Comparison of closed-vessel and focused open-vessel microwave dissolution for determination of cadmium, copper, lead, and selenium in wheat, wheat products, corn bran, and rice flour by transverse-heated graphite furnace atomic absorption spectrometry.

A method is described for the determination of Pb, Cd, Cu, and Se in cereal samples. An atomic absorption spectrometer equipped with a transverse-heated graphite furnace with Zeeman background correction was used for all determinations. Sample preparation was performed by closed-vessel microwave digestion using nitric acid and focused openvessel microwave digestion using nitric acid-hydrogen peroxide. Both techniques were evaluated by using 15 cereal reference materials and comparing results with certified or reference values for each element. Cereal reference standards obtained from the Community Bureau of Reference (Europe), the National Institute of Standards and Technology (USA), the National Institute for Environmental Studies (Japan), the National Research Centre for Certified Reference Materials (People's Republic of China), and the Canadian Grain Commission were used. Application of a series of t-tests, conducted according to Sidak's modified Bonerroni t-procedure, showed that both techniques yielded accurate results for cereal reference materials. Some differences from certified and reference values, however, were found for each element.