• selenized yeast
• acid digestion
• metrology
• isotope dilution
• method development
• aminoacids
• triethyloxonium tetrafluoroborate
• derivatization
• gcms

The assessment of the aminoacidic content of food samples is of crucial importance, both from a health and an industrial point of view. Particular attention is reserved for sulfur-containing amino acids, like Methionine and Cysteine, or the main source of selenium dietary intake, Selenomethionine.
A novel method for the Gas Chromatography – Mass Spectrometry (GC-MS) determination of Methionine and Selenomethionine in food and biological samples is therefore herein proposed. A single step derivatization in aqueous medium employing triethyl oxonium tetrafluoroborate salts allows the extraction and the volatilization of the analytes as ethyl derivatives, enabling their detection in ultra-trace concentrations (low part per billions).
The method is validated by analysis of the selenized yeast Certified Reference Material SELM-1 extract, obtained by microwave assisted acid digestion with methanesulfonic acid 4M.
The main goal of this work is to offer a clean (reagents- and by-products-wise) and simple derivatization procedure as a valid alternative to the standard alkyl chloroformate methods.