Department of Chemishy, University of Florida, 32611, Gainesvtlle, Florida.
J Am Soc Mass Spectrom. 1994 Aug;5(8):757-64. doi: 10.1016/1044-0305(94)80008-1.
The effects of applied voltages and reaction times on negative ion chemical ionization in the quadrupole ion trap are investigated. Mass-selected ejection of undesired reagent ions and selective mass storage of only negative ions are required for practical negative ion chemical ionization. This is achieved by application of rf and dc voltages to the ring electrode to control the mass-to-charge ratios one polarity) of ions stored, as well as by application of a supplemental rf voltage applied across the endcap electrodes to selectively eject ions of a particular mass-to-charge ratio. Even with careful control of these parameters, negative chemical ionization is not as sensitive as electron ionization and positive chemical ionization because of the lack of thermal electrons in the ion trap. Mass selection of the hydroxide anion as a reagent ion and exclusion of all positive ions provide M - H ions with little or no fragmentation for a wide variety of compounds.
研究了外加电压和反应时间对四极离子阱中负离子化学电离的影响。为了实现负离子化学电离的实际应用，需要选择性地从反应混合物中去除不需要的试剂离子，并选择性地存储只有负离子。这可以通过向环电极施加射频（rf）和直流（dc）电压来实现，以控制存储离子的质荷比（m/z）的极性，以及通过施加在端盖电极上的补充射频电压来实现，以选择性地逐出特定质荷比的离子。即使对这些参数进行了仔细的控制，由于离子阱中缺乏热电子，负离子化学电离的灵敏度也不如电子电离和正化学电离高。选择氢氧根阴离子作为试剂离子，并排除所有阳离子，可以为各种化合物提供几乎没有或没有碎片的M - H离子。
