a desiccator and weigh. Find the mass of the driedprecipitate.

15.2.3 Calculation

Copper (as Cu ), mg/kg189200 m~-M-

where

m -- mass in g of the dried precipitate as determined under15.2.2.2, and

M = mass in g of the material 1aken for the test.

15.3 Atomic Absorption Spectrophotometric Method

15.3.1 Principle

15.3.1.1 Samples are wet ashed and after dilution are aspirated intoC2H2 flame. Radiation at 324'7 nm from copper hollow cathode lampis passed through flame. Attenuation is measured in spectrophotometercalibrated with known concentrations of copper in the presence ofmatrix similar to that of samples which avoids interference from elementssuch as Na ami K. Concentration range is 5-100 mgjkg depending onthe sensitivity of the instrument working range is 02-10 ",g!m\'Recommended upper limit is that which gives absorbance about 0'4.

15.3.2 Apparatus

15.3.2.1 Atomic absorption spectrophotometer

15.3.3 Reagents

15.3.3.1 Copper standard solution - 1 000 f£g rnl, Dissolve )'000 g of99'99 percent copper in 20 ml nitric acid, cool and dilute to I litre withwater.

15.3.3.2 Matrix standard solution - Prepar e solutions contai ning0, 0'2, 0'4, 0'8, 1'6, 2'0, 4'0, 8'0 and 10 p.g Cujrnl and major metalmatrix components: (a) for 3 g sample to contain 180 flog Ca, 100 WI, Mgand 40 ~g Al with final concentrations of 8 percent ( uju) perchloricacid and (b) for 6 g sample to contain 7000 f£g K, 70 p.g Na, 700 f£g Mg,and 130 f£g Ca/ml with final nitric acid concentrates of 1:9.

39

18 : 6287 • 1985

15.3." Preparatum oj CalIbratIon Curve

15.3.4.1 With Cu hollow cathode tube In position, energized, andstabihzed, locate wavelength setting that gives maximum response toradiation at 3247 nm. Wash combustion chamber and burners headwith nitric acid (I: I). Light burner, let It reach thermal equilibriumand zero instrument while aspirating water Aspirate 10 flg Cujm]standard solution and adjust burner height, air and fuel pressures andflow rates, aspiration rate of solution, and position of capillary toobtain maximum response. Adjust slit setting and gam to obtainoptimum signal-to-norse rano, Recahbraie when any of these para-meters change, Absorbance should be about 032 for 10 f'g Culm!.Scale expansion IS required to obtain appreciable readings for copperup to 2 "g/m!.

15.3.4.2 Aspirate 10 f'g/ml standard enough times to estabhsh thatabsorbance reading is not dnftmg. Record 6 readings and calculatestandard deviation ( (J ) ( x - y) X 0'40 where x and J are maximumand rmrnmum readings respecnvely and 0'40 IS factor to convert rangeof 6 values to a

15.3.4.:J Beginning With solution containing 0 ",glml Cu, aspirate eachrnatrrx standard solunon and record absorbance IJ value for IO f'g/mlsolution differs from average of 6 values used to calculate a by morethan 001 x (average of the 6 values), repeat measurements If thesedeterrmnauons indicate drrft, determme cause ( for example, deposits inburner or clogged capillary), correct It, add repeat calibranon, Plotabsorbance against f'g rnetal/rnl

15.3.5 Deurminauon

15.3.5.1 Select samples mass to give solution contarrnng 0'05 to10 f'g Cujrnl.

15.3.5.2 Wet ashmg - Accurately weigh sample mto 400 ml beaker,add 100 ml rntric acid and ~WJTI. Cover and let react for 10 mmutes,then place on hot plate Evaporate to near dryness and cool Add 50 mlnitric acrd and 10 ml perchlor:c acid. Continue evapOl anon to obtainclear solution. TI ansfer to 50-ml volumetric fla~k and dilute 10 volumeWith water (Insoluble potassium perchlorate, which settles to bottom offlask and does not mterfere) Prepare reagent blank contaimng sameamounts of acids taken from same lots evaporated as above.

