Tungsten Permanent Chemical Modifier for Fast Estimation of Se Contents in Soil by Graphite Furnace Atomic Absorption Spectrometry

A tungsten carbide coating on the integrated platform of a transversely heated graphite atomizer was used as a modifier for the direct determination of Se in soil extracts by graphite furnace atomic absorption spectrometry. Diethylenetriaminepentaacetic acid (0.0050 mol L-1) plus ammonium hydrogencarbonate (1.0 mol L-1) extracted predominantly available inorganic selenate from soil. The formation of a large amount of carbonaceous residue inside the atomizer was avoided with a first pyrolysis step at 600 °C assisted by air during 30 s. For 20 μL of soil extracts delivered to the atomizer and calibration by matrix matching, an analytical curve (10.0−100 μg of L-1) with good linear correlation (r = 0.999) between integrated absorbance and analyte concentration was established. The characteristic mass was ∼63 pg of Se, and the lifetime of the tube was ∼750 firings. The limit of detection was 1.6 μg L-1, and the relative standard deviations (n = 12) were typically