Application of liquid membranes to sample preconcentration for the spectrometric determination of cadmium in seawater

A bulk liquid membrane system has been used as preconcentration tool for the spectrometric determination of cadmium in seawater. The membrane contained di-(2-ethylhexyl)-phosphoric acid (DEHPA) as mobile carrier dissolved in kerosene. The effects of the composition of both organic and aqueous solutions on the permeation of Cd across the membrane were studied, and optimum conditions were found by the modified simplex method. Maximum preconcentration rates were obtained at a sample pH of 4.7, maintained with a 0.1 mol l−1 acetate buffer solution, a 0.3 mol l−1 HNO3 receiving solution, and a carrier concentration of 0.17 mol l−1. Under optimum conditions, a preconcentration yield of 100% was obtained for both synthetic and real seawater. The method was successfully applied to the determination of cadmium in real seawater.