Radiant energy – Ionic separation or analysis – Methods
Reexamination Certificate
2001-06-01
2004-10-05
Nguyen, Lamson (Department: 2853)
Radiant energy
Ionic separation or analysis
Methods
Reexamination Certificate
active
06800848
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for ion attachment mass spectrometry used for a quantitative analysis for accurately measuring the concentration of a gas to be detected.
2. Description of the Related Art
An ion attachment mass spectrometer is a mass spectrometer designed to accurately measure the molecular weight of the gas to be detected. The analysis executed by this apparatus enables ionization and mass spectrometry of the detection gas without causing cracking. The ion attachment mass spectrometer has been reported in Hodge,
Analytical Chemistry
, vol. 48, no. 6, p. 825 (1976); Bombick,
Analytical Chemistry
, vol. 56, no. 3, p. 396 (1984); and Fujii et al.,
Analytical Chemistry
, vol. 1, no. 9, p. 1026 (1989),
Chemical Physics Letters
, vol. 191, no. 1.2, p. 162 (1992), and Japanese Unexamined Patent Publication (Kokai) No. 6-11485.
The conventional ion attachment mass spectrometers will be explained referring to the drawings.
FIG. 9
shows the apparatus proposed by Fujii. In
FIG. 9
,
901
indicates a reaction chamber,
902
a first differential evacuation chamber,
903
a second differential evacuation chamber,
904
an analysis chamber,
905
a gas introduction mechanism,
906
an evacuation mechanism, and
907
a data processor. Further,
911
indicates an emitter,
912
a first aperture,
913
a reaction chamber seal,
914
a reaction chamber vacuum gauge, and
915
a baking mechanism. Further,
921
indicates a second aperture,
922
a partition of the first differential evacuation chamber,
931
a third aperture,
932
a partition of the second differential evacuation chamber,
933
an electrostatic lens, and
941
a Q-pole mass spectrometer. Further,
951
indicates a space to be measured,
952
a pipe, and
953
a flow rate adjustment valve. Reference numeral
961
indicates a first differential evacuation chamber wet pump,
962
a second differential evacuation chamber wet pump, and
963
an analysis chamber wet pump.
The reaction chamber
901
, the first differential evacuation chamber
902
, the second differential evacuation chamber
903
, and the analysis chamber
904
form a vacuum chamber, that is, a chamber of a reduced pressure atmosphere being not more than atmospheric pressure. In the reaction chamber
901
, an oxide of an alkali metal of an emitter is heated to cause the emission of Li
+
and other positively charged metal ions. The detection gas is introduced into the reaction chamber
901
. The metal ions gradually attach to (associate with) locations where the charges of the gas molecules concentrate and the molecules as a whole are ionized. The excess energy at the time of attachment is an extremely small 0.435 to 1.304 eV/molecule and there is less occurrence of disassociation.
Since the excess energy is low, however, if left as it is, the Li
+
ends up being detached from the molecules again, so the total pressure of the reaction chamber
901
is made about 100 Pa to absorb the excess energy due to the large number of collisions. The gas absorbing the excess energy is neither the attaching ions or gas to be attached to, so is normally called a “third component gas”.
The third component gas may also be the detection gas itself, but normally a low reactivity N
2
gas etc. is used. Further, as the third component gas, there are sometimes cases of a base gas containing the detection gas from the start in the measurement space (carrier gas) or gas separately introduced by the reaction chamber
901
. Due in part to contamination and other reasons, since the partial pressure of the detection gas introduced is normally not more than 1 Pa, almost all of the total pressure of the reaction chamber
901
of about 100 Pa becomes the partial pressure of the third component gas.
The gas molecules (ions) to which the metal ions are stably attached pass through the opening of the aperture and enter the first differential evacuation chamber
902
. The first differential evacuation chamber
902
functions to connect in vacuum the reaction chamber
901
which should be set at about 100 Pa and the analysis chamber
904
which should be set at not more than 1×10
−3
Pa. This results in a total pressure of 0.1 to 10 Pa in the first differential evacuation chamber
902
. The electrostatic lens
933
is provided in the second differential evacuation chamber
903
. The ions are condensed and enter the analysis chamber
904
. The Q-pole mass spectrometer
941
placed in the analysis chamber
904
breaks down and detects the entering ions for each mass of the gas molecules (ions) by electromagnetic force. The Q-pole mass spectrometer
941
outputs a mass signal showing the intensity for each mass number to the data processor
907
. Note that the pressure inside the analysis chamber
904
has to be maintained at not more than 1×10
−3
Pa in order to operate the Q-pole mass spectrometer
941
normally.
FIG. 10
shows the apparatus proposed by Bombick, while
FIG. 11
shows the apparatus proposed by Hodge. In FIG.
10
and
FIG. 11
, components substantially the same as those explained in
FIG. 9
are given the same reference numerals. In the apparatus shown in
FIG. 10
, the reaction chamber
901
is arranged in the first differential evacuation chamber
902
. The total pressure of the reaction chamber
901
is not measured. In the apparatus shown in
FIG. 11
as well, the reaction chamber
901
is placed in the first differential evacuation chamber
902
, but in this case the total pressure of the reaction chamber
901
is measured. Since a long pipe
970
is extended from the reaction chamber
901
and the vacuum gauge
914
attached, accurate measurement of the total pressure is difficult. The rest of the configuration is the same as explained above.
The ion attachment mass spectrometers have been developed as modifications of the chemical ionization mass spectrometers (CIMS) designed for measurement of the molecular weight of the detection gas. In the CIMS, a methane or another reaction gas is ionized by the electron impact to ionize the detection gas to positive charges or negative charges by an ion-molecule reaction. The mechanism of ionization is extremely complicated. Phenomena such as (1) hydrogen ion bonding of the reaction gas, (2) hydrogen ion draining from the detection gas, and (3) charge movement occur. The bonding energy in the case of hydrogen ion bonds is so large as to be 6.957 to 8.696 eV/ molecule, and therefore dissociation often ends up occurring. Peaks of the molecular ions are sometimes observed depending on the type of gas.
Originally, the CIMS was designed for measurement of the molecular weight of the detection gas, that is, “qualitative analysis” for obtaining information on “what are the compositions”. Therefore, the ion attachment mass spectrometer is confirmed to be effective for the qualitative analysis of organic substances or radicals. The ion attachment mass spectrometer, however, suffers from problems such as the stability of the mass signal and therefore is not used at all in industry for the qualitative analysis.
Analysis going further from the qualitative analysis and obtaining information on “what kind of composition is present in what amount” is called “quantitative analysis”. Due to the following reasons, however, the ion attachment mass spectrometers have not been used for the quantitative analysis at all.
First, the quantitative analysis will be explained. In the quantitative analysis, four factors are important: (1) the applicable samples, (2) the signal-to-noise ratio, (3) the signal stability, and (4) the background (interference peaks). The “applicable samples” is the extent of the types of the samples which can be applied, the “signal-to-noise ratio” is the ratio of the mass signal (peak height) and noise (amount of fast cycle fluctuation of base level), the “signal stability” is the reproducibility of the mass signal, and the “background (interference peaks)” is the peaks not inherently present which change th
Fujii Toshihiro
Nakamura Megumi
Sasaki Tohru
Shiokawa Yoshiro
Anelva Corporation
Mouttet Blaise
Nguyen Lamson
Oliff & Berridg,e PLC
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