Desenvolvimento de nova metodologia para extração de cádmio (II) utilizando sistema de extração com membrana líquida renovável e detecção por espectrometria de absorção atômica em chama

Abstract

A hollow fiber renewal liquid membrane (HFRLM) extraction method for determination of cadmium(II) in water samples by Flame Atomic Absorption Spectrometry (FAAS) was developed. Ammonium O,O-diethyl dithiophosphate (DDTP) was used to complex cadmium(II) in an acid pH into a neutral hydrofobic complex (ML2). A solvent extract this complex and carry it over the Poly(dimethylsiloxane) (PDMS) or polypropylene membrane to the stripping phase into the membrane, where at higher pH the complex Cd-DDTP is broken out and cadmium(II) is released into the stripping phase. EDTA was used to complex cadmium(II) helping to trap the analyte into the stripping phase. Multivariate optimization using surface response metodology was used to optimize the studied variables: sample (donor phase) pH 3.25, DDTP concentration 0.05% (m/v), stripping (aceptor phase) pH 8.75, EDTA concentration 1.5x10-2 mol L-1, extraction temperature 40°C, extraction time 40 minutes, a solvent mixture of N-Butyl Acetate and Hexane (60/40% v/v) with volume of 100 ìL and adition of ammonium sulphate to saturate the sample for PDMS membrane. For polypropylene membrane the optimized conditions were: sample (donor phase) pH 3.5, DDTP concentration 0.06% (m/v), stripping (aceptor phase) pH 9.0, EDTA concentration 6.3 x 10-3 mol L-1, extraction temperature 36°C, extraction time 36 minutes, toluene as solvent extractor with volume of 300 ìL and adition of ammonium sulphate to saturate the sample. The sample volume and stripping volume used were 20 mL and 165 ìL, respectivaly. The analyte enrichment factor was 115, limit of detection (LOD) 1.3 ìg L-1, relative standard deviation (RSD) 5.5 % and linear working range 4.5 - 30 ìg L-1 for PDMS membrane. For polypropylene membrane the analyte enrichment factor was 107, limit of detection (LOD) 1.5 ìg L-1, relative standard deviation (RSD) 4 % and linear woking range 5.1 - 30 ìg L.