Applications of Association Reactions in the Gas Phase

1 Alkali Metal Ions in Electron Ionization (El) and Chemical Ionization (Cl) Mass Spectrometry (MS) 

Alkali metal ion/molecule association reactions have been exploited in various mass spectrometric methods since the early 1970s. Initial studies were to determine metal ion affinities of simple compounds, with use of Fourier transform ion cyclotron resonance (FTICR) mass spectrometers. Alkali ions offer unique and interesting potential in analytical chemistry and studies of chemical dynamics. Consequently, the use of metal ions as reagents for Cl mass spectrometry has been developed. The major advances in the apphcation of MS as a routine analytical instmment using the complex ion/molecule chemistry came arotmd in the past decades. They include atmospheric pressure chemical ionization (APCI), proton transfer reaction mass spectrometry (PTR-MS), selected ion flow tube mass spectrometry (SIFT-MS), ion attachment mass spectrometry (lAMS) and ion molecrtle reaction mass spectrometry (IMM-MS). 

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Fujii (ed.), lon/Molecule Attachment Reactions Mass Spectrometry, 

Bombick et al. [3] presented a simple, low cost method for producing thermal potassium metal ions for use as Cl reagents. All studies were performed on a commercial gas chromatography-mass spectrometiy (GC-MS) system. Thermionic emitters of a mixture of silica gel and potassium salts were mounted on a fabricated probe assembly and inserted into the Cl volume of the ion source through the direct insertion probe inlet. Since adduct ions (also referred to as cationized molecular ions or pseudomolecular ion ) of the type (M + K)+ have been observed, molecular weight information is easily obtained. The method is adaptable to any mass spectrometer with a Cl source and direct inlet probe (DIP). In addition, the technique is compatible with chromatographic inlet systems, i.e., GC-MS modes, which will provide additional dimensions of mass spectral information. 

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