Instruction Manual Iodide Electrode
EUTECH INSTRUMENTS PTE LTD.
INSTRUCTION MANUAL
IODIDE ION ELECTRODE
1
Instruction Manual Iodide Electrode
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 an ion meter)..............................................................................................4
MEASUREMENT..............................................................................................................................5
Measuring Hints.......................................................................................................................................5
Sample Requirements...............................................................................................................................5
Units of Measurement..............................................................................................................................5
MEASUREMENT PROCEDURE ...................................................................................................6
Direct Measurement.................................................................................................................................6
Direct Measurement of iodide (using a pH/mV meter)............................................................................6
Direct Measurement of iodide (using an ion meter).................................................................................7
Low Level Iodide Determinations (using a pH/mV meter)......................................................................8
ELECTRODE CHARACTERISTICS.............................................................................................8
Reproducibility.........................................................................................................................................8
Interferences.............................................................................................................................................8
Complexation...........................................................................................................................................9
Temperature Influences..........................................................................................................................10
Electrode Response................................................................................................................................10
Limits of Detection.................................................................................................................................11
pH Effects...............................................................................................................................................11
Electrode Life.........................................................................................................................................11
Electrode Storage ...................................................................................................................................12
ELECTRODE THEORY................................................................................................................12
Electrode Operation ...............................................................................................................................12
TROUBLESHOOTING GUIDE....................................................................................................13
Meter......................................................................................................................................................13
Glassware...............................................................................................................................................13
Electrodes...............................................................................................................................................13
Standards and Reagents..........................................................................................................................14
Sample....................................................................................................................................................14
Technique...............................................................................................................................................14
TROUBLESHOOTING HINTS.....................................................................................................15
SPECIFICATIONS..........................................................................................................................17
ORDERING INFORMATION.......................................................................................................17
2
Instruction Manual Iodide Electrode
EUTECH INSTRUMENTS PTE LTD.
IODIDE ION ELECTRODE
INSTRUCTION MANUAL
GENERAL INSTRUCTIONS
Introduction
Eutech Instruments Iodide Ion Electrode is used to quickly, simply, accurately, and economically
measure free iodide ion in aqueous solutions.
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 Iodide Ion Combination Epoxy-body Electrode, Code no. EC-IO-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
this solution from your own laboratory stock, half-fill a 1,000 ml volumetric flask with
distilled water and add 425 grams of reagent-grade sodium nitrate. Swirl the flask gently to
dissolve the solid. Fill to the mark with distilled water, cap, and upend the flask several
times to mix the solution.
3. Eutech Iodide Standard, 0.1M NaI, Code no. EC-SCS-IO1-BT. To prepare this solution
from your own laboratory stock, half-fill a one liter volumetric flask with distilled water and
add 10.3 grams of reagent-grade sodium iodide, NaBr. 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 Iodide Standard, 1,000 ppm I
-1
, Code No. EC-SCS-IO2-BT. To prepare this solution
from your own laboratory stock, half-fill a one liter volumetric flask with distilled water and
add 1.29 grams of reagent-grade NaBr. Swirl the flask gently to dissolve the solid. Fill the
flask to the mark with distilled water, cap, and upend several times to mix the solution.
Code no. EC-ISA-IO1-BT. To prepare
3,
3
Instruction Manual Iodide Electrode
GENERAL PREPARATION
Electrode Preparation
Remove the rubber caps covering the electrode tips and the rubber insert covering the filling hole of
the combination electrode or of 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 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 either the 0.1M or the 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. 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 a difference of 57±3 mV, assuming the solution
temperature is 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)
1. Prepare standard iodide solutions whose concentrations vary by tenfold. Use either the
0.1M or the 1,000 ppm iodide standard. 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 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 another 150 ml beaker, add 100 ml of the higher value standard and 2 ml of ISA. Place
the beaker on a magnetic stirrer and begin stirring at a constant rate. Lower the electrode
tips into the solution.
