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 NH3 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(NO3)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 (3 s) 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%.

► PHEMA microbeads in a micro-pipette-tip as solid phase enhances the advantages of SPE.
► “Large-volume sample injection” increases sensitivity and precision in GFAAS.
► The developed method integrates the advantages of two approaches for As speciation.