INDIRECT ULTRAVIOLET SPECTROPHOTOMETRIC DETERMINATION OF SMALL AMOUNTS OF CHLORIDE-ION WITH SILVER-DIETHYLDITHIOCARBAMATE COMPLEX

Diethyldithiocarbamate (DDTC) reacts with silver ion to form a stable chelate. The present paper deals with a method for the indirect determination of chloride ion based on the measurement of Ag-DDTC chelate extracted into carbon tetrachloride. The procedure is as follows: a 10 ml aliquot of a sample solution containing less than 5 X 10(-4) M (17.8 ppm) chloride ion is placed in a glass tube with a stopper. One milliliter of 10% (w/v) citric acid solution and 1 ml of 5 X 10(-3) M silver nitrate are added, and mixed. After standing for 10 min, the resulting AgCl-precipitate is filtered with suction through a 0.45-mu-m membrane filter. A 10 ml portion of the filtrate is transferred into a separatory funnel. One milliliter of 2 M aqueous ammonia, 1 ml of 0.2% (w/v) DDTC.Na solution and 10 ml of carbon tetrachloride are added. The mixture is then shaken for 2 min. After the phase sparation, the absorbance of the organic phase is measured at 340 nm with a 1 cm quartz cell using water as a blank. If some interfering ions exist in the sample solution, the resulting AgCl-precipitate collected on the membrane filter can be used for the determination of chloride ion. The precipitate is washed with water and dissolved completely in aqueous ammonia. The subsequent procedure is similar to that for the filtrate as described above. When chloride content is less than 1 X 10(-4) M (3.8 ppm), the absorbance measurement of AgCl-precipitate is performed at 280 nm on an absorption maximum. The relative standard deviation obtained by the filtrate method for the determination of 5.3 ppm chloride ion in a river water sample was 0.83% (n = 10).