Anions in high purity, boiler feed and nuclear reactor cooling waters - Determination of Anions in Natural and Treated Waters - page 609

of freedom
Source: Reproduced with permission from the Electrochemical Society Inc., USA [14]

concentrations of 50, 100 and 250µg L −1 are ±1.7, ±2.8 and ±2.7µg L −1

respectively.

Substances normally present in these waters do not interfere appreciably.
Table 11.1 shows the satisfactory recoveries obtained in some spiking experiments
carried out using this system. In most instances there was no significant interference in
the procedure by substances likely to occur in boiler feed water and in every instance
except one, where an interference was detected, the effect was positive (Table 11.2). The
small effects noted for sodium hydroxide, trisodium orthophosphate and sodium
carbonate could be explained by a change in the pH of the system. The unexpected
interference from sodium sulphate and sodium sulphite could arise from trace amounts of
chloride in the reagent chemicals. However, the effects were so small, even at the excess
levels of these substances added, that for most practical purposes they could be ignored.

Solid state mercurous chloride electrodes
This is the more recent development in the determination of chloride in high purity water.
Marshall and Midgley [15,16] have described a procedure for the determination of 0-
20µg L −1 chloride in high purity water, using two types of ion selective membrane
electrode incorporating mercurous chloride. At these low concentrations, more chloride
will dissolve from the mercury (1) chloride in the electrode than is present in the sample
itself. The extent of the dissolution is controlled, however, by the chloride in the sample.
In these circumstances, the electrode potential is linearly related to the concentration of
chloride in the sample. With the electrode housed in a flow cell with a thermostatically
controlled water

Table 11.2 Effect of other substances at 10°C

Interference effects (µg L −1 ) of chloride at
chloride concentrations of

Substance Concentration of

substance mg L −1

0µg L −1a 50µgL −1a

Na 2 SO 4 75 1.7 3.1

Na 2 HPO 4 50 1.4 2.7

NaOH 4 <1 <1

NaOH 40 4.1 3.8

Na 3 PO 4 50 2.7 <1

Na 2 CO 3

50 2.7 <1

NH 3

10 <1 <1

Morpholine 10 <1 <1