U.S. patent application number 10/323960 was filed with the patent office on 2003-05-15 for method and an apparatus for analyzing trace impurities in gases.
This patent application is currently assigned to NIPPON SANSO CORPORATION. Invention is credited to Nishina, Akira, Satou, Tetsuya.
Application Number | 20030092193 10/323960 |
Document ID | / |
Family ID | 26351565 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030092193 |
Kind Code |
A1 |
Nishina, Akira ; et
al. |
May 15, 2003 |
Method and an apparatus for analyzing trace impurities in gases
Abstract
The present invention relates to a method and an apparatus for
analyzing trace impurities in gases, which enable to analyze a very
small quantity of impurities by only a simple operation, without
making the column arrangement or the structure of flow complicated.
In the apparatus and the method, when the trace impurities are
measured in ppb-sub ppb level by a combined analyzer which is
equipped with an atmospheric pressure ionization mass spectrometer
to the back of a gas chromatography, a mixed gas of various gases
is used as a carrier gas or purified gases added to the gases
outflowed from a gas chromatography.
Inventors: |
Nishina, Akira; (Minato-ku,
JP) ; Satou, Tetsuya; (Minato-ku, JP) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
NIPPON SANSO CORPORATION
Minato-ku
JP
|
Family ID: |
26351565 |
Appl. No.: |
10/323960 |
Filed: |
December 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10323960 |
Dec 18, 2002 |
|
|
|
09491101 |
Jan 25, 2000 |
|
|
|
Current U.S.
Class: |
436/161 ;
436/173 |
Current CPC
Class: |
H01J 49/0422 20130101;
G01N 30/7206 20130101; Y10T 436/22 20150115; Y10T 436/214 20150115;
Y10T 436/100833 20150115; Y10T 436/24 20150115 |
Class at
Publication: |
436/161 ;
436/173 |
International
Class: |
G01N 030/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 1999 |
JP |
11-15421 |
Dec 14, 1999 |
JP |
11-354890 |
Claims
1. A method for analyzing trace impurities in gases, the method
comprising the steps of: separating main components and trace
impurities from a sample gas conveyed by a carrier gas by using a
gas chromatography; introducing the gases outflowed from said gas
chromatography into an atmospheric pressure ionization mass
spectrometer; and analyzing the trace impurities, wherein a mixed
gas is used as the carrier gas.
2. A method for analyzing trace impurities in gases, the method
comprising the steps of: separating main components and trace
impurities from a sample gas conveyed by a carrier gas by using a
gas chromatography; adding purified gas into the gases outflowed
from said gas chromatography; introducing the gases into an
atmospheric pressure ionization mass spectrometer; and analyzing
the trace impurities, wherein a mixed gas is used as at least one
of the carrier gas and the purified gas.
3. A method for analyzing trace impurities in gases according to
claim 1 or 2, characterized in that the mixed gas is Ar--He mixed
gas.
4. A method for analyzing trace impurities in gases, the method
comprising the steps of: separating main components and trace
impurities from a sample gas conveyed by a carrier gas by using a
gas chromatography; introducing the gases outflowed from said gas
chromatography into an atmospheric pressure ionization mass
spectrometer; and analyzing the trace impurities, wherein a single
component gas is used as the carrier gas, and purified gas, the
kind of which is different from the carrier gas, are added to the
outflowed gas.
5. A method according to claim 4, characterized in that if said
carrier gas is He, the added purified gas is one selected from the
group of Ar alone, He--Ar mixed gas, Ar--H.sub.2 mixed gas and
Ar--H.sub.2 mixed gas, and if said carrier gas is Ar, the added
purified gas is He alone, or He--Ar mixed gas.
6. A method for analyzing trace impurities in gases, the method
comprising the steps of: introducing a sample gas into a gas
chromatography using He as a carrier gas; separating main
components and trace impurities from the sample gas; adding a
purified gas of Ar alone or Ar--He mixed gas into the gases
outflowed from the gas chromatography; introducing the gases into
an atmospheric pressure ionization mass spectrometer; and analyzing
the trace impurities, wherein the impurity of H.sub.2 is detected
by mass number 41 or 81, and the impurity of methane is detected by
mass number 16.
7. A method for analyzing the trace impurities in gases, the method
comprising the steps of: introducing a sample gas into a gas
chromatography by using He as a carrier gas; separating main
components and trace impurities from the sample gas; adding a
purified gas into the gases outflowed from the gas chromatography;
introducing the gases into an atmospheric pressure ionization mass
spectrometer; and analyzing the trace impurities, wherein at least
two of i) He alone, ii) He--Ar mixed gas, iii) He--H.sub.2 mixed
gas and iv) Ar--H.sub.2 mixed gas, are selected, and switchably
used as said purified gases.
