Preparation of admicelle and its application to trace analysis

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Separation and preconcentration steps are indispensable prior to the determination, in order to obtain accurate and reproducible analytical results. In the present study, surfactant aggregates formed on solid surfaces (i.e., admicelle) were used for the enrichment of trace heavy metals in water. Because the surface of alumina was positively charged in acidic solutions, sodium dodecyl sulfate (anionic surfactant, SDS) was strongly adsorbed to form admicelles. Nanogram quantities of heavy metals (e.g., Ni, Cu, Cd, Pb) were reacted with pyrrolidinedithiocarbamate (APDC) at pH 2〜6 and the resulting hydrophobic chelate was completely collected on the admicelle column. In the case of dithizone-impregnated admicelles, trace heavy metals were immediately recovered from water without the addition of APDC.Those metals were desorbed from the column with diluted nitric acid, leaving SDS on the column. Because of acidproof admicelles, the column was usable repeatedly.Separation behavior of humic substance was also examined in detail. Humic and fulvic acids were completely adsorbed on the admicelle column at pH 1〜9. It is interesting that negatively charged humic substances are easily adsorbed on the aggregates of anionic surfactant, which indicates that the humic substance interacts with alumina particles strongly than SDS.Humic complexes of heavy metals were also adsorbed on the column. The proposed method is simple and rapid, and it has been successfully applied to the analysis of synthetic water samples as well as certified reference materials.