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PERCHLORATE ION ELECTRODES
INSTRUCTION MANUAL
GENERAL
INSTRUCTIONS
Introduction
The Perchlorate Ion Electrodes are used to quickly, simply,
accurately, and economically measure perchlorate 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. Perchlorate Ion Combination Electrode.
Required Solutions
1. Deionized or distilled water for solution and standard
preparation.
2. Ionic Strength Adjuster (ISA), 2M (NH4)2SO4. To prepare
this solution from your own laboratory stock, half fill a
1000 ml volumetric flask with distilled water and add 264
grams of reagent-grade ammonium sulfate, (NH4)2SO4. 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 contents. ISA is added at the rate of 2 ml of ISA to
each 100 ml of standard or sample to adjust the ionic
strength to about 0.12M.
3. Electrode Filling Solution, 0.1M (NH
4)2SO4
.
4. Perchlorate Standard, 0.1M NaClO4. To prepare this
solution from your own laboratory stock, pipet 200 ml
standard 0.5 M sodium hydroxide into a 600 ml beaker.
Titrate to pH 7.00 against 60% perchloric acid using a
calibrated pH electrode as the endpoint detector. Transfer,
with rinsings, to a one liter volumetric flask and dilute to
volume with distilled water. NOTE: Perchloric acid is
explosive in contact with reducible substances and is a
strong oxidizing agent. Use extreme caution when handling.
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5. Perchlorate Standard, 1000 ppm ClO
-1
. To prepare this
4
solution from your own laboratory stock, pipet 20 ml standard
0.5 M sodium hydroxide into 200 ml distilled water in a 600
ml beaker. Titrate to pH 7.00 against 60% perchloric acid
using a calibrated pH electrode as the endpoint indicator.
Transfer, with rinsings, to a one liter volumetric flask and
dilute to volume with distilled water. NOTE: Perchloric acid
is explosive in contact with reducible substances and is a
strong oxidizing agent. Use extreme caution when handling.
GENERAL PREPARATION
Electrode Preparation
Remove the rubber caps covering the electrode tips and any 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 may be
trapped behind the perchlorate membrane. Prior to first usage,
or after long-term storage, immerse the perchlorate membrane in
perchlorate standard for thirty minutes. The electrode is now
ready for use.
Connect the electrodes to the proper terminals of the meter 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
two 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 0.1M or 1000 ppm perchlorate
standard to the beaker. When the reading has stabilized,
record the mV reading.
3. Using a pipet, add 10 ml of the same perchlorate
standard used above to the beaker. When the reading has
stabilized, record the mV reading.
4. Determine the difference between the two readings. The
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electrode is operating correctly if the mV potential has
changed by 56 " 2 mV assuming the solution temperature is
between 20
o
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.
Electrode Slope Check (with ion meter)
(check electrodes each day)
1. Prepare standard perchlorate solutions whose
concentrations vary by ten fold. Use either the 0.1M or
1000 ppm perchlorate 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 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 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 2% measurement error.
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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, between
the stirrer and beaker.
Always rinse the electrodes with distilled water and blot dry
between measurements. Use a clean, dry tissue to prevent crosscontamination.
For samples with high ionic strength, prepare standards whose
composition is similar to 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 standard solution for about 5 minutes.
Sample Requirements
All samples 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 40
o
C. About a 2% error will
be introduced for a 1oC difference in temperature.
Interferences should be absent. If they are present, use the
procedures found in the Interferences section to remove them.
The pH range for the perchlorate ion electrode is 2.5-11.
Neutralize samples outside this range with acid or base to bring
them in range.
Units of Measurement
Perchlorate concentrations are measured in units of ppm as sodium
perchlorate, ppm as perchlorate, moles per liter, or any other
convenient concentration unit. Table 1 indicates some of the
concentration units.