15.3.5.3 Photometers - Aspirate sample and blank solution andrecord absorbance Measure absorbance of matnx standard solutioncontammg 10 ",g/ml If this value differs from value of the average ofthe 6 values used to calculate (J by more than 2 (1, repeat measurement.If these values mdicate drift, determine cause, correct it, and repeatcahbranon of sample and blank readings

40

IS : 6287 • 1985

15.3.5.4 Calculations - Correct readmgs of sample solution lor blank.Convert corrected absorbance to f'g/ml from calibr arion curve,

C X ICopper, mg/kg = --11'-

where

C =,.,.g metal/rnl from curve,t' final volume sample solution ( 50 ml ), and

W = mass in ~ of sample.

16. DETERMINATION OF ZINC

16.0 Two methods for the deterrmnauon of l1l1L have been prescribed,Any of these may be used

16.1 SpectrophotolDetric/ColorilDetric Method

16.1.0 Prmciple - ThIS method involves wet oxidatron of the material,elimmation of lead, copper, cadmium, bismuth, antimony, nn, mercuryand silver as sulphides, using copper sulphate solution as scavangeragent, snnultaneous ehrnmanon of cobalt and nickel by extractingmetal complexes of «-nitroso ~-naphthol and dimethyl glyoxirne respec-nvely with chloroform, exn action of the zmc dithizonate with carbontetrachloride, transfer of zinc to dilute hydrochloric acid, and finalextraction of zinc dithizonate for colour measurement.

16.1.1 Apparatus

16.1.1.1 Spectrophotometer - of a suitable type.

16.1.2 Reagents

16.1.2.1 Water - Re-distil the water from all-glass Pyrex orequivalent ~las..,ware, which IS srrupulously cleaned with hot concentra-ted nitric ar ](.1.

16.1.2.2 Concentrated nunc acid - re-distilled end of sp ~r 1°4-2.

16.1.2.3 Concentrated sulphuric acid - sp gr 1'84.

16.1.2.4 Perchloru. acid ( HClO J )

16.1.2.5 Methyl red indicator solntion - one percpnt ( m], ), aqueous.

16.1.".6 Copper sulphate solution - Dissolve 8 g of cOPI~e.r sulphate( CuS0.J . 5H20 ) In water and dilute to one lrn e One millilitre of thissolurion contain'> 2 lIlt; of copper ( eu ).

16.1.2.7 Ammomum hydroxide snlution - re-drsulled and of "'p t;r 0'90

16.1.2.6 Concentrated hydro! Mom acid - sp gr I 16.41

18 I 6287 • 1985

16.1.2.9 Hydrogen sulphIde gas - from the generator, passed througha wash bottle contarmng water.

16.1.2.10 DIlute hydrochlorIC acid - containing 5 percent ( : )-

16.1.2.11 Bromine water - saturated.

16.1.2.12 Phenol red tndscator solution - 004 percent ( m/v). Dissolve0'1 g of phenol red In 28'2 ml of 0'01 N 10dJUrn hydroxide solution anddilute to 250 ml with Water.

16.1.2.13 Hydrochloric acid ( 1 . 1) - dilute concentrated hydrochloricacid with an equal volume of water

16.1.2.lf Duhizone ( dlphenylthlocarbazone ) solution - Dissolve 0'05 gof dithizone in 2 ml of ammonium hydroxide solunon and 100 ml ofwater, and extract repeatedly WIth carbon tetrachlonde until solventlayer is clear and of bnght green colour. Discard the solvent layer andfilter the aqueous portion through a washed ashless paper (Thissolution is best prepared as needed smce It is only moderately stable,even when kept in the dark and under refrigeration ).

16.1.2.15 Carbon tetrachloride - re-distilled.

16.1.2.16 Chloroform - re-distilled.

16.1.2.17 AmmOnium CItrate solutton - Dissolve 225 g of ammoniumcitrate [( NH4 )2 HC6H &0 7 ] in water, make alkaline to phenol red withammonium hydroxide (pH 7 4 first distmct colour change) and add75 rnl III excess Dilute to 2 htres Extract this soluuon Immediatelybefore use as given below

Add to the ammonium citrate solution ( see above) a shght excessof duhizone solutron and extract with carbon tetrachlonde until thesolvent layer is clear brrght green. Remove the excess of dnhrzone byrepeated extracnon with chloroform, and finally extract once more withcarbon tetrachlorrde. (J t IS essenual that excess rlJthlzone be ennrelyremoved, as otherwise zinc WIll be lost durmg elirrunanon of cobalt andnickel ).

