Analytical Sciences

Solid Phase Extraction and Spectrophotometric Determination of Au(III) with 5-(2-Hydroxy-5-nitrophenylazo)thiorhodanine

Qiufen HU,*^,** Xiubin CHEN,* Xiangjun YANG,* Zhangjie HUANG,* Jing CHEN,* and Guangyu YANG*

*Department of Chemistry, Yunnan University, Kunming 650091, P. R. China
**Department of Chemistry, Yuxi Teacher's College, Kunming 653100, P. R. China

A new chromogenic reagent, 5-(2-hydroxy-5-nitrophenylazo)thiorhodanine (HNATR) was synthesized. A highly sensitive, selective and rapid method for the determination µg l^-1 level of Au(III) based on the rapid reaction of Au(III) with HNATR and the solid phase extraction of the colored complex with a reversed phase polymer-based C₁₈ cartridge have been developed. The HNATR reacted with Au(III) to form a red complex of a molar ratio 1:2 (Au(III) to HNATR) in the presence of 0.05 - 0.5 mol l^-1 of phosphoric acid solution and emulsifier-OP medium. This complex was enriched by the solid phase extraction with a polymer-based C₁₈ cartridge. The enrichment factor of 100 was achieved. The molar absorptivity of the complex is 1.37 × 10⁵ l mol^-1 cm^-1 at 520 nm in the measured solution. The system obeys Beer's law in the range of 0.01 - 3 µg ml^-1. The relative standard deviation for eleven replicates 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.

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