Submitted to: Journal of Analytical Atomic Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 24, 1996
Publication Date: N/A
Interpretive Summary: The direct analysis of solid materials without a time consuming dissolution process is very desirable. Dr. Miller-Ihli developed an ultrasonic slurry sampling device and the Perkin-Elmer Corp. developed this into a commercial product (USS-100) and USDA has granted them an exclusive license. An international collaborative study was designed to evaluate all different types of approaches for the direct analysis of solids. This manuscript reports on the second phase of the study and all but one collaborator used ultrasonic slurry sampling for their analyses. Benefits and limitations of slurry sampling are highlighted. Overall performance was excellent with an average accuracy of 100 +/- 7% for the 3 elements determined in a wide range of materials. The most problematic samples were those which were high density where sedimentation errors led to low values. Colleagues in industry, academia, and government participated in this study and the wide range of expertise combined with the good results suggests that ultrasonic slurry sampling is a sufficiently mature technique that it can be used for applications analyses. This approach is useful for biological, botanical, and environmental samples and minimizes the risk of sample contamination and analyte loss while saving time.
Technical 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, 8 of which reported complete enough sets of data to be considered. Each collaborator was sent 4 powdered materials and 1 pre-made slurry for analysis. Cu, Cr, and Pb were determined in the various samples. 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. Based on the mean reference concentration for the various analytes in the reference materials analyzed, the average performance for all labs 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.