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EC-AGS-03
Instruction Manual
26 pgs472.35 Kb0

EUTECH INSTRUMENTS EC-AGS-03 Instruction Manual

Instruction Manual Silver/Silver Sulfide Electrode
1
EUTECH INSTRUMENTS PTE LTD.
INSTRUCTION MANUAL
SILVER/SILVER SULFIDE ION ELECTRODE
2
TABLE OF CONTENTS
GENERAL INSTRUCTIONS ..........................................................................................................3
Introduction................................................................................................................................................................ 3
Required Equipment...................................................................................................................................................3
Required Solutions..................................................................................................................................................... 3
GENERAL PREPARATION..........................................................................................................................5
Electrode Preparation................................................................................................................................................. 5
Electrode Slope Check (with pH/mV meter) ............................................................................................................. 5
Electrode Slope Check (with ion meter).................................................................................................................... 6
MEASUREMENT............................................................................................................................................7
Measuring Hints......................................................................................................................................................... 7
Sample Requirements................................................................................................................................................. 7
Units of Measurement................................................................................................................................................ 8
MEASUREMENT PROCEDURE ...................................................................................................8
Direct Measurement................................................................................................................................................... 8
Direct Measurement of Silver (using a pH/mV meter).............................................................................................. 8
Direct Measurement of Silver (using an ion meter)................................................................................................... 9
Direct Measurement of Sulfide (using a pH/mV meter).......................................................................................... 10
Direct Measurement of Sulfide (using an ion meter)............................................................................................... 11
Low Level Silver Determinations (using a pH/mV meter)...................................................................................... 12
TITRATION.....................................................................................................................................13
Titration of Sulfide...................................................................................................................................................14
Titration of Silver.....................................................................................................................................................14
Low Level Chloride Titration .................................................................................................................................. 15
Indicator Titration .................................................................................................................................................... 16
ELECTRODE CHARACTERISTICS........................................................................................... 18
Reproducibility......................................................................................................................................................... 18
Interference .............................................................................................................................................................. 18
Complexation........................................................................................................................................................... 18
Temperature Influences............................................................................................................................................ 18
Electrode Response.................................................................................................................................................. 19
Limits of Detection .................................................................................................................................................. 20
pH Effects ................................................................................................................................................................ 20
Electrode Life........................................................................................................................................................... 20
Electrode Storage.....................................................................................................................................................20
ELECTRODE THEORY................................................................................................................21
Electrode Operation ................................................................................................................................................. 21
TROUBLESHOOTING GUIDE....................................................................................................22
Meter........................................................................................................................................................................ 22
Glassware................................................................................................................................................................. 22
Electrodes................................................................................................................................................................. 22
Standards and Reagents............................................................................................................................................ 23
Sample...................................................................................................................................................................... 23
Technique................................................................................................................................................................. 23
TROUBLESHOOTING HINTS.....................................................................................................24
SPECIFICATIONS..........................................................................................................................26
ORDERING INFORMATION.......................................................................................................26
Instruction Manual Silver/Silver Sulfide Electrode
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EUTECH INSTRUMENTS PTE LTD.
SILVER/SULFIDE ION ELECTRODE
INSTRUCTION MANUAL
GENERAL INSTRUCTIONS
Introduction
Eutech Silver/Sulfide Ion Electrode is used to measure silver and sulfide ions in aqueous solutions quickly, simply, accurately, and economically. The two ions are virtually never present in solution together, owing to the extreme insolubility of silver sulfide. Indirect measurements of cyanide or measurements of halide ions by titration may be done with this electrode.
Required Equipment
1. A pH/mV meter or an ion meter, either line operated or portable.
2. Semi-logarithmic 4-cycle graph paper for preparing calibration curves when using the meter in the mV mode. Gran's plot paper (10% volume corrected) is recommended for low level chloride measurement.
3. A magnetic stirrer.
4. Eutech Silver/Sulfide Ion Combination Epoxy-body Electrode, Code no. EC-AGS-03.
5. Polishing Paper, Code no. EC-MIS-PP, to polish dirty or etched electrode membranes.
Required Solutions
1. Deionized or distilled water for solution and standard preparation. Water used in the preparation of sulfide standards and of SAOB should also be de-aerated.
For Silver:
2. Eutech Ionic Strength Adjuster (ISA), 5M NaNO3, Code no. EC-ISA-SS1-BT. To prepare this solution from your own laboratory stock, half fill a 1,000 ml volumetric flask with distilled water and add 425 grams of reagent- grade sodium nitrate, NaNO3. Swirl the flask to dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend the flask several times to mix the contents.
3. Eutech Silver Standard Solution, 0.1M AgNO3, Code no. EC-SCS-SS1-BT. To prepare this solution from your own laboratory stock, dry reagent-grade, pulverized silver nitrate in a laboratory oven for one hour at 150oC. Quantitatively transfer 16.99 grams of the dried silver nitrate to a 1 liter flask containing about 500 ml of distilled water. Swirl the flask to dissolve the solid. Fill the flask to the mark with distilled water, cap and upend several
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times to mix the solution. Store the solution in a brown bottle, tightly capped, in a dark place.
