TRACE ENRICHMENT OF METALS USING A SUPPORTED LIQUID MEMBRANE-TECHNIQUE

The supported liquid membrane technique offers new possibilities for a nalytical enrichment, field sampling and speciation, The possibility o f using the technique for the enrichment of metals in a flow system wi th off-line atomic absorption spectrometry in the final analysis step is outlined, Five metals (Cu, Cd, Co, Ni and Zn) have been used as mod el substances and different approaches to transport metals across the membrane are demonstrated. In one system 8-hydroxyquinoline was used a s complexing agent in the sample (donor) solution, In a second system potassium thiocyanate was used in the donor solution and an extractant (Aliquat-336) in the membrane liquid, In a third system 8-hydroxyquin oline was used in the donor solution and Aliquat-336 in the membrane l iquid. The parameters important for analytical enrichment are consider ed, These include factors for determining the extraction efficiency, t he possibility of carry-over effects, matrix dependence and longterm m embrane stability, The memory effects were below 2% and high concentra tions of humic acids or salts did not interfere in the analysis, The l ong-term stability using di-n-hexyl ether in the membrane was 1-2 week s and with the extractant Aliquat-336 incorporated in the membrane liq uid it was 4 d, Determination of metals at levels <1 ppb was possible, The limiting factor for the determination at lower concentrations at present is the metal contamination in the reagents used.