16.1.2.18 DlTTlllh)l glyoxlme solution - DIssolve 2 g of dimethylglyoxime 10 10 ml of ammonium hydroxide solution and 200 to 300 mlof water, filter and drlute to one htre.

16.1.2.19 (J,-Nltruso·~·naphthol solution - Dissolve 0 25 g of e-nitroso-B>naphthol in chloroform and dilute with chloroform to 500 mi.

I

16.1.2.20 Hydrochloru: acid - 0 04 N approximate, prepared fromconcentrated hydrochloric acid

IS I 6287 • 1985

16.1.2.21 Stock solution of zinc - Dissolve exactly 0'500 g of puregranulated zinc in a slight excess of dilute hydrochloric acid and diluteto I 000 ml.

16.1.2.22 Standardsolution of zinc - At the time of the experiment,dilute 10 ml of the stock solution of zinc ( see 16.1.2.21 ) to I 000 ml withhydrochloric acid ( 004 N). This solution contains 5 ",g of zinc permillilitre.

16.1.3 Procedure

16.1.3.1 Preparation of material - Accurately weigh into an Erlenmeyerflask of suitable size a quantity of the prepared sample (tee 4.1) notexceeding 25 g, estimated to contain 25 to 100 "'~ of zinc. Acid to theprepared sample concentrated nitric acid and heat cautiously until thefirst vigorous reaction subsides somewhat, then add 2 to 5 ml ofconcentrated sulphuric acid. Continue the healing, adding, if necessary,more of concentrated nitric acid in small increments, to prevent charringuntil fumes of sulphur trioxide are evolved and the solution becomesclear and almost colourless. Add 0'5 ml of perchloric acid and continueheating until it has been completely removed. Allow the solution to cooland dilute it to about 40 ml. (Jfnecessary equipment is available, wetoxidation and subsequent sulphide separation may be advantageouslycarried out in a small Kjeldahl flask ).

16.1.3.2 Separation of sulphide group - To the sulphuric acid solutionof the material (see 16.1.3.1 ) contained 10 the Erlenmeyer flask add 2drops of methyl red indicator solution and one millilitre of coppersulphate solution, and neutralize with ammonium hydroxide solution.Add sufficient quantity of concentrated hydrochloric acid to make thesolution about 0'15 N with respect to this acid ( about 0'75 ml excess in50 ml of solution is satisfactory). The pH of the solution at this pointshould be 1'9 to 2'1 when measured with glass electrode. Pass a streamof hydrogen sulphide gas into the solution until precipitation is complete.Filter the contents of the flask through a fine textured fifter paper( Whatmtln No. 42 or an equivalent) that has been previously fitted intothe funnel and washed first with dilute hydrochloric acid, and then withwater. Collect the filtrate in a beaker and wash the flask and the filterwith 3 or 4 small portions of water. Roil the filtrate gently until thecolour of hydrogen ~ulphide can no longer be detected, then add 5 mlof bromine water and continue boilin-; until bromine has br-en expelled.Allow the solution to cool, neutralize with ammonium hydroxidesolution using phenol red indicator solunon, and then make It slightlyacidic with hydrochloric acid ( I : I ) by a Idiru; an ext e-s of 0'2 ml.Dilute the resultant solution in a volumetric flask to contain 0'2 to 1'0 gof zinc per ml.

43

18 I 6Z87 • 1985

16.1.3.3 Elimination of nickel and 'obalt - Transfer a 20 ml aliquotof the solution ( Ste 16.1.:1.2 ) \0 a separating funnel. Add to it 5 ml ofammonium citrate solution, 2 ml of dimethyl glyoxime solution and 10 rnlof O[·nitroso-~-naphtholsolution, and shake the contents of the separatingfunnel for 2 minutes. Discard the layer of chloroform and extract theaqueous layer with IO rnl of chloroform to remove residual ll·nitroso·~naphthol. Discard the chloroform layer.