8. A method according to one of claims 2, 3, 4, 5, 6 and 7,
characterized in that the added amount of the purified gases is
changed depending on the kind of the outflowed gas.
9. A apparatus for analyzing the trace impurities in gas, the
apparatus comprising a gas chromatography for separating the main
component and trace impurities from a sample gas conveyed by a
carrier gas; an atmospheric pressure ionization mass spectrometer
connected to the back of the gas chromatography; and a purified gas
adding passage for adding the purified gases into the gas outflowed
from the gas chromatography, the purified gases adding passage
being installed in a passage between the gas escaping part of the
gas chromatography and the gas introduction passage of the
atmospheric pressure ionization mass spectrometer, wherein i) a
passage for supplying a purified gas whose kind is the same with
the carrier gas, ii) a passage for supplying another purified gas
whose kind is different from the carrier gas, and iii) a mixed
ratio regulating means for regulating the mixed ratio of both
purified gases are installed in the purified gas adding
passage.
10. An apparatus according to claim 9, wherein an added amount
controlling means for regulating the added amount of the purified
gases depending on the kind of the outflowed gas, is installed in
the purified gas adding passage.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method and an apparatus
for analyzing trace impurities in gases, and particularly to a
method and an apparatus for detecting ppb-sub ppb level of trace
impurities in various high-purified gases, by a combined analyzer
comprised of gas chromatography and atmospheric pressure ionization
mass spectrometer.
[0003] 2. Description of the Prior Art
[0004] In case of analyzing (detecting) the impurities in
high-purified gases by combined analyzer comprised of gas
chromatography and atmospheric pressure ionization mass
spectrometer, the outflowed/gas(30-50 cc/min) from a gas
chromatography which uses packed column, does not reach the gas
flow(100-500 cc/min) necessary for a common atmospheric pressure
ionization mass spectrometer. Therefore, the outflowed gas from a
gas chromatography was added by purified gases, the kind of which
is the same with the carrier gas used in the gas chromatography,
and then introduced into an atmospheric pressure ionization mass
spectrometer(Japanese Patent Laid Open Gazette Hei. 6-3471,
Japanese Patent Laid Open Gazette Hei.9-15207)
[0005] High-purified He(helium) or Ar gas is commonly used as the
carrier gas and the purified gas. In particular, He is much
preferred, because its ionization potential (24.59 eV) is higher
than those of other gases, and all kinds of impurities except He
can be detected.
[0006] Nevertheless, when He gas is used as a carrier gas, it is
also sensitive to some main component such as O.sub.2, N.sub.2 and
Ar, and their ions are generated in a large quantities. Therefore,
some impurities hardly separable from the main components could not
be detected well, and the measurement with a high sensitivity was
hard to be obtained.
[0007] Under the circumstance, a method, in which impurities and
main components are separated before being introduced into the
atmospheric pressure ionization mass spectrometer, has been carried
out to improved the sensitivity of measurement. For example, a
complicated applied flow passage using a method such as "Heart Cut
method", is installed and then cut just before the main component
is outflowed from a gas chromatography, and the outflowed gas is
introduced into the atmospheric pressure ionization mass
spectrometer about at the point of time when the outflow of the
main component ends.
[0008] However, there is a problem in the above method, in that the
main components near the impurities were not separated well, and
the introduction of the main components into the atmospheric
pressure ionization mass spectrometer could not be avoided
completely, which causes increased noises and weakened sensitivity
when analyzing the impurities.
[0009] There is another problem that as columns used for a
long-term could increase the retention time of the main components
and thus the subject impurities could be separated and removed.
Therefore, the retention time should be checked regularly, which
requires much labors, and many columns for removing the main
components and complicated flow are also required.
[0010] There is still another problem in another method of removing
the main components by an absorbent, in that the subject impurities
are removed together with the main components, or the other
impurities are generated from the absorbent in ppb-ppm levels,
resulting that the measurement in ppb level is hard to perform.
[0011] In addition, in case of using a atmospheric pressure
ionization mass spectrometer, as He generates helium cluster ion
(He.sub.4+)(mass number=16) in a large amount, CH.sub.3+(mass
number=15) is measured for analyzing methane(M.W.=16). However,
there is a problem that the sensitivity of mass number 15 is not so
good as mass number 16(CH.sub.4+). Moreover, as the discharge of He
is less stable compared with other gases and the stability of the
main components are not good, the sensitivity to H.sub.2, which is
detected by He.sub.2H+(mass number=9) generated by combining
He.sub.2+ and proton, is also bad.
