Simultaneous determination of arsenic and selenium species in phosphoric acid extracts of sediment samples by HPLC-ICP-MS

A new method for the multielemental determination of arsenic and selenium species in sediment extracts is detailed. Anion exchange separation of As(III), As(V), DMA, MMA, Se(IV) and Se(VI) coupled to ICP-MS detection was accomplished in 10 min on a Hamilton PRP-X100 column with step gradient of a NH4H2PO4 based mobile phase (pH = 6). The extraction procedure used 1 g of dry sediment and 12.5 mL of phosphoric acid. One hour of extraction time (end-over-end shaking) and an acid concentration of 0.3 M were regarded as optimum. The estimated detection limits in the sediment ranged between 2 and 40 ng g(-1) for the species analysed. Precision, determined at two levels of concentration showed values of coefficient of variation below 20% for the low level (near the LOD) and below 10% for the high level (10 times the low level). Accuracy of the method was assessed through calculation of the recovery of the spiked sediment. Recoveries ranged between 80 and 120% for all the species analysed with the exception of As(III). This low recovery was thoroughly studied and explained through a conversion process of As(III) into As(V) by an air-oxygen oxidation mechanism during the drying step. The method was regarded as suitable for the proper assessment of the potential toxicity of the sediment. (C) 2004 Elsevier B.V. All rights reserved.