Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
2000-09-12
2003-05-20
Anderson, Bruce (Department: 2881)
Radiant energy
Ionic separation or analysis
With sample supply means
C250S281000, C250S282000
Reexamination Certificate
active
06566652
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
The present invention relates to a mass spectrometry apparatus in which a sample is ionized at atmospheric pressure, and particularly relates to a mass spectrometry apparatus that is most suitable in regard to protection from an accident and contamination after stopping measurement.
In order to analyze an extremely small amount of a useful or harmful organic compound at high-sensitivity, within heavy organic matrices in an environment, a food or a bio-fluid, a mass spectrometry apparatus directly connected to a liquid chromatograph (LC/MS apparatus) has been widely used. This apparatus is constructed with the liquid chromatograph (LC) acting as a separation means and a mass spectrometer (MS) providing a highly sensitive qualitative analysis and quantitative analysis means connected thereto, and has come to be used in various fields such as pharmaceutical science, medical science, chemistry, and environmental chemistry, etc.
FIG. 3
shows a conventional atmospheric pressure ionization LC/MS apparatus. A sample liquid is injected from a sample injection port
62
of the LC
1
, and is fed into an analytical column
63
with a mobile phase solution sent from a mobile phase bottle
60
by a pump
61
. The sample is separated into all components thereof by the analytical column
63
. A water, methanol, or organic solvent such as acetonitrile etc or a mixture solution thereof are used as the mobile phase.
The sample component being separated is transmitted from the analytical column
63
with the solution of the mobile phase, and is introduced into the nebulizer probe
4
through a capillary tube.
A high voltage of from about 3 kV to 6 kV is applied on the tip part of the nebulizer probe
4
. At this location, the nebulization gas is supplied from the gas cylinder
40
through the stop valve
42
, and the solution is sprayed as minute droplets, each having a charge, into the atmosphere of the atmospheric pressure ion source
7
by a high-speed nebulization auxiliary gas emitted in a coaxial direction of the capillary tube and a high electric field. These fine droplets are further cleaved into tininess by frequent collisions with gas molecules in the atmosphere, and the ions are finally expelled into the atmosphere of the atmospheric pressure ion source
7
. This ionization process is known as an electro spray ionization (ESI).
The ions are introduced into the vacuum chamber of an intermediate pressure chamber
12
through the aperture
11
or a capillary tube (not shown in the figure), and then introduced into a high vacuum chamber
16
from the aperture
14
through a differential pumping system evacuated by plural vacuum pumps
22
and
23
. Using mass spectrometer
15
, disposed in this high vacuum chamber
16
, the ions are mass-analyzed, and a mass spectrum or a chromatogram is provided by a data processor
19
.
In this atmospheric pressure ionization LC/MS apparatus, the ion source is extremely important, because neutral molecules of the sample must be released in a gas phase as the ions in a stable manner while maintaining a high efficiency. In the present invention, in accordance with the target sample for an analysis and the mobile phase of the LC, different plural atmospheric pressure ion sources may be used. That is, other than above-mentioned ESI used as the atmospheric pressure ion source, atmospheric pressure chemical ionization (APCI) for ionizing by a corona discharge from a needle electrode to which is applied a high voltage, and sonic spray ionization (SSI) which ionizes sample molecules in coincidence with the spray of the solution with the help of the spray gas of subsonic velocity, are well known.
A toxic organic solvent such as methanol or acetonitrile is used as the mobile phase of the liquid chromatograph (LC). As for this mobile phase, it is nebulized and vaporized within the atmospheric pressure ion source, and generates a large quantity of poisonous gas. In order to let the nebulized droplets evaporate, an internal chamber of the atmospheric pressure ion source
7
is kept at a high temperature (not less than 300). In addition, a high voltage (about 3 kV to 6 kV) is applied to the electrode for the ionization. Accordingly, the atmospheric pressure ion source
7
is isolated from an operator with a cover case
8
shaped like a tube or a box in order to prevent leakage of the poisonous gas externally and to prevent the operator from coming in contact with parts that are at a high voltage or at a high temperature.
Furthermore, U.S. Pat. No. 4,209,696 discloses promoting the evaporation of the nebulized droplets, by forming the atmospheric pressure ion source into an air tight structure so as to raise the pressure in the ion source, and to prevent invasion of an impurity from the outside atmosphere into the ion source so as not to generate unnecessary ions.
In Japanese patent 2854761 furthermore, surrounding the atmospheric pressure ion source with a double cover is shown, and stabalizing flow of the nebulization gas so as to stabilize the ionization thereof.
By forming the atmospheric pressure ion source
7
with an air tight structure, it becomes possible for the operator to continue the measurement safely. However, certain serious problems of accident and contamination can be caused by this air tight structure.
The sample solution which is nebulized into the atmosphere of the atmospheric pressure ion source
7
from the tip of the nebulizer probe
4
so as to be a gas, has a part thereof introduced into an intermediate pressure chamber
12
or into a high vacuum chamber
16
with the ions, and is evacuated by the vacuum pumps
22
and
23
. The largest part of the nebulization gas and the sample solution which is vaporized goes outside and is disposed of through a disposal gas pipe
31
provided on a wall of the cover case
8
of the atmospheric pressure ion source
7
. As the disposal gas contains harmful organic solvent in large quantities, it cannot be drained into laboratory directly. The disposal gas vapor is condensed in a waste liquid bottle
33
cooled by a freezer. The non-toxic nitrogen gas which is not condensed is disposed of from a disposal port
34
of the waste liquid bottle
33
. As a simple method which does not use the freezer, instead uses a method of filling the water
32
in the effluent bottle
33
, to bubble the disposal gas in the water in the waste bottle
33
, and to absorb and dissolve freely methanol and acetonitrile in the exhaust gas into the water so as to remove them.
In the condition where the LC/MS apparatus is working, a large quantity of the nebulization gas is introduced in the atmospheric pressure ion source
7
, and it is disposed of through a disposal gas pipe
31
. When the measurement is finished, first of all, the operator stops the pump
61
of the LC
1
, and stops sending the liquid of the mobile phase. The power supply of the heater of the atmospheric pressure ion source (not shown in the figure) is then turned on, the temperature is cooled down, and the power supply which is supplied to the high voltage ion source (not shown in the figure) is intercepted. The data processor
19
is stopped, the stop valve
42
is closed, and the feeding of nebulization gas is stopped.
Even if the measurement is finished, the evacuation system of the mass spectrometer does not stop. That is, the vacuum pumps
22
and
23
continue the evacuation. This is because there is a need to always keep the mass spectrometry apparatus in a high vacuum for the stable measurement of the LC/MS. The waste solution
32
is not disposed of to the outside when the measurement is stopped, and is put in the waste liquid bottle
33
, and the end of the disposal pipe
31
inserted in the waste liquid bottle
33
sinks in the waste liquid
32
. In such a state, if the vacuum system of LC/MS continues working during the night and the holidays, a possibility of a big accident exists.
That is to say, the atmospheric pressure ion source
7
becomes an air tight structure by means of a cover case
8
. Therefore the atm
Anderson Bruce
Souw Bernard
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