Improved molecular fluorescence method for the determination of selenium in biological samples

Abstract

A procedure for the determination of selenium in whole blood and urine has been improved by optimization of the digestion and derivatization procedures. An overnight pre-digestion step with 4 + 1 concentrated nitric–perchloric acids reduced the time of mineralization at 170 °C from 4 h to 30–45 min. Conversion of all the selenium to selenite (Se^IV) was optimized by addition of 1 ml of concentrated hydrochloric acid, with heating to 100 °C for 30 min. The rate of formation of the 2,3-diaminonaphthalene (DAN) complex of selenium was improved by heating to 70–100 °C for a minimum of 30 min. Co-addition of hexane during derivatization simplified the extraction procedure. The modified method was applied successfully to the analysis of Seronorm quality control whole blood and urine (83 and 24 µg l^–1 Se, respectively). Samples from 12 healthy adults, gave results in expected ranges (mean concentrations of 75 ± 8 µg l^–1 in blood and 25 ± 8 µg l^–1 in urine). The structure of the Se–DAN complex was investigated using elemental analysis, FTIR spectrometry, ¹H and ¹³C NMR spectroscopy, and FAB MS. The information obtained indicates that the selenodiazo group does not contain an Se—O bond or protonated nitrogens, as proposed in other studies.