Speciation analysis of As, Sb and Se in leachates of cementitious construction materials using selective solid phase extraction and ICP-MS

A solid phase extraction (SPE) method has been developed for the separation of As(III), Sb(III) and Se(IV) from As(V), Sb(V) and Se(VI) in leachates of cementitious construction materials. The leachates were treated with ammonium pyrrolidine dithiocarbamate (APDC) and the APDC complexes of As(III), Sb(III) and Se(IV) were retained on a non-polar (C-18) sorbent, whereas As(V), Sb(V) and Se(VI) passed through. The SPE method was optimized in a multivariate approach: the effect of sample pH, APDC concentration, mixing time and sample percolation rate on the extraction of the analyte species was studied, and the optimum conditions of the significant parameters, i.e. sample pH and APDC concentration, were identified and experimentally verified. The two oxidation states of the elements can be separated using the SPE method from solutions of pH 3-8 (As), pH 4-10 (Sb) and pH 3-9 (Se) treated with 0.08% (w/v) APDC. The effect of matrix interferences was studied and the use of benzene sulfonate to remove interfering matrix metal ions by ion-pair SPE was demonstrated. The limit of detection of As(V), Sb(V) and Se(VI) by ICP-MS was 0.09, 0.14 and 0.37 mu g L-1, respectively. A condition was established for the preconcentration of As(III), Sb(III) and Se(IV) by elution with 3.0 M HNO3 in a back-flushing mode. With a preconcentration factor of 50, concentrations of As(III), Sb(III) and Se(IV) down to 1 6 ng L-1 could be detected using the SPE method in combination with ICP-MS. The SPE method was validated using spike recovery tests, and was used to determine the oxidation states of the target elements in leachates of a concrete material. As(V), Sb(V) and Se(VI) were found to be the major species in most of the leachates.