Photolytic oxidation of As species for determination of total As (including the 'hidden' As fraction) in coastal seawater by hydride generation-atomic fluorescence spectrometry

摘要

Ultraviolet irradiation (photolysis) in alkaline medium was applied for pretreatment of seawater samples so as to accurately determine total As by continuous-flow hydride generation-atomic fluorescence spectrometry. This sample pretreatment is meant to convert non-reducible As forms into inorganic As, which easily forms arsine. The optimised parameters were the treatment time and the pH of the medium. The behaviour of four hydride-reactive As species [As(III), As(V), MMA, DMA], and AsB, i.e. a typical non-hydride-reactive As species, when subjected to UV irradiation was studied. UV irradiation at pH I lead to conversion of all species into As(V) with the exception of AsB and DMA. Conversions of DMA and AsB into As(V) at pH I I in less than 30 min were observed under UV irradiation. The limit of detection of As (measured as As(V)) by hydride generation-atomic fluorescence spectrometry was 0.1 mu g/L and the repeatability of the oxidation procedure was about 10%. The method was applied to determination of total and directly reducible As at I I sampling points of the Galician Coast (Atlantic Ocean, Spain). Total As concentrations were in the range 1.4-4.8 mu g/L. A significant As fraction, between 20 and 44%, depending on the sampling point, corresponded to non-reducible As which was converted by UV irradiation into hydride-reactive As. This fraction should represent the sum of DMA, which yields a low sensitivity in the continuous flow-AFS system, and the hidden As fraction. (c) 2006 Elsevier B.V. All rights reserved.