TABLE 1
: Concentration Unit Conversion Factors
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ppm NaClO
ppm ClO
4
-1
moles/liter
4
1225.0 995.0 1.0X10-2
122.5 99.5 1.0X10-3
12.2 10.0 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 for all perchlorate
solutions. The temperature of both sample solution and standard
solutions should be the same.
Direct Measurement of Perchlorate (using a pH/mV meter)
1. By serial dilution, prepare three standard solutions
from the 0.1 M or 1000 ppm stock standard. The resultant
concentration should be 10-2, 10-3, and 10-4M or 1000, 100 and
10 ppm perchlorate standards. Add 2 ml of ISA per 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 (10-4M 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 the mid-range solution (10
-3
M or 100 ppm) in a 150
ml beaker on the magnetic stirrer and begin stirring. 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 value.
4. Place the most concentrated solution (10-2M or 1000 ppm)
in a 150 ml beaker on the magnetic stirrer and begin
stirring. 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 the semi-logarithmic graph paper, plot the mV
reading (linear axis) against the concentration (log axis).
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A calibration curve is constructed on semi-logarithmic paper
when using the 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 non-linear 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 the electrode
tips into the solution. When the reading has stabilized,
record the mV reading. Using the calibration curve,
determine the sample concentration.
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 Perchlorate (using an ion meter)
1. By serial dilution of the 0.1M or 1000 ppm perchlorate
standard, prepare two perchlorate standards whose
concentration is near the expected sample concentration.
Measure out 100 ml of each standard into individual 150 ml
beakers and add 2 ml of ISA to each.
2. Place the most 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 perchlorate
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.
5. Place the more concentrated solution on the magnetic
stirrer and begin stirring at a constant rate. Lower the
electrode tips into the solution.
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6. Adjust the meter to the concentration of the perchlorate
standard and fix the value in the memory according to the
meter manufacturer's instructions after stabilization of the
reading.
7. For low level 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 in 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 the beaker 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 perchlorate 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 ambient temperature will necessitate the repetition
of Steps 2-6 above. The meter should be re-calibrated daily.
Low Level Perchlorate Determination (using a pH/mV meter)
This procedure is recommended for solutions with ionic strengths
less than 1.0X10
-2
M. If the solution is high in ionic strength,
but low in perchlorate, use the same procedure, but prepare a
calibration solution with a composition similar to the sample.
1. Using 20 ml of standard ISA, dilute to 100 ml with
distilled water. This low level ISA [0.4M (NH
4)2SO4
] is added
at the rate of 1 ml low level ISA to each 100 ml of sample.
The background ionic strength will be 4.0X10-3M.
2. Dilute 1 ml of 0.1M standard to 100 ml to prepare a
1.0X10-3M ClO
Use the 1000 ppm standard for preparing a 100 ppm ClO
-1
solution for measurements in moles per liter.
4
-1
4
standard by diluting 10 ml of the 1000 ppm standard to 100
ml. Standards should be prepared fresh daily.
3. Add 1 ml of the low level ISA to a 100 ml volumetric
flask and fill to the mark with distilled water. Pour this
solution into a 150 ml beaker and place the beaker on the
magnetic stirrer. Begin stirring at a constant rate.
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4. Place the electrode tips in the solution. Assure that
the meter is in the mV mode.
5. Add increments of the 1.0X10
-3
M or 100 ppm standards as
given in Table 2 below.
6. After the reading has stabilized, record the mV reading
after each addition.
TABLE 2: Step-wise Calibration for Low Level Perchlorate
Measurements
Added Concentration
Step Pipet Volume (ml) M ClO
-1
ppm ClO
4
-1
4
1 A 0.1 1.0X10-6 0.1
2 A 0.1 2.0X10-6 0.2
3 A 0.2 4.0X10-6 0.4
4 A 0.2 6.0X10-6 0.6
5 A 0.4 9.9X10-6 1.0
6 B 2.0 2.9X10-5 2.9
7 B 2.0 4.8X10-5 4.8
Pipet A = 1 ml graduated pipet
Pipet B = 2 ml pipet
Solutions: additions of 1.0X10-3M or 100 ppm standard to 100 ml of
ISA as prepared in Step 3 above.
