Utilization of W/Mg(NO3)2 modifiers for the direct determination of As and Sb in soils, sewage sludge and sediments by solid sampling electrothermal atomic absorption spectrometry

A simple method has been developed for the determination of arsenic and antimony in environmental samples by solid sampling electrothermal atomic absorption spectrometry, which was validated using certified reference materials of soils (S-VM - Soil Eutric Cambisol; S-MS - Soil Orthic Luvisols; S-SP - Soil Rendzina), sewage sludge (WT-L; WT-M) and sediments (NIES2; GBW07906). The analytical procedure combines solid sampling with utilization of a matrix modifier admixture containing 5 μg of W and 5 μg of Mg. The tungsten in the admixture serves to stabilize the solid matrix during atomisation, which results in dramatically reduced non-specific absorption compared with the conventional palladium modifier. Magnesium was efficient in reducing the accumulation of the matrix residue on the platform. An alternative resonance line of 197.2 nm for arsenic and 206.8 nm for Sb was used in order to eliminate the spectral interferences caused by aluminum compounds, and silicon and iron compounds, respectively. Under optimized experimental conditions, the effective in situ analyte/matrix separation was achieved so that the use of aqueous standards for calibration became possible. With the modifier, a 3 SD detection limit of 0.5 μg g-1 As and 0.1 μg g-1 Sb and 10 SD quantification limit of 1.7 μg g-1As and 0.3 μg g-1 Sb and a characteristic mass of 65 pg As and 53 pg Sb were obtained. For all the matrices under scrutiny, a good agreement with certified values was achieved with RSD values less than 10%.