mode/1755 refractive index monitor - bio-rad …...section 3 principle of operation bio-rad's...
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Mode/1755 Refractive Index Monitor
Instruction Manual
Model __________________________________ __
Serial No.----------------------------------
Date of Delivery----------------------------
Warranty Period----------------------------
Warranty Bio-Rad Laboratories' Model 1755 Refractive Index Monitor is warranted against defects in materials and workmanship for one year. If any defects occur in the instrument during this warranty period, Bio-Rad Laboratories will repair or replace the defective parts free. The following defects, however, are specifically excluded:
1. Defects caused by improper operation.
2. Repair or modification done by anyone other than Bio-Rad Laboratories or their authorized agent.
3. Use of fittings or other spare parts supplied by anyone other than Bio-Rad Laboratories.
4. Damage caused by accident or misuse.
5. Damage caused by disaster.
6. Corrosion due to use of improper solvent or sample.
This warranty does not apply to fuses.
For any inquiry or request for repair service, contact Bio-Rad Laboratories after confirming the model and serial number of your instrument.
© 1987 Bio-Rad Laboratories. All Rights Reserved.
Table of Contents Page
Section 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 General Information ..................................................................... . 1.2 Specifications ........................................................................... .
Section 2: Unpacking and Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1 Unpacking the Unit ....................................................................... 2 2.2 Instrument Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.3 Connecting a Recorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.4 Connecting an Integrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.5 Preparation for Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.6 Connecting a Column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. 7 Influence of Temperature on the Refractive Index of Solvents Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.8 Choosing an Appropriate Time Constant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Section 3: Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Section 4: Description of Major Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.2 Back Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Section 5: Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.1 Preparation for Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.2 Notes on Preparation for Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.3 Measurement with the Refractive Index Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.4 Remote Auto Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Section 6: Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.1 General Troubleshooting Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.2 Troubleshooting Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Section 7: Miscellaneous Problems Encountered in Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.1 Pump Pulsation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.2 Gradient Elution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.3 Preventing Disturbances Caused by Gas and Vapor Bubbles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.4 Selecting the Operating Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.5 Creating a Counter-Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.6 Filling the Reference Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7. 7 Exceeding the Detectable Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.8 Selecting the Solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.9 Checking the Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.10 Preventing Blockage in the Inflow Capillary Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.11 Working with Salt Solutions or Aggressive Solvents as the Eluant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.12 Shortening the Capillary Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.13 Leaks in the Flow Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Section 8: Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
SECTION 1 INTRODUCTION 1.1 Genera/Information Refractive index, unlike UV absorption, fluorescence, or electrochemical activity, is a universal property of all substances. Measurement of refractive index differences between HPLC peaks and mobile phases is, therefore, an essentially universal detection method.
Bio-Rad's Model 1755 refractive index monitor allows the qualitative and quantitative determination of substances which do not have measurable UV absorption. The refractive index monitor may also be used with eluants which have high UV absorbance. The refractive index monitor provides a continuous indication of the differential refractive index between a pure solvent and a dilution of the solvent by the eluted solutes. Because the refractive index monitor has a small volume flow cell, it is especially useful in HPLC applications.
The use of silicon photodiodes in the electronics results in a high degree of response linearity. The use of an infrared light emitting diode at 950 nm prevents the linearity deviations which often appear in other RI detectors, caused by the use of a white light source. The low heat dissipation of this LED adds to the refractive index monitor's high temperature stability, making thermostatting generally unnecessary. A water-bath thermostat is recommended only in the highest sensitivity ranges, or when great demands are placed on the refractive index monitor's long-term stability.
In the analytical refractive index monitor the capillary tubes to the sample and the reference cells have different internal diameters. The 0.3 mm I.D. capillary tube, on the sample side, is used for flow rates up to 5.0 mllmin. The 0.5 mm I.D. capillary tube, on the reference side, is used for flow rates up to 30 mil min. The cell is divided at a 45° angle to the path of the light beam. The reference cell is flushed with pure solvent, or filled with pure solvent in a stationary state.