7. On semi-logarithmic graph paper, plot the millivolt
reading (linear axis) against the concentration (log axis)
as in Figure 1.
8. Rinse the electrodes with distilled water and blot dry.
9. Measure out 100 ml of the sample into a 150 ml beaker,
add 1 ml of low level ISA. Place the beaker on the magnetic
stirrer and begin stirring. Lower the electrode tips into
the solution. After the reading has stabilized, record the
mV reading and determine the concentration from the low level
calibration curve.
10. Prepare a new low level calibration curve daily. Check
the calibration curve every two hours by repeating Steps 2-
7.
Low Level Perchlorate Determination (using an ion meter)
Follow the procedure given for normal perchlorate determinations
using an ion meter and the blank correction procedure.
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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
Certain anions are electrode interferences and will cause
electrode malfunction, drift or measurement errors if present in
high enough levels. The level of interfering common anions that
will cause a 10% error at three levels of perchlorate is given in
Table 3.
TABLE 3: Concentration of Possible Interferences Causing a 10%
Error at Various Levels of Perchlorate; Background
Ionic Strength of 0.12M (NH4)2SO4.
Interferences
(moles/liter) 10-2M 10-3M 10-4M ClO
NO
NO
-1
5.0x10-1 5.0x10-2 5.0x10-3
3
-1
5.0x10-1 1.0x10-2 1.0x10-3
2
-1
4
Br-1 4.0x10-1 4.0x10-2 4.0x10-3
CN-1 4.0x10-1 4.0x10-2 4.0x10-3
ClO
I
-1
2.0x10-1 2.0x10-2 2.0x10-3
3
-1
2.0x10-2 2.0x10-3 2.0x10-4
Interferences
(ppm) 100 ppm 10 ppm 1 ppm
NO
NO
-1
3.1x103 3.1x102 3.1x101
3
-1
2.3x103 2.3x102 2.3x101
2
Br-1 3.2x103 3.2x102 3.2x101
CN-1 1.0x103 1.0x102 1.2x101
ClO
-1
1.7x103 1.7x102 1.7x101
3
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-1
I
2.5x102 2.5x101 2.5
Interferences such as bromide, iodide and cyanide can be removed
by precipitation with 0.5 grams of silver sulfate added to 100 ml
of sample. Nitrite interference can be removed by adding 0.3
grams of sulfamic acid to 100 ml of sample.
The above interference removal procedures require similar
treatment of standards as well as samples.
If the electrode is exposed to high levels of interfering ions
which cannot be removed, the electrode reading may drift and the
response may become sluggish. Restore performance by soaking in
distilled water for 30 minutes followed by soaking in perchlorate
standard for 30 minutes.
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 10-3M
level. Because of the solubility equilibria on which the
electrode depends, the absolute potential of the reference
electrode changes slowly with temperature. The slope of the
perchlorate electrode, as indicated by the factor "S" in the
Nernst equation, also varies with temperature. Table 4 gives
values for the "S" factor in the Nernst equation for the
perchlorate ion.
The operating range of the perchlorate ion electrode is 0o-40oC,
provided that temperature equilibrium has occurred.
If the temperature varies substantially from room temperature,
equilibrium times up to one hour are recommended.
TABLE 4
: Temperature vs. Values for the Electrode Slope
Temp (oC) "S"
0 54.20
10 56.18
20 58.18
25 59.16
30 60.15
40 62.13
50 64.11
Electrode Response
Plotting the mV potential against the perchlorate concentration on
semi-logarithmic paper results in a straight line with a slope of
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about 56 mV per decade. )
The time needed to reach 99% of the stable electrode potential
reading, the electrode response time, varies from one minute or
less in highly concentrated solutions to several minutes near the
detection limit.
