Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 133

Basson and Van Staden [179] have described an automatic method for the simultaneous
determination of chloride and sulphate in non saline water based on an adaptation of the
flow injection concept. About 200 samples per hour can be analysed by this procedure
with a coefficient of variation for chloride of less than 1.3%. This FIA method compares
favourably with the standard segmented automated methods for chloride. Application of
Student's t -test reveals differences insignificant at a 5% probability level.
A schematic diagram of the system employed is shown in Fig. 2.13. The manifold
consists of Tygon tubing with tube lengths and inside diameters as indicated in the figure.
The sample is automatically injected into the system from a Breda Scientific flow
injection sampler containing a valve with a capacity of 200µL. Using a sampling time of
18s gives a capacity of 200 samples per hour. The valve system is actuated on a time
basis which is correlated with the sampler unit. The sampling valve actuates ever 16s
after movement to the next sample.
The performance of this flow injection analysis procedure is shown in Table 2.8 for
chloride. The coefficient of variation for chloride is less than 1.3%.
Workers at Tecator Ltd have described a flow injection analysis procedure [180,181]
for the determination of 1-11mg L −1 of chloride in
Fig. 2.14 Flow injection manifold, determination of chloride
Source: Reproduced with permission fromTecator Ltd [180]
non saline waters. In this procedure chloride reacts with mercury(II) thiocyanate to form
a soluble nonionic compound
The thiocyanate ions released reacts with iron(III)-nitrate to form the red iron(III)
thiocyanate complex
The aqueous sample containing chloride is injected into a carrier stream of distilled water
and mixed with a reagent consisting of mercury(II) thiocyanate and iron(III) nitrate.
Released thiocyanate ions react in the acid solution with iron(III) to give a red coloured
iron(III) thiocyanate complex. The resulting colour is measured photometrically at