SUPPORTED LIQUID MEMBRANE ENRICHMENT USING AN ORGANOPHOSPHORUS EXTRACTANT FOR ANALYTICAL TRACE-METAL DETERMINATIONS IN RIVER WATERS

Metal ions were preconcentrated from water supported liquid membranes containing 40% w/w di-2-ethylhexyl phosphoric acid (DEHPA) dissolved i n kerosene as the membrane Liquid, The driving force for the mass tran sport of analytes in this system is the pH gradient across the membran e. The effect of the carrier concentration on the extraction efficienc y tvas studied. The mechanism for the mass transport in the system was investigated by measuring changes in pH and analyte ion concentration as well as changes in the concentration of other interfering metal io ns present in large excess during the enrichment. The extraction effic iency was found to be unchanged as long as the pH difference across th e membrane was more than 2 pH units. The long-term stability of the sy stem was investigated at different pHs in the donor solution, Under op timal conditions, the membrane was stable for at least 200 h with reag ent water samples and at least 80 h for river water samples, Enrichmen t-factors of approximately 15 times could be obtained. The correspondi ng extraction efficiencies were over 86% for some of the investigated metal ions. The detection Limits of blank samples for Cu2+, Cd2+ and P b2+ using 120 min processing time were 0.19, 0.024 and 0.09 ng/mL, res pectively.