Determination of Cd and Cr in tannin samples by high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample sequential analysis (HR-CS SS-GF AAS)

Abstract

A fast and reliable analytical method for the sequential determination of Cd and Cr in tannin samples by high-resolution continuum source graphite furnace atomic absorption spectrometry with direct solid sampling from the same sample aliquot (HR-CS SS-GF AAS) is proposed. A pyrolysis temperature of 400 °C and atomisation temperature of 1500 °C were used for the determination of Cd; no losses of Cr were observed at these temperatures. After the atomisation of Cd, the wavelength was changed and Cr was atomised at 2500 °C. Several studies with different modifiers were performed, but no chemical modifier was needed. Calibration was achieved using aqueous standards. The linearity of the response, performed by evaluating the absorbance value relative to the sample mass, was investigated as well. Relative standard deviation (RSD) values lower than 15% were found, which are acceptable for direct analysis. The parameters of merit were: a characteristic mass of 0.3 pg and 2.2 pg for Cd and Cr, respectively; the limit of detection (LOD) of 0.5 μg kg⁻¹ and 17 μg kg⁻¹ for Cd and Cr, respectively; the limit of quantification (LOQ) of 2 μg kg⁻¹ and 57 μg kg⁻¹ for Cd and Cr, respectively. The accuracy was validated by analysing three certified reference materials (tea, pine needles and bush branches). The results were not statistically different from the certified values at a 95% confidence level. Therefore, calibration using aqueous standards is suitable for this application. This method is simple, fast and suitable for routine analysis.