Effectiveness of microwave based digestion procedures for the demineralization of human milk and infant formulas prior to fluorometric determination of selenium.

The use of two types of microwave oven, one domestic (A) and the other specially designed for laboratory (B) for microwave-based digestion, to destroy the organic matter in milk and infant formulas prior to fluorometric determination of selenium is studied in order to check their applicability and reliability. In both systems the best results were obtained using the acid mixture HNO3-H2O2, and additional treatment with perchloric acid (60%) in a Thermoblock. The application of two different microwave-based digestion procedures to infant formulas was free of interferences. In the case of human milk, it was necessary to use the standard addition method. Values obtained for detection and quantification limits, precision and accuracy of the fluorometric determination of selenium show the usefulness of both digestion procedures. The oven designed for laboratory use (B) is preferential as it permits simultaneous digestion of eight samples.