Thermo Fisher Scientific Ion Selective Electrodes Chloride - Manual (Page 7)

Instruction Manual Chloride Electrode
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, ethanol, benzene, and acetonitrile are permitted. Highly polar
solvents slowly attack the electrode. Please check with Eutech Instruments Pte Ltd. before using the
electrode in other organic solvents.
The temperature of the standard solutions and of the sample solutions should be the same and
below 50
o
C.
Interferences should be absent. If they are present, use the procedures found in the
Interferences
and Electrode Response sections to remove them.
The pH range for the chloride ion electrode is 2-12. Neutralize samples outside this range with acid
or base to bring them in range.
Units of Measurement
Chloride concentrations are measured in units of parts per million, equivalents per liter, moles per
liter, or any other convenient concentration unit. Table 1 indicates some of the concentration units.
TABLE 1: Concentration Unit Conversion Factors
ppm
Cl
-1
moles/liter Cl
-1
354.50 1.0X10
-2
35.45 1.0X10
-3
3.55 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 chloride solution. The temperature of both sample
solution and of standard solutions should be the same.
Direct Measurement of Chloride (using a pH/mV meter)
1. By serial dilution of the 0.1M or 1,000 ppm standards, prepare 10
-2
, 10
-3
, and 10
-4
M or 100
and 10 ppm chloride standards. Add 2 ml of ISA per 100 ml of standard. Prepare standards
with a composition similar to the samples if samples have an ionic strength above 0.1M.
2.
Place the most dilute solution (1.0x10
-4
M or 10 ppm) 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.
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