WO1997047024A1 - A method of injecting a gas into a mass spectrometer and apparatus therefor - Google Patents

A method of injecting a gas into a mass spectrometer and apparatus therefor Download PDF

Info

Publication number
WO1997047024A1
WO1997047024A1 PCT/GB1997/001541 GB9701541W WO9747024A1 WO 1997047024 A1 WO1997047024 A1 WO 1997047024A1 GB 9701541 W GB9701541 W GB 9701541W WO 9747024 A1 WO9747024 A1 WO 9747024A1
Authority
WO
WIPO (PCT)
Prior art keywords
gas
carrier gas
pressure
supply
flow
Prior art date
Application number
PCT/GB1997/001541
Other languages
French (fr)
Inventor
Elizabeth Janine Jumeau
Original Assignee
Analytical Precision Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Analytical Precision Limited filed Critical Analytical Precision Limited
Priority to AU30403/97A priority Critical patent/AU3040397A/en
Publication of WO1997047024A1 publication Critical patent/WO1997047024A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/02—Details
    • H01J49/04—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components
    • H01J49/0422—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components for gaseous samples
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/02—Details
    • H01J49/04—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components
    • H01J49/0495—Vacuum locks; Valves

Definitions

  • This invention relates to a method of injecting gas into a mass
  • sample gas is calculated by comparison with the isotopic composition of a
  • reference sample can be introduced into the mass spectrometer at a time
  • a method of injecting a gas into a gas spectrometer comprising firstly introducing said gas into a supply of carrier gas to a mass
  • pressure PT being substantially greater than pressure P 2
  • the pressure P 3 is arranged to be substantially
  • gas injection apparatus for carrying out the method of the
  • said apparatus comprising a carrier gas supply which feeds carrier
  • gas injection means linked to a supply of gas which is operable to supply
  • said gas is introduced into said carrier gas supply through
  • the supply may comprise a hollow tubular member of substantially larger
  • capillary tube can extend into the interior of the carrier gas supply.
  • said pressure switch means comprises a multiport valve
  • carrier gas supply is connected to a source of atmospheric pressure.
  • the source of atmospheric pressure comprises an outlet to
  • carrier gas supply is controlled selectively by a pressure regulator.
  • a carrier gas feed 1 1 is linked to a sample preparation system of
  • the inlet 1 2 of the mass spectrometer may be of conventional 'open split'
  • the carrier gas feed 1 1 is linked to both the inlet 1 2 of the mass
  • T-shape 14 The T-shaped tubular connection ensures that the carrier gas
  • feed 1 1 , inlet 12 and gas injection system 13 can be in gas flow connection
  • the gas injection system comprises a gas injection capillary 16 which
  • injection capillary 16 opens into the inlet 17 of the valve 18 and the other
  • end 21 of the capillary opens into the carrier feed 1 1 at a position spaced
  • the multiport valve 1 8 has two outlets 23, 24 to which the inlet 1 7
  • a first outlet 23 is connected to atmosphere
  • outlet 24 of the valve 18 is linked to a pressure relief outlet 28 which
  • valve 18 The inlet 17 of valve 18 is a T-shaped tubular connection, into which
  • reference gas is supplied via gas supply feed 13.
  • the inlet 1 2 of the mass spectrometer is of conventional open split
  • spectrometer can also be of any suitable conventional form.
  • valve 18 is switched into a position in which the
  • inlet 17 is connected to the outlet 23 whereby reference gas is supplied to
  • This pressure at which reference gas is supplied will be designated as P, .
  • capillary tube 1 6 is exposed to reference gas at Pressure P very quickly.
  • the mixed gas passes through the carrier feed and
  • T-connector 17 The output signal remains steady and stable for as long as
  • valve 18 is retained in the position mentioned above.
  • the valve 1 8 is
  • capillary 16 is immediately connected to a substantially reduced pressure P 3
  • valve 18 to a position in which the inlet 17 is connected to the outlet 23 of
  • valve 18 which results in a sharp increase in supply of reference gas to the
  • the inlet 1 7 results in this rise in the signal being almost instantaneous.

Abstract

A method and apparatus for injecting a gas into a mass spectrometer are disclosed. The apparatus comprises a carrier gas supply (11) which feeds carrier gas, e.g. helium, to an inlet of a mass spectrometer. A gas injection capillary (16) introduces a supply of gas to be analysed into the flow of carrier gas in a direction of flow substantially opposite to the direction of flow of carrier gas. A pressure switch (18) is provided which is operable to control the pressure which gas to be analysed is supplied, in a first position of the valve the gas being supplied at a pressure greater than the pressure of carrier gas and in a second position the gas being supplied at a pressure substantially lower than the pressure of carrier gas whereby movement of the valve between the two positions allows pressure control of feed of gas to the mass spectrometer inlet (12).

