Highly selective speciation and fluorimetric determination of Se(iv) in infant formulas using micelle-capped nile blue A

A simple and very selective spectrofluorimetric method for the detection of ng mL−1 levels of inorganic selenium species in infant formulas has been performed. It is based on the oxidation of micelle-capped nile blue A (MCNBA) by sodium selenite under neutral conditions (pH 7.0). A specific quenching of the fluorescence of MCNBA was observed and the response signals were linearly correlated with the concentration of sodium selenite over the ranges of 4.17 × 10−9 to 4.5 × 10−6 mol L−1 (0.73–787.1 ng mL−1). The limit of detection was 1.25 nmol L−1 (0.22 ng mL−1). Different parameters such as selectivity, recovery, linearity, limits of detection and quantification of the measurements were evaluated in order to validate the proposed method. Then, the new method was applied to the analysis of several infant formula samples with satisfactory results.