Cluster Ions Observed by Liquid Ionization Mass Spectrometer

Abstract

Variety of cluster ions were observed by using the liquid ionization mass spectrometer we have developed. ^6,9) Metastable argon atoms were used to ionize a liquid sample at atmospheric pressure. This paper describes cluster ions composed of water, ethanol, a mixture of methanol and ethanol, acetonitrile and acetone molecules. Major ions observed were (H₂O)_nH⁺, (C₂H₅OH)_nH⁺, (CH₃OH)_nH⁺(C₂H₅OH)_m, (CH₃CN)_nH⁺H₂O and (CH₃COCH₃)_nH⁺H₂O, respectively. Hydrogen bonds played important roles for formation of cluster ions.
A molecule containing a hydroxy group combined with two molecules, because an oxygen atom of the hydroxy group combined with two hydrogen atoms. Therefore molecules of methanol and ethanol combined each other nearly freely by hydrogen bonds. In contrast, a molecule of acetonitrile or acetone was restricted to combine other molecules in production of cluster ions, because a nitrile or a carbonyl group was able to produce only one hydrogen bond. The method gives information about cluster ions which may be related with cluster molecules existed at liquid surface and/or in gas phase where hydrogen bonds are important.