oa South African Journal of Chemistry - Solid phase extraction and spectrophotometric determination of gold with 5-(2-hydroxy-4-nitrophenylazo)-rhodanine as chromogenic reagent



This paper presents the synthesis and application of 5-(2-hydroxy-4-nitrophenylazo)-rhodanine (HNAR) as a new chromogenic reagent for the determination of gold. Based on the rapid reaction of gold with HNAR and the solid phase extraction of the coloured chelate with a reversed phase polymer-based C cartridge, a highly sensitive, selective and rapid method for the determination of gold has been developed. In the presence of 0.05-0.5 mol L-1 of phosphoric acid solution and emulsifier-OP medium, HNAR reacted with gold to form a red chelate of a molar ratio 1:3 (gold to HNAR). This chelate was enriched by the solid phase extraction with a polymer-based C cartridge and the retained chelate was eluted from the cartridge with dimethyl formamide (DMF). An enrichment factor of 100 was achieved. In DMF medium, the molar absorptivity of the chelate was found to be 1.51 x 105 L mol-1 cm-1 at 496 nm. Beer's law was obeyed in the range of 0.01~2 g mL-1. The relative standard deviation for eleven replicates with a concentration of 0.5 g L-1 level was 2.31%. The detection limit based on three times the standard deviation was 0.01 g L-1 in the original sample. This method was applied to the determination of gold with good results.


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