Study on the Solid Phase Extraction and Spectrophotometric Determination of Gold with 5- (2-Hydroxy-4-nitrophenylazo)thiorhodanine

Abstract

In this paper, a new chromogenic reagent, 5-(2-hydroxy-4-nitrophenylazo)thiorhodanine (HNATR) was synthesized. A highly sensitive, selective and rapid method for the determination of gold based on the rapid reaction of gold with HNATR and the solid phase extraction of the coloured chelate with a reversed phase polymerbased C₁₈ cartridge has been developed. In the presence of 0.05-0.5 mol L^-1 of hydroch1oric acid solution and emulsifier-OP medium, HNATR reacts with gold to form a red chelate of molar ratio 1:2 (gold: HNATR). This chelate was enriched by solid phase extraction with a polymer-based C₁₈ cartridge and eluted form the chelate from cartridge with dimethyl formarnide (DMF). The enrichment factor of 100 was achieved. In the DMF medium, the molar absorptivity of the chelate is 1.23 x 105 L mol^-1 cm^-1 at 550 nm. Beer's law is obeyed in the range of 0.01-3 μg mL^-1 in the measured solution. The relative standard deviation for eleven replicate sample of 0.5 μg L^-1 level is 2.18 %. The detection limit, based on the three times of standard deviation is 0.02 μg L^-1 in the original sample. This method was applied to the determination of gold in water and ore with good results.