Determination of Trace Elements in Whole Milk by PIXE

The potential presence of toxic metals in food is being recognized as a priority by international food standards organizations, and constitutes an analytical challenge. In this work the PIXE method has been applied to study the trace element content in milk. In order to increase sensitivity the following procedure was developed for element concentration: raw milk samples were lyophilized, dry ashed, diluted in nitric acid (65%) and further pre-concentrated with carbamates. Quantitative determination of the recovery factor, reproducibility and confidence intervals were made by analyzing a certified standard reference (Whole Milk NIST 8435). Elements such as Fe, Cu, Zn and Pb were recovered with a factor close to 100%. For elements such as Se the recovery factor was close to 50%. After evaluating the method we used it to determine the trace element content of milk samples collected from Mixquiahuala, Hidalgo State in Mexico. Mixquiahuala is located in a valley that has been irrigated with wastewater from Mexico City for more than 50 years. We focused our study to the difference in trace elements of milk from cows fed with a commercial formula and with local corn and alfalfa. Lead and cupper were significantly higher, while Zn was significantly lower in the first group. Elements such as Fe, Ni and Se were similar in both groups.