A comparison of different derivatisation approaches for the determination of selenomethionine by GC-ICP-MS

Two different approaches for the derivatisation of selenomethionine and detection by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS) are compared and applied for the determination of the amino acid in pharmaceutical preparations used as selenium nutritional supplements. The first derivatisation is accomplished in two steps, starting with the esterification of the carboxylic acid group of the seleno-amino acid using propan-2-ol, followed by the acylation of the amino group with trifluoroacetic acid anhydride. Alternatively, the ethyl chloroformate-ethanol method was carried out for the simultaneous esterification and acylation steps catalysed by a pyridine solution. The derivatives were finally extracted into chloroform and injected into the gas chromatograph. The different parameters affecting the efficiency of both derivatisation approaches were optimised, as well as the instrumental operating conditions. Standard GC-MS chromatograms and mass spectra for both derivatisation procedures were also obtained to confirm the structure of the corresponding derivatised amino acids. The propan-2-ol-trifluoroacetic acid anhydride procedure was finally selected and was used to determine selenomethionine in a parenteral solution by GC-ICP-MS. The advantages and disadvantages of both procedures are discussed.