Description

A METHOD OF INJECTING A GAS INTO A MASS
SPECTROMETER AND APPARATUS THEREFOR
This invention relates to a method of injecting gas into a mass
spectrometer and apparatus for carrying out such a method.
In Isotopic Ratio Mass Spectrometers, the isotopic composition of a
sample gas is calculated by comparison with the isotopic composition of a
reference gas whose composition has been calculated with reference to an
International Standard.
In order for such a comparison to be made it is necessary to introduce
a reference gas into the mass spectrometer as a discrete pulse whereby the
reference sample can be introduced into the mass spectrometer at a time
which does not coincide with the sample gas to be analysed. It has been
determined that rectangular pulses of reference gas having a pulse width of
approximately 30 seconds yield the optimum precision of measurement
provided that these pulses are as close to perfect rectangular pulses as is
possible, i.e. rise rapidly to a steady and stable value and also decay rapidly
with a minimum of tailing.
It is an object of the present invention to provide a simple and low
cost method of injecting a gas into a mass spectrometer in an accurate and
controlled manner.
According to a first aspect of the present invention therefore there is
provided a method of injecting a gas into a gas spectrometer comprising firstly introducing said gas into a supply of carrier gas to a mass
spectrometer at a pressure P in a direction of flow opposite to a direction
of flow of said carrier gas, said carrier gas being at a pressure P2 where the
gas is introduced, pressure PT being substantially greater than pressure P2
whereby flow of gas into the carrier gas takes place, and secondly reducing
said pressure P, to a value P3 less than P2 whereby flow of said gas into
said carrier gas is prevented.
With this method it is possible to introduce a gas into a mass
spectrometer in a particularly accurate and controlled manner.
Preferably the pressure P3 is arranged to be substantially
atmospheric pressure whereby a rapid reversal of flow of gas can be
achieved.
According to a second aspect of the present invention therefore there
is provided gas injection apparatus for carrying out the method of the
invention, said apparatus comprising a carrier gas supply which feeds carrier
gas containing a sample to be measured to an inlet of a mass spectrometer,
gas injection means linked to a supply of gas which is operable to supply
gas into said carrier gas supply in a direction of flow opposite to the
direction of flow of carrier gas and a pressure switch which is movable
between at least two positions, in a first position in which said gas is
supplied at a pressure substantially greater than the pressure of carrier gas
in said supply and a second position in which said carrier gas supply is linked to a pressure substantially lower than pressure of the carrier gas in
the supply.
With this arrangement it is possible to provide a gas injection
apparatus which is capable of introducing a gas into a carrier gas supply in
a particularly controlled and accurate manner.
Preferably said gas is introduced into said carrier gas supply through
a small bore capillary tube which extends into the carrier gas supply and
links said carrier gas supply and said gas supply. In this case the carrier gas
supply may comprise a hollow tubular member of substantially larger
diameter than the capillary tube linked to a carrier gas reservoir whereby the
capillary tube can extend into the interior of the carrier gas supply.
Preferably said pressure switch means comprises a multiport valve,
in a first position of which, preferably, the flow of gas from a gas supply to
said carrier gas supply is permitted and in a second position of which said
carrier gas supply is connected to a source of atmospheric pressure. Most
preferably the source of atmospheric pressure comprises an outlet to
atmosphere.
Preferably the pressure of gas supplied from the gas supply to the
carrier gas supply is controlled selectively by a pressure regulator.
The invention will now be described further by way of example only
and with reference to the accompanying drawings, the single figure of
which shows in diagrammatic form, one embodiment of gas injector for carrying out the method according to the present invention .
A carrier gas feed 1 1 is linked to a sample preparation system of
conventional form in which a sample to be analysed is mixed with carrier
gas for supply to an inlet 1 2 of a mass spectrometer of conventional form .
The inlet 1 2 of the mass spectrometer may be of conventional 'open split'
form . The carrier gas feed 1 1 is linked to both the inlet 1 2 of the mass
spectrometer and the gas injection system 1 3 via a tubular connection of
T-shape 14. The T-shaped tubular connection ensures that the carrier gas
feed 1 1 , inlet 12 and gas injection system 13 can be in gas flow connection
in a manner to be described hereinafter.
The gas injection system comprises a gas injection capillary 16 which
extends through the tubular connection 14 between an inlet 1 7 of multiport
valve 18 and an interior of the carrier gas feed 1 1 . One end 19 of the gas
injection capillary 16 opens into the inlet 17 of the valve 18 and the other
end 21 of the capillary opens into the carrier feed 1 1 at a position spaced
from the inlet 1 2 to the mass spectrometer. The gas injection capillary 16
is supported at one end 19 by a ferrule 22 mounted adjacent the valve inlet
17 and which acts to seal the valve inlet 17 from the tubular connection 1 4
and hence the interior of the carrier gas feed 1 1 save for via the capillary
1 6. The multiport valve 1 8 has two outlets 23, 24 to which the inlet 1 7
can be selectively connected. A first outlet 23 is connected to atmosphere
via a flow restrictor 26 which can induce a substantial pressure into inlet 17 when inlet 1 7 and outlet 23 of the valve 1 8 are in connection. A second
outlet 24 of the valve 18 is linked to a pressure relief outlet 28 which
through which inlet 17 of the valve 18 can be connected with no restriction
to atmospheric pressure and therefore acts as a vent to atmosphere for gas
