Effect of coexisting metals on determination of lead and cadmium in the plastic materials test of the Japanese Food Sanitation Law

The effect of coexisting metals in a sample on the determination of lead and cadmium in plastics used for food contact materials was investigated. In the official method specified in the Japanese Food Sanitation Law, contents of lead and cadmium are determined by a dry incineration method using sulfuric acid. It was assumed that sometimes, coexisting metals in a sample may form insoluble sulfate and that lead sulfate might be adsorbed into the insoluble sulfate. Therefore, hydrochloric acid was added to the ash, to turn formed insoluble sulfate into soluble compounds (HCl addition method). We found that recoveries of cadmium were not affected in the presence of other metals except when calcium exceeded 20 mg/g in both methods. Recoveries of lead decreased in the presence of barium exceeding 0.1 mg/g or calcium exceeding 10 mg/g in the official method. However, improvement of recoveries was achieved with the HCl addition method and by reducing the sample amount to one-tenth (0.1 g) of that specified in the official method.