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Instruction Manual Iodide Electrode
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 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 styrofoam sheet, between the stirrer and beaker.
Always rinse the electrodes with distilled water and blot dry between measurements. Use a clean,
dry tissue to prevent cross contamination.
For samples with high ionic strength, prepare standards whose composition is similar to the sample.
Dilute concentrated samples (>0.1M) before measurement.
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.
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.
The pH range for the iodide ion electrode is 0-14. Neutralize samples outside this range with acid or
base to bring them in range.
Interferences should be absent. If they are present, use the procedure found in the Interference and
Electrode Response sections to remove them.
Units of Measurement
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Instruction Manual Iodide Electrode
Iodide ions can be measured in units of moles/liter, parts/million, or any other convenient
concentration unit. Table 1 indicates some of the concentration units.
TABLE 1: Concentration Unit Conversion Factors
moles/liter ppm I-1
1.0X10-4 12.7
1.0X10-3 127.0
1.0X10-2 1,270.0
1.0X10-1 12,770.0
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 iodide solutions. The temperature of both sample
solutions and of standard solutions should be the same.
Direct Measurement of iodide (using a pH/mV meter)
1. By serial dilution prepare three standard solutions from the 0.1M or 1,000 ppm standard.
The resultant concentrations should be 10-2, 10-3, and 10-4M or 1,000, 100 and 10 ppm
iodide 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 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. When the reading has stabilized, record the mV
reading.
3. Place the mid-range solution (1.0X10-3M or 100 ppm) in a 150 ml beaker on the magnetic
stirrer and begin stirring at a constant rate. After rinsing the electrodes in distilled water,
blot dry and immerse the electrode tips in the solution. When the reading has stabilized,
record the mV reading.
4. Place the most concentrated solution (1.0X10-2M or 1,000 ppm) in a 150 ml beaker on the
magnetic stirrer and begin stirring at a constant rate. After rinsing the electrodes in
distilled water, blot dry and immerse the electrode tips in the solution. When the reading
has stabilized, record the mV reading.
5. Using semi-logarithmic graph paper, plot the mV reading (linear axis) against the
-5
concentration (log axis). Extrapolate the curve down to about 1.0X 10
M or l ppm. A
typical calibration curve for iodide can be found in Figure 1.
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Instruction Manual Iodide Electrode
A calibration curve is constructed on semi-logarithmic paper when using a
pH/mV meter in the millivolt mode. The measured electrode potential in mV
(linear axis) is plotted against the standard concentration (log axis). In the linear
region of the curve, only three standards are necessary to determine a calibration
curve. In the non-linear region, additional points must be measured. The direct
measurement procedures given are for the linear portion of the curve. The nonlinear portion of the curve requires the use of low level procedures.
6. To a clean, dry 150 ml beaker, add 100 ml of the sample and 2 ml of ISA. Place the beaker
on the magnetic stirrer and begin stirring at a constant rate. Rinse the electrode tips with
distilled water, blot dry and lower into the solution. When the reading has stabilized,
record the mV reading. Using the calibration curve, determine the concentration directly
from the calibration curve.
7. The calibration should be checked every two hours. Assuming no change in ambient
temperature, place the electrode tips in the mid-range standard. After the reading has
stabilized, compare it to the original reading recorded in Step 3 above. A reading differing
by more than 0.5 mV or a change in the ambient temperature will necessitate the repetition
of Steps 2-5 above. A new calibration curve should be prepared daily.
Direct Measurement of iodide (using an ion meter)
1. By serial dilution of the 0.1M or 1,000 ppm iodide standard, prepare two standards whose
concentration is near the expected sample concentration. Measure 100 ml of each standard
into individual 150 ml beakers and add 2 ml of ISA to each.
2. Place the more dilute solution on the magnetic stirrer and begin stirring at a constant rate.
Assure that the meter is in the concentration mode. Lower the electrode tips into the
solution.
3. Adjust the meter to the concentration of the standard and fix the value in the memory
according to the meter manufacturer's instructions after stabilization of the reading.
