Thermo Fisher Scientific Ion Selective Electrodes Iodide User Manual

Instruction Manual Iodide Electrode

EUTECH INSTRUMENTS PTE LTD.

INSTRUCTION MANUAL

IODIDE ION ELECTRODE

Instruction Manual Iodide Electrode

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

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 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, NaI. 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

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, 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 NaI. 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.

Code no. EC-ISA-IO1-BT. To prepare

Instruction Manual Iodide Electrode

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

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

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

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concentration (log axis). Extrapolate the curve down to about 1.0X 10

M or l ppm. A

typical calibration curve for iodide can be found in Figure 1.

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