Comparative analysis of dry ashing and wet digestion methods for the determination of trace and heavy metals in food samples

This study compared the dry ashing and wet digestion methods of processing food samples for elemental analysis. The concentrations of trace elements (manganese, iron, copper and zinc) and heavy metals (chromium, cadmium, lead and nickel) were determined in varieties of samples classified as fruits, leafy and fruity vegetables, tubers, legumes and cereals, obtained from Abeokuta, South-West, Nigeria. The metal concentrations were determined using atomic absorption spectrophotometer according to standard methods. The accuracy of the procedures was confirmed by spiking some samples and evaluating their recoveries. The metal levels evaluated were relatively higher in the dry-ashed samples than the wet-digested samples. However, the results showed non-significant differences in most data obtained after processing with the two methods. The dry ashing method is recommended for digestion of food items in these categories because: it involves lesser amount of chemical reagents and related hazards; it requires simple equipment and achieved better recovery.