EUTECH INSTRUMENTS CYANIDE ION ELECTRODE Instruction Manual

Instruction Manual Cyanide Electrode

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EUTECH INSTRUMENTS PTE LTD.

INSTRUCTION MANUAL

CYANIDE ION ELECTRODE

Cyanide 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 an ion meter)..............................................................................................4

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

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

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

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

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

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

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

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

Low-Level Cyanide Measurements (using a pH/mV meter)....................................................................8

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

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

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

Complexation.........................................................................................................................................10

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

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

Limits of Detection.................................................................................................................................12

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

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

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

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

Electrode Operation ...............................................................................................................................13

TROUBLESHOOTING GUIDE....................................................................................................14

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

Plastic-ware............................................................................................................................................14

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

Standards and Reagents..........................................................................................................................15

Sample....................................................................................................................................................15

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

TROUBLESHOOTING HINTS.....................................................................................................16

SPECIFICATIONS..........................................................................................................................18

ORDERING INFORMATION.......................................................................................................18

Instruction Manual Cyanide Electrode

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EUTECH INSTRUMENTS PTE LTD.

CYANIDE ION ELECTRODE

INSTRUCTION MANUAL

GENERAL INSTRUCTIONS

Introduction

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

*IMPORTANT NOTICE*

Acidic cyanide solutions produce hydrogen cyanide (HCN) gas, highly toxic whether breathed or
absorbed through the skin. Use of the proper and recommended ionic strength adjuster (ISA) will
keep the solution pH above 10. If measurements in acidic solution are necessary (decomplexing
procedure as given in the section Complexation), THIS PROCEDURE MUST BE DONE IN A
FUME HOOD.

Use a pipet bulb when pipeting cyanide solutions, as these solutions are highly toxic.

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 Cyanide Ion Combination Epoxy-body Electrode, Code no. EC-CN-03.

5. Lab-ware made of plastic, not glass.

6. 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 Cyanide Ionic Strength Adjuster (ISA), 10M NaOH, Code no. EC-ISA-CN1-BT.
To prepare the ISA from your own laboratory stock, fill a 1,000 ml beaker with about 900
ml of distilled water. While gently stirring the solution under a hood, slowly add 400
grams of reagent-grade sodium hydroxide. Transfer the solution quantitatively to a one
liter volumetric flask after the solid NaOH has dissolved and the beaker has cooled. Dilute
to the mark with distilled water, cap, and upend several times to thoroughly mix the
solution. Store in a plastic bottle.

Cyanide Electrode Instruction Manual

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3. Cyanide Standard, 1X10-2M. To prepare this solution from your own laboratory stock, add
10 ml of ISA and about 500 ml of distilled water to a one liter volumetric flask. Add 0.49
grams of dry, reagent-grade sodium cyanide, NaCN, to the solution and swirl the flask
gently to dissolve the solid. Dilute to the mark with distilled water, cap, and upend the
flask several times to thoroughly mix the contents. Store all standards in plastic bottles and
prepare weekly.

4. Cyanide Standard, 1,000 ppm. To prepare this solution from your own laboratory stock,
add 10 ml of ISA and about 500 ml of distilled water to a one liter volumetric flask. Add

1.88 grams of dry, reagent-grade NaCN and swirl the flask gently to dissolve the solid.
Dilute to the mark with distilled water, cap, and upend the flask several times to
thoroughly mix the contents. Store all standards in plastic bottles and prepare weekly.

GENERAL PREPARATION

Electrode Preparation

Remove the rubber caps covering the electrode tips and the rubber insert covering the filling hole of
the cyanide combination ion 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 pH/mV meter)

(Check electrodes each day)

1. To a 150 ml beaker, add 100 ml of distilled water and 1 ml of 10M NaOH 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 1.0X10-2M or 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. After the reading
has stabilized, record the mV reading.

4. The electrode is operating correctly if the mV potential has changed by 57±2 mV,
assuming the solution 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 an ion meter)

(Check electrodes each day)

Instruction Manual Cyanide Electrode

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

1.0X10-2M or the 1,000 ppm cyanide standard. Use the serial dilution method for this
preparation.

2. To a 150 ml beaker, add 100 ml of the lower value standard and 1 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 a 150 ml beaker, add 100 ml of the higher value standard and 1 ml of ISA. Place the
beaker on a 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 93-100%. See 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. 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 the beaker.

Always rinse the electrodes with distilled water and blot dry between measurements. Use a clean,
dry tissue to prevent cross contamination.

When making low level measurements (below 1X10-5M), use only plastic lab-ware and cover the
beaker with Parafilm to avoid loss of cyanide. When making high cyanide measurements (above
1X10-3M), samples should be diluted before measurements.

Use fresh standards for calibration. Use 1 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

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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 epoxy body electrode. Please check with Eutech Instruments Pte Ltd. before using the
electrode in other solvents.

The temperature of the sample solutions and of the standard solutions should be the same and below
80oC.

Interferences should be absent. If they are present, use the procedure found in the Interferences
and Electrode Response sections to remove them.
Measurements above 1X10-3M should be done infrequently, as cyanide ion slowly erodes the
membrane. (See section Electrode Life.) It may be necessary to polish the membrane occasionally
with polishing paper or jeweller's rouge as the electrode is used. Samples should be diluted below
1X10-3M if possible.

Proper pH is ensured if ISA is used. The pH should be above 10 so that cyanide is present as CN-1
rather than as HCN in all standards and samples.

Units of Measurement

Cyanide ions can be measured in units of ppm, moles per liter, or any other convenient
concentration unit. Table 1 indicates some concentration units and conversion factors.

TABLE 1: Concentration Unit Conversion Factors

ppm CN

-

moles/liter

26.00 1.0X10-3

10.00 3.8X10

-4

2.60 1.0X10-4

1.00 3.8X10

-5

0.26 1.0X10

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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 standard
solutions should be the same.

Direct Measurement of Cyanide (using a pH/mV meter)

1. By serial dilution, prepare 10-3, 10-4, and 10-5M or 10, 1 and 0.1 ppm standards for the
cyanide ion from the 0.01M or 1,000 ppm standards. 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 standard solution in a 150 ml plastic beaker. Place the
beaker on the magnetic stirrer and begin stirring at a constant rate. Add 1 ml of 10M