4. Eutech Silver Standard, 1,000 ppm as Ag+, Code no. EC-SCS-SS2-BT. To prepare this solution from your own laboratory stock, dry reagent-grade, pulverized silver nitrate in a laboratory oven for one hour at 150oC. Quantitatively transfer 1.57 grams of the dried silver nitrate to a 1 liter volumetric flask containing about 500 ml of distilled water. Swirl the flask to dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend several times to mix the solution. Store the solution in a brown bottle, tightly capped, in a dark place.
5. Chloride Titrant (low level), 2.82X10-3M AgNO3. Dry reagent-grade, pulverized silver nitrate as described above in Silver Standards. Quantitatively transfer 0.479 grams of dried silver nitrate to a 1 liter volumetric flask about half-full of distilled water. Swirl the flask to dissolve the solid. Fill to the mark with distilled water, cap, and upend several times to mix the solution. Store in a brown bottle in a dark place.
For Sulfide:
6. Eutech Sulfide Anti-Oxidant Buffer (SAOB) kit, Code No. EC-ISA-SS2-BT. This buffer must be used fresh and will range in color from clear to yellow-brown. It has become oxidized when it turns dark brown and should then be discarded. Store fresh SAOB in a tightly closed bottle. To prepare SAOB from your own stock, fill a 1 liter volumetric flask with about 500 ml of distilled, de-aerated water, 200 ml of 10M NaOH, 35 grams of ascorbic acid, and 67 grams of disodium EDTA. Swirl the mixture until the solids dissolve and fill to the mark with distilled, de-aerated water.
7. Sulfide Standard. To prepare a stock solution of saturated sodium sulfide, add about 100 grams of reagent grade Na2S.9H2O to 100 ml of distilled, de-aerated water. Shake well and let stand overnight, storing in a tightly closed bottle in a hood.
Prepare a weekly sulfide standard by adding 500 ml SAOB to a 1 liter volumetric flask, pipetting 10 ml of the stock solution into the flask, and diluting to the mark with distilled, de-aerated water.
The exact concentration, C, can be determined by titrating 10 ml of the standard with 0.1M lead perchlorate. Use silver/sulfide ion electrode (and the reference electrode) to indicate the endpoint.
The calculation is as follows:
C = 3206 (Vt/Vs)
where
C = concentration as ppm sulfide Vt = volume of titrant at endpoint Vs = volume of standard used (10 ml)
Prepare other standards each day by serial dilution of the weekly standard. To do a ten-fold dilution, accurately measure 10 ml of the standard and add it to a 100 ml volumetric flask. Add 45 ml of SAOB and dilute to the mark with distilled, de-aerated water.
Instruction Manual Silver/Silver Sulfide Electrode
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GENERAL PREPARATION
Electrode Preparation
Remove the rubber caps covering the electrode tips and the rubber insert covering the filling hole of the reference electrode. Fill the combination electrode or the reference electrode with the filling solution shipped with the electrode to a level just below the fill hole. No preparation is required for a sealed reference electrode. Connect the electrodes to the proper terminals as recommended by the meter manufacturer.
Electrode Slope Check (with pH/mV meter)
(Check electrodes each day)
Using silver standards:
1. To a 150 ml beaker, add 100 ml of distilled water and 2 ml of ISA. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the mV mode, lower the electrode tips into the solution.
2. Using a pipet, add 1 ml of 0.1M or 1,000 ppm silver standard to the beaker. When the reading has stabilized, record the millivolt reading.
3. Using a pipet, add 10 ml of the same silver standard used above to the beaker. When the reading has stabilized, record the millivolt reading.
4. Determine the difference between the two readings. A difference of 57±2 mV indicates correct electrode operation, assuming the solution temperature is between 20o and 25oC. See the TROUBLESHOOTING section if the potential change is not within this range.
Using sulfide stock solutions:
1. To a 150 ml beaker, add 50 ml of distilled water and 50 ml of SAOB solution. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the mV mode, lower the electrode tips into the solution.
2. Using a pipet, add 1 ml of weekly standard sulfide solution to the beaker. When the reading has stabilized, record the millivolt reading.
3. Using a pipet, add 10 ml of weekly standard sulfide used above to the beaker. When the reading has stabilized, record the millivolt reading.
4. Determine the difference between the two readings. A difference of 26±2 mV indicates correct electrode operation, assuming the solution temperature is between 20o and 25oC. See the TROUBLESHOOTING section if the potential change is not within this range.
Slope is defined as the change in potential observed when the concentration changes by a factor of
10.
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Electrode Slope Check (with ion meter)
(Check electrodes each day)
Using silver standards:
1. Prepare standard silver solutions whose concentrations vary by tenfold. Use either the
0.1M AgNO3 or 1,000 ppm stock solutions. Use the serial dilution method for this preparation.
2. To a 150 ml beaker, add 100 ml of the lower value standard and 2 ml of ISA. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips into the solution. Assure that the meter is in the concentration mode.
3. Adjust the meter to the concentration of the standard and fix the value in the memory according to the meter manufacturer's instructions.
