Negative ion mode electrospray ionization mass spectrometry study of ammonium-counter ion clusters

TitleNegative ion mode electrospray ionization mass spectrometry study of ammonium-counter ion clusters
Publication TypeJournal Article
Year of Publication2007
AuthorsLentz NB, Houk RS
Journal TitleJournal of the American Society for Mass Spectrometry
Volume18
Pages285-293
Date PublishedFeb
Type of ArticleArticle
ISBN Number1044-0305
Accession NumberISI:000244109300015
KeywordsANIONS, CHLORIDE, FUNDAMENTALS, SALT CLUSTERS
Abstract

Electrospray ionization mass spectrometry (ESI-MS) was used to examine clusters of protonated amine salt solutions with chloride counter ions in the negative ion mode. These ions have the general formula [(RNH3)(x)Clx+1](-). Primary amines generate a wide cluster distribution with clusters up to 14 mer for methylamine hydrochloride clusters. Secondary and quaternary amines only generate the monomer ion under identical conditions. Collision induced dissociation (CID) of the cluster ions generates cluster ions of lower m/z with the next lower cluster being the most abundant. The product ions from MeNH3Cl2-, Me2NH2Cl2- and (MeNH3)(2)Cl-3(-) have low threshold appearance energies of 1.24 to 2.22 eV center-of-mass frame. Secondary amine monomer ions have lower threshold CID energies than primary amine monomer ions. The amine threshold CID energy decreases as the carbon chain length increases. As an electrospray solvent, isopropyl alcohol (IPA) promotes the formation of counter ions and clustering.

DOI10.1016/j.jasms.2006.09.028
Alternate JournalJ. Am. Soc. Mass Spectrom.