4. Rinse the electrodes with distilled water and blot dry.
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Instruction Manual Iodide Electrode
5. Place the more concentrated solution 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
according to the meter manufacturer's instructions after stabilization of the reading.
7. For low level iodide measurements, place the rinsed, dried electrodes into a solution
containing 100 ml of distilled water and 2 ml of ISA. After stabilization, fix the blank
value into the meter according to the meter manufacturer's instructions.
8. Place 100 ml of the sample and 2 ml of ISA in a 150 ml beaker, place it on the magnetic
stirrer, and begin stirring.
9. Immerse the electrode tips in the solution and wait for the reading to stabilize. Read the
concentration directly from the meter display.
10. The calibration should be checked every two hours. Assuming no change in ambient
temperature, place the electrode tips in the first iodide standard. After the reading has
stabilized, compare it to the original reading in Step 3 above. A reading differing by more
than 0.5 mV or a change in the ambient temperature will necessitate the repetition of steps
2-6 above. The meter should be re-calibrated daily.
Low Level Iodide Determinations (using a pH/mV meter)
For the iodide electrodes, no special low level determination is necessary. Linear response is
possible down to 2.0X10-8M.
ELECTRODE CHARACTERISTICS
Reproducibility
Electrode measurements reproducible to ±2% can be obtained if the electrode is calibrated every
hour. Factors such as temperature fluctuations, drift, and noise limit reproducibility. Reproducibility
is independent of concentration within the electrode's operating range.
Interferences
A layer of silver may form on the electrode surface in the presence of strong reducing agents.
Insoluble salts of silver may be deposited on the membrane, causing electrode malfunction if high
levels of ions forming these salts are present in the sample. Proper performance can be restored by
polishing. See the section Electrode Response for proper polishing procedure.
Solutions containing oxidizing agents such as MnO
-1
, Fe+3, and Cu+2, may be measured without
4
problem. All samples must be free of mercury.
The maximum allowable ratio of interfering ion to iodide ion is given in Table 2. This ratio is
expressed as the ratio of the interfering ion molarity to the iodide molarity. Readings will be in error
if this ratio is exceeded. Neither accuracy of the measurement nor surface of the electrode
membrane will be affected if the ratio is less than that listed in the table.
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Instruction Manual Iodide Electrode
TABLE 2: Maximum Allowable Ratio of Interfering Ion to Iodide Ion
Interference Maximum Ratio
Cl-1 (1) 1.0X106
S
Br
CN
S
-2
(2) 1.0X105
2O3
-1
(1) 5.0X103
-1
(3) 4.0X10-1
-2
(3) 1.0X10-6
(1) Gran's plot titration can be used to measure mixed halides in solution.
(2) These substances represent complexing species whose maximum level can be exceeded
without electrode damage. Values shown represents a 1% error.
(3) Add Ni+2 to remove sulfide or cyanide interferences.
As an example of Table 2's use when using the iodide ion electrode:
What is the maximum level of iodide tolerable in a sample whose iodide concentration is 10-4M?
Using Table 2, the maximum ratio is:
[Br-1]
⎯⎯⎯⎯ = 5X10
3
[I-1]
or [Br-1] = 5X103 [I -1]
= 5X103 (1X10-4)
[Br-1] = 5X10-1M maximum bromide concentration for no interference
Complexation
Total concentration (C
) consists of free ions (Cf) and complexed or bound ions (Cc) in solutions:
t
C
= Cf + Cc
t
Since the electrode only responds to free ions, any complexing agent in the solution reduces the
measured concentration of ions.
Iodide ions complex with some metal ions. Table 3 lists the levels of complexing metals causing a
20% error.