16.1.3.4 Isolation and estimation of zin'

a) To the aqueous layer obtained after eliminating nickel and cobalt( see 16.1.3.3 ), which at this point has a pH of 8'0 to 8'2, add2'0 ml of the dithizone solution and IO ml of carbon tetra-chloride, and shake after 2 minutes. Allow the layers to separateand remove the aqueous layer as completely as possible with-drawing it by means of a pipette attached to the vacuum line.Wash down the sides of the separating funnel with about 25 mlof water and without shaking again draw off the aqueous layer.Add 25 ml of hydrochloric acid ( 0'04 N ) to the carbon tetra-chloride layer in the separating funnel and shake for one minuteto transfer the zinc to the acid-aqueous layer. Drain off anddiscard the carbon tetrachloride layer; being careful to dislodgeand remove the drop that usually floats on the surface. To theacid-aqueous layer add 5'0 ml of ammonium citrate solution and10'0 ml of carbon tetrachloride ( pH of the solution at this pointis 8'8 to 9-0). Determine the volume of dithizone solution to beadded as given in (b).

b) Pipette 4'0 ml standard solution of zinc into a separating funnel.add to it 21 ml of hydrochloric acid ( 0'04 N) from a burette.5 ml of ammonium citrate solution and 10'0 ml of carbontetrachloride, and then add dithizone solution in 0'1 mlincrements, shaking briefly after each addition until a faintyellow colour in the aqueous layer indicates a bare excess of thereagent. Note the total volume of dithizone solution added.Multiply this volume by 1'5.

c) Add the volume [ see 16.1.3.4 (b)] of dithizone solution to thesolution contained in the separating funnel ( see 16.1.3.4) andshake it for two minutes. Pipette 5'0 ml of the cabon tetrachloridelayer and transfer it to the spectrophotometer cell. Dilute thesolution with 10'0 ml of carbon tetrachloride, mix and determineits spectral transmission at 540 nJ""

Dilution may be made in a clean and dry test-tube, if thedesign of the cell does not permit mixing directly.

44

IS : 6287 • 198.')

d) Pipette mto a series of separating funnels, 0, 1,2,3 and 4 m'of standard solution of zrnc and add the necessarv volume 0 ~hydrochloric awl (004 r'\) to make 25 m! Add into cacl:separator 5'0 ml of ammonium CItrate solution and thecalculated volume of du hrzonc solution I see 16.1.3.4 (b)] Shak»the separaung funnels for two mmutes 1- rom the fii st scparatrncfunnel pipette Out 5 0 rnl of the carbon tet r achlorrdc layer amitransfer it to the spectrophotometer c('11 Dilute the solutronwith 100 ml of (arbon retrachloride, Ill)" and detcrrnme It,spectral transmission at 540 ll1j.£ Proceed In the same mannerwith the solutions contained in other s('parating funn.-l ,

e) Plot the transmittance on Iogarrth nnc vcale obtained fur ear h o,the series of separating funnels ( see 16.1.2.4) aga mvt concentra-tion of zinc in micrograms present In 25 ml of the dIlutedstandard zinc solution in the parucul.ir separat intr funnel anddraw a smooth curve through the points (T nter rC"rt of tillcurve may vary from dav to day, depenc!Jng on the actualconcent ration of dithizone used In the final ext I at tio n, bu- t hr-slope of the curve should remain p\sf'ntlally same \ FlOI', Ii'"~curve obtain the mass of zmc III rmrrol.'(rams present 1I1 ?-, m'of the acid aqueous layer ( for final (''{tractIOn of zinr from t nematerial, see 16.1.3.4 )

16.1.4 Calculauon

16.1.4.1 Zinr, rnb/k::;

where

Af = rna" III g of zrn c present III 2'j III I of Ill' 'lCI

IS I 6287 • 1985

16.2.2.1 Sulphuric acid, d20 - 1'83 g ml.

16.2.2.2 Nitric acid, d20 = 1'38 g(ml.

16.2.2.3 Perchloric acid, d20 = 1'67 g(m!.

16.2.2.4 Hydrochloric acid, d20 = 1'19 g/m!.16.2.2.5 Hydrochl onc acid, 1 + 1 solution - Mix one volume of the

hydrochloric acid ( sa 6.2.2.4) with one volume of water.

