Evaluation of two sample preparation methods for the determination of cadmium, nickel and lead in natural foods by graphite furnace atomic absorption spectrophotometry

Environmental pollution allows heavy metals to interact with ecosystems, bioaccumulating and passing through the food chain. Animals and humans can consume contaminated species and reach toxic and harmful concentrations in their organisms. While there are international regulatory frameworks for heavy metal contents, these are not always known or suitable for local conditions. This situation calls for the development of locally-applicable analytical methods for the determination of heavy metal concentrations in common vegetal and animal food products. Two established methods (AOAC 999.11, based on sample drying and calcination, and IPN AC-06-00, based on microwave-assisted acid digestion) were comparatively tested at the CESAQ-PUCE laboratory in Quito, Ecuador, to determine their suitability. Sample matrices used were non-industrial, non-organic tomato, lettuce, and beef commonly found in local markets. Heavy metals tested were cadmium, nickel, and lead. Test guidelines and comparative parameters were based on AOAC (2002) and included quantification limits, repeatability variation coefficients, intermediate precision percentages, accuracy and calculated expanded uncertainties. Unlike method AOAC 999.11, method IPN AC-06-00 performance for all parameters was within the range of recommended expected values as per AOAC, and was therefore deemed more suitable to be applied under the local CESAQ-PUCE laboratory conditions. The validation of method IPN AC-06-00 demonstrated its local applicability. In addition, IPN AC-06-00 can be used by similar laboratories to assess contaminants concentrations and improve the baseline information concerning human exposure to toxic metals.