Abstract
The proposed method is to extract arsenic(III) by benzene as its pyrrolidinedithiocarbamate (PDTC), back-extract arsenic with dilute bromine water and to determine arsenic as its molybdenum heteropoly blue. The method could be applied to determine ppm levels of arsenic in environmental samples with deviation of ±0.2ppm. Tin, bismuth, and molybdenum interfered seriously, but these metal ions amounting 4 times, 20 times, and 1.5 times for arsenic could be permitted, respectively. Treat (0.51) g of a sample with nitric acid and (45) ml of conc. sulfuric acid. After destruction of organic matter with nitric acid, expel the acid by heating to fumes of sulfuric acid. Dissolve the treated mass with water in hot, filter of insoluble matter and dilute the filtrate to 100 ml with water. To this add some ascorbic acid and 0.2 g of thiomalic acid, and heat the solution at temperature near boiling for 10 min to obtain arsenic(III). To extract arsenic(III) from the solution with 20 ml of extractant (5 v/v % ethanol-benzene solution of 0.1 w/v % PDTC-ammonium salt), and remove the excess of the carbamic acid from the organic extract by shaking with 2 w/v % NaHCO3solution. Obtain arsenic in aqueous solution with 4 ml of dilute bromine water successively with 3 ml of water. With the combined extract, prepare a molybdenum heteropoly blue complex in a volume of 10 ml and measure the absorbance at 840 nm with a spectrophotometer using 1 cm cells.
