When using a mass spectrometer for example, proteomics, the MSn analysis which performs mass analysis in a multistage mode becomes important.
As a mass spectrometry in which MSn analysis is possible, there is available a three-dimensional quadrupole ion trap mass spectrometer. In a three-dimensional quadrupole ion trap, ions with a specific mass/charge ratio (m/z) can be stably accumulated in the ion trap by applying RF voltage to the ion trap as disclosed in U.S. Pat. No. 2,939,952.
Furthermore, in the three-dimensional quadrupole ion trap, where ions are accumulated in the ion trap by scanning the voltage amplitude of the RF voltage, the ions in the ion trap become unstable in the order of their increasing m/z, and exit the trap in that order as disclosed in U.S. Pat. No. 4,540,884. Thus mass spectrometry becomes possible by detecting the order of the ejected ions.
Furthermore, in the three-dimensional quadrupole ion trap, a supplemental AC voltage is applied apart from the RF voltage, as disclosed in U.S. Pat. No. 4,736,101. Only those ions with the characteristic frequency for a specific m/z oscillate resonantly to the frequency of the supplemental AC voltage by resonance excitation are ejected from the ion trap and then detected, and mass analyzed, resulting in an enhanced resolution for mass spectrometry.
Furthermore, the technology disclosed in U.S. Pat. No. 4,736,101 enabled the MSn analysis to perform using the ion trap, which is important in proteomics. By resonance excitation caused by the supplemental AC voltage, ions accumulated in the ion trap are ejected from the trap except the ions with a specific m/z from the ion trap, and only specific ions are isolated in the ion trap. In the following process, the isolated ions are excited to oscillate by resonance excitation caused by the supplemental AC voltage, and made to collide with neutral gas filling the ion trap for multiple-times, resulting in dissociation of the isolated ions. Fragment ions generated by dissociation are ejected from the trap by scanning the voltage amplitude of the RF voltage in their order of m/z, and mass spectrometry is performed by detecting the order of ejection. By this technique, the more detailed structural information on sample molecules can be acquired from the decomposition state of fragment ions generated by dissociation.
Since a quadrupole linear ion trap disclosed in U.S. Pat. No. 5,420,425 enables a MSn analysis to perform as a three-dimensional quadrupole ion trap, and with higher ion accumulation efficiency than the three-dimensional quadrupole ion trap, this device realizes improvement in sensitivity. Furthermore, since there is little influence of the space charge resulting from the saturation of the accumulated ions in the ion trap, a resolution of mass analysis improves.
Moreover, by combining a quadrupole linear ion trap and a time-of-flight mass spectrometer, and by performing MSn analysis with the ion trap and mass analysis with the time-of-flight mass spectrometer, as disclosed in U.S. Pat. No. 6,020,586, a higher mass resolution and the MSn analysis of mass spectrometry are made possible.
In addition, as disclosed in JP-A No. 044594/2005, by providing a collision dumping chamber due to a neutral gas between the quadrupole linear ion trap and the time-of-flight mass spectrometer, the energy and the position of ions ejected from the ion trap are converged, improving ion introduction efficiency into the acceleration region of time-of-flight mass spectrometer, and a high sensibility analysis can be realized.
The U.S. Pat. No. 5,783,824 discloses a system wherein by applying a direct current (DC) voltage to the electrodes inserted between rod electrodes of the quadrupole linear ion trap, an electrostatic harmonic potential is formed in the axial direction of the trap to accumulate ions. Furthermore, if the electrostatic harmonic potential is formed in the axial direction, and by applying the supplemental AC voltage to the inserted electrodes, ions can be ejected in the axial direction mass-selectively via resonance excitation. Mass spectrometry becomes available by detecting the ejected ions.
U.S. Pat. No. 5,847,386 discloses a system that controls the time to pass a quadrupole electrode for ions by arranging an electrode between each rod electrode of a quadrupole electrode, and forms an electric field in an axial direction. Furthermore, improvement in dissociation efficiency of ions is attempted by varying the electric field in the axial direction, and ions go and come back along the axis and then collide with a neutral gas molecule in the quadrupole electrode.
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