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

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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.

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