Solid phase extraction and a spectrophotometric method for the determination of trace amounts of gold with 4-rhodanineazo benzoic acid

Abstract

The synthesis and application of 4-rhodanineazo benzoic acid (4-BARA) as a new chromogenic reagent for the determination of gold is described. A highly sensitive, selective, and fast method for the determination of gold based on its rapid reaction with 4-rhodanineazo benzoic acid and the solid phase extraction of the colored complex on a reversed phase Clean-up® C5 cartridge was developed. In the presence of 0.02-0.2 mol/L phosphoric acid solution and a polyoxyethylene nonylphenol ether (emulsifier-OP) medium, 4-rhodanineazo benzoic acid reacted with gold to form a colored complex with a gold-to-4-BARA molar ratio of 1:2. The complex was enriched by solid phase extraction with a reversed phase Clean-up® C5 cartridge. The complex was eluted from the cartridge with ethanol and an enrichment factor of 50 was achieved. In ethanol medium, the molar absorptivity of the complex was 2.39×105 L mol-1 cm-1 at 505 nm. The Beer Law was obeyed in the concentration range 0.01-~1.2 μg/mL. The relative standard deviation for eleven replicate samples at the 0.001 μg/mL level was 2.3%. In the original sample, the detection limit was 8.0×10-5 μg/mL. This method was applied to the determination of trace amounts of gold in ore samples with good result.

Keywords

• 4-rhodanineazo benzoic acid
• gold
• spectrophotometry
• solid phaseextraction