Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
2001-11-05
2003-05-06
Lee, John R. (Department: 2881)
Radiant energy
Ionic separation or analysis
With sample supply means
C250S286000, C250S282000, C250S292000, C250S281000
Reexamination Certificate
active
06559443
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ionization apparatus and ionization method for mass spectrometry, and more particularly relates to an apparatus and method for ionization using an ion trap type ion source and metal ion attachment method in ion mass spectrometry.
2. Description of the Related Art
A mass spectrometry apparatus generally introduces a sample gas including a target substance for analysis, ionizes the sample gas, separates and takes out the ions relating to the target substance for analysis from the ions not analyzed, and measures and analyzes the mass. The mass spectrometry apparatus includes an ion source for ionization of the sample gas and a mass spectrometry unit for measuring and analyzing the ions desired to be analyzed. An ion trap type mass spectrometry apparatus can trap ions of a specific mass by a structural unit serving both as the ion source and mass spectrometry unit, so alternately ionizes the gas and analyzes the mass.
There are various methods for ionization of a sample gas in an ion source of a mass spectrometry apparatus. In the electron impact method (EI), electrons are fired at an ionization region into which only the sample gas is introduced so as to directly ionize the sample gas. Further, in the chemical ionization method (CI), electrons are fired into an ionization region where a reaction gas including a small amount of the sample gas is introduced and the reaction gas ionized. Next, the ionized reaction gas (reaction ions) is reacted with the sample gas and the H
+
in the reaction ions attached to the sample gas to ionize the sample gas.
In the chemical ionization method, the above ion trap type mass spectrometry apparatus traps the reaction ions, so the opportunities for impact between the reaction ions and sample gas increase. Therefore, compared with an ordinary two-dimensional Q-pole (quadrapole) type mass spectrometry apparatus which does not trap ions, there is the advantage that use is possible at a low pressure.
An ion trap type mass spectrometry apparatus has a structural unit serving as both an ion source and mass spectrometry unit, but a mass spectrometry apparatus of a type with these as independent separate structural units configured so as to use the above characterizing structural unit positively as an ion source has also been proposed (Japanese Patent No. 2679026). In this patent, electron impact ionization or chemical ionization is used as the ionization method in the ion source. The conventional ion source described in that patent is configured to switch between electron impact ionization and chemical ionization as the ionization method. It does this just by changing the parameter of the alternating current or direct current applied to the structural unit, so does not use a mechanical switching operation. Further, in the ionization, ions of all of the ingredients of the sample gas are produced, so only the ions desired to be measured and analyzed are roughly separated and ejected to the mass spectrometry unit. By changing the parameter to control the stable state and unstable state of the ions, the ions desired to be analyzed are ejected to the Z-direction (axial direction of electrode unit) and the ions not analyzed are scattered in the R-direction (radial direction of electrode unit) so as to roughly separate the ions.
Further, one of the methods of ionization is the metal ion attachment method. The metal ion attachment method uses the property that for example the Na
+
or other metal ions emitted from the ion emitter gently attach to and ionize the gas molecules in their original form. According to the metal ion attachment method, the production of low molecular weight substances by the disassociation of the sample gas is suppressed and efficient ionization becomes possible.
In an apparatus making positive use of the ion trap structural unit as an ion source such as the mass spectrometry apparatus disclosed in the above Japanese Patent No. 2679026, when using the chemical ionization method, the chemical ionization method (1) produces not the H
+
finally added as the reaction ions to react with the sample gas, but CH
5
+
or C
2
H
6
including the same and (2) adds hydrogen to the molecules contained in the sample gas in the reaction, so shifts the ingredients included in the sample gas in mass by exactly 1 amu (atomic mass unit). Therefore, the following problems arise with respect to the separation of the ions desired to be analyzed and the ions not analyzed.
The problem at the time of chemical ionization in a mass spectrometry apparatus using an ion trap structural unit as an ion source is that a high resolution is required for separating [1] the ions to be scattered and extinguished inside the structural unit, [2] the ions to be trapped (reaction ions), and [3] the ions to be ejected to the mass spectrometry unit (ions of target substance for analysis). Further, some ions are not accurately separated even with a high resolution. This will be explained with reference to FIG.
7
and FIG.
8
. In FIG.
7
and
FIG. 8
, the abscissas indicate the mass number, while the ordinates indicate the intensity. These figures show the distribution of the ingredients of the sample gas or the reaction ions or other gases or ions on the abscissas of the mass number.
FIG. 7
is a view for explaining the state of separation of the ions of the above [2] and [3], that is, the ions to be scattered and extinguished inside the structural unit since they are unnecessary for analysis and interfere with the mass spectrometry and the reaction ions to be trapped inside the structural unit for efficient reaction with the target substance for analysis (gas ingredients of sample gas). In
FIG. 7
, when the reaction gas is methane CH
4
(mass
16
)
101
as shown in the top graph (A), if an electron beam is fired, as shown by the bottom graph (B) of
FIG. 7
, a plurality of ions (CH
+
, CH
2
+
, CH
3
+
, CH
4
+
, CH
5
+
, C
2
H
3
+
, C
2
H
4
+
, C
2
H
5
+
, C
3
H
3
+
, C
3
H
4
+
, C
3
H
5
+
and C
3
H
7
+
) are produced. Among these ions, the CH
5
+
(
102
) or C
2
H
5
+
(
103
) shown by the hatching in the figure are reaction ions reacting with the sample gas. The other ions shown by the regions
104
,
105
, and
106
are unnecessary and rather interfere with the mass spectrometry, so should be scattered and extinguished inside. In the case of the above example, the reaction ions have to be trapped in the ion source, while the other ions have to be scattered and extinguished inside the container of the ion source.
As clear from (B) of
FIG. 7
, since the ions to be scattered and extinguished inside adjoin the reaction ions to be trapped (CH
5
+
or C
2
H
5
+
) at the low mass side, it is difficult to separate the two. This requires a hardware configuration having a high resolution, that is, a high precision structural unit and a high degree of voltage control with respect to the structural unit. Further, if set to trap specific ions for separation, the ions on the low mass side from the trapped ions are scattered and extinguished and the ions on the high mass side are ejected to the mass spectrometry unit (the movement of the low mass side and high mass side can also be reversed). Therefore, ions (ions of region
106
) are also present at the high mass side of the reaction ions
102
and
103
trapped, but it is impossible to extinguish these.
FIG. 8
is a view for explaining the state of separation of ions of the above [2] or [3] emitted to a mass spectrometry unit for analysis at the mass spectrometry unit. In
FIG. 8
, the top graph (A) shows two types of reaction ions CH
5
+
(
201
) and C
2
H
5
+
(
202
), the middle graph (B) shows the analyzed gas before ionization, and the bottom graph (C) shows the analyzed gas and reaction ions ionized by chemical ionization. The analyzed gas includes as ingredient
Fujii Toshihiro
Hirano Yoshiki
Nakamura Megumi
Shiokawa Yoshiro
Anelva Corporation
Hashmi Zia R.
Oliff & Berridg,e PLC
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