Slurry Sampling Electrothermal Atomic Absorption Spectrometry: Results From the Second Phase of an International Collaborative Study

Abstract

The second phase of an international collaborative study designed to evaluate the current state-of-the-art for solid sampling was completed. Samples were sent to more than 20 laboratories who participated in the first phase, eight of which reported complete enough sets of data to be considered. Each collaborator was sent four powdered materials and one pre-made slurry for analysis. Different elements were determined in the various samples including Cu, Cr, and Pb. Average performance for all elements determined in all materials was excellent with the overall mean concentrations±uncertainties computed for all collaborators overlapping the reported reference ranges in all instances. Some of the laboratories demonstrated consistently good expertise whereas others utilized analysis conditions which led to poorer performance. Based on the mean reference concentration for the various analytes in the reference materials analyzed, the average performance for all laboratories was 100±7% and the range of recoveries was 78–107%. The importance of using secondary wavelengths and the importance of using sufficiently large amounts of solid to be representative of the bulk material is demonstrated. Possible problems affecting analytical accuracy are discussed, including the use of mini-flows, inappropriate amounts of matrix modifier, high thermal pretreatment temperatures, low atomization temperatures, short atomization and/or read times, expulsion losses, inadequate background correction and sample sizes which were too small. The effect of sedimentation errors due to high density materials is discussed. Analytical results for a pre-made slurry were not found to be significantly different from results for slurries of the same material which were prepared by the collaborators. Data are presented which show that analyte extraction into the liquid phase of the slurry is not a prerequisite for accurate slurry analyses.