Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
2003-07-02
2004-07-27
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Ionic separation or analysis
With sample supply means
C250S42300F, C250S424000
Reexamination Certificate
active
06768108
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to JP2002-193665 filed in Japan on July 2, 2002; the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ion attachment mass spectrometry apparatus, ionization apparatus, and ionization method, more specifically relates to an apparatus able to analyze the mass of a sample gas at a high sensitivity without causing disassociation of molecules of the sample gas and an ionization apparatus and ionization method suitable for that apparatus.
2. Description of the Related Art
A mass spectrometry apparatus for measuring the molecular weight of a sample gas passes an ionized sample gas through an electromagnetic field (one or both of an electric field and magnetic field) to separate it by mass and detect the weight. The electron impact method, the most general of the ionization methods, causes electrons to strike the sample gas at a high energy of about 70 eV and uses the impact energy to strip electrons from the molecules of the sample gas to obtain positive ions. However, according to the electron impact method, there was the problem that the molecules of the sample themselves are split (disassociated) by the high impact energy and therefore correct measurement was not possible.
Therefore, the ion attachment method has been developed as a method for ionization of molecules of a sample gas without causing disassociation. This ion attachment method has been reported in Hodges,
Analytical Chemistry
, vol. 48, no. 6, p. 825 (1976); Bombick,
Analytical Chemistry
, vol. 56, no. 3, p. 396 (1984); Fujii et al.,
Analytical Chemistry
, vol. 61, no. 9, p. 1026 (1989),
Chemical Physics Letters
, vol. 191, no. 1.2, p. 162 (1992), Japanese Unexamined Patent Publication (Kokai) No. 6-11485, and Japanese Examined Patent Publication (Kokoku) No. 7-48371.
In the ion attachment method, first, an emitter including a metal salt of Li, Na, Al, etc. is heated to cause the generation of metal ions such as Li
+
, Na
+
, and Al
+
. Next, the metal ions are brought into contact with the sample molecules, whereupon the metal ions attach to locations where the charges of the sample molecules concentrate and the sample molecules as a whole become ions (hereinafter called “attached ions or pseudo-molecule ions”). The energy of attachment of the metal ions to the sample molecules, that is, binding energy, is an extremely small one of about 1 eV. This is smaller than the normal binding energy of compounds of 2 to 3 eV, so the molecules will not easily disassociate even after attachment.
However, if the surplus energy remains in the above attached ions, the metal ions with the surplus energy will disassociate and in turn the sample gas will return to its original neutral molecules. Therefore, by making the attached ions and atmospheric gas collide, the surplus energy is quickly removed and stable attached ions are obtained. The atmospheric gas may be the sample gas itself or a gas other than the sample gas, but a pressure of about 100 Pa is required. If below 100 Pa, the number of frequency of collisions is small and surplus energy cannot be sufficiently removed.
A mass spectrometry apparatus using the ion attachment method is called an “ion attachment mass spectrometry apparatus”. The overall configuration of a conventional ion attachment mass spectrometry apparatus is shown in FIG.
17
. As shown in this figure, an ion attachment mass spectrometry apparatus is usually comprised of a first chamber
102
provided with an emitter
101
for emitting ions, a second chamber
103
comprising an intermediate chamber, and a third chamber
105
provided with a mass spectrometer
104
for mass spectrometry. The first chamber
102
and second chamber
103
are provided between them with a partition
107
having an aperture
106
of a diameter of about 1 mm is provided between the first chamber
102
and the second chamber
103
. The aperture
106
is normally given by a nozzle structure. An aperture
108
is provided between the second chamber
103
and third chamber
105
. By evacuation by a vacuum pump, the first chamber
102
is reduced to pressure of 100 Pa, the second chamber
103
to 0.1 Pa, and the third chamber
105
to 10
−3
Pa or so. Note that the gas
109
introduced into the first chamber
102
may be comprised of the sample alone or may be comprised of mixed gas comprising a base gas such as an inert gas and sample gas. In
FIG. 17
, details of the configuration of the emitter
101
are omitted.
On the other hand, for an object different from that of an ion attachment mass spectrometry apparatus, there are an inductively coupled plasma (ICP) mass spectrometry apparatus and atmospheric pressure ionization (API) mass spectrometry apparatus, which can measure a sample gas at an extremely high sensitivity. These mass spectrometry apparatuses are provided with first chambers, second chambers, and third chambers similar to those explained above. In both cases, the pressure of the first chamber for ionization is made 1×10
5
Pa (atmospheric pressure), the pressure of the second chamber is made 10 to 1000 Pa, and the pressure of the third chamber for mass spectrometry is made 10
−3
Pa or so.
As a means for ionization, an inductively coupled plasma mass spectrometry apparatus uses plasma, while an atmospheric pressure ionization mass spectrometry apparatus uses a corona discharge. In both cases, the electrons generated are made to collide with the sample gas by an energy of several tens of eV to strip off electrons from the sample molecules and obtain positive ions, then ion exchange or another ionization reaction is caused in a chain to realize highly efficient ionization.
In general, when the pressure is high, the number of collision frequency increases, the chain reaction proceeds faster, and the plasma spreads the ionization reaction by itself (self expansion action), so low ion mobility due to the high pressure does not become a problem. Therefore, in all of the above conventional mass spectrometry apparatuses, the optimal pressure of the first chamber is the atmospheric pressure. Normally, a nozzle having an aperture of a diameter of about 1 mm is provided between the first chamber and the second chamber. Since the first chamber is a high pressure, the gas blown out from the nozzle forms a supersonic jet. This supersonic jet causes the ionized sample to be efficiently transported to the mass spectrometer.
In the ordinary vacuum state, a gas spreads uniformly randomly. The translation energy (speed) of this movement is a thermal motion energy at room temperature, so is 0.03 eV or so. As opposed to this, the supersonic jet is extremely characteristic and is comprised of an “expansion part”, a “silent part”, a “Mach disk”, and a “barrel shock” (see FIG.
2
).
The “expansion part” is the part forming a peak of pressure higher than the surroundings near the nozzle outlet. Therefore, the gas or ions collide at a high frequency, a rapid drop in pressure and expansion of gas flow arises, and the gas or ions are cooled by adiabatic expansion. The “silent part” is after the expansion part and forms a bowl of pressure lower than the ambient atmospheric gas. The gas or ions proceed forming beams of uniform direction and speed. This thermal energy also reaches about 3 eV or 100 times as high as the thermal energy at room temperature. Note that an inductively coupled plasma mass spectrometry apparatus and atmospheric pressure ionization mass spectrometry apparatus use this characteristic to raise the transport efficiency of ions. The “Mach disk” is the end of the silent part, while the “barrel shock” is at the side. Both form barriers of pressure higher than the ambient atmospheric gas. The atmospheric gas is blocked by these and cannot penetrate into the silent part.
For the supersonic jet to be formed, it is necessary that the Knudsen number (&lgr;/D) of the length of mean free path (&lgr;) of the gas in the first chamber divid
Fujii Toshihiro
Hirano Yoshiki
Nakata Munetaka
Shiokawa Yoshiro
Takayanagi Masao
Anelva Corporation
Burns Doane Swecker & Mathis L.L.P.
Nguyen Kiet T.
LandOfFree
Ion attachment mass spectrometry apparatus, ionization... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ion attachment mass spectrometry apparatus, ionization..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ion attachment mass spectrometry apparatus, ionization... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3236480