[0012] In case of Ar, which has a good discharge nature, there is a
problem that the ionization potential of Ar(15.76 eV) is near that
of N.sub.2 (15.58 eV), and thus transfer of electric charges is
hardly generated and the measurement of the impurities like N.sub.2
or Ne, whose ionization potentials are higher than those of Ar, is
impossible.
[0013] Under the circumstance, when the impurities are measured to
the level of sub ppb in high purified O.sub.2, He is used for Ne or
N.sub.2 of impurities, Ar is used for of H.sub.2, CH.sub.4, CO or
CO.sub.2 of impurities. That is, He should be supplied for
analyzing N.sub.2 etc., and Ar should be supplied for analyzing
H.sub.2 etc., as a carrier gas and purified gases added. Therefore,
much labor and time were required for switching the supply of the
gases, and the measurement cannot be carried out quickly.
[0014] The other method has been proposed, in which a third
component gas is incorporated into the sample gas when the analysis
is performed by atmospheric pressure ionization mass spectrometer
alone (Japanese Patent Laid-Open Gazette Hei.6-74940). However, the
method has a problem that the impurities in the third component gas
should be checked in advance, because they could have an effect on
the analysis of the impurities in the sample gas.
[0015] For example, when analyzing N.sub.2 as an impurity in Ar, as
the ionization potentials of both gases are mutually near each
other, the sensitivity of the analysis is very bad and the
measurement cannot be carried out at ppb level. Therefore, a method
has been proposed, in which the measurement is performed by an
atmospheric pressure ionization mass spectrometer using proton
transfer rection after adding H.sub.2 in the level of % into the
sample gas of Ar. In this method, the check of the impurity N.sub.2
in H.sub.2 added , or the separation of CO in Ar both of which have
the same mass number is hardly performed. Therefore, the
measurement is carried out for N.sub.2+CO, and thus the
concentration of CO in the sample gas should be checked in advance,
resulting in a very tedious and bothering work.
SUMMARY OF THE INVENTION
[0016] The present invention is purposed to provide a method and an
apparatus for analyzing trace impurities in gases, which enable to
analyze a very small quantity of impurities by a simple operation,
without making the column arrangement or the structure of flow
complicated.
[0017] In accordance with the object of the present invention,
there is provided a method for analyzing the trace impurities in
gases, the method comprising-the steps of:
[0018] separating main components and trace impurities from a
sample gas conveyed by a carrier gas by gas chromatography;
[0019] introducing the gases outflowed from said gas chromatography
into an atmospheric pressure ionization mass spectrometer; and
[0020] analyzing the trace impurities, wherein a mixed gas is used
as the carrier gas.
[0021] In accordance with another object of the present invention,
there is provided a method of analyzing the trace impurities in
gases, the method comprising the steps of:
[0022] separating main components and trace impurities from a
sample gas conveyed by a carrier gas by gas chromatography;
[0023] adding purified gas into the gases outflowed from said gas
chromatography; introducing the gases into an atmospheric pressure
ionization mass spectrometer; and
[0024] analyzing the trace impurities, wherein a mixed gas is used
as at least one of the carrier gas and the purified gas.
[0025] In accordance with still another object of the present
invention, there is provided a method of analyzing the trace
impurities in gases, the method comprising the steps of:
[0026] separating main components and trace impurities from a
sample gas conveyed by a carrier gas by gas chromatography;
[0027] introducing the gases outflowed from said gas chromatography
into an atmospheric pressure ionization mass spectrometer; and
[0028] analyzing the trace impurities, wherein a single component
gas is used as the carrier gas, and purified gas which are
different from the carrier gas, are added to the outflowed gas.
[0029] In the above case, the method is characterized in that if
said carrier gas is He, the added purified gas is Ar alone, or
He--Ar mixed gas, or He--H.sub.2 or Ar--H.sub.2 mixed gas, and if
said carrier gas is Ar, the added purified gas is He alone, or
He--Ar mixed gas.
[0030] In accordance with still another object of the present
invention, there is provided a method of analyzing the trace
impurities in gases, the method comprising the steps of:
[0031] introducing a sample gas into a gas chromatography using He
as a carrier gas;
[0032] separating main components and trace impurities from the
sample gas;
[0033] adding a purified gas of Ar alone or Ar--He mixed gas into
the gases outflowed from the gas chromatography;
[0034] introducing the gases into an atmospheric pressure
ionization mass spectrometer; and
[0035] analyzing the trace impurities, wherein the impurity of
H.sub.2 is detected by mass number 41 or 81, and the impurity of
methane is detected by mass number 16.
