Study of Solid Phase Extraction Prior to Spectrophotometric Determination of Platinum with N-(3,5-Dimethylphenyl)-N′-(4-Aminobenzenesulfonate)-Thiourea

A highly sensitive, selective and rapid method for the determination of platinum based on the rapid reaction of platinum(IV) with N-(3,5-dimethylphenyl)-N′-(4-aminobenzenesulfonate)-thiourea (DMMPT) and the solid phase extraction of the Pt(IV)-DMMPT complex with C18 membrane disks was developed. In the presence of pH = 3.8 buffer solution and cetyl trimethylammonium bromide (CTMAB) medium, DMMPT reacts with platinum to form a violet complex of a molar ratio of 1:3 (platinum to DMMPT). This complex was enriched by solid phase extraction with C18 membrane disks, and an enrichment factor of 200 was obtained. The molar absorptivity of the complex is 9.51 × 104 L · mol−1 · cm−1 at 755 nm, and Beer’s law is obeyed in the range of 0.01–3.0 µg mL−1 in the measured solution. The relative standard deviation for eleven replicate samples of 0.01 µg mL−1 level is 1.79%. The detection limit reaches 0.02 µg L−1 in the original samples. This method was applied to the determination of platinum in water and soil samples. The relative standard deviations are 2.9–3.4%. The recoveries are 94–105%. The values of determination obtained agree with those of the ICP-MS method. The results are satisfactory.