Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
2002-05-01
2003-06-24
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Ionic separation or analysis
With sample supply means
C250S285000
Reexamination Certificate
active
06583409
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mass analysis apparatus and, more particularly to a mass analysis apparatus suitable for improving measuring efficiency and for increasing volume of information obtainable per unit time.
2. Description of the Prior Art
Analyzers such as a mass spectrometer direct-coupled to a gas chromatograph (GC/MS), a mass spectrometer direct-coupled to a liquid chromatograph (LC/MS), a plasma-ionization mass spectrometer (plasma-ionization MS) and the like have been widely used in the fields of environmental science, medical since, pharmacy and so on.
The GC/MS and the LC/MS are used for qualitative and quantitative analysis of an extremely small amount of an organic chemical compound, and the plasma-ionization MS is used for qualitative and quantitative analysis of a small amount of metal. The GC/MS or the LC/MS is an analyzer which is formed by coupling a mass spectrometer (MS) to a gas chromatograph or a liquid chromatograph, respectively. The plasma-ionization MS is an analyzer which is formed by coupling a mass spectrometer (MS) to a plasma ion source operable under atmospheric pressure.
The LC/MS is composed of the liquid chromatograph, an atmospheric pressure ion source, a data processor and so on. The mass spectrometer (MS) requires a high vacuum higher than 10
−3
Pa. On the other hand, the LC is an apparatus in which liquid such as water, an organic solvent or the like is handled under atmospheric pressure (10
5
Pa). Therefore, the two units are not compatible with each other, and accordingly it has been difficult to couple them together. However, the LC/MS becomes practical due to progress of the vacuum technology and development of the atmospheric pressure ion source.
FIG. 31
a schematic view showing a common LC/MS.
Measurement using the LC/MS is generally performed according to the following procedure.
A sample is automatically injected by an auto-sampler
12
into a mobile phase transferred by a pump
11
. The sample is separated into components each by a separation column
13
. Each of the separated components is introduced into an atmospheric pressure ion source
20
of the LC/MS. The introduced component is ionized by the atmospheric pressure ion source
20
. The produced ions are introduced into a high vacuum chamber
80
evacuated by a turbo-molecular pump
26
through an intermediate pressure chamber
21
evacuated by an oil rotary pump
22
. The ions are mass-analyzed by a mass spectrometer
82
placed in the high vacuum chamber
80
to be detected by a detector
83
as an ion current. Finally, a mass spectrum or a mass chromatogram is obtained by a data processor
84
.
In a case of common LC/MS measurement, the required time for measuring one sample from starting of introducing the sample to completion of analysis is approximately one hour. The reason is that separation time (approximately 30 minutes) is required in the first place. Further, in the LC analysis there is gradient analysis in which the component of the mobile phase is changed with time. In that case, the time (20 to 30 minutes) for returning the component of the mobile phase to the original state is necessary. consequently, the sample measuring cycle becomes approximately one hour. Therefore, number of measured samples per day per one LC/MS becomes only 20 to 30.
As the ion source of the LC/MS, an atmospheric pressure chemical ionizer ion source (APCI), an electrospray ion source (ESI), and a sonic spray ion source (SSI) are widely used in the present time. The APCI is suitable for ionizing neutral or weak polar chemical compounds, and the ESI or the SSI is suitable for ionizing high polar or ionic chemical compounds. These ionizers provide complimentary information. Further, obtainable information is different depending on the polarity (positive, negative) of ionization. In order to extract various kinds of information as much as possible from the LC/MS analysis of one sample, an operator of the LC/MS frequently switches the ion source (ESI, APCI, SSI), switches the polarity of ionization, and changes analysis conditions such as the mobile phase, the column and so on.
Among them, a widely employed method of switching the ion source is performed by taking a mounted ion source off by hand and mounting a new ion source. The reason is that the structures of the ion sources, the ESI, the APCI and the SSI, are largely different. The switching of the ion source requires large amounts of work and working time, as to be described below.
The switching of the ion source comprises the steps of initially stopping operation of the LC and the ion source; waiting until temperature of the ion source returns to room temperature; taking the ion source off; mounting the new ion source; switching on the power supply of the ion source to heat the ion source; performing conditioning by making the mobile phase flow through the LC column; and performing calibration and the like using a standard sample.
As described above, the switching of the ion source requires a large amount of procedures, work, time and labor. Many operators sometime try to analyze all of samples using one mounted ion source to avoid the troubles described above. As a result, a negative analysis result is often obtained. This means that although at least six different kinds of data (three kinds of ion sources×positive and negative spectra=3×2=6) for one sample may be obtained in the LC/MS analysis if measurement is performed using the three kinds of ion sources, the operator abandons the possibility for himself. Of course, the whole analysis can not be automated because the switching of the ion source is performed by hand.
Various methods of easily switching a plurality of ion sources have been proposed in order to solve the problem of lack of processing ability of the LC/MS.
A mechanism capable of easily switching the ion source between an APCI and an ESI is disclosed in Japanese Patent Application Laid-Open No. 7-73848. A large rotatable table is disposed in an ion source portion of the LC/MS unit, and the two ion sources of the ESI and the APCI are mounted on the rotatable table. Switching between the ESI and the APCI is performed by rotating the rotatable table. In this method, the trouble of switching the ion source can be simplified, but the time for analysis can not be shortened because the analyses of the APCI and the ESI have to be performed in series. Of course, the time for conditioning can not be shortened. Further, Japanese Patent Application Laid-Open No.7-73848 does not describe any method of shortening the time for work to cope with the variety of measurement (switching of the ionization method, switching of positive
egative polarity). It does not describe any technology for improving the measurement efficiency per unit time either.
Another technology of connecting a mass spectrometer to a plurality of ion sources is described in Journal of American Society for Mass Spectrometry, Vol. 3 (1992), pp. 695-705. In this technology, ions produced in two atmospheric pressure ion sources are introduced into the mass spectrometer separately through two inlet ports of a Y-shaped capillary. By sampling the ions from one of the ion sources under atmospheric pressure, switching of the ion source can be performed without mechanically switching between the ion sources. However, the method has a large problem. While one of analyses is being performed, one of the two ion sources needs to be in operation and the other needs to be out of operation. In order to stop operation of an ion source, the power source to the ion source needs to be switched off, and the transferring of the mobile phase from the LC also needs to be stopped. The reason is that if the ions and neutral gas molecules of the LC solution are sucked through the two inlet ports of the Y-shaped capillary, the ions and the solution molecules are mixed in the midway of the Y-shaped capillary. Reaction between the ions and the solution molecules occurs there, and consequently
Hitachi , Ltd.
Kenyon & Kenyon
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