Radiant energy – Ionic separation or analysis
Reexamination Certificate
2001-03-15
2003-09-02
Lee, John R. (Department: 2881)
Radiant energy
Ionic separation or analysis
C250S288000
Reexamination Certificate
active
06614017
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a liquid chromatograph mass spectrometer (hereinafter referred to as LC/MS).
FIG. 2
is a schematic structural view showing one example of a general LC/MS. A liquid sample temporally separated and eluted from a column
11
of a liquid chromatograph (LC) section
10
is introduced into an interface section
20
, and is sprayed in a spray chamber
22
from a nozzle
21
to be ionized. Generated ions pass through a solvent removing tube
23
, such as a heated capillary, located in front of the nozzle
21
, and the ions are sent to a mass spectrometer (MS) section
30
.
The MS section
30
is formed of three chambers, that is, a first intermediate chamber
31
, a second intermediate chamber
32
and an analysis chamber
33
, wherein the aforementioned solvent removing tube
23
is provided between the spray chamber
22
and the first intermediate chamber
31
, and a skimmer
35
having a through hole (orifice) with a very small diameter is formed between the first intermediate chamber
31
and the second intermediate chamber
32
. An inside of the spray chamber
22
is maintained at an approximately atmospheric pressure, the first intermediate chamber
31
is exhausted to become an approximately 100 Pa by a rotary pump, and the second intermediate chamber
32
and the analysis chamber
33
are respectively exhausted by a turbo-molecular pump to become a range from approximately 10
−1
Pa to 10
−2
Pa and a range from approximately 10
−3
to 10
−4
Pa, respectively. That is, the vacuum conditions are gradually increased from the spray chamber
22
toward the analysis chamber
33
.
Ions which have passed through the solvent removing tube
23
as described above are converged by deflector electrodes
34
into the orifice of the skimmer
35
such that the ions pass through the skimmer
35
and are introduced into the second intermediate chamber
32
. Then, the ions are focused by ion lenses
36
and accelerated to be sent to the analysis chamber
33
, and only objective ions having specific mass numbers (mass m/charge z) pass through a quadrupole filter
37
disposed in the analysis chamber
33
to thereby reach a detector
38
. In the detector
38
, an electric current in accordance with a number of the ions which have reached is taken out.
The interface section
20
is provided for generating gas ions by atomizing the liquid sample by heating, a high-speed air flow, a high electric field or the like, and an atmospheric pressure chemical ionization (APCI) method or an electrospray ionization (ESI) method has been used most widely. In the APCI method, a needle electrode is disposed in front of a distal end of the nozzle
21
, and droplets of the liquid sample atomized by heating in the nozzle
21
are chemically reacted with carrier gas ions (buffer ions) generated by a corona discharge from the needle electrode, to conduct ionization. On the other hand, in the ESI method, a high voltage in the order of several kV is applied to the distal end of the nozzle
21
, to thereby generate a strong non-uniform electric field. The liquid sample is subjected to a charge separation by this electric field, and the separated ions are pulled apart by a Coulomb attraction, so that the liquid sample is sprayed. By contacting the surrounding air, the solvent in the droplet is evaporated, and the gas ions are generated.
As shown in FIG.
3
(
a
), a small droplet containing ions, which is generated by either the APCI method or ESI method described above, enters the solvent removing tube
23
due to momentum in case of being sprayed from the nozzle
21
and the aforementioned pressure difference between the spray chamber
22
and the first intermediate chamber
31
. The solvent removing tube
23
is heated, and in the small droplet passing through the heated solvent removing tube
23
, the evaporation of the solvent is accelerated by the heat. At the same time, as the size of the droplet is reduced, a voluntary destruction of the droplet due to Coulomb repulsion is further progressed, so that the droplet is ionized.
Ideally, the solvent in the small droplet sprayed from the nozzle
21
is supposed to be evaporated in the solvent removing tube
23
completely, and only ions proceed to the first chamber
31
and the subsequent sections to be subjected to the mass spectrometry. In reality, however, although a part of the small droplet is lessened, the liquid sample in the droplet condition proceeds to the first intermediate chamber
31
, the skimmer
35
and so on, and enters the detector to generate a noise.
Therefore, in order to reduce the noise described above, various contrivances have been made to the solvent removing tube
23
and a positional relationship between the solvent removing tube
23
and the nozzle
21
. Structures shown in FIG.
3
(
b
) and FIG.
3
(
c
) are respectively made such that the droplet is not directly sprayed toward the solvent removing tube
23
. In FIG.
3
(
b
), the nozzle
21
is disposed such that a spraying direction is oblique with respect to a central axis of the solvent removing tube
23
, and in FIG.
3
(
c
), the nozzle
21
is disposed such that the spraying direction is perpendicular to the central axis of the solvent removing tube
23
. As described above, however, since the droplet is sucked or attracted not only by the momentum due to the spraying but also by the pressure difference between both chambers, those structures can not fully prevent the droplet from entering a subsequent chamber (first intermediate chamber
31
).
Thus, as shown in FIG.
3
(
d
), a system has been proposed, wherein a solvent removing tube
24
is bent at 90 degrees, and furthermore, the spraying direction of the nozzle
21
is directed perpendicular to a central axis of an entrance side of the solvent removing tube
24
. According to this system, since the droplets entering the solvent removing tube
24
once collide against a tube wall of the de-solvent tube
24
at a bent portion, it is possible to greatly reduce a number of the droplets which advance straight and enter the subsequent chamber as they are.
In the structure as shown in FIG.
3
(
d
), however, there were the following problems. Firstly, since the nozzle
21
is located at a position close to a partition wall
25
between the nozzle
21
and the subsequent chamber, the partition wall
25
is contaminated with the sample droplets sprayed from the nozzle
21
. In the LC/MS in which the components of the sample change momentarily, contamination by the components at one point effects an analysis of the components at a next or subsequent point (so-called memory effect). This appears as a tail in the latter half of the component peak in a chromatograph, resulting in preventing an accurate analysis of the sample.
Also, since the partition wall
25
is contaminated, it has to be cleaned properly before an analysis for another sample. Further, since the spraying direction is perpendicular to the partition wall
25
, the sprayed droplets collide against the partition wall
25
, so that the droplets are gathered with the droplets nearby to grow into a larger droplet while the droplets are bouncing back. When the larger droplet described above reaches the entrance of the solvent removing tube
24
to be sucked, there is increased a possibility that the droplet does not evaporate in the solvent removing tube
24
, and reaches the subsequent chamber.
The present invention has been made in order to solve the foregoing problems, and an object of the invention is to provide a liquid chromatograph mass spectrometer in which a noise is lowered and a memory effect is prevented in a high-density sample to thereby conduct an accurate analysis.
Further objects and advantages of the invention will be apparent from the following description of the invention.
SUMMARY OF THE INVENTION
To achieve the aforementioned object, the present invention provides a liquid chromatograph mass spectrometer, in which a solvent removing tube is dispose
Johnston Phillip A.
Kanesaka & Takeuchi
Lee John R.
Shimadzu Corporation
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