EUTECH INSTRUMENTS EC-IO-03, EC-SCS-IO1-BT, EC-SCS-IO2-BT, EC-ISA-IO1-BT, EC-MIS-PP Instruction Manual
Instruction Manual Iodide Electrode
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EUTECH INSTRUMENTS PTE LTD.
INSTRUCTION MANUAL
IODIDE ION ELECTRODE
Instruction Manual Iodide Electrode
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TABLE OF CONTENTS
GENERAL INSTRUCTIONS ..........................................................................................................3
Introduction..............................................................................................................................................3
Required Equipment.................................................................................................................................3
Required Solutions...................................................................................................................................3
GENERAL PREPARATION............................................................................................................4
Electrode Preparation...............................................................................................................................4
Electrode Slope Check (with a pH/mV meter).........................................................................................4
Electrode Slope Check (with an ion meter)..............................................................................................4
MEASUREMENT..............................................................................................................................5
Measuring Hints.......................................................................................................................................5
Sample Requirements...............................................................................................................................5
Units of Measurement..............................................................................................................................5
MEASUREMENT PROCEDURE ...................................................................................................6
Direct Measurement.................................................................................................................................6
Direct Measurement of iodide (using a pH/mV meter)............................................................................6
Direct Measurement of iodide (using an ion meter).................................................................................7
Low Level Iodide Determinations (using a pH/mV meter)......................................................................8
ELECTRODE CHARACTERISTICS............................................................................................. 8
Reproducibility.........................................................................................................................................8
Interferences.............................................................................................................................................8
Complexation...........................................................................................................................................9
Temperature Influences..........................................................................................................................10
Electrode Response................................................................................................................................10
Limits of Detection.................................................................................................................................11
pH Effects...............................................................................................................................................11
Electrode Life.........................................................................................................................................11
Electrode Storage ...................................................................................................................................12
ELECTRODE THEORY................................................................................................................12
Electrode Operation ...............................................................................................................................12
TROUBLESHOOTING GUIDE....................................................................................................13
Meter......................................................................................................................................................13
Glassware...............................................................................................................................................13
Electrodes...............................................................................................................................................13
Standards and Reagents..........................................................................................................................14
Sample....................................................................................................................................................14
Technique...............................................................................................................................................14
TROUBLESHOOTING HINTS.....................................................................................................15
SPECIFICATIONS..........................................................................................................................17
ORDERING INFORMATION.......................................................................................................17
Instruction Manual Iodide Electrode
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EUTECH INSTRUMENTS PTE LTD.
IODIDE ION ELECTRODE
INSTRUCTION MANUAL
GENERAL INSTRUCTIONS
Introduction
Eutech Instruments Iodide Ion Electrode is used to quickly, simply, accurately, and economically
measure free iodide ion in aqueous solutions.
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.
3. A magnetic stirrer.
4. Eutech Iodide Ion Combination Epoxy-body Electrode, Code no. EC-IO-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.
2. Eutech Ionic Strength Adjuster (ISA), 5M NaNO
3,
Code no. EC-ISA-IO1-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. Swirl the flask gently to
dissolve the solid. Fill to the mark with distilled water, cap, and upend the flask several
times to mix the solution.
3. Eutech Iodide Standard, 0.1M NaI, Code no. EC-SCS-IO1-BT. To prepare this solution
from your own laboratory stock, half-fill a one liter volumetric flask with distilled water and
add 10.3 grams of reagent-grade sodium iodide, NaBr. Swirl the flask gently to dissolve the
solid. Fill to the mark with distilled water, cap, and upend several times to mix the solution.
4. Eutech Iodide Standard, 1,000 ppm I
-1
, Code No. EC-SCS-IO2-BT. To prepare this solution
from your own laboratory stock, half-fill a one liter volumetric flask with distilled water and
add 1.29 grams of reagent-grade NaBr. Swirl the flask gently to dissolve the solid. Fill the
flask to the mark with distilled water, cap, and upend several times to mix the solution.
Instruction Manual Iodide 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 combination electrode or of the reference electrode. Fill the reference electrode or the
combination electrode with the filling solution shipped with the electrode to a level just below the
fill hole. No preparation is required with a sealed reference electrode.
Connect the electrodes to the proper terminals as recommended by the meter manufacturer.
Electrode Slope Check (with a pH/mV meter)
(Check electrodes each day)
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
millivolt mode, lower the electrode tips into the solution.
2. Using a pipet, add 1 ml of either the 0.1M or the 1,000 ppm standard to the beaker. When
the reading is stable, record the mV reading.
3. Using a pipet, add 10 ml of the same standard used above to the beaker. When the reading
has stabilized, record the mV reading.
4. Determine the difference between the two readings. The electrode is operating correctly if
the mV potential has changed by a difference of 57±3 mV, assuming the solution
temperature is 25oC. See the TROUBLESHOOTING sections 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.
Electrode Slope Check (with an ion meter)
(Check electrodes each day)
1. Prepare standard iodide solutions whose concentrations vary by tenfold. Use either the
0.1M or the 1,000 ppm iodide standard. 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.
Instruction Manual Iodide Electrode
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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 93-100%. See the TROUBLESHOOTING
sections 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 1oC 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.
Always rinse the electrodes with distilled water and blot dry between measurements. Use a clean,
dry tissue to prevent cross contamination.
For samples with high ionic strength, prepare standards whose composition is similar to the sample.
Dilute concentrated samples (>0.1M) before measurement.
Use fresh standards for calibration.
Use 2 ml of ISA for each 100 ml of sample or standard.
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 the cement bonding the sensing crystal to the electrode body. Infrequent measurements in
solutions containing methanol, benzene, or acetonitrile are permitted. Highly polar solvents slowly
attack the electrode. Please check with Eutech Instruments Pte Ltd. before using these electrodes in
other organic solvents.
The temperature of the sample solutions and of the standard solutions should be the same and below
80oC.
The pH range for the iodide ion electrode is 0-14. Neutralize samples outside this range with acid or
base to bring them in range.
Interferences should be absent. If they are present, use the procedure found in the Interference and
Electrode Response sections to remove them.
Units of Measurement
Instruction Manual Iodide Electrode
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Iodide ions can be measured in units of moles/liter, parts/million, or any other convenient
concentration unit. Table 1 indicates some of the concentration units.
TABLE 1: Concentration Unit Conversion Factors
moles/liter ppm I-1
1.0X10-4 12.7
1.0X10-3 127.0
1.0X10-2 1,270.0
1.0X10-1 12,770.0
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 ISA for all iodide solutions. The temperature of both sample
solutions and of standard solutions should be the same.
Direct Measurement of iodide (using a pH/mV meter)
1. By serial dilution prepare three standard solutions from the 0.1M or 1,000 ppm standard.
The resultant concentrations should be 10-2, 10-3, and 10-4M or 1,000, 100 and 10 ppm
iodide standards. Add 2 ml of ISA to each 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) in a 150 ml beaker 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 mid-range solution (1.0X10-3M or 100 ppm) in a 150 ml beaker on the magnetic
stirrer and begin stirring at a constant rate. After rinsing the electrodes in 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 (1.0X10-2M or 1,000 ppm) in a 150 ml beaker on the
magnetic stirrer and begin stirring at a constant rate. After rinsing the electrodes in
distilled water, blot dry and immerse the electrode tips in the solution. When the reading
has stabilized, record the mV reading.
5. Using semi-logarithmic graph paper, plot the mV reading (linear axis) against the
concentration (log axis). Extrapolate the curve down to about 1.0X 10
-5
M or l ppm. A
typical calibration curve for iodide can be found in Figure 1.
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