Athula B Attygalle
Posters-Accepted Abstracts: J Chromatogr Sep Tech
Some ambient-ionization techniques have revolutionized direct sample analysis by mass spectrometry because the need of a solvent spray can be eliminated. Recently described Helium-Plasma Ionization Mass Spectrometry (HePI) has been recognized as one of the promising novel procedures for ionizing a variety of organic and inorganic compounds. Under positiveion generating HePI conditions some molecules undergo protonation [(M + H)+] while others generate molecular ions (M+�?�). Our recent results show that the formation of molecular ions or protonated molecules can be swung back and forth in a controlled manner. By manipulating the atmosphere surrounding the source, we can generate molecular ions from aromatic hydrocarbons, and virtually eliminate the protonated species. The ionization is effected by a direct Penning mechanism due to interactions of the gas-phase analyte with meta stable helium atoms. However, when the ambient gases bear even traces of moisture, the analytes are ionized by proton transfer reactions with gaseous H3O+. We demonstrate that by controlling experimental conditions, the abundance of molecular ions and protonated molecules in a HePI source can be manipulated.