within the capillary 16 and for the reference gas supplied from system 13.
The inlet 17 of valve 18 is a T-shaped tubular connection, into which
reference gas is supplied via gas supply feed 13.
The inlet 1 2 of the mass spectrometer is of conventional open split
form and therefore no further description will be given herein. The mass
spectrometer can also be of any suitable conventional form.
When a reference gas is required to be injected into the mass
spectrometer inlet 12, the valve 18 is switched into a position in which the
inlet 17 is connected to the outlet 23 whereby reference gas is supplied to
the end 19 of the capillary 16 at a pressure substantially greater than
atmospheric pressure and induced by the presence of the flow restrictor 26.
This pressure at which reference gas is supplied will be designated as P, .
By arranging the internal volume in the inlet 17 to be low when the valve
1 8 is switched into this above mentioned position, the end 1 9 of the
capillary tube 1 6 is exposed to reference gas at Pressure P very quickly.
With the valve 18 in this position, reference gas flows through the capillary
tube 16 and is introduced into the carrier gas feed 1 1 at the opposite end
21 of the capillary tube. Since initially the flow of carrier gas and reference gas are in opposite directions, good mixing of these gases is achieved at the
end 21 of the capillary thereby ensuring a homogenous mixture of gases for
supply to the mass spectrometer. Some of the reference gas flowing from
the supply does not enter the capillary tube 16 and this gas is vented to
atmosphere through outlet 23 and restrictor 26.
After mixing, the mixed gas passes through the carrier feed and
passes around the inlet 1 2 of the mass spectrometer and is vented to
atmosphere through a vent outlet 31 . However, a small and significant
portion is drawn into the inlet 1 2 of the mass spectrometer analysis
chamber and provides a sharp rise in the signal output by the mass
spectrometer due to the detected presence of the reference gas. The rise
in the output signal is almost instantaneous upon switching of the valve 1 8
to the position mentioned above due to there being little volume within the
T-connector 17. The output signal remains steady and stable for as long as
the valve 18 is retained in the position mentioned above. The valve 1 8 is
then switched to a position in which the inlet 1 7 is connected to the
pressure relief outlet 28. In this position of the valve 18, substantially all
reference gas from the reference gas supply is vented to atmosphere
through vent outlet 24. With the valve 18 in this position the end 19 of the
capillary 16 is immediately connected to a substantially reduced pressure P3
at outlet 28. This reduced pressure P3 is advantageously atmospheric
pressure . This causes an almost instantaneous reversal of flow of gas in the capillary 16 towards the outlet 28. A small amount of the carrier gas
and sample being fed through the feed 1 1 will be entrained into the capillary
1 6 and will pass through outlet 28, however most of the carrier gas will
pass around the capillary 16 and a small but significant part will pass into
the inlet 1 2 and will be sensed by the mass spectrometer. The remainder
of carrier gas will flow around the inlet 12 and pass out through outlet 31 .
Flow of carrier gas in this position of the valve 18 is controlled also to some
extent by the fact that the capillary 16 is of considerably smaller diameter
than the carrier feed 1 1 . This ensures that there is an impedance to flow
of the carrier gas into the capillary tube 16 and therefore only a small
amount of carrier gas enters this tube 16 and is required to be vented
through the pressure relief outlet 28.
Thus it can be seen that, with the valve 18 initially set with the inlet
17 connected to the pressure relief vent 28, an accurate rectangular pulse
of reference gas can be introduced into the carrier feed 1 1 by switching the
valve 18 to a position in which the inlet 17 is connected to the outlet 23 of
valve 18 which results in a sharp increase in supply of reference gas to the
carrier feed 1 1 which is introduced into the mass spectrometer causing a
sharp increase in the signal output by the mass spectrometer due to the
detected presence of reference gas. The lack of significant dead volume in
the inlet 1 7 results in this rise in the signal being almost instantaneous.
Furthermore the opposite direction of flow of carrier gas and reference gas initially, with the valve 1 8 in this position, results in good mixing of the
gases at the end of the capillary whereby an almost homogeneous mixture
of gases can be provided for supply to the mass spectrometer. This
homogeneity of the mixture of gases ensures that the signal output by the
mass spectrometer, whilst the valve is in this position, remains steady and
stable thereby allowing a particular reference signal to be maintained for any
desired Iength of time. Switching the valve 18 back to its initial position in
which the inlet 1 7 is connected to a vent outlet 28 results in a reversal of
the flow of reference gas in the capillary 16 and flow of carrier gas into the
capillary 16 and an almost instantaneous drop in the supply of reference gas
to the carrier feed 1 1 resulting in an almost instantaneous drop in the signal
provided by the mass spectrometer since all the spectrometer will sense is
carrier gas.
Thus it will be appreciated that by use of the arrangement of gas
injector according to the present invention it is possible to introduce very
accurate and controlled rectangular pulses of reference gas into a mass
spectrometer in a simple and convenient manner.
It is of course to be understood that the invention is not intended to
be restricted to the details of the above embodiments which are described
by way of example only.
Whilst in the description above the gas injection system is described
for use in the injection of a reference gas into a carrier gas supply, it is to be understood that the method and apparatus of the invention can be used
to inject any gas into a mass spectrometer carrier gas supply for example
a sample gas or any other gas as desired.