1
1.2 Specifications Differential Refractive Index Monitor
Measuring ranges
Sensitivity (full scale)
Noise
Drift (If temperature changes <0.1 °K)
Linearity error
Light source
Recorder output
Integrator output
Marker internal (by push button) external (by contact to ground)
Time constant
Cell volume
Maximum flow rate analytical channel semi·preparative channel
Power requirements
Analytical Model
1/4, 1/2, 1..128
1.2 x 10 -s 4 n
<:t4x10-84n
<2 x 10- 7 4 n/hour
0.2% in ranges <8
light emitting diode (LED) infrared wavelength 950 :t 3 nm
100mV
1V
10mV
5mV
0.25, 1.0, and 4.0 sec
81-11
5 ml/min
30 ml/min
198-264/95-132V /50-60Hz/10 VA
SECTION 3 PRINCIPLE OF OPERATION Bio-Rad's refractive index monitor measures the differential refractive index between a pure solvent and solutes in low concentrations, like those normally used in an HPLC system. Figure 3.1 illustrates the refractive index monitor's principle of operation.
Silicon Photodlode
Beam
Splitter
LED (Infrared Diode)
FlowCeli
Concave Mirror
Fig. 3.1. Refractive Index monitor, Block Diagram.
The light from the infrared light emitting diode (LED, }. approximately 950 nm) is reflected onto the semi-permeable mirror, through the flow cell, and onto the concave mirror. The light then passes through the flow cell again, through the semi-permeable mirror, and finally through the zero glass. The beam splitter divides the light and reflects it to the two silicon photodiodes.
In Figure 3.1 the zero glass is adjusted so that the beam splitter divides the beam into two equal parts, creating equivalent photo currents it and iz in the photodiodes. The values of it and i2 will vary according to the concentration of the solution in the measurement cell. Thus the difference between the values of it and i2 gives a signal which is proportional to the concentration difference between the measurement cell and the reference cell.
Both the measurement and the reference sides of the flow cell are equipped with inlet and outlet capillaries, so that the solvent stream enters the cell from below and moves to the top. This design feature allows the rapid passage of air bubbles.
In the Modell755 refractive index monitor, 60 em of the inlet tube is molded in sleeve form into the optical bench, to allow the best possible heat exchange between the eluant and the optical system. An additional25 em of inlet tube is located in the preheat exchanger. This preheat exchanger is only for use on the sample side.
3
SECTION4 DESCRIPTION OF MAJOR PARTS 4.1 Front Panel
7
Fig. 4.1. Front panel.
Name
1. Power switch
2. Output
3. Zero button
4. Zero knob (coarse)
5. Range switch
6. Marker button
7. Time constant
8. Sample OUT
9. SampleiN
10. Reference OUT
11. Reference IN
MOHL1711 IMI'IUCTIV'.IIfHX MOIIIJ'Oif
8 9 10 11
Function
4 5
6
Turns instrument power on and off.
Digital display of integrator output in millivolts.
Luminous push-button for Auto-Zero.
Adjusts optical zero.
Selects full-scale sensitivity of the output.
Superimposes a mark on the recorder output.
Three-place switch for selecting 0.25, 1, or 4 second time constant.
Outlet tube for reference. 1.0mm I.D.
Inlet tube for reference. 0.3mmi.D.
Outlet tube for sample. 1.0mm I.D.
Inlet tube connection for sample. 0.5mmi.D.
Connection 8, 9, 10, 11 accept 1/16" (1.6 mm) O.D. tubing.
4.2 Back Panel
4
5
6
7
3 2
Fig. 4.2. Back panel.
Name Function
1. Power cord Plug one end of the power cord into this connector connector.
2. Fuse holders 2 x 100 mA
3. Voltage selector Sets refractive index monitor for 110V or 220V operation.
4. Recorder (100 mV) Connect cable from the recorder to this terminal.
5. Integrator (1V)
6. Marker
7. External zero
SECTIONS OPERATION
Connect cable from the integrator to this terminal.
Allows external actuation of marker signal.
Input for external zero adjustment.
5.1 Preparation for Operation 1. Connect the refractive index monitor to a recorder, as described
in Section 2.3.
