Gas chromatographic determination of nickel, zinc, and cadmium by ammonium diisopropyldithiophosphinate

Abstract

A chelating reagent containing sulfur ligands, ammonium diisopropyldithiophosphinate, was synthesized and various metal ions were reacted with it to form the chelates. The thermal properties, the extractability into organic solvents and the gas chromatographic behavior of the metal chelates were investigated. Metal ions used were nickel, zinc, cadmium, cobalt, mercury, lead, and bismuth. The thermogravimetric analysis of these chelates showed that cobalt, nickel, zinc, and cadmium chelates can sublime (94100) % below 300 °C. Only the cobalt chelate is not extracted intoorganic solvents at all. Therefore, a gas chromatographic method for the simultaneous determination of nickel, zinc, and cadmium was investigated. Typical procedure was shown as follows. Add 1 ml of a solution containing nickel, zinc, and cadmium (more than 2 ×10^-6 mol dm^-3, respectively), 0.5 ml of a 0.5 mol dm-3 phosphate buffer solution (pH 7.5) and 1 ml of the reagent solution (7.5 × 10^-2 mol dm^-3) into a stoppered test tube and dilute to 10 ml with distilled water. Extract the chelate formed with 1 ml of chloroform with shaking for 15 min and inject 4μl of the extract into the FID gas chromatograph. Measure the peak height or the peak area. Less than 1 × 10^-4 mol dm^-3 Mg²⁺, Co²⁺, Mn²⁺, Al³⁺, Sn⁴⁺, and SiO₃^2- did not interfere. The disturbance by Fe³⁺ could be effectively eliminated by adding triethanolamine.