[0036] In accordance with still further object of the present
invention, there is provided a method of analyzing the trace
impurities in gases, the method comprising the steps of:
[0037] introducing a sample gas into a gas chromatography using He
as a carrier gas;
[0038] separating main components and trace impurities from the
sample gas;
[0039] adding a purified gas into the gases outflowed from the gas
chromatography;
[0040] introducing the gases into an atmospheric pressure
ionization mass spectrometer; and
[0041] analyzing the trace impurities, wherein at least two
purified gases selected from i) He alone, ii) He--Ar mixed gas and
iii) He--H.sub.2 mixed gas or Ar--H.sub.2 mixed gas, are selected
and switchably used as said purified gas.
[0042] In accordance with still further object of the present
invention, there is provided an apparatus for analyzing the trace
impurities in gas, the apparatus comprising:
[0043] a gas chromatography for separating the main component and
trace impurities from the sample gas conveyed by carrier gas;
[0044] an atmospheric pressure ionization mass spectrometer
connected to the back part of the gas chromatography; and
[0045] a purified gas adding passage for adding the purified gas
outflowed from the gas chromatography, the purified gas adding
passage being installed in a passage between the gas escaping part
of the gas chromatography and the gas introduction passage of the
atmospheric pressure ionization mass spectrometer,
[0046] wherein i) a passage for supplying a purified gas whose kind
is the same as the carrier gas, ii) a passage for supplying a
purified gas whose kind is different from the carrier gas, and iii)
mixed ratio regulating means installed in the purified gas adding
passage for regulating a mixed ratio of both purified gases, and
added amount controlling means installed in the purified gas adding
passage for regulating the added amount of purified gases depending
on the kind of the outflowed gas are further provided.
BRIEF DESCRIPTION OF THE DRAWING
[0047] For fuller understanding of the nature and objects of the
invention, reference should be made to the following detailed
description taken in conjunction with the accompanying drawing in
which"
[0048] FIG. 1 is a flow diagram for showing a first example of the
present apparatus.
[0049] FIG. 2 is a flow diagram for showing a second example of the
present apparatus.
[0050] FIG. 3 is a flow diagram for showing a third example of the
present apparatus.
[0051] FIG. 4 is a flow diagram for showing a fourth example of the
present apparatus.
[0052] FIG. 5 is a diagram for showing the relation between the
concentration of Ar and the peak intensity of the respective
impurities in the first example.
[0053] FIG. 6 is a drawing for comparing the peaks of methane
according to the existence of Ar of the first example.
[0054] FIG. 7 is a diagram for showing the calibration curve, in
the case of adding Ar of the first example.
[0055] FIG. 8 is a drawing for comparing the peaks of CO according
to the existence of Ar of the second example.
[0056] FIG. 9 is a diagram for showing the calibration curve of CO,
in the case of adding Ar of the second example.
[0057] FIG. 10 is a drawing for comparing the peaks of CO according
to the existence of He of the third example.
[0058] FIG. 11 is a diagram for comparing the peaks of N.sub.2, in
the case of adding H.sub.2 of the fifth example.
[0059] FIG. 12 is a diagram for showing the calibration curve of
N.sub.2, in the case of adding H.sub.2 of the fifth example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0060] FIG. 1 is a flow diagram for showing a first example of the
present apparatus.
[0061] The apparatus is provided with i) a main purified gas supply
system (30) for supplying a main purified gas for use as a purified
gas to be added to the carrier gas of the gas chromatography(10)
and a gas outflowed from the gas chromatography(10),
[0062] ii) a sub-purified gas supply system(31) for supplying a
sub-purified gas to be mixed with the main purified gas and then
added to the outflowed gas, and
[0063] iii) a purified gas supply regulating means(32) for
regulating the supplied amount of the main purified gas and
sub-purified gas to be added into the outflowed gas, together with
iv) an atmospheric pressure ionization mass spectrometer(11) as a
detecting part of a gas chromatography(10), which is installed in
the back of the gas chromatography(10), for separating the main
components and trace impurities from the sample gas.
[0064] The gas chromatography(10), formed by connecting i) a
separating column(13) packed with a separator through an 8 way gas
switching cock(12), ii) two sample loop(14a, 14b), iii) a sample
gas introduction passage(15) connected to the sample gas source,
iv) a carrier gas introduction passage(16) connected to the main
purified gas supply system(30) and an exhaust passage(20) provided
with a pressure gauge(17), a back pressure regulator(18) and a mass
flow meter(19), serves to introduce the sample gas metered by a
sample loop(14a,14b) into the separating column(13) by operating
the 8 way gas switching cock(11), and to separate the respective
components of the sample gas in the separating column(13) so that
the components may be moved in order into the separated gas
outflowing passage(21).
