The spectrophotometric determination of arsenic in sea water, potable water and effluents

Abstract

Procedures are described for the determination of arsenic in sea water, potable waters and effluents. The sample is treated with sodium borohydride added at a controlled rate. The arsine evolved is absorbed in a solution of iodine and the resultant arsenate ion is determined photometrically by a molybdenum blue method. The time required for a complete analysis is about 90 min, but of this only 15 min is operator time. For sea water the range, standard deviation, and detection limit are 1–4 μgl -1, 1.4 % and O.14 μg l -1, respectively; for potable waters they are 0–800 μg l -1, about 1 % (at 20μg l -1 level) and 0.5μg l -1, respectively. Silver and copper cause serious interference at levels of 0.5 mgl -1, and nickel, cadmium and bismuth interfere at concentrations of a few tens of mg l -1; however, these elements can be removed either by preliminary extraction with a solution of dithizone in chloroform or by ion exchange. Arsenic present in organo-arsenic compounds is not directly determinable, but can be rendered reactive either by photolysis with ultraviolet radiation or by oxidation with permanganate or nitric—sulphuric acid mixture. Arsenic(V) can be determined separately from total inorganic arsenic after extracting arsenic(III) as its pyrrolidine dithiocarbamate into chloroform.