TABLE 3: Levels of Complexing Agents Causing a 20% Error at 1.0X10-4M Iodide
Ion
Bi
Cd
Pb
Concentration
+3
2.0X10-5M ( 4 ppm)
+2
5.0X10-4M ( 50 ppm)
+2
5.0X10-3M (1,000 ppm)
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Instruction Manual Iodide Electrode
Temperature Influences
Samples and standards should be at the same temperature since electrode potentials are influenced
by changes in temperature. A 1oC difference in temperature results in a 2% error at the 1.0X10-3M
concentration level. Because of solubility equilibrium on which the electrode depends, the absolute
potential of the reference electrode changes slowly with the temperature. The slope of the electrode,
as indicated by the factor "S" in the Nernst equation, also varies with temperature. Table 4 gives
values of the "S" factor in the Nernst equation for the iodide ion.
TABLE 4: Temperature vs. Values for the Electrode Slope
Temp (oC) "S"
0 54.2
10 56.2
20 58.2
25 59.2
30 60.1
40 62.1
50 64.1
If changes in temperature occur, the electrodes should be recalibrated.
The temperature range of the Eutech Iodide Ion Electrodes is 0o-80oC, provided that temperature
equilibrium has occurred. If temperature varies substantially from room temperature, equilibrium
times up to one hour are recommended.
Electrode Response
Plotting the electrode mV potential against the iodide concentration on semi-logarithmic paper
results in a straight line with a slope of about 57 mV per decade. (Refer to Figure 1.)
The time needed to reach 99% of the stable electrode potential reading, the electrode response time,
varies from several seconds in highly concentrated solutions to several minutes near the detection
limit. (Refer to Figure 2.)
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Instruction Manual Iodide Electrode
A drifting potential reading or a decrease in electrode slope may mean that the electrode membrane
needs polishing.
To polish the membrane:
1. If using polishing paper, cut off a 1-2" piece and place it face up on the lab bench.
2. Put a few drops of distilled or deionized water in the center of the paper.
3. Holding the paper (cotton) steady with one hand, bring the membrane of the
electrode down perpendicular to the paper and, with a slight swirling motion, gently
polish the tip of the electrode against the surface of the polishing paper (cotton) for a
few seconds.
4. Rinse the electrode surface with distilled or deionized water and soak the electrode
tip in standard solution for about five minutes before use.
5. If using jeweller's rouge, place a cotton ball on the table top and flatten it using the
bottom of a beaker.
6. Put 1-2 drops of distilled or deionized water in the center of the cotton pad.
7. Add a small amount of jeweller's rouge to the damp cotton.
8. Continue with Steps 3 and 4 above.
Limits of Detection
The upper limit of detection in pure sodium iodide solutions is 1M. In the presence of other ions,
the upper limit of detection is above 1.0x10-1M iodide, but the possibility of a liquid junction
potential developing at the reference electrode and the "salt extraction effect" are two limiting
factors. Some salts may infuse into the electrode membrane at high salt concentrations, causing
deviation from the theoretical response. Either dilute samples between 1M and 1.0x10-1M or
calibrate the electrode at 4 or 5 intermediate points.
The lower limit of detection is influenced by the slight water solubility of the electrode pellet.
Refer to Figure 1 for a comparison of the theoretical response to the actual response at low levels of
iodide.
pH Effects
The electrode can be used over the pH range 0-14.
Electrode Life
An iodide ion electrode will last for six months in normal laboratory use. On-line measurements
might shorten operational lifetime to several months. In time, the response time will increase and
the calibration slope will decrease to the point calibration is difficult and electrode replacement is
required.
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Instruction Manual Iodide Electrode
Electrode Storage
The iodide ion electrode may be stored for short periods of time in 1.0x10
-2
M iodide solution. For
longer storage (longer than two weeks), rinse and dry the sensing pellet and cover the membrane tip
with any protective cap shipped with the electrode. The reference portion of the combination
electrode (or the outer chamber of the reference electrode) should be drained of filling solution, if
refillable, and the rubber insert placed over the filling hole.