[0065] The atmospheric pressure ionization mass spectrometer(11)
has an ion source part(22) and a mass separating part/detecting
part(23), the ion source part(22) being connected with a gas
introduction passage connected with the separated gas outflowing
passage(21) and a gas escaping passage(25) for discharging the
surplus gases. Further, the gas escaping passage(25) is provided
with a pressure gauge(26) for maintaining the pressure of the ion
source part(22), a back pressure regulator(27) and a mass flow
meter(28).
[0066] The main purified gas supply system(30) and the sub-purified
gas supply system(31) are provided with pressure regulators(33,34)
and purifier(35,36) respectively. The main purified gas supply
system(30) is diverged in two parts in the lower of the
purifier(35), a passage(37) of the two parts is connected to the
carrier gas introduction passage(16) of the gas chromatography(10)
through the mass flow controller(38), whereas the other passage(39)
of the two parts is connected to the purified gas supply regulating
means(32). In addition, in the sub-purified gas supply system(31),
the back of the purifier(36) is connected to the purified gas
supply regulating means(32).
[0067] The purified gas supply regulating means(32), for mixing the
main purified gas from the passage(39) and the sub-purified gas
from the sub-purified gas supply system(31) in a fixed ratio, and
for regulating the added amount into the outflowed gas, is provided
with a mass flow controller for main purified gas(40) and a mass
flow controller for sub purified gas(41), as well as a supply valve
for controlling the supply of the sub-purified gas and a exhaust
valve. The passage for discharging the purified gas after
mixing(gas adding passage)(44) is connected in the way of the
passage from the separated gas outflowing passage(21) to the gas
introduction passage(24).
[0068] In addition, if an automatic controller(program controller)
for controlling the flowing amount of the two mass flow controller
and the opening/shutting of the valves(42,43) at the purified gas
supply regulating means(32), the regulation of the mixed ratio of
the purified gas or the added amount of the gas could be carried
out automatically by connecting the controller with the operation
of the gas chromatography(10).
[0069] As the purified gas and sub-purified gas, a single component
gas such as He, Ar, N.sub.2 and H.sub.2, or a mixed gas such as
He--Ar mixed gas, He--H.sub.2 mixed gas, and Ar--H.sub.2 mixed gas
may be used. As a filler filled in the separating column, various
filler such as molecular sieve type or Uni beads type can be
used.
[0070] The following is an example of the processing to analyze
trace impurities in a sample gas by using the above apparatus.
[0071] First, a mass flow controller or a back pressure regulator
is set to a fixed value and the flow of the gases or the pressure
in the system is set according to a required condition for the
analysis. The sample gas is introduced from the sample gas
introduction passage(15), and flowed into one of the sample loop
(14a, 14b), for example the sample loop(14a), through the 8 way gas
switching cock(12).
[0072] Then, if the 8 way gas switching cock(12) is operated so as
to make the carrier gas flow into the sample loop(14a) in which the
sample gas flows, the fixed amount of the sample gas metered in the
sample loop(14a) is incorporated into the carrier gas and
introduced into the separating column(13) where the components of
the gas are separated in the dispersant as they proceed into the
separating column(13), and outflowed from the separated gas
outflowing passage(21) in a predetermined order.
[0073] The purified gas introduced from the gas adding passage(44)
is added into the gas outflowed to the separated gas outflowing
passage(the outflowed gas of the gas chromatography) in a fixed
amount, and introduced into the ion source part(22) of the
atmospheric pressure ionization mass spectrometer(11) through the
gas introduction passage(24). The ion source part(22) is maintained
to a predetermined pressure, such as 0.4 kg/cm.sup.2(0.04 Mpa) by
the back pressure regulator(27). Then, a part of the ionized gas
after being introduced into the ion source part(22) passes through
a slit and is introduced into the mass separating part/detecting
part(23), and the ion current of the respective components is
detected after the separation of each mass.
[0074] As explained in the above, the impurities in the sample gas
can be analyzed in a very sensitive and accurate way, by properly
selecting the main purified gas and the sub-purified gas, and
setting the added amount and the mixed ratio into the outflowed gas
of the gas chromatography. In addition, as the components are
separated in advance in the gas chromatography(10), even in the
case that the added purified gases contain impurities, the kind of
which is the same with the subject impurities to be analyzed, the
peaks of the impurities in the sample gas can be clearly detected,
and thus no prior check of the impurities in the purified gas is
required, contrary to the conventional method in which only the
atmospheric pressure ionization mass spectrometer is used.
