Submitted to: Spectrochimica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 1996
Publication Date: N/A
Interpretive Summary: Results from a recent international collaborative study on solid sampling indicated that collaborators had the most difficulty in determining trace elements in a high density glass sample. Analyses were done using ultrasonic slurry sampling and that technology was developed in the Food Composition Laboratory (FCL) and Perkin-Elmer now has an exclusive license to market an autosampler accessory which allows analysts to analyze solid material prepared as slurries or suspensions. Collaborators reported results which on average were 20% lower than the certified Cr concentration and some reported results which were almost 50% low. A careful evaluation of the physical properties of the glass was conducted at FCL and density and particle size information were generated. A systematic evaluation of analysis parameters was also done in an effort to see what the most likely source of low values was. The data suggest that sedimentation errors are the cause of low values. This study provided guidelines for sampling depths for high density materials and highlighted the possibility of minimizing sedimentation errors by grinding samples further to reduce particle sizes to <38 m. This study will prove useful to any analysts interested in performing slurry analyses and will also prove useful to Perkin-Elmer Corp. who is marketing the USS-100 ultrasonic slurry sampling accessory.
Technical Abstract: A high density borosilicate glass reference material was distributed to collaborators participating in a collaborative study to evaluate the state-of-the-art of solid sampling. Several collaborators reported low values for Cr in the glass material, US Geological Survey GSD, as compared to the reference concentration of 46.5 +/- 9.2 g/g. On average, results were 20% low as compared to the mean reference concentration but some labs reported results which were nearly 50% low. As a result, the glass sample was evaluated and it's physical properties characterized including particle size distribution and density. Also a systematic evaluation of analysis parameters was conducted including: slurry preparation, analysis volume, pipetting accuracy, and sampling depth. The data suggest that the low analytical values are most likely the result of sedimentation errors with this high density (2.6 g/cm3) material. Studies suggest that an optimum sampling depth for this high density material is approximately 10 mm below the surface. The feasibility of reducing particle size by grinding the glass material to a particle size of <38 m to allow sampling at a range of depths is also demonstrated.