EUTECH INSTRUMENTS CADMIUM EPOXY, CADMIUM ION ELECTRODE Instruction Manual

Instruction Manual Cadmium Electrode

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EUTECH INSTRUMENTS PTE LTD.

INSTRUCTION MANUAL

CADMIUM ION ELECTRODE

Cadmium 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 a 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 Cadmium (using a pH/mV meter).........................................................................6

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

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

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

Titration ......................................................................................................................................................9

Titration of Cadmium ...............................................................................................................................10

ELECTRODE CHARACTERISTICS........................................................................................... 11

Reproducibility.........................................................................................................................................11

Interferences .............................................................................................................................................11

Precipitation and Complexation................................................................................................................11

Temperature Influences ............................................................................................................................12

Electrode Response...................................................................................................................................12

Limits of Detection...................................................................................................................................13

pH Effects.................................................................................................................................................13

Electrode Life ...........................................................................................................................................14

Electrode Storage......................................................................................................................................14

ELECTRODE THEORY................................................................................................................14

Electrode Operation..................................................................................................................................14

TROUBLESHOOTING GUIDE....................................................................................................15

Meter.........................................................................................................................................................16

Glass-ware ................................................................................................................................................16

Electrodes .................................................................................................................................................16

Standards and Reagents............................................................................................................................16

Sample ......................................................................................................................................................17

Technique .................................................................................................................................................17

TROUBLESHOOTING HINTS.....................................................................................................18

SPECIFICATIONS..........................................................................................................................20

ORDERING INFORMATION.......................................................................................................20

Instruction Manual Cadmium Electrode

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EUTECH INSTRUMENTS PTE LTD

CADMIUM ION ELECTRODE

INSTRUCTION MANUAL

GENERAL INSTRUCTIONS

Introduction

Eutech Instruments Cadmium Ion Electrode is used to measure cadmium 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 Cadmium Ion Combination Epoxy-body Electrode, Code. no. EC-CD-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-CD1-BT. To prepare
this solution from your own laboratory stock, half fill a one liter volumetric flask with
distilled water and add 425 grams reagent-grade sodium nitrate, NaNO

3

. 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. Cadmium Nitrate Standard Solution, 0.1M. To prepare this solution from your own
laboratory stock, half fill a one liter volumetric flask with distilled water and add 30.85
grams of reagent-grade Cd(NO3)

2

.

4H2O. 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. Cadmium Nitrate Standard Solution, 1,000 ppm. To prepare this solution from your own
laboratory stock, half fill a one liter volumetric flask with distilled water and add 2.74
grams of reagent-grade Cd(NO3)

2

.

4H2O. 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. EDTA Titrant 1M stock solution for the titration of cadmium. To prepare this solution
from your own laboratory stock, add 37.2 grams of reagent-grade Na2EDTA to a 100 ml
volumetric flask about three-fourths full of distilled water. Swirl the flask gently to

Cadmium Electrode Instruction Manual

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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 cadmium combination electrode or 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 the
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 1,000 ppm cadmium standard to the beaker.
When the reading has stabilized, record the mV reading.

3. Using a pipet, add 10 ml of the 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 27±2 mV, assuming the temperature is between 20o and
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 ion meter)

(Check electrodes each day)

1. Prepare standard cadmium solutions whose concentrations vary be tenfold. Use either the

0.1M or 1,000 ppm standard and 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.

Instruction Manual Cadmium Electrode

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5. To a 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%. If the slope is not within this range,
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 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 whose composition is similar to the sample.

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. Dilute concentrated samples (>0.1M) before measurement.

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. About a 4% error in the slope will occur for each 1oC difference in temperature. Interferences
should be absent. If they are present, use the procedure found in the

Interference and Electrode

Response

sections to remove them.

Adjust sample pH with 1M HNO3 to below pH 7 to avoid precipitation of cadmium hydroxide,
Cd(OH)2.

Cadmium Electrode Instruction Manual

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Units of Measurement

Cadmium ion concentrations are measured in units of parts per million, moles per liter, equivalents
per liter, or any other convenient concentration unit. Table 1 indicates some of these concentration
units.

TABLE 1

: Concentration Unit Conversion Factors

ppm Cd+2 moles/liter

1124.0 1.0X10

-2

112.4 1.0X10

-3

11.2 1.0X10-4

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

Direct Measurement of Cadmium (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 1,000, 100 and 10
ppm 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 100 ml of 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. After the reading has stabilized, record
the mV reading.

3. Place 100 ml of the mid-range solution (1.0X10

-3

M or 100 ppm) in a 150 ml beaker on the
magnetic stirrer and begin stirring at a constant rate. After rinsing the electrodes with
distilled water, blot dry and immerse the electrode tips in the solution. After the reading
has stabilized, record the mV reading.

4. Place 100 ml of the most concentrated solution (1.0X10

-2

M or 1,000 ppm) in a 150 ml
beaker on the magnetic stirrer and begin stirring at a constant rate. After rinsing the
electrodes with distilled water, blot dry and immerse the electrode tips in the solution.
After the reading has stabilized, record the mV reading.

5. Using the semi-logarithmic graph paper, plot the mV reading (linear axis) against
concentration (log axis). Extrapolate the curve down to about 1.0X10-5 or 1 ppm. A typical
calibration curve can be found in Figure 1.