Rapid determination of gold in geological materials by amyl acetate extraction, ascorbic acid reduction and electrothermal atomisation atomic absorption spectrometry

Abstract

This paper describes an accurate method for determining gold in large numbers of geochemical samples at low cost. Pulverised geological samples are digested in large test-tubes with an orthophosphoric-perchloric acid mixture. Sulphides and carbonaceous material are oxidised at this stage and emulsion-forming clays and silicates are eliminated. This is followed by a hydrobromic acid-bromine attack to dissolve and oxidise the gold to the trivalent state. The bromo-aurate complex formed is concentrated and separated from the interfering matrix by extraction into amyl acetate. Excess of bromine, co-extracted iron and manganese are removed from the bromo-aurate-amyl acetate layer by reduction with ascorbic acid. Aliquots of the resulting colourless organic phase are then transferred into sample vials via an auto-pipette and the gold content is determined by electrothermal atomistion atomic absorption spectrometry.