The development of methods for the determination of selenium using spectrofluorimetric and ICP-MS techniques.

Methods for both the on-line and off-line fluorimetric determination of total selenium and selenium species using 2-(alpha-pyridyl)-thioquinaldinamide (PTQA) as a fluorimetric reagent have been developed. As PTQA is not available on the market, methods for its synthesis were critically reviewed, and in the light of the information obtained, modifications were made to the synthesis and purification conditions in order to improve yield from 16 % to 38.9 %. The synthesised PTQA was used for the optimisation of a batch fluorimetric method based on the reaction between the reagent and Se (IV) in acidic medium. The developed method was applied to the determination of total selenium in nutritional supplements after microwave digestion and photoreduction of Se (VI) to Se (IV). The analytical precision in the concentration range 0. 5 - 1000 mug ml[-1] was better than 5%. Excellent agreement (r[2] = 0.9960) between the results of the fluorimetric and ICP-MS methods was obtained when a reference material, TMDA 51.2 supplied by National Water Research Institute Environment Canada and three nutritional supplements were analysed.A novel automated fluorimetric method for the simultaneous determination of Se (VI) and Se (IV) is described in which a purpose built flow injection system was used for the on-line photoreduction of Se (VI) to Se (IV) before detection. Variables such as tube diameter, flow rates, type of acids (HNO[3], H[2]SO[4], CH[3]COOH, H[3]PO[4] and HCI) that affect the rate at which PTQA reacted with Se (IV) were investigated and optimised. The linear calibration range was found to depend on the type and concentration of acid. The most intense fluorescence signals were observed in HNO3 and at a PTQA concentration of 5x10[-4] M. A sample throughput of 8 samples/hr was achieved. Method validation was by comparing the results obtained for the determination of selenium in nutritional supplements with those from ICP-MS.Selenium speciation in the nutritional supplements was studied using a developed method in which the selenium species selenomethionine, Se (IV), and Se (VI) were extracted, separated by HPLC prior to on-line photoreduction of Se (VI), and post column hydride generation before ICP-MS detection. Separation of the three species was achieved with excellent resolution in less than 18 minutes. The limit of determination for the three species was 0.50 mug L[-1].