Resumo:
High-resolution continuum source graphite furnace atomic absorption spectrometry, because of the use of only one radiation source for all elements, offers the possibility of sequential determination of two or more elements from the same sample aliquot if their volatilities are significantly different. Cd and Cr were determined sequentially in samples of biomass and biomass ashes employing direct solid sample analysis. The use of a chemical modifier was found to be not necessary, and calibration could be carried out using aqueous standard solutions. A pyrolysis temperature of 400 °C and an atomization temperature of 1500 °C were used for the determination of Cd; no losses of Cr were observed at this temperature. After the atomization of Cd the wavelength was changed and Cr atomized at 2600 °C. The limits of detection (LOD) and quantification (LOQ) were 1.1 μg kg−1 and 3.7 μg kg−1, respectively, for Cd and 21 μg kg−1 and 70 μg kg−1, respectively, for Cr using the most sensitive line at 357.869 nm, or 90 μg kg−1 and 300 μg kg−1, respectively, using the less sensitive line at 428.972 nm. The precision, expressed as relative standard deviation was around 10%, which is typical for direct solid sample analysis. The values found for Cd in biomass samples were between <1.1 µg kg−1 and 789 µg kg−1, whereas those for Cr were between 7.9 mg kg−1 and 89 mg kg−1; the values found in the ashes were significantly lower for Cd, between <1.1 µg kg−1 and 6.3 µg kg−1, whereas the trend was not so clear for Cr, where the values were between 3.4 mg kg−1 and 28 mg kg−1.
