Atmospheric pressure ionization mass spectrometer

摘要

In a first-stage intermediate vacuum chamber, cluster ions causing a background noise are dominantly formed in area (A), while fragment ions are dominantly generated in area (B). Taking this fact into account, when no in-source CID analysis is performed, voltages applied to the first-stage plate electrode of an ion guide and the exit end of a desolvation tube are adjusted to create an accelerating electric field only in area (A) without creating such a field in area (B). Meanwhile, voltages applied to the electrodes of the ion guide are adjusted to create an electric field for separating ions according to their mobility and selecting a specific ion. Such an operation suppresses the cluster-ion formation, removes ions which originate from impurities and have mass-to-charge ratios close to or equal to those of the ions originating from a target substance, and suppresses the fragment-ion generation. As a result, the target ions are detected with high S/N.

主权项

1. An atmospheric pressure ionization mass spectrometer having a multi-stage differential pumping system including one or more intermediate vacuum chambers between an ionization chamber for generating ions under atmospheric pressure and an analysis chamber for mass-separating and detecting the ions under high vacuum, wherein:
either a partition wall separating the ionization chamber and a neighboring first-stage intermediate vacuum chamber, or an exit end of an ion introduction part for making these two chambers communicate with each other, is used as a first electrode; either a partition wall separating the first-stage intermediate vacuum chamber and either a second-stage intermediate vacuum chamber or an analysis chamber in a next stage, or an entrance end of an ion transport part for making these two chambers communicate with each other, is used as a second electrode; and an ion transport electrode is provided in the first-stage intermediate vacuum chamber, the ion transport electrode having an ion mobility separation function for creating an electric field which separates ions according to a mobility of the ions and selectively allows an ion having a specific degree of mobility to pass through and be transported to the next stage, and the atmospheric pressure ionization mass spectrometer further comprising: a) a first voltage setting section for setting voltages individually applied to the first electrode and the ion transport electrode, to adjust a direct-current potential difference between these two electrodes so that a smaller amount of cluster ions will be formed; and b) a second voltage setting section for setting voltages individually applied to the ion transport electrode and the second electrode, to adjust a direct-current potential difference between these two electrodes according to whether or not it is necessary to create fragment ions.