[0075] The composition(mixed ratio) or the added amount of the
purified gas to be added to the outflowed gas, can be set according
to the main components of the sample gas, the impurities to be
analyzed, the kinds of the main purified gas and the sub-purified
gas and the like. In the above example, the mixed ratio can be
selected by properly setting the flowing amount from both the mass
flow controllers(40,41). Further, only the main purified gas may be
added into the outflowed gas in a predetermined amount, by shutting
off the supply valve(42) and opening the exhaust valve(43).
[0076] As above, the effect by the main components of the sample
gas can be removed by adding a sub-purified gas different from the
carrier gas. For example, in case the main purified gas is He, the
sub-purified gas is Ar, and the main components of the sample gas
are not only Ar but also N.sub.2, almost all the N.sub.2 in the
main components would be removed by adding He--Ar mixed gas. In
addition, in case the main component is O.sub.2, as the reaction
rate of O.sub.2 is slower by about one digit and the effect by the
main component is decreased as much, it would be possible to
measure the impurities to a more accurate degree. In addition, the
addition of Ar makes the discharge of the atmospheric pressure
ionization mass spectrometer(11) more stable. Noises are reduced
and the base lines are also stabilized.
[0077] In addition, in case of using He as a main purified gas and
Ar as a subpurified gas, as the carrier gas could be He, the
separating column(13) of the gas chromatography(10) gets more
stable. Further, by adding He--Ar mixed gas into the outflowed gas,
the H.sub.2 impurities, which has been detected by mass number 9,
can be detected by mass number 41 or 81, and methane, which has
been detected by mass number 15, can be detected by mass number 16,
and thus the sensitivity of the detection can be markedly
improved.
[0078] That is, in case of adding He--Ar mixed gas, the generated
He.sub.4+ can be destroyed and the background can be reduced, and
it can be possible to measure the methane of impurity by mass
number 16. At the same time, in case of using Ar in which case
Ar+or Ar.sub.2+ becomes the main reactant, the detection of
impurities H.sub.2 could be possible by mass number 41(ArH+) or
mass number 81(Ar.sub.2H+) with less noise, instead of the
detection by the mass number 9(He.sub.2H+) with greater noise.
[0079] In case of using He as a main purified gas, and Ar as a
sub-purified gas, by switching the gases added to the outflowed gas
with He alone and He--Ar mixed gas, the impurities undetectable by
adding a mixed gas, such as N.sub.2, Ne, Ar, etc., can be detected
by He alone, while the scope of the subject components detectable
can be enlarged and the sensitivity can be improved. Further, as
the main purified gas of He can be also used as a carrier gas, the
labor and time for changing a carrier can be saved. Besides, the
amount of the purified gas added to the outflowed gas can be
increased or decreased according to the kinds of the outflowed
gases from the gas chromatography(10).
[0080] In case of using He and Ar, the ratio of Ar to He can be
established freely. If the carrier gas is He, the concentration of
the Ar in the added gas is preferably settled to be 0-50%.
[0081] In addition, in case of measuring impurities of N.sub.2 in
Ar, for which many steps of work are needed up to now, the effect
of N.sub.2 impurity in H.sub.2 can be ignored, by using a
H.sub.2-contained mixed purified gas as a mixed gas to be added
after being separated by gas chromatography, without introducing
H.sub.2 into the sample gas in the ion source part of the
atmospheric pressure ionization mass spectrometer, such as
He--H.sub.2, mixed gas or Ar--H.sub.2 mixed gas; and the N.sub.2
impurity in Ar can be discriminated and measured in detail, because
the CO and N.sub.2 can be separated by the gas chromatography.
Moreover, as a H.sub.2-added method, a H.sub.2--contained mixed gas
can be used as a carrier gas, or the improved sensitivity can be
expected by adding H.sub.2 in measuring impurities, the sensitivity
of which can be increased by using proton transfer reaction.
[0082] As the gas chromatography(10) or the atmospheric pressure
ionization mass spectrometer(11), the conventional ones can be
used. Moreover, the scope of the main components of the sample and
the impurities to be analyzed are not limited specifically; not
only the highly purified gas such as O.sub.2, N.sub.2, H.sub.2 Ar,
He, Xe, Kr, and the like but also the gases used as material for a
semiconductor can be applied for this analyzing method. Further, it
is possible to add a purified gas comprising of 3 and more
components, for example He, Ar and Ne, into the outflowed gas.
[0083] FIG. 2 is a flow diagram for showing a second example of the
present apparatus. In this analyzing apparatus, the gas outflowed
into the separated gas outflowing passage(21), is added by the main
purified gas in a predetermined amount, and then added by the
sub-purified gas in the back. Like in the above case, the purified
gas can be added into the outflowed gas in a desired amount or in a
desired mixed ratio, by controlling the flow of the both mass flow
controllers(40,41) or by opening or shutting the valves(42,43).
