High preconcentration of ultra-trace metal ions by liquid-liquid extraction using water/oil/water emulsions as liquid surfactant membranes

摘要

A high preconcentration method by liquid-liquid extraction using liquid surfactant membranes was developed.The water-in-oil (w/o) emulsion containing dilute hydrochloric acid,2-ethylhexyl hydrogen 2-ethylhexylphosphonate (PC-88A),liquid paraffin,and kerosene was used for the extraction.In a resulting volume of 1000 cm~3 of an aqueous sample solution(pH 5.0) containing less than 1 mg of each metal ion,2 cm~3 of w/o emulsion droplets coated with sorbitan monnoleate were dispersed.The analyte metal ions in the outer bulk aqueus phase were extracted into the organic phase to form a complex with PC-898A and successively back-extracted into the inner aqueous phase.The analytes inthe resulting inner aqueous phase were determine dsubsequently by graphite furnace atomic absorption spectrometry applied as a detector.By this procedure,concentration factors of 570,820,750,970,860,and 880 were achiveved for chromium(III),manganese (II),cobalt(II),nicke(II),coper(II),and cadmium(II),respectively,and also the respective detection limits (3#delta#) of 0.4,20,1.2,18,18,and 0.7 pg cm~(-3) were obtained.