16.2.2.6 Hydrochloric acid ( nc: ) ~ 0'1 molj l ".16.2.2.7 Zwc, standard solution COTTtsfondlTlg to 1 g oj

IS I 6217 • 1985

means of Bunsen burner; continue the decomposition in the mufflefurnace controlled at 525 :I:: 25°C until white ashes are obtained. Dissolvethe ashes in I to 2 ml of the dilute hydrochloric acid ( see 16.2.2.5 ). addabout 20 ml of water and place in the boiling water bath until completelyevaporated. Add 20 ml of the hydrochloric aciel solution and heat onthe water bath for about 5 min. Filter through an ashless filter paper.Collect the filtrate in one of the 50 ml volumetric flasks ( see 16.2.3 ) andrinse the dish and filter paper repeatedly with 5 to IO ml of the hydro-chloric acid solution (see 16.2.2.6). Cool and dilute to the mark withthe same hydrochloric acid solution.

16.2.4.2 Blank test - Carry out a blank test, replacing the testportion by 10 ml of water, and proceeding as described in 16.2.4.1.

16.2.4.3 Decomposition by wet method - Introduce the test portion intoone of the round bottom flasks. Add 10 ml of nitric acid and 5 ml ofsulphuric acid together with some glass beads. Place the flask containingthe mixture on the digestion rack and heat, cautiously to avoid excessivefrothing. If necessary, interrupt heating and begin again only whenvigorous frothing has ceased. As soon as possible, bring the liquid to boiland continue boiling until It begins to turn brown. Then add I to 2 ml ofnitric acid drop by drop. Boil again after every addition, but avoidingvigorous heating. Care shall be taken to always have some nitric aridin the mixture as indicated by the presence of nitrous vapours. Stop theaddition of nitric acid when the solution no longer turns brown onaddition of the acid. Continue heating until white fumes appear,indicating a high concentration of sulphuric acid and a reduction innitric acid. If the solution turns brown again, continue the addition ofnitric acid and repeat the operation described above until browningceases. Allow the solution to cool. The absence of colour or the presenceof a light green or yellow colour indicates that the digestion is complete.Carefully add 15 ml of water to the cold solution, and boil until whitefumes appear. Repeat this operation twice more.

When decomposition is terminated, dilute the solution with a fewmillilitres of water and filter through an ashlevs filter paper Collectthe filtrate in one of the 50 ml volumetric flasks and rinse the Ilask andthe filter paper with a few millilitres of water, collecting the rinsings inthe volumetric flask. Shake, cool, dilute to the mark and homogenize byshaking.

16.2.4.4 Blank test - Car:'y out a blank test, replacing the testportion by 10 ml of water, and proceeding as described in 16.2.4.3.

NOT!!: - The blank test is unnecessary if the .•bsence of zinc in the reagents fordecomposition has been verified.

47

IS : 6287 • 1985

16.2.4.5 Determination

a) Sample decomposed by dry method

i) Preparation of the calibration curve - Dilute the standard zincsoluuon with the hydrochloric acid (see 16.2.2.6 ) to obtainfour solutrons containing 0'25 - 0'5 - I and 1'5 mg of zincper lure. Aspirate each of these solutions into the flame of thespectrometer, at a rate of approximately 4 mljmin. Recordthe correspondmg values of absorbance and draw thecalibration curve.

ri) Spectrometric measurement on the test solution - Aspirate the testsolution (see 16.2.4.1 ) into the flame of the spectrometer at arate of approximately 4 mljrmn. Record the absorbance.

iii) Speetrometric measurement on the blank tnt solution - Aspirate theblank test solution ( sre 16.2.4.2 ) into the flame of the spectro-meter, and record the absorbance. The absorbance shall beless than or equal to 0'002. Subtract the absorbance of theblank test solution from that of the test solution ( Jet 16.2.4.1 ).

b) Sample decomposed by wet method

i) Preparauon of the