Gas chromatography with parallel hard and soft ionization mass spectrometry

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Chromatography

Background:

• Mass spectrometry provides compound identification through molecular masses (soft ionization, e.g., field ionization/FI) and fragmentation patterns (hard ionization, e.g., electron ionization/EI).
• Simultaneous detection using both EI and FI mass spectrometry allows for the integration of complementary data from each technique.

Purpose of the Study:

• To report the construction and characteristics of a combined instrument integrating gas chromatography with parallel EI and FI mass spectrometry sources.
• To demonstrate the simultaneous acquisition of high-quality EI and FI mass spectra for analyzing complex mixtures.

Main Methods:

• A combined instrument was constructed featuring a gas chromatograph coupled with two parallel mass spectrometry ionization sources: EI and FI.
• A post-column splitter with a 1:10 split fraction for EI/FI was employed to achieve simultaneous detection, optimizing for ion yield and signal-to-noise ratio.

Main Results:

• Statistically insignificant differences in full width at half maximum (FWHM) were observed between EI and FI chromatograms.
• Retention times of EI and FI chromatograms were highly correlated (r² = 0.9999) with no detectable bias, indicating excellent chromatographic alignment.
• The instrument's applicability was demonstrated through the analysis of diverse standard samples, fatty acids, fish oil, hydrocarbons, and yeast metabolites.

Conclusions:

• The combined dual-source instrument offers significant time and resource savings.
• It generates equivalent, time-aligned chromatograms in EI and FI, featuring similar peak shapes and identical positions.
• Identical FWHMs and retention times facilitate accurate assignment of EI fragment ions to their corresponding FI molecular ions, enhancing compound identification.