ELECTRODE THEORY
Electrode Operation
An iodide ion electrode consists of a sensing membrane bonded into a glass or an epoxy body. The
membrane is composed of silver iodide/silver sulfide. When an electrode potential develops across
the membrane, the electrode is in contact with solution containing iodide ions and is capable of
measuring free iodide ions. This electrode potential is measured against a constant reference
potential, using a standard pH/mV meter or an ion meter. The level of the iodide ions,
corresponding to the measured potential, is described by the Nernst equation:
E = E
- S log X
o
where:
E
E
S
X
= measured electrode potential
= measured potential (a constant)
o
= electrode slope (∼57 mV/decade)
= level of iodide ions in solution
The activity, X, represents the effective concentration of the ions in solution. The activity is related
to the free ion concentration, Cf, by the activity coefficient, γ, by:
X = γ Cf
Activity coefficients vary, depending on total ionic strength, I, defined as:
I = ½ Σ CxZ
2
x
where:
C
Z
= concentration of ion x
x
= charge of ion x
x
Σ = sum if all the types of ions in the solution
In the case of high and constant ionic strength relative to the sensed ion concentration the activity
coefficient, γ , is constant and the activity, X, is directly proportional to the concentration.
To adjust the background ionic strength to a high and constant value, ionic strength adjuster is
added to samples and standards. The recommended ISA for iodide ions is NaNO3. Solutions other
than this may be used as ionic strength adjusters as long as ions that they contain do not interfere
with the electrode's response to the iodide ions. Samples with high ionic strength (greater than
0.1M) do not need ISA added and standards for these solutions should be prepared with a
composition similar to the samples.
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Instruction Manual Iodide Electrode
The reference electrode must also be considered. When two solutions of different composition are
brought into contact with one another, liquid junction potentials arise. Millivolt potentials occur
from the inter-diffusion of ions in the two solutions. Electrode charge will be carried unequally
across the solution boundary resulting in a potential difference between the two solutions, since
ions diffuse at different rates. When making measurements, it is important to remember that this
potential be the same when the reference is in the standardizing solution as well as in the sample
solution or the change in liquid junction potential will appear as an error in the measured electrode
potential.
The composition of the liquid junction filling solution in the reference electrode is most important.
The speed with which the positive and negative ions in the filling solution diffuse into the sample
should be equitransferent. No junction potential can result if the rate at which positive and negative
charge carried into the sample is equal.
Strongly acidic (pH = 0-2) and strongly basic (pH = 12-14) solutions are particularly troublesome to
measure. The high mobility of hydrogen and hydroxide ions in samples make it impossible to mask
their effect on the junction potential with any concentration of an equitransferent salt. One must
either calibrate the electrodes in the same pH range as the sample or use a known increment method
for ion measurement.
TROUBLESHOOTING GUIDE
The goal of troubleshooting is the isolation of a problem through checking each of the system
components in turn: the meter, the glass-ware, the electrodes, the standards and reagents, the
sample, and the technique.
Meter
The meter may be checked by following the check-out procedure in the instrument instruction
manual.
Glassware
Clean glassware is essential for good measurement. Be sure to wash the glassware well with a mild
detergent and rinse very well with distilled or deionized water. Clean glassware will drain without
leaving water droplets behind.
Electrodes
The electrode may be checked by using the procedure found in the sections entitled Electrode
Slope Check.
1. Be sure to use distilled or deionized water when following the procedures given in
Electrode Slope Check.
2. If the electrode fails to respond as expected, see sections Measuring Hints and Electrode
Response
. Repeat the slope check.
3. If the electrode still fails to respond as expected, substitute another iodide ion electrode
that is known to be in good working order for the questionable electrode. If the problem
13
Instruction Manual Iodide Electrode
persists and you are using an electrode pair, try the same routine with a working reference
electrode.
4. If the problem persists, the standards and/or reagents may be of poor quality, interferences
in the sample may be present or the technique may be faulty. (See Standards and
Reagents, Sample,
and Technique sections below.)
5. If another electrode is not available for test purposes, or if the electrode in use is suspect,
review the instruction manual and be sure to:
- Clean and rinse the electrodes thoroughly.
- Prepare the electrodes properly.
