Artifacts related to N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide derivatization of citrulline revealed by gas chromatography–mass spectrometry using both electron and chemical ionization

Derivatization with N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) was used for gas chromatography–mass spectrometry (GC–MS) analysis of citrulline and ornithine. Aqueous 50 μl aliquots at 1 and 10 mM concentrations were dried and derivatized separately, and 70 eV electron ionization or CH4 positive chemical ionization were used. Ornithine produced a single GC peak. Physiological citrulline concentrations produced GC artifact peaks for the ornithine derivative, and a compound consistent with elimination of a water molecule from the tri-tert-butyldimethylsilyl (TBDMS) citrulline derivative. A third GC peak obtained using 10 mM citrulline concentrations gave a mass spectrum consistent with a mixture of true tri- and tetra-TBDMS citrulline. Analyses of 13C-ureido-labeled citrulline confirmed the presence of the true TBDMS citrulline derivatives produced from 10 mM samples and provided evidence that the TBDMS ornithine artifact results from loss of TBDMS isocyanate from tetra-TBDMS citrulline. Linear-programmed temperature GC retention index data relative to n-alkanes are reported for observed GC peaks.