Comparison of three digestion methods for determination of lead and cadmium in milk and dairy products

Background: Toxic metals enter the human food chain through water, soil, and plants. High consumption of dairy products makes it necessary to measure their concentrations in milk and its products. Methods: In this study, four samples of dairy products, including milk, dough, yogurt, and cream were selected. They were spiked with concentrations of 0, 20, 40, and 60 μg/kg of lead (Pb) and cadmium (Cd) separately. In all samples, the concentration of these metals was determined using graphite furnace atomic absorption spectroscopy (GFAAS) after microwave, wet, and dry ashing digestion methods. To select the best digestion method, recovery percentage, linearity of increasing concentrations, relative standard deviation (RSD), and the limit of detection were used. Results: According to the results, the RSD of all measurements was less than 5%. The instrument detection limit for Pb and Cd were 0.188 and 0.157 μg/L, respectively. The recovery efficiency of all digested samples by three methods was between 75.7% and 120%. According to the linearity index and R2, the microwave digestion method with 90 to 110% efficiency was the best for Pb-spiked samples, and the dry digestion method was the best for Cd-spiked samples. Conclusion: Considering all indexes, microwave digestion was the best method for Pb and Cd samples.