Enhanced metabolite profiling using a redesigned atmospheric pressure chemical ionization source for gas chromatography coupled to high-resolution time-of-flight mass spectrometry.

An improved atmospheric pressure chemical ionization (APCI II) source for gas chromatography-high-resolution time-of-flight mass spectrometry (GC-HRTOFMS) was compared to its first-generation predecessor for the analysis of fatty acid methyl esters, methoxime-trimethylsilyl derivatives of metabolite standards, and cell culture supernatants. Reductions in gas turbulences and chemical background as well as optimized heating of the APCI II source resulted in narrower peaks and higher repeatability in particular for late-eluting compounds. Further, APCI II yielded a more than fourfold median decrease in lower limits of quantification to 0.002-3.91 μM along with an average 20 % increase in linear range to almost three orders of magnitude with R (2) values above 0.99 for all metabolite standards investigated. This renders the overall performance of GC-APCI-HRTOFMS comparable to that of comprehensive two-dimensional gas chromatography (GC × GC)-electron ionization (EI)-TOFMS. Finally, the number of peaks with signal-to-noise ratios greater than 20 that could be extracted from metabolite fingerprints of pancreatic cancer cell supernatants upon switching from the APCI I to the APCI II source was more than doubled. Concomitantly, the number of identified metabolites increased from 36 to 48. In conclusion, the improved APCI II source makes GC-APCI-HRTOFMS a great alternative to EI-based GC-MS techniques in metabolomics and other fields.