Simultaneous determination of fatty, dicarboxylic and amino acids based on derivatization with isobutyl chloroformate followed by gas chromatography—positive ion chemical ionization mass spectrometry

Gas chromatography–mass spectrometry (GC–MS) with positive ion chemical ionization (PICI) using isobutane as reagent gas was applied for analysis of isobutoxycarbonyl/isobutyl derivatives of 13 fatty, 6 dicarboxylic and 13 amino acids in a single run. For all investigated compounds (except several amino acids) the quasimolecular ions [MH]+ were registered. Asparagine underwent fragmentation via decarboxylation followed by elimination of OC4H9 ([M−117]+), whereas serine and tyrosine produced the cluster ions [M+C4H9OCO]+. Estimated detection limits were 6–250 pg in the total ion current (TIC) mode and 3–10 times lower using the selected-ion monitoring (SIM) mode.