4. Rinse the electrodes with distilled water and blot dry.
5. To another 150 ml beaker, add 100 ml of the higher value standard and 2 ml of ISA. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips into the solution.
6. Adjust the meter to the concentration of the standard and fix the value in the memory.
7. Read the electrode slope according to the meter manufacturer's instructions. Correct electrode operation is indicated by a slope of 90-100%. See the TROUBLESHOOTING section if the potential is not within this range.
Using sulfide stock solutions:
1. Prepare standard sulfide solutions whose concentrations vary by tenfold. Use the serial dilution method and the weekly sulfide standard to prepare these solutions.
2. To a 150 ml beaker, add 50 ml of the lower value standard, 25 ml of SAOB, and 25 ml of distilled water. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips into the solution. Assure that the meter is in the concentration mode.
3. Adjust the meter to the concentration of the standard and fix the value in the memory according to the meter manufacturer's instructions.
4. Rinse the electrodes with distilled water and blot dry.
5. To a 150 ml beaker, add 50 ml of the higher value standard, 25 ml of SAOB, and 25 ml of distilled water. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips into the solution.
6. Adjust the meter to the concentration of the standard and fix the value in the memory.
Instruction Manual Silver/Silver Sulfide Electrode
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7. Read the electrode slope according the meter manufacturer's instructions. Correct electrode operation is indicated by a slope of 90-100%. See the TROUBLESHOOTING section if the slope is not within this range.
MEASUREMENT
Measuring Hints
All samples and standards should be at the same temperature for precise measurement. A difference of 1 oC in temperature will result in about a 2% measurement error.
Constant, but not violent, stirring is necessary for accurate measurement. Magnetic stirrers can generate sufficient heat to change the solution temperature. To counteract this effect, place a piece of insulating material, such as styrofoam sheet, between the stirrer and beaker.
All silver samples and silver standards should be stored away from light.
Always dilute sulfide samples with SAOB (1:1) when they are collected.
Always rinse the electrodes with distilled water and blot dry between measurements. Use a clean, dry tissue to prevent cross-contamination.
A slow-responding electrode may point to deposits on the membrane. Use polishing paper to remove such deposits. See the section on Electrode Response.
For low level silver measurements, use labware made of plastic.
For samples with high ionic strength, prepare standards whose composition is similar to the sample.
Always check to see that the membrane is free from air bubbles after immersion into the standard or sample.
Sample Requirements
All samples must be aqueous and not contain organics which can dissolve the epoxy electrode body and/or cement bonding the sensing crystal to the electrode body. Infrequent measurements in solutions containing methanol, benzene, or acetone are permitted. Please check with Eutech Instruments Pte Ltd. before using the electrode in other organic solvents.
The temperature of the standard solution and of the sample solution should be the same and below 80oC.
Samples containing sulfide must be buffered with SAOB to convert HS
-
1
and H2S to S-2.
Samples containing silver must be below pH 8 to avoid reaction with OH-1. Silver samples should be acidified with 1M HNO3, if necessary.
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Mercury cannot be present in silver samples. Since HgS and Hg2S are insoluble, no mercury will be present in sulfide samples. Other interference should be absent. If they are present, use the procedures found in the Interference and Electrode Response sections to remove them.
Units of Measurement
Silver and sulfide concentrations are measured in units of parts per million, equivalents per liter, moles per liter, or any other convenient concentration unit. Table 1 indicates some of the concentration units.
TABLE 1: Concentration Unit Conversion Factors
ppm S-2 ppm Ag+1 N(S-2) M(Ag+1)
321.0 1079.0 2.00X10-2 1.00X10-2
100.0 --- 6.23X10-3 3.12X10-3
32.1 108.0 2.00X10
-3
1.00X10-3
--- 100.0 1.84X10-3 9.27X10
-4
3.2 10.8 2.00X10-4 1.00X10-4
MEASUREMENT PROCEDURE
Direct Measurement
Direct measurement is a simple procedure for measuring a large number of samples. A single meter reading is all that is required for each sample. The ionic strength of samples and standards should be made the same by adjustment with SAOB for all sulfide solutions and with ISA for all silver solutions. The temperature of both sample solution and standard solution should be the same.
Direct Measurement of Silver (using a pH/mV meter)
1. By serial dilution of the 0.1M or 1,000 ppm standards, prepare 10-2, 10-3, and 10-4M or 100 and 10 ppm silver standards. Add 2 ml of ISA per 100 ml of standard. Prepare standards with a composition similar to the samples if the samples have an ionic strength above
0.1M.
2. Place the most dilute solution (1.0X10-4M or 10 ppm) on the magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the mV mode, lower the electrode tips into the solution. When the reading has stabilized, record the mV reading.
3. Place the midrange solution (1.0X10-3M or 100 ppm) on the magnetic stirrer and begin stirring. After rinsing the electrodes with distilled water, blot dry and immerse the electrode tips in the solution. When the reading has stabilized, record the mV reading.
4. Place the most concentrated solution (1.0X10
-
2
M or 1,000 ppm) on the magnetic stirrer and begin stirring. After rinsing the electrodes with distilled water, blot dry and immerse the electrode tips in the solution. When the reading has stabilized, record the mV reading.
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