| 摘要 |
Improved methods and apparatus suitable for use in mass spectrometry are provided for dissociating ions by achieving electronic excitation of the ions using electrons. In MS-MS applications, ion dissociation is induced by electron impact on an ion beam after the beam has exited a first mass analyzer, and before the beam enters a second analyzer. An efficient method for dissociating ions is achieved by providing a low velocity ion beam traveling substantially along the axis of an RF excited multipole field, and intersecting sheet electron beams traveling transverse to the axis of the field. When used in the analysis of high molecular weight, nonvolatile molecules, the teachings of the present invention yield the extensive and reproducible fragmentation characteristics generally associated with electron ionization of lower mass, volatile molecules. The methods and apparatus of the present invention may therefore be used in conjunction with mass spectrometry to qualitatively and quantitatively analyze a significantly greater quantity of samples. The techniques of the present invention are also well suited for dissociating high-mass, even-electron ions produced by thermospray and other soft ionization techniques.
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