[0084] As the other parts of the apparatus can be organized as in
the first example, the same numbers will be given to the same
constitutions, without repeating the detailed explanation (It will
be the same in the other examples in the following).
[0085] FIG. 3 and FIG. 4 are flow diagrams showing the third and
fourth examples of the present apparatus. The examples show
apparatuses by which the amount of the outflowed gas from the gas
chromatography(11) can be increased to a minimum amount commonly
required for the atmospheric pressure ionization mass spectrometer;
or a minimum amount of the gas of the atmospheric pressure
ionization mass spectrometer(11) can be decreased to the common
amount of the outflowed gas from the gas chromatography(10); or the
analysis can be performed by the atmospheric pressure ionization
mass spectrometer(11) without adding the purified gas into the
outflowed gas from the gas chromatography(10).
[0086] In the apparatus of the third example, the main purified gas
supply system (57) and the sub-purified gas supply system (58),
which have the pressure regulators(51,52), the purifiers(53,54) and
mass flow controllers (55,56) respectively, are connected to the
carrier gas introduction passage(16) of the gas chromatography(10),
so that one of the main purified gas and the sub-purified gas, or
the mixed gases of the main purified gas and the sub-purified gas
in an appropriate ratio, can be supplied as a carrier gas.
[0087] In the analyzing apparatus like the above, the most
appropriate carrier gas can be selected and used, depended on the
kinds of the main components of the sample gas or the impurities to
be measured; and a high sensitive detection can be performed by
selecting the gases which are properly mixed according to the
outflow timing of the subject impurities.
[0088] Further, in the apparatus of FIG. 4, the mixed gases in a
fixed ratio are filled into the gas cylinder(61), which is
connected to the carrier gas introduction passage(16) through the
pressure regulator(62), purifier63) and mass flow controller(64).
That is, if the subject sample gas to be analyzed is determined,
the predetermined mixed gas is to be supplied from the gas
cylinder(61), such that the apparatus can be simplified without
diminishing of the accuracy of the analysis. Further, as a
purifier(63) for refining the mixed gas, a purifier of getter type
is recommended.
EXAMPLE 1
[0089] The impurities contained in O.sub.2 gas(H.sub.2, methane,
N.sub.2, CO, CO.sub.2) was measured by using the apparatus of the
FIG. 1. As the gas chromatography, Uni beads 1S was filled for
measuring CO.sub.2, and molecular sieve 13XS was filled for
measuring others, into the separating column which had a diameter
of 4 mm and a length of 2 m and was made from stainless steel. The
obtained amount of the sample gas was 3 cc, and the flow amount of
the carrier(main purified gas) of He was 42 cc/min.
[0090] As for the measurement of N.sub.2, was performed, after He
was added into the outflowed gas in 1000 cc/min. Then, after the
amount of the gas added to the outflowed gas was changed to 328
cc/min and Ar(sub-purified gas) was added to He, the measurements
of H.sub.2, methane, CO and CO.sub.2 were performed while changing
the Ar concentration in the range of 0-90%. The relations between
the Ar concentration and the intensities of the peaks of the
respective impurities are shown in FIG. 5
[0091] As apparent in FIG. 5, the intensities of the peaks in the
Ar-added case were higher than in the Ar-free case(Ar
concentration=0), in all the cases.
[0092] In addition, FIG. 6 shows the measured peaks in the Ar-free
case(FIG. 6(a)) and in 5% Ar concentration case(FIG. 6(b)), for the
measurement of methane. It is recognized that if Ar is added, the
noises of the background were decreased- and the base line became
stabilized. FIG. 7 shows the calibration curve of methane in
Ar-added cases, in which the obtained linearity was satisfactory
and the accuracy was also high enough.
[0093] The result was that in case of using He--Ar mixed gas(Ar
concentration=5%), the detection limit value of H.sub.2 in O.sub.2
gas(S/N=2, the same in the following) was 0.5 ppb, that of methane
was 0.2 ppb and that of CO was 0.3 ppb. In case of Ar-free, the
detection limit value was 2 ppb for H.sub.2, 2 ppb for methane, 1
ppb for CO and 0.5 ppb for N.sub.2.
[0094] When measuring the impurities of the high purified O.sub.2
gas(.gtoreq.99.99995%), the result was 1 ppb for H.sub.2, less than
0.3 ppb for methane, 1.5 ppb for CO and 11 ppb for N.sub.2. In this
method in which the kind of the carrier was not changed and the gas
added to the outflowed gas was switched with He alone and He--Ar
mixed gas(Ar 5%), the analysis of impurities of 4 component was
carried out successfully in a short period of time of 30 minutes in
a sub-ppb level.
