Flow Injection On-Line Sorption Preconcentration Coupled with Hydride Generation Atomic Fluorescence Spectrometry for Determination of (Ultra)trace Amounts of Arsenic(III) and Arsenic(V) in Natural Water Samples

Abstract

A flow injection on-line sorption preconcentration and separation in a knotted reactor (KR) was coupled to hydride generation atomic fluorescence spectrometry (HG-AFS) for speciation of inorganic arsenic in natural water samples. The method involved on-line formation of the As(III)−pyrrolidinedithiocarbamate (PDC) complex over a sample acidity of 0.001−0.1 mol L^-1 HCl, its adsorption onto the inner walls of the KR made from 150-cm long × 0.5-mm i.d. PTFE tubing, elution with 1 mol L^-1 HCl, and detection by HG-AFS. Total inorganic arsenic was determined after prereduction of As(V) to As(III) with 1% m/v L-cysteine. The concentration of As(V) was calculated by the difference of the total inorganic arsenic and As(III). A 1 mol L^-1 concentration of HCl was employed not only as the efficient eluent but also as the required medium for subsequent hydride generation. Potential factors that affect adsorption, rinsing, elution, and hydride generation were investigated in detail. The low cost, easy operation, and high sensitivity are the obvious advantages of the present system. With consumption of a 6 mL sample solution, an enhancement factor of 11 and a detection limit (3s) of 0.023 μg L^-1 As(III) were obtained at a sample throughput of 32 h^-1. The precision for 14 replicate measurements of 1 μg L^-1 As(III) was 1.3% (RSD). The recoveries from natural water samples varied from 96.7 to 105% for 2 μg L^-1 of As(III) spike and from 97.1 to 107% for 2 μg L^-1 of As(V) spike. The analytical results obtained by the present method for total arsenic in the certified reference materials, SLRS-4 (river water) and NASS-5 (seawater), agreed well with the certified values. The developed method was also successfully applied to the speciation of inorganic arsenic in local natural water samples.