Preparation of admicelle and its application to trace analysis

为了获得准确和重现性好的分析结果，分离和预浓缩步骤在测定前是必不可少的。在本研究中，在固体表面上形成的表面活性剂聚集体（即，胶束）富集水中痕量重金属。由于氧化铝表面在酸性溶液中带正电荷，十二烷基硫酸钠（阴离子表面活性剂，SDS）被强烈吸附形成亚胶束。纳克数量的重金属（例如，在pH 2 ~ 6条件下，将Ni、Cu、Cd、Pb等金属离子与吡咯烷二硫代氨基甲酸酯（APDC）反应，得到的疏水螯合物完全收集在胶束柱上。在双硫腙浸渍的胶束的情况下，痕量重金属立即从水中回收，而无需添加APDC。这些金属从柱上用稀硝酸解吸，留下SDS在柱上。该柱具有耐酸性胶束，可重复使用，并对腐殖酸类物质的分离行为进行了详细的考察。腐殖酸和富里酸在pH 1 ~ 9时完全吸附在胶束柱上。有趣的是，带负电荷的腐殖物质更容易吸附在阴离子表面活性剂的聚集体上，这表明腐殖物质与氧化铝颗粒的相互作用比SDS强。该方法简单、快速，已成功地应用于合成水样和标准物质的分析。

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.