Alternative extraction methods for arsenic speciation in hair using ultrasound probe sonication and pressurised liquid extraction

Abstract

The methods for arsenic speciation in hair currently available are scarce and highly time consuming, especially during sample preparation. This work presents alternative methods providing better recoveries and similar species distribution compared with established methods, but the extraction time is reduced from about 6 h to only a few minutes. First, several extraction media were studied and evaluated using ultrasound probe sonication. Either a solution of 0.5% performic acid or an enzymatic treatment (mixture of lipase and protease in aqueous media) was selected as the best treatment, which allowed us to reduce the extraction time to 5 or 10 min, respectively, achieving a slightly higher species recovery in the latter case. Second, a laboratory-made miniaturised device for pressurised liquid extraction is employed and compared with the previous methods. Initially, temperature, pressure and extraction time were optimised by applying chemometrics, in particular the use of a multivariate experimental design and analysis of variance. In order to improve the obtained results, additional variables such as type of solvent, particle size of dispersant medium and number of extraction cycles were further optimised. Optimum conditions were obtained using a mixture of 1% SDS and 5% isopropanol as extraction solvent at a temperature of 125 °C and an applied pressure of 6 MPa for two cycles of 5 min each. The optimal particle size of dispersant was 35 μm. Total arsenic was determined by ICP-MS and the species present in hair were quantified by HPLC-ICP-MS. For method validation a certified reference material (Human Hair GBW 07601) was used all throughout this study.