GC ‐MS with Photoionization of Cold Molecules in Supersonic Molecular Beams – Approaching the Softest Ionization Method

AbstractA new type of photoionization ion source was developed for the ionization of cold molecules in supersonic molecular beams (named Cold PI). The system was based on a GC ‐MS with supersonic molecular beams and its fly‐through EI of cold molecules ion source (Cold EI) plus quadrupole mass analyzer. A continuously operated deuterium VUV photoionization lamp was added and placed above and between the supersonic nozzle and skimmer while the Cold EI ion source served only as a portion of the ion transfer ion optics. The supersonic nozzle and skimmer were voltage biased and the VUV light crossed the supersonic expansion about 10 mm from the nozzle. We obtained over three orders of magnitude enhancement in the relative abundance of the molecular ion of squalane i n Cold PI versus in photoionization of this compound as a thermal compound. Accordingly, we also proved that standard photoionization is not as soft ionization method as previously perceived for large compounds. We found that Cold PI is as soft as and possibly softer than field ionization thus it co uld be the softest known ionization method. The ionization yield was about 200‐300 times weaker than with Cold EI yet our limit of detection was about 200 femtogram in SIM mode for cholesterol and pyrene which is reasonable. Practically all hydrocarbons gave only molecular ions with rather uniform response while alcohols gave some molecular ions plus major fragment ions particularly with a loss of water (similarly to...

Source: Journal of Mass Spectrometry - March 27, 2020 Category: Chemistry Authors: Alexander B. Fialkov, Elias Ikonen, Tiina Laaksonen, Aviv Amirav Tags: RESEARCH ARTICLE Source Type: research