Slurry sampling of sediments and coals for the determination of Sn by HG-GF AAS with retention in the graphite tube treated with Th or W as permanent modifiers.

Abstract

A method for the determination of Sn in slurry samples of sediment and coal by hydride generation graphite furnace electrothermal atomic absorption spectrometry (HG-GF AAS) is proposed. The slurries were prepared by mixing the ground sample (particle size < or =50 microm) with 2.0 mol L(-1) HCl for the sediment samples or with 2.0 mol L(-1) HCl+1.0% v/v HF in a saturated boric acid medium for the coal samples. The slurry was placed in an ultrasonic bath for 30 min, before and after standing for 24 h, with occasional manual stirring. The graphite tube was treated with 0.5 mg of Th or W as a permanent modifier. Sn determination was carried out by electrothermal atomic absorption spectrometry at the optimized retention temperatures of 450 and 300 degrees C for Th and W treatment, respectively. With this coupling, kinetic interference in the formation of the hydrides is avoided, and excellent detection limits can be obtained by using peak height. For the chemical vapor generation device, an optimized volume of 2 mL of sample slurry and an optimized NaBH4 concentration of 5% m/v were employed. The vapor produced was transported and retained on the graphite tube surface, which was further heated for Sn atomization. The accuracy of the method was verified by analyzing five certified sediments and three coals. By using the external calibration against aqueous standard solutions, the results obtained were in agreement with the certified values only for the sediment samples. For the coal samples, an addition calibration curve, obtained for one certified coal, was necessary to achieve accurate results. The obtained limits of detection were 0.03 microg g(-1) for sediment and 0.09 microg g(-1) for coal with Th as permanent modifier. The relative standard deviations were lower than 15%, demonstrating an adequate precision for slurry analysis. Sediment and coal samples from Santa Catarina, Brazil, were also analyzed.