EUTECH INSTRUMENTS POTASSIUM EPOXY, EC-K03, EC-SCS-KO1-BT, EC-SCS-KO2-BT, EC-ISA-KO1-BT Instruction Manual

Instruction Manual Potassium Electrode

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EUTECH INSTRUMENTS PTE LTD.

INSTRUCTION MANUAL

POTASSIUM ION ELECTRODE

Instruction Manual Potassium 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 pH/mV meter) ...........................................................................................4

Electrode Slope Check (with ion meter) ..................................................................................................4

MEASUREMENT..............................................................................................................................5

Measuring Hints.......................................................................................................................................5

Sample Requirements...............................................................................................................................5

Units of Measurement..............................................................................................................................6

MEASUREMENT PROCEDURE ...................................................................................................6

Direct Measurement.................................................................................................................................6

Direct Measurement of Potassium (using a standard pH/mV meter) .......................................................6

Direct Measurement of Potassium (using an ion meter)..........................................................................7

Low Level Potassium Determination (using a standard pH/mV meter) ..................................................8

Low Level Potassium Determination (using an ion meter)......................................................................9

ELECTRODE CHARACTERISTICS............................................................................................. 9

Reproducibility.........................................................................................................................................9

Interferences.............................................................................................................................................9

Temperature Influences..........................................................................................................................10

Electrode Response................................................................................................................................11

Detection Limit ......................................................................................................................................11

pH Effects...............................................................................................................................................12

Electrode Life.........................................................................................................................................12

Electrode Storage ...................................................................................................................................12

ELECTRODE THEORY................................................................................................................12

Electrode Operation ...............................................................................................................................12

TROUBLESHOOTING GUIDE....................................................................................................13

Meter......................................................................................................................................................14

Glassware...............................................................................................................................................14

Electrodes...............................................................................................................................................14

Reagents.................................................................................................................................................14

Sample....................................................................................................................................................14

Technique...............................................................................................................................................15

TROUBLESHOOTING HINTS.....................................................................................................15

SPECIFICATIONS..........................................................................................................................17

ORDERING INFORMATION.......................................................................................................17

Instruction Manual Potassium Electrode

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EUTECH INSTRUMENTS PTE LTD.

POTASSIUM ION ELECTRODE

INSTRUCTION MANUAL

GENERAL INSTRUCTIONS

Introduction

Eutech Instruments Potassium Ion Electrode is used to measure potassium ions in aqueous solutions
quickly, simply, accurately, and economically.

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 Potassium Ion Combination Epoxy-body Electrode, Code no. EC-K-03.

Required Solutions

1. Deionized or distilled water for solution and standard preparation.

2. Eutech Potassium Standard, 0.1M KCl, Code no. EC-SCS-KO1-BT. To prepare this
solution from your own laboratory stock, half fill a one liter volumetric flask with distilled
water and add 7.46 grams of reagent-grade potassium chloride. Swirl the flask gently to
dissolve the solid. Fill to the mark with distilled water, cap, and upend several times to mix
the solution.

3. Eutech Potassium Standard, 1,000 ppm K+1, Code no. EC-SCS-KO2-BT. To prepare this
solution from your own laboratory stock, half fill a one liter volumetric flask with distilled
water and add 1.91 grams of reagent-grade potassium chloride. 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 Ionic Strength Adjuster (ISA), 5M NaCl, Code no. EC-ISA-KO1-BT to keep a
constant background ionic strength present in the solution. To prepare this solution from
your own laboratory stock, half fill a 1,000 ml volumetric flask with distilled water and
add 292 grams of reagent-grade sodium chloride (NaCl). Swirl the flask gently to dissolve
the solid. Fill to the mark with distilled water, cap, and upend several times to mix the
solution. Add 2 ml of ISA to every 100 ml of sample or standard solution for a back­ground ionic strength of 0.10M.

