EUTECH INSTRUMENTS CALCIUM ION ELECTRODE Instruction Manual
Instruction Manual Calcium Electrode
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EUTECH INSTRUMENTS PTE LTD.
INSTRUCTION MANUAL
CALCIUM ION ELECTRODE
Calcium Electrode Instruction Manual
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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) ..................................................................................................5
MEASUREMENT..............................................................................................................................5
Measuring Hints.......................................................................................................................................5
Sample Requirements...............................................................................................................................6
Units of Measurement..............................................................................................................................6
MEASUREMENT PROCEDURE ...................................................................................................6
Direct Measurement.................................................................................................................................6
Direct Measurement of Calcium (using a pH/mV meter)........................................................................6
Direct Measurement of Calcium (using an ion meter).............................................................................8
Low Level Calcium Determination (using a pH/mV meter)....................................................................8
Low Level Calcium Determination (using an ion meter).........................................................................9
Titration....................................................................................................................................................9
Titration of Calcium...............................................................................................................................10
ELECTRODE CHARACTERISTICS........................................................................................... 11
Reproducibility.......................................................................................................................................11
Interferences...........................................................................................................................................11
Complexation.........................................................................................................................................12
Temperature Influences..........................................................................................................................12
Electrode Response................................................................................................................................13
Limits of Detection.................................................................................................................................13
Electrode Life.........................................................................................................................................13
Electrode Storage ...................................................................................................................................14
ELECTRODE THEORY................................................................................................................14
Electrode Operation ...............................................................................................................................14
TROUBLESHOOTING GUIDE....................................................................................................15
Meter......................................................................................................................................................15
Glass-ware..............................................................................................................................................15
Electrodes............................................................................................................................................... 15
Standards and Reagents..........................................................................................................................16
Sample....................................................................................................................................................16
Technique...............................................................................................................................................16
TROUBLESHOOTING HINTS.....................................................................................................17
SPECIFICATIONS..........................................................................................................................19
ORDERING INFORMATION.......................................................................................................19
Instruction Manual Calcium Electrode
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EUTECH INSTRUMENTS PTE LTD.
CALCIUM ELECTRODE
INSTRUCTION MANUAL
GENERAL INSTRUCTIONS
Introduction
Eutech Instruments Calcium Ion Electrode is used to measure calcium 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 Calcium Epoxy-body Combination Electrode, Code. no. EC-CAL-03.
Required Solutions
1. Deionized or distilled water for solution and standard preparation.
2. Eutech Calcium Standard, 0.1M CaCl2, Code. no. EC-SCS-CA1-BT. To prepare this
solution from your own laboratory stock, half fill a one liter volumetric flask with distilled
water and add 14.7 grams of reagent-grade calcium chloride (CaCl2.2H2O). 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 Calcium Standard, 1,000 ppm Ca
+2
, Code. no. EC-SCS-CA2-BT. To prepare this
solution from you own laboratory stock, half fill a one liter volumetric flask with distilled
water and add 3.67 grams of reagent-grade calcium chloride (CaCl
2
.2H2O). 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 Calcium Standard, 100 ppm Ca+2 as CaCO3, Code. no. EC-SCS-CA3-BT. To
prepare this solution from your own laboratory stock, half fill a one liter volumetric flask
with distilled water and add 0.15 grams of reagent-grade calcium chloride (CaCl2.2H2O).
Swirl the flask gently to dissolve the solid. Fill to the mark with distilled water, cap, and
upend several times to mix the solution.
5. Eutech Ionic Strength Adjuster (ISA), 4 M KCl, Code. no. EC-ISA-CA1-BT. To prepare
this solution from your own laboratory stock, half fill a 1,000 ml volumetric flask with
distilled water and add 298 grams of reagent-grade potassium chloride (KCl). Swirl the
Calcium Electrode Instruction Manual
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flask gently to dissolve the solid. Fill to the mark with distilled water, cap, and upend
several times to mix the solution.
6. EDTA titrant, 1M stock solution, for the titration of calcium. To prepare this titrant, add
37.2 grams of reagent grade Na2EDTA.2H2O, ethylenediaminetetraacetic acid dihydrate,
disodium salt, to a 100 ml volumetric flask, add about 75 ml of distilled water, and swirl
the flask gently to dissolve the solid. Fill to the mark with distilled water, cap, and upend
several times to mix the solution.
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
with 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 calcium
membrane. Prior to first usage, or after long-term storage, immerse the calcium membrane in
calcium 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. 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, 1,000 ppm, or 100 ppm (as calcium carbonate) standard
and 2 ml of ISA to the beaker. When the reading is stable, record the mV reading.
3. Using a pipet, add 10 ml of the same calcium 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 27±2 mV, 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.
Instruction Manual Calcium Electrode
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Electrode Slope Check (with ion meter)
(Check electrodes each day)
1. Prepare standard calcium solutions whose concentrations vary by tenfold. Use either the
0.1M Ca+2, 1,000 ppm Ca+2, or the 100 ppm Ca+2 (as calcium carbonate) 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.
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
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 1
o
C in temperature will result in a 4% measurement error.
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 a styrofoam sheet, between the stirrer and beaker.
Always rinse the electrode tips with distilled water and blot dry. Use a clean, dry tissue to prevent
cross-contamination.
For samples with high ionic strength, prepare standards with compositions similar to that of the
sample. Always check to see that the membrane is free from air bubbles after immersion into
standard or sample.
A slow responding electrode may be caused by interferences to the electrode. To restore proper
performance, soak the electrode in distilled water for about 5 minutes to clean the membrane, rinse,
and soak in diluted standard solution for about 5 minutes.
Calcium Electrode Instruction Manual
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Dilute concentrated samples (over 0.1M) before measurement. Recalibrate every few hours for
routine measurement.
Sample Requirements
All samples and standards must be aqueous and not contain organics which can dissolve in the
membrane or extract out the liquid ion exchanger.
The temperature of the standard solutions and of the sample solutions should be the same and below
40oC. About a 2% error will be introduced for a 1oC difference in temperature.
The pH range for the calcium ion electrode is 3-10. Neutralize samples outside this range with
NaOH or HCl to bring them in range.
Interferences should be absent. If they are present, use the procedures found in the Interferences
section to remove them.
Units of Measurement
Calcium concentrations are measured in units of ppm as calcium, ppm as CaCO3, moles per liter, or
any other convenient concentration unit. Table 1 indicates some of the concentration units.
TABLE 1: Concentration Unit Conversion Factors
ppm Ca+2 ppm CaCO3 moles/liter
4.01 10.0 1.0X10-4
10.00 24.9 2.5X10-4
40.10 100.1 1.0X10-3
400.80 1,000.9 1.0X10
-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 temperature of both sample solution and of
standard solutions should be the same.
Direct Measurement of Calcium (using a pH/mV meter)
1. By serial dilution prepare three standard solutions from the 0.1M, 1,000 ppm, or 100 ppm
standard. The resultant concentrations should be 10
-2
, 10-3, and 10-4M or 100, 10 and 1
ppm standards. Add 2 ml of ISA to each 100 ml of standard.
2. Place the most dilute solution (1.0X10-4M or 1 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. After the reading has stabilized, record the mV
reading.
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