An evaluation of analytical techniques for determination of lead, cadmium,chromium, and mercury in food-packaging materials

Closed microwave digestion and a high-pressure asher have been evaluated fo r wet-oxidation and extraction of lead, cadmium, chromium, and mercury from a range of typical packaging materials used for food products. For the hig h-pressure asher a combination of nitric and sulfuric acids was efficient f or destruction of a range of packaging materials; for polystyrene, however, nitric acid alone was more efficient. For microwave digestion, a reagent c ontaining nitric acid, sulfuric acid, and hydrogen peroxide was used for al l materials except polystyrene. Use of the high-pressure asher resulted in the highest recoveries of spiked lead (median 92%), cadmium (median 92%), c hromium (median 97%), and mercury (median 83%). All samples were spiked bef ore digestion with 40 mug L-1 Cd, Cr, and Pb and 8 mug L-1 Hg in solution. The use of indium as internal standard improved the accuracy of results fro m both ICP-MS and ICP-AES. Average recovery of the four elements from spike d packaging materials was 92 +/- 14% by ICP-MS and 87 +/- 15% (except for m ercury) by ICP-AES. For mercury analysis by CVAAS, use of tin(II) chloride as reducing agent resulted in considerably better accuracy than use of sodi um borohydride reagent.