Radiant energy – Ionic separation or analysis – Cyclically varying ion selecting field means
Reexamination Certificate
1998-08-28
2001-02-27
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Ionic separation or analysis
Cyclically varying ion selecting field means
C250S282000, C250S252100
Reexamination Certificate
active
06194716
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for mass calibration, and more particularly a method for mass calibration in a mass spectrometer having an ion trap type mass analysis region.
2. Description of Related Arts
At present, it has been required to establish a technology for performing an analysis of mixture in the field of the analysis technology. For example, in the case that some harmful substances in environment are analyzed, various kinds of substances are contained in the collected samples (for example, water of lake or pond). In addition, a similar state occurs also in the field of analysis of biological compound. It is known that some various kinds of substances are contained in the samples based on the biological compounds such as blood or urine. As described above, in the case that the environmental compounds or biological compounds are analyzed, it is required to provide a technology in which mixtures are processed and analyzed.
Since it is generally difficult to perform a direct analysis of the mixture, each of the components is detected and identified after the desired components in the mixture are separated. In such a circumstance as described above, a liquid chromatograph/mass spectrometer (hereinafter abbreviated as an LC/MS) in which a liquid chromatograph showing a superior separation of mixture and a mass spectrometer showing a superior identification for substances are coupled to each other is quite effective for analyzing some compounds containing several kinds of compounds such as the aforesaid environmental compounds or biological compounds to be analyzed.
Referring now to
FIG. 1
, the prior art LC/MS using the mass spectrometer having an ion trap type mass analysis region will be described.
A liquid chromatograph
1
is comprised of a liquid chromatograph pump
2
, a mobile phase reservoir
3
, a sample injector
4
, a separation column
5
and a tube
6
. The mobile phase solvent in the mobile phase reservoir
3
is fed in its specified flow rate to the separation column
5
by the liquid chromatograph pump
2
. Sample of mixture is fed into the mobile phase solvent by the sample injector
4
arranged between the liquid chromatograph pump
2
and the separation column
5
. The sample of mixture reached to the separation column
5
is separated for every components under interaction with the packing material filled in the separation column
5
. The separated sample substances are fed into an ion source
7
together with the mobile phase solvent.
Although there are several kinds of ion sources to be applicable, the case in which the ion source
7
operated under an electrospray will be described as one typical example of it. The sample component reached to the ion source
7
is fed into a metal tube
9
through a connector
8
. As a high voltage of several kilo-volts is applied between the metal tube
9
and an electrode
10
arranged in opposition to the terminal end of the metal tube
9
by a high voltage power supply
11
, electrospray may be produced from the terminal end of the metal tube
9
toward the opposing electrode
10
. In this case, although a flow rate of solution capable of keeping a stable electrospray is several micro-litters per minute, a flow rate of solution fed from the liquid chromatograph
1
to the ion source
7
is normally 1 milli-litter per minute. In view of this fact, nebulization gas
13
supplied from a gas supplying tube
12
is flowed along the outer circumference of the metal tube
9
and then the aforesaid electrospray is assisted by the high speed gas flow. Since some ions related to the components in the sample are contained in liquid droplets generated by the electrospray, the liquid droplets are dried to enable ions of gaseous sample component to be attained.
The ions produced in this way are fed through an ion introduction aperture
14
a
arranged in the opposing electrode
10
into a differential pumping region
16
evacuated by a vacuum pumping system
15
a,
and further fed through an ion introduction aperture
14
b
into a vacuum region
17
evacuated by a vacuum pumping system
15
b.
Ions fed into the vacuum region
17
are focused by an ion focusing lens
18
composed of electrodes
18
a,
18
b
and
18
c,
thereafter the ions are fed into the ion trap type mass analysis region
20
. In addition, the gate electrode
21
is arranged in order to control injection of ions into the ion trap type mass analysis region
20
.
The ion trap type mass analysis region
20
is comprised of endcap electrodes
19
a,
19
b
and a ring electrode
19
c.
In
FIG. 2
are indicated an amplitude of a high frequency voltage applied to the ring electrode
19
c
and a change in time of a control voltage applied to the gate electrode
21
only for a time in which a mass spectrum is taken once (a relation in variation of time in respect to a voltage applied to each of the electrodes shown in
FIG. 2
is hereinafter called as a scan function).
As shown in
FIG. 2
, at first, a high frequency voltage is applied to the ring electrode
19
c
within an ion accumulating period
101
and then a potential for use in trapping the ions is formed within a space enclosed by the endcap electrodes
19
a,
19
b
and the ring electrode
19
c
(hereinafter called as an ion trap space). In this case, when positive ions are analyzed, a control voltage applied to the gate electrode
21
is decreased (on) in order to enable the positive ions to pass through the gate electrode
21
. Ions introduced into the vacuum region
17
are focused by the focusing lens
18
, pass through the opening of the endcap electrode
19
a
and then incident into the aforesaid ion trap space.
Collision gas such as helium gas or the like is fed into the aforesaid ion trap space and it is kept at a pressure of about 1 mTorr or the like, so that ions injected into the aforesaid ion trap space strike against molecules of the aforesaid collision gas to lose their energy, wherein the ions are trapped into the ion trap space by the ion trap potential formed in the aforesaid ion trap space.
Then, an amplitude of the high frequency voltage applied to the ring electrode
19
c
in the scan period
102
is increased in sequence to perform a mass scanning. In this case, the control voltage applied to the gate electrode
21
is increased (off) to prevent the ions from passing through the gate electrode
21
. As an amplitude of the high frequency voltage applied to the ring electrode
19
c
is gradually increased, an orbit of ions having a lower value (m/z) in which a mass (m) of ions is divided by an electrical charge (z) of ions becomes unstable and then the ions are discharged out of the mass analysis region
20
through the opening of the endcap electrode
19
b.
The discharged ions are detected by an ion sensor
22
, its detected signal is sent to a data processing unit
24
through a signal line
23
and processed there.
Upon completion of the scan period
102
, the high frequency voltage applied to the ring electrode
19
c
is turned off to diminish an ion trapping potential and further remove ions remained in the mass analysis region
20
(the residual ion eliminating period
103
). Such a series of operations (ion accumulation
101
, scanning
102
and residual ion eliminating
103
) are performed in a repetitive manner, resulting in that the mass of samples fed in sequence from the liquid chromatograph
1
can be analyzed.
In addition, although not illustrated in
FIG. 1
, the liquid chromatograph
1
, the ion source
7
and the ion trap mass analysis region
20
are controlled by a control system (including a power supply for controlling operation, a control circuit or a control software or the like
ot shown).
The mass spectrometer having the aforesaid electrospray region and the ion trap type mass analysis region is already disclosed in Analytical Chemistry, 1991, Volume No. 63 and page 375, for example. In addition, a principle in operation of the ion trap type mass analysis region is already disclosed in the official gazett
Hashimoto Yuichiro
Nabeshima Takayuki
Sakairi Minoru
Takada Yasuaki
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Nguyen Kiet T.
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