2. Fill the reference side (see Figure 4.1) with solvent from the chromatographic procedure.
3. Be sure the eluate from the column flows through the measuring side of the cell.
4. Turn the RANGE switch to 0 to set electrical zero.
5. Adjust the recorder to the desired baseline (e.g. lOOJo of the full deflection) by using the zero adjust knob on the recorder.
6. Press the marker button on the refractive index monitor. A deviation of 10 m V will appear on the recorder. If the recorder deflection is in the negative direction, this can be adjusted to positive by reversing the polarity of the recorder connector cable.
7. Turn the RANGE switch on the refractive index monitor to 128 to set optical zero.
8. Press and hold the fine zero button and turn the zero knob on the refractive index monitor until the display reads between ± 7 m V. Release the fine zero button, and it should remain unlit. If not repeat.
The zero-glass is adjusted so that the light beam is symmetrical to the center of the reflecting beam-splitting prism. The zeroglass consists of a plane of parallel glass fitted with a gear having a 1:300 ratio. Approximately 300 turns of the knob are required to rotate the zero-glass 360°. The normal position of the
4
zero-glass is at an approximate right angle to the light beam, which, on passing through the glass, undergoes only a slight parallel displacement (see Figure 5.1).
.. II=--------Fig. 5.1. Zero-glass.
Note: If the narrow end of the zero-glass is pointing toward the light beam, a pseudo-zero setting will be obtained, since stray light also produces optical symmetry. With the zero-glass in this position, the sensitivity and response are not linear. Symptoms of a pseudo-zero setting include low response and reversed polarity.
When the zero-glass is rotated, recorder movements will clearly indicate the correct position of the zero-glass. Turning the zero glass clockwise increases the output (positive response). If the position of the zero-glass is not known, always turn the dial in a clockwise direction.
9. After adjusting zero, the RANGE knob can be set at a higher sensitivity, with further adjustment of optical zero if necessary.
5.2 Notes on Preparation for Operation The electrical zero of the recorder and the optical zero of the refractive index monitor must be set identically so that there is no baseline shift after setting the sensitivity range. If the sample peaks of the components are both positive and negative, set the electrical and optical zero of the recorder at about 50% scale (see Figure 5.2).
0 2 3 4 5 6 7 8 9 10
Start
Fig. 5.2. Baseline in the middle of the recorder chart.
If the solvent gives a negative deflection and the dissolved components give positive deflections, the baseline can be set on the right side of the chart paper (see Figure 5.3).
0 2 3 4 5 6 7 8 9 10
Start
llllllll
Fig. 5.3. Baseline right side.
However, if all the peaks of the sample being separated give negative values, the baseline can be set on the left side of the chart paper.
Fig. 5.4. Baseline left side.
5.3 Measurement with the Refractive Index Monitor l. After completing all preparation steps (Section 5.1), including
filling the reference side with solvent, allow time for the baseline to stabilize.
2. Inject the sample.
3. Press the MARKER button briefly so that the baseline shows a start mark of about lOo/o of the full scale recorder deflection.
4. If an external marker contact is connected to the refractive index monitor, a mark of about 5% full scale deflection will appear on the recorder.
Note: The marker signals do not appear at the integrator output.
5. Use the RANGE switch to adjust the sensitivity of the refractive index monitor so that actual peaks are shown in full scale.
5.4 Remote Auto Zero 1. An additional signal cable is connected to the external zero
port.
2. Attach the other end to a normally open relay.
3. A momentary contact closure will cause the monitor to adjust to zero.
5
SECTION 6 TROUBLESHOOTING 6.1 General Troubleshooting Guide
Problem Cause
Optical zero line cannot be set 1. Instrument not receiving voltage. by turning the zero glass ac· 2. Sensitivity switch in the 0 position. cording to Section 5.1.
3. One or both cell chambers not filled.
4. Solvent in reference side of cell different from that in the sample side.
5. Residues of a solvent not miscible with the last solvent used in the cell.
6. Zero glass has its narrow side to the light beam.
Too strong or too weak a signal 1. The recorder used is not set at 100 mV full·scale is given by the recorder when deflection but is set at a lower or higher input the start button "marker" is voltage. pressed.
