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Ion Selective Electrodes Potassium
User Manual
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Thermo Fisher Scientific Ion Selective Electrodes Potassium User Manual

Instruction Manual Potassium Electrode
EUTECH INSTRUMENTS PTE LTD.
INSTRUCTION MANUAL
POTASSIUM ION ELECTRODE
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Instruction Manual Potassium Electrode
TABLE OF CONTENTS
Introduction..............................................................................................................................................3
Required Equipment.................................................................................................................................3
Required Solutions...................................................................................................................................3
Electrode Preparation...............................................................................................................................4
Electrode Slope Check (with pH/mV meter) ...........................................................................................4
Electrode Slope Check (with ion meter) ..................................................................................................4
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 Operation ...............................................................................................................................12
TROUBLESHOOTING GUIDE....................................................................................................13
Meter......................................................................................................................................................14
Glassware...............................................................................................................................................14
Electrodes...............................................................................................................................................14
Reagents.................................................................................................................................................14
Sample....................................................................................................................................................14
Technique...............................................................................................................................................15
TROUBLESHOOTING HINTS.....................................................................................................15
ORDERING INFORMATION.......................................................................................................17
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Instruction Manual Potassium Electrode
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.
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Instruction Manual Potassium Electrode
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
o
and 25oC. See the TROUBLESHOOTING section if the potential change is not within this
20 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.
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Instruction Manual Potassium Electrode
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.
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Instruction Manual Potassium Electrode
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.
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