Collaborative study of a graphite-furnace atomic-absorption screening method for the determination of lead in infant formulas

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Abstract
Blind duplicates of three infant formulas and one evaporated milk were analysed by nine laboratories. Lead levels in the samples ranged from 29 to 200 ng g–1. Only one of the laboratories obtained good agreement with reference values for all samples; two laboratories were outliers. Analysis of the data indicated that the remaining laboratories had instrumentation problems, the main cause of which was inadequate simultaneous background correction. The mean over-all sample reproducibility (relative standard deviation; RSD) was 66.8% for the data as submitted and 18.7% after adjustment for background correction. The mean precision between blind duplicates was 38.9%(RSD) for the submitted data and 6.6% after adjustment and rejection of statistical outliers. The results imply that for matrices and elements for which moderate (0.2 absorbance unit) non-specific background can be expected, most laboratories with conventional background correctors will have difficulty in obtaining accurate results using graphite-furnace atomic-absorption spectrometry.

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