Thermo Fisher Scientific Ion Selective Electrodes Chloride - Manual (Page 15)

Instruction Manual Chloride Electrode
Limits of Detection
The upper limit of detection in pure sodium chloride solutions is 1M. In the presence of other ions,
the upper limit of detection is above 1.0x10
-1
M chloride, 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 extract into the electrode membrane at
high salt concentrations, causing deviation from the theoretical response. Either dilute samples
between 1M and 1.0x10
-1
M 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
chloride. Chloride measurements below 10
-4
M CL
-1
should employ low level procedures.
pH Effects
Hydroxide ion interferes with measurements of low levels of chloride although the electrode can be
used over a reasonable pH range. Table 3 should be used to determine the minimum pH at which
low level chloride measurements can be made without more than a 10% error due to hydroxide ion
interference.
Electrode Life
A chloride 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.
Electrode Storage
The electrode may be stored for short periods of time in 1.0x10
-2
M chloride 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.
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