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

Abstract

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 30mg poly(hydroxyethyl methacrylate) (PHEMA) micro beads, which is simply packed into a micro-pipette-tip. The adsorbed arsenic was quantitatively eluted by 700μL 0.25M NH3 and determined by graphite furnace atomic absorption spectrometry (GFAAS). Injection of larger volume (i.e., 50μL v.s. conventional 10–20μL) 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 25pg) and precision (RSD of 2.6%, c=10μgL−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 10ngL−1 As(III) with an enrichment factor of 86. The relative standard deviation and relative error for six replicate determinations of 0.5μgL−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 1.0μgL−1 As(III) and As(V), the recoveries varied between 96 and 100%.