Iron(I) Chemical Ionization for Analysis of Alkene and Alkyne Mixtures by Tandem Sector Mass Spectrometry or Gas Chromatography/Fourier Transform Mass Spectrometry

Simple mixtures of alkene or alkyne isomers were analyzed by using Fe₊ chemical Ionization and tandem mass spectrometry (MS/MS). The approach Is successful over a ca. 1:10 dynamic range. However, mixtures of Isomers over greater concentration ranges and the presence of congeners require chromatographic separation prior to MS/MS analysis. One means of overcoming the requirements of fast scanning and high resolution In conventional sector mass spectrometry Is Fourier transform mass spectrometry (FTMS) In a pulsed valve mode. Ionization was by multiphoton dissociation/ multiphoton Ionization of Fe(CO)₅ to produce nearly exclusively gas-phase Fe₊. Detection limits are In the nanogram range. A problem Is encountered for alkenes having 12 or more carbons because the high reactivity of Fe₊ leads to consecutive reactions with the hydrocarbon, particularly in the low-pressure regime of an FT mass spectrometer cell.