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

Abstract

A method is described for the selective determination of selenomethionine 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 for GC. The derivatization reaction consists in esterification of the carboxylic acid group with propan-2-ol in 4 mol l -1 HCl medium and subsequent acylation of the amino group with heptafluorobutyric anhydride. The parameters affecting the efficiency of both reactions were optimized, as well as the esterification medium. Other esterification and acylation reagents were also tested. Three different detection techniques were evaluated using selenomethionine standard solutions: FPD, MIP-AES and MS. Electrothermal AAS was also tested, but proved to be unreliable. MS was selected as the best option.