Sampling procedure and determination of lead in canned foods

A method is presented for improving within-can homogeneity and simplifying the determination of lead in canned foods. The entire content of a canned food product is blended with 2N HNO3 and allowed to stand 16 h; then the sample is again blended and a subsample is taken. The subsample is digested by wet ashing using nitric acid-perchloric acid or nitric acid-sulfuric acid-hydrogen peroxide. The pH of the sample is adjusted with ammonium hydroxide, and the lead is extracted into butyl acetate as the pyrrolidinecarbodithioate complex. Lead concentration is determined by flame atomic absorption spectrometry. Recoveries of lead ranged from 92 to 104% for added 100-mesh lead particulate. Within-sample variability for green beans was reduced from 37% obtained with blending alone to 3.7% using the proposed procedure at the 3.1 micrograms/g added lead level. Variability was 7.6% at the 0.68 microgram/g level and 16.4% at the 0.20 microgram/g level of added lead. The use of nitric acid-sulfuric acid-hydrogen peroxide for digestion has the advantage of not forming a precipitate during the neutralization step, as occurs when nitric acid-perchloric acid is used for dissolution.