Determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in Milk, Cheese and Chocolate

Abstract

Combined analytical procedures consisting of wet digestion step followed by instrumental determination - differential pulse cathodic stripping voltammetry (DPCSV) or electrothermal atomic absorption spectrometry (ETAAS) - as well as a direct analysis method - slurry sampling ETAAS - for the determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in milk, cheese and chocolate are described and compared. Wet digestion using a mixture of HNO3-HClO4-H2O2 is proposed for complete matrix decomposition prior to trace analyte determination by DPCSV or ETAAS. A mixture of HNO3-H2O2 is used for slurry preparation. Optimal instrumental parameters for trace analyte measurements are presented. The reliability of the procedures has been verified by analyzing standard reference materials. Results obtained are in good agreement with the certified values and the relative standard deviations (for these results) are in the range 5-10 % for wet digestion DPCSV or ETAAS and 3-9 % for slurry sampling ETAAS in the range of 2mg g ˇ1 (Cd) to 12mg g ˇ1 Fast, sensitive, accurate and precise analytical meth- ods are required for daily quality control of milk and milk products. The importance of elements such as Cu, Cr and Fe is related to lipid oxidation involved in storage and processing (1). Serious attention is paid to the toxicological effects of other heavy metals such as Cd, Co, Ni and Pb in view of the importance of milk and its by-products in the diet of infants and children (2-4).