Methods of analysis used for the determination of selenium in milk and infant formulae: a review

Selenium (Se) occurs naturally in a range of oxidation states as volatile species or analogues of organic sulphur compounds. Over a narrow concentration range (< 4 mg/day), selenium is an essential element for growth of animals and man. However at higher concentrations (>3 mg/day) it possesses toxicological properties. Low levels of the element in most foods including milk and infant formulae require a sampling procedure to be followed and the use of certified reference material. Accurate quantitative analysis is dependent on the initial digestion stage of the food matrix and the reduction of Se(VI) to Se(IV) in the final determination. In view of the difficulty in obtaining some reagents (e.g. 2,3-diaminonapthalene), alternative procedures to the classical fluorometric technique need to be evaluated. Methods for the determination of Se are described detailing detection limits, sensitivity, interferences and matrix-related problems.