Sensitivity of the refractive 1. Flow cell dirty. index monitor is too low. 2. Sensitivity of the recorder is greater than 100 mV
FSD.
3. Injection system leaks or the injection volume is incorrect.
4. Proceed as described in 5.2.
Sensitivity of the refractive 1. The sensitivity of the recorder is less than 100 index monitor is too high. mV.
Spikes or saw·tooth irregulari· 1. Solvent not degassed. ties of baseline due to gas and 2. The temperature of the optical bank is too near vapor bubbles. the boiling point of the solvent used thus caus·
ing the formation of vapor bubbles.
Baseline noise 1. A recorder with too high a sensitivity is connect· ed; test by pressing the marker button.
2. Electrostatic influence.
3. Electrical influence from the power line.
4. Air bubbles in the reference side of the flow cell.
5. Air bubbles in the measurement side.
6. Periodic noise due to pressure pulsations from the pump; effect stops when pump is stopped.
7. Periodic noise due to eluant dripping from the detector outflow tube.
8. Detector contaminated by residual solvent not miscible with the solvent now being used.
9. Temperature·dependent absorption of substanc· es in the column; can be tested by warming col· umn with the hand giving a very high peak in the recorder first in one direction and then in the other. Warming the eluant between the column and the detector does not produce such an ef· feet.
Baseline drift 1. Thermal drift of the refractive index monitor after starting.
2. A new column has been connected or the sol· vent changed.
3. Solvent mixture used for the elution is not prop· erly mixed or a part of the mixture has been lost due to evaporation.
6
Remedy
1. Check voltage supply.
2. Set sensitivity switch at position 128.
3. Fill reference and measurement sides with sol· vent free of air bubbles.
4. Fill both cell chambers with the same solvent.
5. Rinse both cell chambers with acetone when changing solvent or starting operation.
6. Proceed as described in Section 5.1.
1. Use a recorder for 100 mV FSD.
1. Clean cell (see Section 6.2).
2. Check by pushing the start button "marker" (see Section 7.9) to see whether the signal reaches 10% of the full·scale deflection and if necessary set the recorder at 100 mV.
3. Check the injection volume of the sample loop and the sealing of the injection syringe.
4. Proceed as described in 5.2.
1. Check, by pressing the start button "marker" (see Section 7.9), whether the signal reaches 10% of the record's full·scale deflection; use a recorder for 100 mV FSD.
1. Degas the solvent according to Section 7.3.
2. Set the working temperature lower (see Section 7.4).
1. Connect a recorder with a sensitivity of 100 mV.
2. Check the grounding of the instrument.
3. a. Switch off disturbing current consumers. b. Use separate current supply. c. Reverse detector and recorder plugs in the
electrical sockets in order to ground the other wire in the power cable.
4. See Sections 2.5 and 7.6.
5. Check whether the column outlet is connected to the inflow capillary of the cell. The solvent should flow upwards through the cell from bot· tom to top.
6. Eliminate pulsation by properly adjusting the pump (see manual for Bio·Rad Model1350 HPLC Pump) or use a damping system.
7. Place the outflow tube along the wall of the re· ceiving vessel or dip it into the solvent.
8. Clean the cell with acetone.
9. Insulate the column better, thermostat with a column heater.
1. Wait for instrument to warm up. Observe temper· ature stability of the surroundings.
2. Allow the chromatography system to equilibrate longer.
3. Stir solvent mixture constantly with a magnetic stirrer; keep the supply bottle closed as much as possible to prevent evaporation.
6.2 Troubleshooting Procedures Changing the Flow Cell (Refer to Figure 6.1). The procedure for changing the flow cell is the same for both the analytical and preparative refractive index monitor. The flow cell holder is removable only in the preparative model.
1. Unplug the instrument.
2. Remove the instrument cover plate.
3. Unscrew the cell holder cover (2), Figure 6.1.
4. Take out the cell holder cover carefully.
5. Carefully lift out the cell including the two top seals (if these are not already removed with the cover) with fine tweezers.
