Sample homogenization procedure for determination of lead in canned foods

To improve the homogeneity of canned foods before Pb determination, composited samples or single can contents (150--500 g) are treated with an equal weight of dilute nitric acid, and then thoroughly blended in a high efficiency, probe-type Polytron homogenizer; subsamples are then either dry-ashed or wet-ashed in preparation for analysis. Within-can variability is reduced from the 20--50% coefficient of variation range obtained with conventional blending procedures to a coefficient of variation of less than 5% by using the proceudre described. Precision data for Pb, using both the probe-type and conventional blade-type homogenizers, are compared. The procedure described for Pb determination was used to analyze a number of canned products. Data indicate that the Polytron plus dilute acid procedure improves overall Pb homogeneity for subtle as well as severe initial Pb heterogeneity.