DETERMINATION OF SELENOMETHIONINE IN WHEAT SAMPLES - COMPARISON OF GAS-CHROMATOGRAPHY MICROWAVE-INDUCED PLASMA-ATOMIC EMISSION-SPECTROMETRY, GAS-CHROMATOGRAPHY FLAME PHOTOMETRIC DETECTION AND GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A method is described for the selective determination of selenomethion ine in wheat samples, The method is based on three steps prior to the determination: (1) hydrolysis of the proteins with tetramethylammonium hydroxide, (2) clean-up on an aluminium oxide column (acid form), (3) derivatization to convert selenomethionine into a compound suitable f or GC, The derivatization reaction consists in esterification of the c arboxylic acid group with propan-2-ol in 4 mol l(-1) HCl medium and su bsequent acylation of the amino group with heptafluorobutyric anhydrid e. The parameters affecting the efficiency of both reactions were opti mized, as well as the esterification medium, Other esterification and acylation reagents were also tested, Three different detection techniq ues were evaluated using selenomethionine standard solutions: FPD, MIP -AES and MS, Electrothermal AAS was also tested, but proved to be unre liable, MS was selected as the best option.