Indirect determination of small amounts of chloride ion in natural water by AAS

The present paper deals with a simple method for the indirect determination of chloride ion based on the measurement of silver by AAS. A sample solution (10 ml) containing less than 1×10-4 M (3.6 ppm) chloride ion is placed in a glass tube with a stopper. One milliliter of 0.1 M nitric acid and 1 ml of 1×10-3 M silver nitrate are added, and mixed. After standing for 10 min, the AgCl-precipitate is filtered with suction through a 0.45 p.m membrane filter. The absorption of silver ion in the filtrate is measured at 328.1 nm by an atomic absorption spectrometer. If some interfering ions such as iodide, thiosulfate and sulfide exist in the sample solution, the resulting AgCl-precipitate can be used for the determination of chloride. The precipitate on the filter is washed with water, dissolved completely in aqueous ammonia and the absorption of silver is measured at 328.1 nm. The relative standard deviation obtained from the filtrate method for the determination of 2.3 ppm chloride ion in an underground water sample was 1.9% (n = 10).