Thermo Fisher Scientific Ion Selective Electrodes Chloride - Manual (Page 11)

Instruction Manual Chloride Electrode
9.
Measure out 100 ml of the sample into a 150 ml beaker, add 1 ml of low level ISA, and
place the beaker on the magnetic stirrer. 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 Chloride Determination (using an ion meter)
Follow the procedure given for normal chloride determinations using an ion meter and the blank
correction procedure.
ELECTRODE CHARACTERISTICS
Reproducibility
Electrode measurements reproducible to ±2% can be obtained if the electrode is calibrated every
hour. Factors like temperature fluctuations, drift, and noise limit reproducibility. Reproducibility is
independent of concentration within the electrode's operating range.
Interferences
A surface layer of silver metal may be formed by strongly reducing solutions. A layer of silver salt
may be deposited on the membrane if high levels of ions forming very insoluble salts are present in
the sample. Performance may be restored by polishing. See the section
Electrode Response
for
proper polishing procedure.
Though measurements can be made in solutions containing oxidizing agents such as MnO
4
-1
,
mercury ions must not be present in the samples.
The maximum allowable ratio of interfering ion to chloride ion is given in Table 3. This ratio is
expressed as the ratio of the interfering ion molarity to the chloride 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.
TABLE
3: Maximum Allowable Ratio of Interfering Ion to Chloride Ion
Interferences
Chloride Ion (M)
OH
-1 (1)
80
NH
3
(2)
1.2X10
-1
S
2
O
3
-2 (2)
1.0X10
-2
Br
-1 (3)
3.0X10
-3
S
-2 (4)
1.0X10
-6
I
-1 (3) 5.0X10 -7
CN
-1 (4)
2.0X10
-7
11