Radiant energy – Ionic separation or analysis
Reexamination Certificate
2000-03-27
2002-10-29
Lee, John R. (Department: 2881)
Radiant energy
Ionic separation or analysis
C250S282000, C250S286000, C250S287000, C250S288000
Reexamination Certificate
active
06472661
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a mass spectroscope used in liquid chromatography, or a mass spectroscope for a liquid chromatograph (herein abbreviated into “LC-MS”).
As shown in
FIG. 5
, a representative example of currently available LC-MS may be described as consisting of a liquid chromatograph (LC) part
10
, an interface part
20
and a mass chromatograph (MS) part
30
, and a liquid sample which elutes from a column
11
in the LC part
10
in a time-wise separated manner is introduced into the interface part
20
and is sprayed into an atomization chamber
22
through a nozzle
21
to be ionized. The ions thus generated are passed into the MS part
30
through a solvent-removing tube
23
such as a heated capillary. The MS part
30
consists of a first intermediate chamber
31
, a second intermediate chamber
32
and an analyzer chamber
33
, the solvent-removing tube
23
and a skimmer
35
having an orifice with an extremely small diameter being provided respectively between the atomization chamber
22
and the first intermediate chamber
31
and between the first intermediate chamber
31
and the second intermediate chamber
32
. The interior of the atomization chamber
22
is maintained approximately at an atmospheric pressure but the interior of the first intermediate chamber
31
is reduced to about 1 Torr by means of a rotary pump while the interior of the second intermediate chamber
32
and the analyzer chamber
33
is reduced by means of a turbo molecular pump respectively to about 10
−3
-10
−4
Torr and about 10
−5
-10
−6
Torr. In other words, it is so arranged that the degree of vacuity becomes progressively higher from the atomization chamber
22
to the analyzer chamber
33
.
The ions which have passed through the solvent-removing tube
23
are caused to converge to the orifice of the skimmer
35
by means of deflector electrodes
34
, pass through the skimmer
35
and are introduced into the second intermediate chamber
32
. They are then transported into the analyzer chamber
33
, being converged and accelerated by ion lenses
36
, and only the target ions having a specified mass number (or the ratio between the mass m and its electric charge z) are allowed to pass through a quadrupole filter
37
disposed inside the analyzer chamber
33
and to reach a detector
38
which is adapted to output a current determined by the number of ions which have been received thereby.
The interface part
20
is for generating gas ions by atomizing the liquid sample through heating, a high-speed gas flow or a high electric field. The so-called atmospheric pressure chemical ionization (APCI) and electro-spray ionization (ESI) methods are most commonly used for this purpose. By the APCI method, a needle electrode is disposed in front of the forward end of the nozzle
21
and the ionization process is carried out by causing the drops of the sample liquid atomized by the heating at the nozzle
21
to undergo a chemical reaction with the carrier gas ions (buffer ions) generated by the corona discharge from the needle electrode. By the ESI method, a highly uneven electric field is generated by applying a high voltage of several kV to the tip of the nozzle
21
. The liquid sample is separated according to the charge by this electric field and atomization takes place by the Coulomb attraction. The solvent in the liquid drops is evaporated by contacting the environmental air and gas ions are thus generated.
By either of these methods, the generated small liquid drops containing ions are introduced into the heated solvent-removing tube
23
and the evaporation of the solvent inside these liquid drops takes place while these liquid drops are transported into the first intermediate chamber
31
. Since the spontaneous destruction of the liquid drops due to the Coulomb repulsion is accelerated as the liquid drops become smaller, the generation of the target ions is also accelerated.
In order to improve the sensitivity of analysis by using an LC-MS thus structured, it is important to ionize the liquid sample efficiently at the interface part
20
and to introduce the generated ions efficiently into the quadrupole filter
37
(or any other kind of mass analyzer). These can be accomplished only if various parameters for the operations of the interface part
20
and the MS part
30
(such as the temperatures and applied voltages) are properly set. With a prior art LC-MS, the voltages to be applied to the solvent-removing tube
23
and the deflector electrodes
34
are adjusted such that the number of ions reaching the detector
38
will be maximized, for example, when a standard sample containing a specified component is introduced, that is, such that the peak of the mass spectrum corresponding to this specified component will reach a highest value. In practice, however, the voltage at which the solvent-removing tube
23
and the deflector electrodes
34
pass the ions most efficiently depends on the mass number of these ions. When a measurement is taken by scanning over a certain range of masses, therefore, the solvent-removing tube
23
and the deflector electrodes
34
are not necessarily in optimum conditions for passing the ions, and this has been one of the factors preventing the prior art LC-MS from operating under an optimum condition in terms of the sensitivity and accuracy of the detection.
SUMMARY OF THE INVENTION
It is therefore an object of this invention in view of these problems to provide an improved mass spectroscope for a liquid chromatograph capable of efficiently introducing target ions to be analyzed into the mass spectroscope part such that its detection sensitivity and detection accuracy can be improved.
A mass spectroscope for a liquid chromatograph embodying this invention, with which the above and other objects can be accomplished, may be characterized not only as comprising an interface including an atomization chamber into which a liquid sample from the liquid chromatograph is sprayed to be converted into ions, an intermediate chamber at a reduced inner pressure and a detection chamber at a lower inner pressure than the intermediate chamber and containing a mass analyzer but also as having a solvent-removing tube for causing liquid droplets containing these ions to pass through from the atomization chamber into the intermediate chamber, means for causing these ions to travel along a travel path through the intermediate chamber into the detection chamber, a deflector having at least one pair of planar electrodes disposed inside the intermediate chamber and opposite each other sandwiching the travel path in between, a voltage generating means for applying a variable DC voltage to the solvent-removing tube, separate voltage generating means for independently applying a different variable DC voltages to each of these electrodes, a memory which stores data on voltages to be applied to the solvent-removing tube and to the electrodes for optimizing efficiency with which ions with different mass numbers are received by the mass analyzer, and a control unit for applying a specified voltage to the mass analyzer and simultaneously controlling the voltage generating means so as to have voltages selected according to the data stored in the memory and applied to the solvent-removing tube and to the electrodes.
In using a mass spectrometer according to this invention, one or more standard samples containing components with different mass numbers are preliminarily analyzed to determine optimum voltages to be applied to the solvent-removing tube and the deflector electrodes for each of the mass numbers. A voltage scan pattern is produced on the basis of these data such that optimum or nearly optimum voltages can be applied corresponding to all mass numbers of interest, and the pattern thus produced is stored in a memory device. At the time of a measurement, the voltages to be applied are varied such that only the ions having particular mass numbers are sequentially allowed to pass through. At the same time, the control unit cont
Tanaka Yasufumi
Yamamoto Yoshitake
Beyer Weaver & Thomas LLP
Lee John R.
Shimadzu Corporation
Vanore David A.
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