Determination of Cr, Cu and Pb in industrial waste of oil shale using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample analysis

Abstract

Industrial waste of oil shale can be used to correct soil acidity and in the production of fertilizers and agricultural inputs. However, it may contain potentially toxic elements. Analytical lines at 360.532 nm, 327.396 nm and 283.306 nm for Cr, Cu and Pb, respectively, were used in the development of methods for these analytes, using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample analysis, with evaluation of the center pixel and an argon gas flow rate of 0.1 L min⁻¹ for Cr atomization in order to reduce the sensitivity of the determination. Pyrolysis and atomization temperatures for Cr were 1500 °C and 2500 °C, respectively and, for Cu, they were 900 °C and 2400 °C, both without the use of a chemical modifier. For Pb, pyrolysis and atomization temperatures were 900 °C and 1900 °C, respectively, using Ru as a permanent chemical modifier, and a Pd/Mg mixture as a chemical modifier in solution was injected over the solid sample prior to every determination. Molecular absorption due to the diatomic molecule CS was observed for the determination of Pb, which, however, did not cause any spectral interference when only the center pixel was evaluated. The characteristic mass for Cr, Cu and Pb was 25 pg, 19 pg and 24 pg, respectively. The limits of detection and quantification obtained were 102 μg kg⁻¹ and 342 μg kg⁻¹ for Cr, 39 μg kg⁻¹ and 130 μg kg⁻¹ for Cu and 28 μg kg⁻¹ and 92 μg kg⁻¹ for Pb, respectively. The accuracy of the methods was verified by the analysis of seven certified reference materials and the values found were in agreement (Student's t-test) with the certified values.