Instruction Manual Potassium Electrode

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GENERAL PREPARATION

Electrode Preparation

Remove any rubber caps covering the electrode tips and the rubber inserts covering the filling holes
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. Gently shake the electrode downward in the same manner as a clinical
thermometer to remove any air bubbles which might be trapped behind the potassium membrane.
Prior to first usage, or after long term storage, immerse the potassium electrode in potassium
standard for thirty minutes. The electrode is now ready for use.

Connect the electrodes to the proper terminals as recommended by the meter manufacturer.

Electrode Slope Check (with 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. If drifting or instability is
observed, see the TROUBLESHOOTING section.

2. Using a pipet, add 1 ml of 0.1M or 1,000 ppm potassium standard to the beaker. When the
reading is stable, record the mV reading.

3. Using a pipet, add 10 ml of the same potassium 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 56±2 mV, assuming the solution temperature is between
20

o

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.

Electrode Slope Check (with ion meter)

(Check electrodes each day)

1. Prepare standard potassium solutions whose concentrations vary by tenfold. Use either the

0.1M K+1 or the 1,000 ppm K+1 standard 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 the 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.

Instruction Manual Potassium Electrode

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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 the 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 slope is not within this range.

MEASUREMENT

Measuring Hints

All samples and standards should be at the same temperature for precise measurement, preferably
ambient temperature.

The sensing membrane is normally subject to water uptake and might appear milky. This has no
effect on performance.

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 or asbestos sheet, between the stirrer and beaker.

Always rinse the electrode tip(s) with distilled water and blot dry with a fresh tissue between
readings to prevent solution carryover.

Check the electrode for air bubbles adhering to the membrane surface after immersion in solution.
Agitate the electrode gently to remove the air bubbles.

A slow or sluggish electrode response may indicate surface contamination of the potassium
electrode membrane. Soak the electrode tip in distilled water for about 5 minutes to clean the
membrane. Rinse the membrane and soak in diluted standard solution for about 5 minutes to restore
performance.

When measuring samples with high ionic strength, prepare standards with compositions similar to
that of the sample.

Dilute concentrated samples (over 0.1M) before measurement. Recalibrate every few hours for
routine measurement.

Sample Requirements

Make sure that the samples and standards are at the same temperature. About a 2% error will be
introduced for a 1oC difference in temperature. Temperature should normally be less than 40oC with
intermittent measurements allowed to 50oC.

Instruction Manual Potassium Electrode

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All samples and standards must be aqueous. They must not contain organic solvents. Interferences
found in Table 3 should be absent.

Units of Measurement

Potassium concentrations are measured in units of parts per million as potassium, parts per million
as KCl, moles per liter, or any other convenient concentration unit. Table 1 indicates some of the
concentration units.

TABLE 1: Concentration Unit Conversion Factors

ppm K+1 ppm KCl moles/liter K

+1

3.91 7.46 1x10-4

39.10 74.60 1x10-3

391.00 746.00 1x10

-2

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 potassium samples. The temperature of both
sample solution and of standard solutions should be the same.

Direct Measurement of Potassium (using a standard pH/mV meter)

1. Prepare 10-2, 10-3, and 10-4M or 100, 10, and 1 ppm standards by serial dilution of the

0.1M or 1,000 ppm standard. Measure out 100 ml of each standard into individual 150 ml
beakers. Add 2 ml of ISA per 100 ml of standard.

2. Place the most dilute solution (10-4M or 1 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
tip(s) into the solution. When the reading has stabilized, record the mV reading.

3. Place the midrange solution (10-3M or 10 ppm) on the magnetic stirrer and begin stirring.
After rinsing the electrode(s) with distilled water and blotting dry, immerse the electrode
tip(s) in the solution. When the reading has stabilized, record the mV reading.

4. Place the most concentrated solution (10-2M or 100 ppm) on the magnetic stirrer and begin
stirring. After rinsing the electrode(s) with distilled water and blotting dry, immerse the
electrode tip(s) in the solution. When the reading has stabilized, record the mV reading.

5. Using the semi-logarithmic graph paper, plot the mV reading (linear axis) against the
concentration (log axis). Extrapolate the curve down to about 1x10-5M or 0.2 ppm. A
typical calibration curve can be found in Figure 1.