EXAMPLE 2
[0095] The operation was carried out in almost the same condition
with the EXAMPLE 1, except that the subject impurities to be
measured was CO, and the total amount of the gases added to the
outflowed gas was 420 cc/min. FIG. 8 shows the measured peaks for
the Ar-free case (FIG. 8(a)) and for the case of 3% of Ar
concentration(FIG. 8(b)).
[0096] As apparent in FIG. 8, the peak in the case of 3% of Ar was
stronger and more. stable in the base line compared with the cases
of Ar-free. FIG. 9 shows a calibration curve for the case of 3% of
Ar concentration. From the above, the detection limit of CO was 0.3
ppb.
EXAMPLE 3
[0097] The measurement of CO.sub.2 in N.sub.2 was carried out in
the apparatus of FIG. 1, by using Ar as a main purified gas and He
as a sub-purified gas. The separating column had 4 mm of diameter
and 1 m of length, and was made from stainless steel, being filled
with Uni beads 1S. The obtained amount of the sample gas was 4 cc,
and the flow of the carrier gas was 112 cc/min.
[0098] The measurement of CO.sub.2 was carried out for the He-free
case(FIG. 10(a)) and for the case that the He concentration was 50%
in the purified gas(FIG. 10(b)), while the amount of the gases
added to the outflowed gas was 420 cc/min.
[0099] As apparent in FIG. 10, the intensity of the peak has become
several times higher by adding He. Further, the detection limit of
the case of Ar alone was 0.6 ppb, while the detection limit was
improved to 0.2 ppb by adding Ar with 50% of He concentration into
the outflowed gas.
EXAMPLE 4
[0100] The measurement of CO.sub.2 in N.sub.2 gas was carried out
by using the apparatus showed in FIG. 3.
[0101] The separating column of the gas chromatography had 4 mm of
diameter and 2 m of length and was made from stainless steel, being
filled with molecular sieves 13XS. The obtained amount of the
sample gas was 5 cc, and the flow of the carrier gas was 112
cc/min.
[0102] A mixed purified gas(Ar concentration=about 2%), in which 2
cc of Ar was mixed to 110 cc of He, was used as a carrier gas. The
temperature of the separating column was 35.degree. C. For the
atmospheric pressure ionization mass spectrometer, the slit
diameter was set to be small and the outlet valve was regulated, so
that the inside of the ion source part may not fall under the
atmospheric pressure, even in the case that the purified gas is not
supplemented to the outflowed gas from the gas chromatography.
[0103] As a result of the above, the detection limit of CO.sub.2
was improved to 0.5 ppb by adding Ar, compared with the case that
the limit was 5 ppb when He alone was used as a carrier gas.
EXAMPLE 5
[0104] The measurement of N.sub.2 in Ar was carried out by using
the apparatus of FIG. 1. The separating column of the gas
chromatography had 4 mm of diameter and 2 m of length and was made
from stainless steel, being filled with molecular sieve 13XS. The
obtained amount of the sample gas was 3 cc, and the flow of the
carrier gas (main purified gas) was 42 cc/min, in which He was used
as a carrier gas.
[0105] He--H.sub.2 mixed gas was used as the gas added to the
outflowed gas, and the H.sub.2 contents were set to be in the range
of 0.05-0.4%. The added amount of the mixed gas was determined so
that the amount of the gas introduced into the atmospheric pressure
ionization mass spectrometer is 500 cc/min.
[0106] As for analyzing N.sub.2, the measured result of H.sub.2
free case is shown in FIG. 11(a) and that of H.sub.2-added case is
shown in FIG. 11(b). As apparent in both figures, N.sub.2, which
was never detected in H.sub.2--free case, was detected as
N.sub.2.multidot.H+ (mass number=29) by a proton transfer reaction
resulted from the addition of H.sub.2.
[0107] Moreover, as shown in FIG. 12, the calibration curve line of
the H.sub.2--added case was satisfactory. In the result of the
measurement, when the mixed gas(He+0.05% of H.sub.2) was used as an
added gas, the detection limit of N.sub.2 in Ar was 1 ppb.
[0108] In addition, when the amount of N.sub.2 contained in Ar in a
high purified Ar gas cylinder was measured, 72 ppb of N.sub.2 was
detected. Further, when N.sub.2 was measured after being purified
through getter type purifier, the N.sub.2 amount was less than 1
ppb.
[0109] As explained in the above, the present method has made it
possible for the trace impurities in various gases to be detected
in a sensitive and detailed way, and to be analyzed in ppb-ppt
levels in a short period of time, without the requirement of the
complicated operation and constitution of the apparatus.
* * * * *