Arsenic speciation in water and snow samples by adsorption onto PHEMA in a micro-pipette-tip and GFAAS detection applying large-volume injection.

A miniaturized solid phase extraction procedure has been developed for ultra-trace determination of inorganic arsenic species. Arsenic(III) as pyrrolidinedithiocarbamate complex was selectively adsorbed on 30 mg poly(hydroxyethyl methacrylate) (PHEMA) micro beads, which is simply packed into a micro-pipette-tip. The adsorbed arsenic was quantitatively eluted by 700 μL 0.25 M NH(3) and determined by graphite furnace atomic absorption spectrometry (GFAAS). Injection of larger volume (i.e., 50 μL v.s. conventional 10-20 μL) eluent into graphite furnace and the use of Mg(NO(3))(2) as chemical modifier have improved atomic absorption signal intensity (sensitivity as characteristic mass of 25 pg) and precision (RSD of 2.6%, c=10 μg L(-1), n=11). Total arsenic amount was determined after reduction of arsenic(V) to arsenic(III) by thiourea-HCl system. As(V) concentration was calculated by the difference between As(III) and total arsenic. The detection limit (3s) of the method was found as 10 ng L(-1) As(III) with an enrichment factor of 86. The relative standard deviation and relative error for six replicate determinations of 0.5 μg L(-1) As(III) were found to be 4.0% and -0.7%, respectively. The method was successfully applied to drinking water, snow and reference water (SEM-2011) samples. When the samples were spiked with 0.5 and 1.0 μg L(-1) As(III) and As(V), the recoveries varied between 96 and 100%.