Slurry sampling electrothermal atomic absorption spectrometry as screening method for chromium in compost

Progress in direct solid sampling analysis using line source and high-resolution continuum source electrothermal atomic absorption spectrometry

The literature about direct solid sample analysis of the past 10-15 years using electrothermal atomic absorption spectrometry has been reviewed. It was found that in the vast majority of publications aqueous standards were reported as having been used for calibration after careful program optimization. This means the frequently expressed claim that certified reference materials with a matrix composition and analyte content close to that of the sample have to be used for calibration in solid sample analysis is not confirmed in the more recent literature. There are obviously limitations, and there are examples in the literature where even calibration with certified reference materials did not lead to accurate results. In these cases the problem is typically associated with spectral interferences that cannot be corrected properly by the systems available for conventional line source atomic absorption spectrometry, including Zeeman-effect background correction. Using high-resolution continuum source atomic absorption spectrometry, spectral interferences become visible owing to the display of the spectral environment at both sides of the analytical line at high resolution, which makes program optimization straightforward. Any spectrally continuous background absorption is eliminated automatically, and even rapidly changing background absorption does not cause any artifacts, as measurement and correction of background absorption are truly simultaneous. Any kind of fine-structured background can be eliminated by "subtracting" reference spectra using a least-squares algorithm. Aqueous standards are used for calibration in all published applications of high-resolution continuum source atomic absorption spectrometry to direct solid sample analysis.

Mobilization and speciation of chromium in compost: a methodological approach

An integral approach to study the mobility of chromium in compost is presented. The approach is based on batch pH dependence leaching tests and the analysis of the leachates for total chromium, chromium(VI) and complexes of chromium(III) with natural organic matter. As leachings are performed with no aggressive reagents (ultrapure water with added nitric acid or potassium hydroxide), the method can be considered a good approach to simulate natural scenarios. The analysis of leachates is complemented with the determination of total chromium and total Cr(VI) in the solid sample. Speciation analysis are done by high performance liquid chromatography with inductively coupled plasma mass spectrometry as detection technique; Cr(VI) is determined by ion chromatography, whereas Cr(III) complexes with natural organic matter by size exclusion chromatography. In the compost studied, Cr(VI) accounted for 6% of the total chromium in the solid, whereas no significant amounts of Cr(VI) were mobilized in the pH range studied (4-10). Chromium is mobilized as Cr(III) bound to organic matter, both to humic and fulvic acids, with an increasing contribution of humic acids at higher pHs.