Limits of Detection
The upper limit of detection in pure sodium perchlorate solutions
is 1M. In the presence of other ions, the upper limit of
detection is above 10
-1
M perchlorate, but two factors influence
this upper limit. Both the possibility of a liquid junction
potential developing at the reference electrode and the salt
extraction effect influence this upper limit. Some salts may
infuse into the electrode membrane at high salt concentrations,
causing deviation from the theoretical response. Either dilute
samples between 1M and 10-1M or calibrate the electrode at 4 or 5
intermediate points.
The lower limit of detection is influenced by the slight water
solubility of the ion exchanger used in the sensing portion of the
electrode. Refer to Figure 1 for a comparison of the theoretical
response to the actual response at low levels of perchlorate.
Perchlorate measurements below 10-5M ClO
-1
(1.0 ppm as ClO
4
-1
) should
4
employ low level procedures.
pH Effects
The operating range of the perchlorate electrode is from pH 2.5 to
pH 11.
Electrode Life
The perchlorate electrode will last six months in normal
laboratory use. On-line measurement 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.
Electrode Storage
The perchlorate electrodes may be stored for short periods of time
in 10
-2
M perchlorate solution. For longer storage (longer than two
weeks), rinse and dry the perchlorate membrane and cover the tip
with any protective cap shipped with the electrodes. 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.
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ELECTRODE
THEORY
Electrode Operation
The perchlorate electrode consists of an electrode body containing
a liquid internal filling solution in contact with a gelled
organophilic membrane containing a perchlorate ion exchanger.
When the membrane is in contact with a solution containing free
perchlorate ions, an electrode potential develops across the
membrane. This electrode potential is measured against a constant
reference potential, using a standard pH/mV meter or an ion meter.
The level of perchlorate ions, corresponding to the measured
potential, is described by the Nernst equation:
E = E$ - S log X
where: E = measured electrode potential
E$= reference potential (a constant)
S = electrode slope (-56 mV/decade)
X = level of perchlorate ions in
solution
The activity, X, represents the effective concentration of the
ions in solution. The total perchlorate ion concentration, Ct, is
the sum of free perchlorate ion, Cf, and complexed or bound
perchlorate ion, Cb. The electrode is able to respond to only the
free ions, whose concentration is :
Cf = Ct - Cb
Since perchlorate ions form very few stable complexes, the free
ion concentration may be equated to the total ion concentration.
The activity is related to the free ion concentration, Cf, by the
activity coefficient, ã, by:
X = ã C
f
Activity coefficients vary, depending on total ions strength, I,
defined as:
I = 1/2 3C
xZx
?
where: C
Z
3
= concentration of ion X
x
= charge of ion X
x
= sum of all of the types
of ions in the solution
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In the case of high and constant ionic strength relative to the
sensed ion concentration, the activity coefficient, ã, 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 (ISA) is added to samples and
standards. The recommended ISA for perchlorate is (NH
4)2SO4
.
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 perchlorate ions.
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 solutions diffuse into
the samples should be as nearly equal as possible, that is, the
filling solution 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 equitransferent salt. One must either calibrate
the electrodes in the same pH range as the sample or use a known
incremental 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
plastic-ware, the electrodes, the standards & reagents, the
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sample, and the technique.
Meter
The meter may be checked by following the check-out procedure in
the instrument instruction manual.
Plastic-ware
Clean plastic-ware is essential for good measurement. Be sure to
wash the plastic-ware well with a mild detergent and rinse very
well with distilled or deionized water.
Electrodes
The electrodes 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 the
section Measuring Hints. Repeat the slope check.
3. If the electrodes still fail to respond as expected,
substitute another perchlorate ion electrode that is known
to be in good working order for the questionable electrode.
If the problem persists and you are using an electrode pair,
try the same routine with a working reference electrode.
