Anions in high purity, boiler feed and nuclear reactor cooling waters - Determination of Anions in Natural and Treated Waters - page 608

[15,16] have been used to determine traces of chloride in high purity power station
waters. Detection limits claimed are 6-100µg L −1 [14] for silver-silver chloride
electrodes and 1-10µg L −1 solid-state mercurous chloride electrodes.

Silver-silver chloride electrodes
Measurements have been made in two ways. In one method [14] two solid-state Orion
94-17A silver chloride membrane electrodes are used. The reference electrode is
contained in a compartment connected to the sample compartment by a ground glass
sleeve. The reference compartment contains a 100µg L −1 solution of chloride in 0.1mol
L −1 nitric acid. A graph is constructed from cell potential readings after adding
increments of standard chloride solution to the sample solution (made 0.1mol L −1 in
nitric acid) in the sample compartment. A similar graph is obtained by adding increments
of the chloride solution to a blank solution containing 0.1mol L −1 nitric acid. The
chloride content of the sample is given by the distance along the concentration axis
between the two lines.
Concentrations of copper(II), iron(II), nickel(II) and aluminium interfere when present
at concentrations exceeding 10mg L −1 and ammonia and hydrazine also interfere. It is
claimed that better precision is obtained using these electrodes than by using the
conventional silver-silver chloride electrodes discussed below.
In the alternative method, measurements are made using silver-silver chloride
electrodes vs a mercurous sulphate reference electrode [11,13].
A manual version of this procedure has been described having a detection limit of
100µg L −1 . The continuous analyser version (discussed below) has been described with a
detection limit nearer to 1µg L −1 [11].
In this apparatus the electrodes are immersed in a buffered sample stream. The
temperature of the electrode flow cell is controlled at 10 (±0.1)°C at which level the
sensitivity of 3.54mV per 100µg L −1 is approximately 50% greater than that at 25 (±0.1)°
C, and a linear response of cell potential to changes in chloride concentration is observed
up to 0.150µg L −1 . The standard deviations at 10°C for nominal chloride

Table 11.1 Recovery of chloride from samples of power station waters

Sample Initial chloride

concentration µg L −1

Chloride spike
added µg L −1

Final chloride
concentration µg L −1

Recovery
%

5.3 a (0.23) b

Condensed <1 5.0 106.0

steam (A)
Condensed

<1 19.7 19.5(0.40) 98.9

steam (B)
Boiler
water

108.0 47.2 156.9(0.40) 103.6

a Each result is the mean of six determinations
b The figures in parenthesis are the standard deviations for single determinations with five degrees