Colorimetric determination of arsenic in geochemical samples

Abstract

Abstract A colorimetric method and apparatus for the determination of arsenic in batches of geochemical survey samples is described. The powdered material can be digested with a perchloric/nitric acid mixture, or most conveniently by an HF/aqua regia attack utilizing aliquots from the same acid solution as used for routine multi-element atomic absorption analyses. Aliquots are treated with potassium iodide and stannous chloride to reduce arsenic to the trivalent state, and arsine is liberated by the action of zinc pellets. The arsine is absorbed in a solution of silver diethyldithiocarbamate in chloroform-quinoline, the reaction being carried out in batches using very simple, inexpensive apparatus which is easily constructed. Detection limits are variable according to aliquot quantities taken, but in routine use working ranges of 1–800 ppm As are readily achieved. Coefficient of variation is 6.6% at the 5 μg As level. The method is shown to be virtually free from matrix interferences commonly encountered in gossans, soils, rocks and many ores. At least 100 powdered samples can be analyzed per man-day.