Redox speciation analysis of antimony in soil extracts by hydride generation atomic fluorescence spectrometry

Abstract

A sensitive atomic spectrometric method for the redox speciation analysis of antimony in soils is described. The method is based on the selective generation of stibine from Sb(III) in a continuous flow system using atomic fluorescence spectrometry for detection. Sb(V) is masked by citric or oxalic acid in HCl medium. The procedure was optimized with synthetic solutions of Sb(III) and Sb(V). The effect of carboxylic acid and HCl concentration on the recovery of Sb(Ill) and Sb(V) species from standard solutions, and on the fluorescence signal were studied. Both species were extracted from soil with H2O, 0.05 mol l(-1) EDTA and 0.25 mol l(-1) H2SO4. Since the soil samples were collected from sites impacted by copper mining activities, the effect Of Cu2+ on the determination of antimony in synthetic solutions and soil extracts was studied. Cu2+ decreased the Sb(III) signal, but had no effect on the total antimony determination. Therefore, the selective determination of Sb(III) was carried out in citric acid-HCl medium, using the analyte addition technique. Total antimony in soil extracts was determined using the standard calibration technique after reducing Sb(V) to Sb(III) at room temperature with KI-ascorbic acid. The Sb(V) concentration was calculated from the difference between total antimony and Sb(III). The limits of detection (PS Analytical, Excalibur Millennium model) were 17 and 10 ng l(-1) for Sb(III) and total antimony, respectively, and the R.S.D. at the 0.5-mug l(-1) level were 2.5 and 2.4%, respectively. The total antimony concentration of soils is in the mg kg(-1) range; the Sb recovery from the different soils by the extracting solutions was between less than 0.02% and approximately 10%. Similar recoveries were obtained using EDTA and sulfuric acid solutions. Sb(V) was found to be the main antimony species extracted from soils.