- Use the proper filling solution.
- Adjust the pH and the ionic strength of the solution by the use of the proper ISA.
- Measure correctly and accurately.
- Review TROUBLESHOOTING HINTS.
Standards and Reagents
Whenever problems arise with the measuring procedure that has been used successfully in the past,
be sure to check the standard and reagent solutions. If in doubt about the credibility of any of the
solutions, prepare them again. Errors may result from contamination of the ISA, incorrect dilution
of standards, poor quality distilled/deionized water, or a simple mathematical miscalculation.
Sample
Look for possible interferences, complexing agents, or substances which could affect the response
or physically damage the sensing electrode (or reference electrode) if the electrodes work perfectly
in the standard, but not in the sample.
Try to determine the composition of the samples prior to testing to eliminate a problem before it
starts. (See Measuring Hints, Sample Requirements, and Interferences.)
Technique
Be sure that the electrode's limit of detection has not been exceeded. Be sure that the analysis
method is clearly understood and is compatible with the sample.
Refer to the instruction manual again. Reread sections on GENERAL PREPARATION and
ELECTRODE CHARACTERISTICS.
If trouble still persists, call Eutech Instruments Pte Ltd. at (65) 6778-6876 and ask for the Customer
Services Department.
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Instruction Manual Iodide Electrode
TROUBLESHOOTING HINTS
Symptom Possible Causes Next Step
Out of Range defective meter check meter with shorting strap
Reading (see meter instruction manual)
defective electrode check electrode operation
electrodes not unplug electrodes and reset
plugged in properly
reference electrode be sure reference electrode
not filled is filled
air bubble on membrane remove bubble by redipping
electrode
electrodes not put electrodes in solution
in solution
Noisy or Unstable defective meter check meter with shorting strap
Readings (readings
continuously or air bubble on membrane remove bubble by re-dipping electrode
rapidly changing)
electrode exposed soak electrode in iodide standard
to interferences
defective electrode replace electrode
ISA not used use recommended ISA
meter or stirrer ground meter or stirrer
not grounded
Drift (reading samples and standards allow solutions to come to room
slowly changing at different temperatures temperature before measurement
in one direction)
electrode exposed check section entitled
to complexing agents Complexation
incorrect reference use recommended
filling solution filling solution
Low Slope or standards contaminated prepare fresh standards
No Slope or incorrectly made
ISA not used use recommended ISA
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Instruction Manual Iodide Electrode
standard used as ISA use ISA
electrode exposed check section entitled
to complexing agents Complexation
air bubble on membrane remove bubble by re-dipping
probe
"Incorrect Answer" incorrect scaling plot millivolts on the linear axis.
(but calibration of semi-log paper On the log axis, be sure that
curve is good) concentration numbers within
each decade are increasing with
increasing concentration.
incorrect sign be sure to note sign of the
millivolt number correctly
incorrect standards prepare fresh standards
wrong units used apply correct conversion factor:
10-3M = 127.0 ppm as I-1
complexing agents check section entitled
in sample Complexation
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Instruction Manual Iodide Electrode
SPECIFICATIONS
Concentration Range: 1M to 1.0X10-8M
127,000 ppm to 0.4 ppm
pH Range: 0-14
Temperature Range: 0° to 80°C
Resistance: <1 Mohm
Reproducibility: ±2%
Samples: Aqueous solutions only; avoid organic solvents
Size: 110 mm in length; 12 mm in diameter; 1 m cable length
Storage: Store in iodide solution
ORDERING INFORMATION
CODE/NO. DESCRIPTION
EC-IO-03 Iodide Ion Combination Electrode, epoxy body
EC-SCS-IO1-BT Iodide Standard, 0.1M NaI
EC-SCS-IO2-BT Iodide Standard, 1,000 ppm NaI
EC-ISA-IO1-BT Ionic Strength Adjuster (ISA), 5M NaNO
3
EC-MIS-PP Polishing Paper for the Iodide Ion Electrodes
17
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