Gas-phase chemistry of collisionally activated ions

Liquid ion evaporation/mass spectrometry/mass spectrometry for the detection of polar and labile molecules

Formation, characteristics of, and applications rising doubly and multiply charged ions are reviewed in the present article. The main emphasis is on medium- to large-sized molecules, from the point-of-view of organic, physico-organic, and bioorganic mass spectrometry. Multiply charged species can be studied by all conventional mass spectrometric techniques. Those techniques and reaction types that are particularly relevant to multiply charged ions are discussed in some detail in Section III. Studies on small- to medium-sized molecules are discussed in Section N. A particularly interesting aspect, the distinction of doubly charged isomeric ions, is also treated here. Multiply charged ions of large (bio-)molecules are discussed in Section V. This area is fast expanding, mainly due to the spread of electrospray ionization. Fragmentation and conformation of multiply protonated peptides is discussed in detail.

Multiply charged ions

Polyatomic anions derived from several dinitrotoluene isomers, 2,4,6-trinitrotoluene, and 1,3,5-trinitro-1,3,5-triazacyclohexane have been formed by use of negative ion chemical ionization and trapped in an ion trap mass spectrometer. Mass spectrometry/mass spectrometry daughter ion spectra were obtained for most of these ions. In most cases, the parent anions were converted very efficiently to daughter ions (>10%), but for the (M - H)/sup -/ ions the efficiencies were relatively low. Conversion efficiencies were observed to differ by as much as 2 orders of magnitude between anions. The major cause for these differences is attributable to differences in the propensity for collisional electron detachment vs. that for collision-activated dissociation.

Collision-activated dissociation of negative ions in an ion trap mass spectrometer

Particular nitrogen-containing compounds, in some cases individual isomers, can be identified in coal liquid samples by mass-analyzed ion kinetic energy spectrometry (MIKES). This is done directly, without prior treatment or fractionation of the sample. Isobutane chemical ionization (CI) is employed to give an approximate molecular weight profile of the coal liquid. Nitrogen-containing ions are recognized by their enhanced tendency for charge stripping as evident in E/2 mass spectra or by using ammonia as the CI reagent. In selected cases, comparison with authentic compounds has been used to verify the MIKES identifications.

Analysis of coal liquids by mass-analyzed ion kinetic energy spectrometry

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Analysis of coal liquids by mass-analyzed ion kinetic energy spectrometry