Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
2003-09-10
2004-10-05
Wells, Nikita (Department: 2881)
Radiant energy
Ionic separation or analysis
With sample supply means
C250S42300F, C250S424000
Reexamination Certificate
active
06800850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflection type ion attachment mass spectrometry apparatus, and more particularly, relates to a reflection type ion attachment mass spectrometry apparatus for measuring ingredients of a measured gas with a high sensitivity and high precision, and a method of reflection type ion attachment mass spectrometry.
2. Description of the Related Art
Ion attachment mass spectrometry (IAMS) is a method of ionizing the molecules of a measured gas without causing fragmentation (causing the generation of fragments, that is, breaking up the original molecules), making the ions of the molecules move to the mass spectrometry region, and analyzing their mass there. There are the following documents concerning apparatuses for working the ion attachment mass spectrometry method in the related art.
As patent documents, there are JP-A-6-11485, JP-A-2001-174437, JP-A-2001-351567, JP-A-2001-351568, JP-A-2002-124208, JP-A-2002-170518, U.S. Pat. No. 4,933,551, and U.S. Pat. No. 4,649,278. Further, as other documents, there are (1) Hodge, “Analytical Chemistry”, 1976, vol. 48, no. 6, p. 825, (2) Bombick, “Analytical Chemistry”, 1984, vol. 56, no. 3, p. 396, (3) Fujii, “Analytical Chemistry”, 1986, vol. 61, no. 9, p. 1026, and (4) Fujii, “Chemical Physics Letters”, 1992, vol. 191, no. 1.2, p. 162.
Referring to
FIG. 22
, the general configuration of an apparatus for ion attachment mass spectrometry of the related art will be explained in relation to the present invention. In
FIG. 22
,
1
indicates a metal ion generation region,
2
an attachment region, and
3
a mass spectrometry region. The metal ion generation region
1
and attachment region
2
form a common compartment having a common vacuum environment. A partition
6
is provided between the attachment region
2
and mass spectrometry region
3
. The partition
6
is formed with an aperture
6
a.
The metal ion generation region
1
is provided with a metal ion emitter
4
. In
FIG. 22
,
5
shows the path of movement of the metal ions and attached ions. The mass spectrometry region
3
is provided with a mass spectrometer
8
and is additionally provided with a vacuum pump
7
.
The metal ion generation region
1
, the attachment region
2
, and the mass spectrometry region
3
all are at reduced pressures of not more than atmospheric pressure. In the metal ion generation region
1
, a metal ion emitter
4
of an oxide of an alkali metal is heated to generate Li
+
and other positively charged metal ions. The metal ion emitter
4
is heated by supplying current by application of voltage by a not shown power source. The metal ions are transported to the attachment region
2
from the metal ion generation region
1
by an electric field. The measured gas (or sample gas) is introduced into the attachment region
2
by a measured gas introduction mechanism
30
. The metal ions gently attach to locations with a concentration of charges of molecules of the measured gas. The molecules to which the metal ions are attached become positively charged ions as a whole, whereby attached ions (pseudo molecular ions) are generated.
At the time of attachment, the surplus energy is extremely small, so fragmentation does not occur. However, to prevent the metal ions from again disassociating from the attached ions (prevent the metal ions from detaching from the molecules of the measured gas), it is necessary to strip the surplus energy by having the ions collide with the ambient gas. To raise the efficiency of attachment, it is necessary to decelerate the metal ions emitted from the metal ion emitter
4
by the high voltage down to a translational energy of not more than 1 eV by colliding with the ambient gas. Even if the metal ions having a translational energy of at least 1 eV contact the molecules of the measured gas, almost all of them end up separating without attachment. To maximize these two effects, the general practice in an ion attachment mass spectrometry apparatus of the related art is to make the pressure in the attachment region
2
about 100 Pa. With a pressure of 100 Pa, the movement of the ions is not smooth and a problem arises in the quantitativeness of the results of measurement. Therefore, recently, methods of deceleration by an electric field and operation at a pressure of about 1 Pa in the attachment region are being developed.
The attached ions produced as explained above are again accelerated by the electric field, passed through the partition
6
with the aperture
6
a,
and transported to the mass spectrometry region
3
. A Q-pole type mass spectrometer or other mass spectrometer
8
using electromagnetic force measures the attached ions separated in mass-charge ratio (mass number). The mass spectrometer normally can only operate by at a pressure of not more than 10
−3
Pa, so a pressure difference is generated by the partition
6
with the aperture
6
a.
FIG. 22
shows a general example of the related art, but in different related arts, the differential regions exist in some cases, and do not exist in the other cases, and the number of vacuum pumps, etc. differ.
Therefore, in the past, an electron attachment mass spectrometry apparatus has also been proposed (U.S. Pat. No. 4,933,551). According to the electron attachment mass spectrometry apparatus disclosed in the above-mentioned document, electrons are made to attach to the neutral gas to form negative ions as a whole for mass spectrometry. Further, the technical idea has been proposed of slowing the speed of the electrons using an electric field and causing the electrons to attach to the gas molecules to create negative ions (U.S. Pat. No. 4,649,278). According to this document, a mirror electrostatic field is used to make the speed of the electrons zero or nearly zero and enable electrons to be attached to the gas.
The ion attachment mass spectrometry apparatuses of the related art all could ionize molecules without causing fragmentation and could correctly identify the ingredients of the measured gas (quantitative analysis). This surpasses other techniques. The scientific and industrial fields have large expectations vis-a-vis ion attachment mass spectrometry apparatuses. However, ion attachment mass spectrometry apparatuses have the weak point that the measurement sensitivity is insufficient and detection of trace ingredients is difficult. In particular, with the method of making the pressure of the attachment region
2
1 Pa for the purpose of improving the quantitativeness, the measurement sensitivity ends up deteriorating more, so the insufficient measurement sensitivity becomes a serious problem.
The reasons for the insufficient sensitivity will be explained in the following. As shown in
FIG. 22
, in the ion attachment mass spectrometry apparatus of the related art, the metal ion generation region
1
, attachment region
2
, and mass spectrometry region
3
are positioned adjoining each other in that order, while the metal ion emitter
4
and the mass spectrometer
8
are arranged on substantially the same straight line straddling the attachment region
2
. Therefore, even if the metal ions generated from the metal ion emitter
4
change to attached ions in the attachment region
2
, they are not changed in direction and proceed straight to the mass spectrometer
8
as they are. If there is no change in the translational energy on the way, the system of the conventional art of making the ions proceed straight is easiest and most reliable in control of the ions. However, in fact, the ions are greatly decelerated and accelerated in the process. Sufficient control has not been possible in the conventional art.
Specifically, for extracting and transporting the metal ions from the metal ion emitter
4
, first, the translational energy of the metal ions is 10 to 20 eV, but at the attachment region
2
, the ions are decelerated to less than 1 eV to improve the attachment efficiency. Next, the attached ions produced are accelerated and again transported to the mass spectrometer
8
Hirano Yoshiki
Shiokawa Yoshiro
Anelva Corporation
Burns Doane Swecker & Mathis L.L.P.
Quash Anthony
Wells Nikita
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