6. Remove the two lower seals if they have not been removed with the cell from the cell holder.
(1) Optical bench (2) Cell holder cover (3) Outlet lines (4) Zero mechanism (5) Inlet lines
Fig. 6.1. Changing the Flow Cell.
7
Cleaning the Flow Cell If the cell is merely dirty, it is best cleaned in hot HN03 and then rinsed with water and dried.
Assembly is carried out with new seals (Catalog No. 167-0460).
1. Lay the two seals exactly over the two holes in the bottom of the cell holder of the optical bench (first clean and dry the cell holder block).
2. Using the fine tweezers, place the cell on the seals. The seals must slide into the grooves provided for this on the cell. If assembled wrong, the flow path may be blocked.
3. Lay two seals in the grooves provided on the cell.
4. Replace the cell cover.
After installing the cuvette, perform a leak test. To do this the instrument is plugged in and set at zero on the recorder using the "zero glass knob" in range 64. When a completely dry 10 ml syringe is attached to the inflow tube and pressure is applied to the cell using the syringe while the outflow tube is held shut with the finger, an appreciable deflection should be visible on the recorder. If this is the case in both channels, the two channels should be filled with acetone and the recorder zero reset using the zero knob.
The pressure test should also cause a deflection on the recorder. The acetone must be able to be conveyed through both channels despite the resistance offered by the instrument and the diameter of its capillary tubes.
Attention: Do not place too much pressure on the syringe, and thus on the cell, by using excessive force.
SECTION 7 MISCELLANEOUS PROBLEMS ENCOUNTERED IN OPERATION 7.1 Pump Pulsation Periodic baseline noise, due to the pulsation of the solvent pumping system, is caused by brief pressure pulses to which the refractive index monitor responds with high sensitivity. If the pump is switched off, this type of noise is eliminated. Pressure pulsation must always be eliminated (refer to the manual for the pump being used). A pulse damping system can be assembled between the pump and the injection system, generally comprising an elastic tube system and a flow resistor. ·
7.2 Gradient Elution In gradient elution, it is generally not possible to use the refractive index monitor as a detector, since the refractive index "n" of the solvent mixture varies markedly as the mixing ratio constantly changes. However, the refractive index monitor is a suitable instrument, in some cases, for monitoring the reproducibility of the mixing ratios in elution mixtures with two or more components.
Since the blocking particles are often compacted at the front of the inflow tube, this tube can be shortened centimeter by centimeter. If the blockage is in the external heat exchanger and is not removable by flushing, it is easier to replace the heat exchanger with a new one. However, if the blockage is in the optical bench, this repair can only be carried out in the factory.
7.11 Working with Salt Solutions or Aggressive Solvents as the Eluant In case of lengthy pauses in the work (night or week-end) both sides of the flow cell should be rinsed with water, acetone, or methanol (the rinsing solvent should be miscible with the eluant used). The remaining rinsing solvent is drawn off to insure that the flow cell is empty. During brief pauses, the end of the outflow tube can be dipped into a beaker of eluant to prevent the drying of the eluant in the outlet tube.
7.12 Shortening the Capillary Tube To shorten a capillary tube, it must be cut in such a way that the tube opening is not compressed. For this, score the tube with a sharp file and break it off at the notch. The site of the break should be carefully smoothed with the file.
7.13 Leaks in the Flow Cell Sometimes baseline noise and drift are caused by a leak in the flow cell. Slight leaks may allow air to enter the flow cell without loss of solvent. A leak leads to total failure of the instrument since the baseline may no longer be adjusted with the zero glass. A hole in the optical bench allows the solvent, leaking from the flow cell, to flow out of the instrument through a hole in the bottom.
After removal of the flow cell (see Section 6.2) the optical bench must be dried. This can be speeded up by heating the optical bench. After drying, the replacement cell or the cleaned cell with a new seal is assembled as described in Section 6.2. If the optical bench and the mirror are damaged by aggressive solvents so that the instrument no longer operates properly, repairs in the factory are necessary.
SECTION 8 PARTS LIST 167-0458 Refractive Index Monitor, 110/220V 167-0456 Analytical Flow Cell for Refractive Index Monitor 167-0460 Pack of 10 seals for Analytical Cell
9
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