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

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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 (SeIV) 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.

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