Differential determination of traces of arsenic (III) and arsenic (V) in water by flow injection on-line preconcentration-graphite furnace AAS

Abstract

A flow injection (FI) on-line preconcentration-graphite furnace atomic absorption spectrometric method was developed for the determination of traces of As^III and As^V in water. For an As^III determination, 2 ml of sample was mixed in a FI system with an ammonium pyrrolidinedithiocarbamate (APDC) solution; an As^III-PDC complex was formed. The complex was adsorbed on a C₁₈ silica gel microcolumn and then eluted with ethanol. The eluate zone containing the highest analyte concentration was injected into the graphite furnace via an autosampler nozzle. After the injection of a Pd matrix modifier solution, As^III was atomized. The determination of As^V was performed by the same FI system by replacing the APDC solution and ethanol with a Mo-Malachite Green (MG) solution and dimethylsulfoxide (DMSO), respectively. Four milliliters of the sample were mixed with a Mo-MG solution, and the resulting As^V-Mo-MG aggregate was adsorbed on the microcolumn and then eluted with DMSO. The eluate zone containing the highest analyte concentration was injected into a graphite furnace and atomized in the same way as in the As^III determination. The method was successfully applied to the determination of As^III and As^V in lake water. The sensitivity enhancement was about 20-fold for both 2 ml of an As^III solution and 4 ml of an As^V solution. The detection limits, based on three-times the standard deviation of six replicate measurements of a blank solution, were 0.042 and 0.017 μg l^-1 for As^III and As^V, respectively. The recoveries were 98±6.₅ and 98±6.₀%, and the sample throughputs were 15 and 12 samples per hour for As^III and As^V, respectively.