4. If the problem persists, the standards or reagent may be of
poor quality, interferences in the sample may be present or
the technique may be faulty. (See Standards & 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 & Reagents
Whenever problems arise with the measuring procedure that has been
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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 the 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 GENERAL
PREPARATION and ELECTRODE
CHARACTERISTICS.
If trouble still persists, call pHoenix Electrode Company at
1-800-522-7920 and ask for the Technical Services Department.
TROUBLESHOOTING HINTS
Symptom Possible Causes Next Step
Out of Range defective meter check meter with
Reading shorting strap
(see meter
instruction
manual)
defective electrode check electrode
operation
electrodes not unplug electrodes
plugged in properly and reseat
reference electrode be sure reference
not filled electrode is filled
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air bubble on remove bubble by
membrane re-dipping electrode
electrodes not in put electrodes in
solution solution
Noisy or Unstable defective meter check meter with
Readings (readings shorting strap
continuously or
rapidly changing) air bubble on remove bubble by
membrane re-dipping electrode
defective electrode replace electrode
ISA not used use recommended ISA
meter or stirrer ground meter or
not grounded stirrer
electrode exposed soak electrode in
to interferences perchlorate
standard
outer filling fill electrode to
solution level level just below
too low the fill hole
Drift (reading samples and standards allow solutions to
slowly changing at different come to room temperin one direction) temperatures ature before
measurement
electrode exposed soak electrode in
to interferences perchlorate
standard
incorrect reference use recommended
filling solution filling solution
Low Slope or standards contamin- prepare fresh
No Slope ated or incorrectly standards
made
ISA not used use recommended
ISA
standard used as ISA use ISA
electrode exposed soak electrode in
to interferences perchlorate
standard
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defective electrode check electrode
operation
air bubble on remove bubble by
membrane re-dipping probe
"Incorrect Answer" incorrect scaling plot millivolts on
(but calibration of semi-log paper the linear axis. On
curve is good) the log axis, be
sure concentration
numbers within
each decade are
increasing
with increasing
concentration
incorrect sign be sure to note sign
of millivolt number
correctly
incorrect standards prepare fresh
standards
wrong units used apply correct
conversion factor:
10
NaClO4= 99.5 ppm as
ClO
-3
M = 122.5 ppm as
-1
4
sample carryover rinse electrodes
thoroughly between
samples
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SPECIFICATIONS
Concentration Range: 1M to 7 x 10-6M
(1.0 x 105 to 0.7 ppm as ClO
-1
)
4
pH Range: 2.5 to 11
Temperature Range: 0o to 40oC
Resistance: 100 Mohms
Reproducibility: "2%
Samples: aqueous solutions only
no organic solvents
Size: 110 mm in length
12 mm in diameter
1 m cable length
Storage: Store in dilute perchlorate solution
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TABLE
OF CONTENTS
General Instructions.......................................1
introduction..........................................1
required equipment....................................1
required solutions....................................1
General Preparation........................................2
electrode preparation.................................2
electrode slope check (with pH/mV meter)..............3
electrode slope check (with ion meter)................3
Measurement................................................4
measuring hints.......................................4
sample requirements...................................4
units of measurement..................................5
Measurement Procedure......................................5
direct measurement....................................5
direct measurement of perchlorate
(using a pH/mV meter).............................5
direct measurement of perchlorate
(using an ion meter).............................7
low level perchlorate determination
(using a pH/mV meter)............................8
low level perchlorate determination
(using an ion meter).............................9
Electrode Characteristics..................................9
reproducibility.......................................9
interferences........................................10
temperature influences...............................11
electrode response...................................11
limits of detection..................................12
pH effects...........................................12
electrode life.......................................12
electrode storage....................................13
Electrode Theory..........................................13
electrode operation..................................13
Troubleshooting Guide.....................................15
Troubleshooting Hints.....................................16
Specifications............................................19
Table of Contents.........................................20
M-4811
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