Study on the Solid Phase Extraction and Spectrophotometric Determination of Cadmium

Abstract

In this paper, a new chromogenic reagent, 5-(2-hydroxy-4-nitrophenylazo)thiorhodanine (HNSR) was synthesized. A high sensitive, selective and rapid method for the determination of cadmium based on the rapid reaction of cadmium with 5-(2-hydroxy-4-nitrophenyl-azo)thiorhodanine and the solid phase extraction of the coloured chelate with a MCI-GEL reversed phase polymer resin has been developed. In the presence of 0.05-0.5 mol L^-1 of hydrochloric acid solution and emulsifier-OP medium, 5-(2-hydroxy-4-nitrophenylazo)thiorhodanine reacts with cadmium to form a red chelate of a molar ratio 1:2 (cadmium to 5-(2-hydroxy-4-nitrophenylazo)thiorhodanine). This chelate was enriched by the solid phase extraction with a cartridge packed with MCI-GEL polymer resin and eluted the chelate from cartridge with dimethyl formamide (DMF). The enrichment factor of 100 was achieved. In the DMF medium, the molar absorptivity of the chelate is 1.54 × 10⁵ L mol^-1 cm^-1 at 505 nm. Beer’s law obeyed in the range of 0.01~2.0 μg mL^-1 in measured solution. The relative standard deviation for eleven replicates sample of 0.5 μg L^-1 level is 2.64 %. The detection limit, based on the three times of standard deviation is 0.01 μg L^-1 in original sample. This method was applied to the determination of cadmium in tobacco and water sample with good results.