Claims

1 . A method of injecting a gas into a gas spectrometer comprising firstly
introducing said gas into a supply of carrier gas to a mass spectrometer at
a pressure Pl f in a direction of flow opposite to a direction of flow of said
carrier gas, said carrier gas being at a pressure P2 where the gas is
introduced, pressure P^ being substantially greater than pressure P2 whereby
flow of gas into the carrier gas takes place, and secondly reducing said
pressure P, to a value P3 less than P2 whereby flow of said gas into said
carrier gas is prevented.
2. A method according to claim 1 wherein the pressure P3 is arranged
to be substantially atmospheric pressure whereby a rapid reversal of flow
of gas can be achieved.
3. Gas injection apparatus for carrying out the method of the invention,
said apparatus comprising a carrier gas supply which feeds carrier gas
containing a sample to be measured to an inlet of a mass spectrometer, gas
injection means linked to a supply of gas which is operable to supply gas
into said carrier gas supply in a direction of flow opposite to the direction
of flow of carrier gas and a pressure switch which is movable between at
least two positions, in a first position in which said gas is supplied at a
pressure substantially greater than the pressure of carrier gas in said supply
and a second position in which said carrier gas supply is linked to a pressure
substantially lower than pressure of the carrier gas in the supply.
4. Apparatus according to claim 3 wherein said gas is introduced into
said carrier gas supply through a small bore capillary tube which extends
into the carrier gas supply and links the carrier gas supply and said gas
supply.
5. Apparatus according to claim 4 wherein the carrier gas supply
comprises a hollow tubular member of substantially larger diameter than the
capillary tube linked to a carrier gas reservoir whereby the capillary tube can
extend into the interior of the carrier gas supply.
6. Apparatus according to any one of claims 3 to 5 wherein the pressure
switch means comprises a multiport valve, in a first position of which, the
flow of gas from a gas supply to a carrier gas supply is permitted and in a
second position of which said carrier gas supply is connected to a source
of atmospheric pressure.
7. Apparatus according to claim 6 wherein the source of atmospheric
pressure is an outlet to atmosphere.
8. Apparatus according to any one of claims 3 to 7 wherein the pressure
of gas supplied from the gas supply to the carrier gas supply is controlled
selectively by a pressure regulator.
9. A method of injecting a gas into a mass spectrometer substantially as
hereinbefore described with reference to the accompanying drawing.
10. Gas injection apparatus substantially as hereinbefore described with
reference to the accompanying drawing.
PCT/GB1997/001541 1996-06-06 1997-06-06 A method of injecting a gas into a mass spectrometer and apparatus therefor WO1997047024A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU30403/97A AU3040397A (en) 1996-06-06 1997-06-06 A method of injecting a gas into a mass spectrometer and apparatus therefor

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB9611820.3A GB9611820D0 (en) 1996-06-06 1996-06-06 A method of injecting a gas into a mass spectrometer and apparatus therefor
GB9611820.3 1996-06-06

Publications (1)

Publication Number Publication Date
WO1997047024A1 true WO1997047024A1 (en) 1997-12-11

Family

ID=10794832

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1997/001541 WO1997047024A1 (en) 1996-06-06 1997-06-06 A method of injecting a gas into a mass spectrometer and apparatus therefor

Country Status (3)

Country Link
AU (1) AU3040397A (en)
GB (1) GB9611820D0 (en)
WO (1) WO1997047024A1 (en)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4970905A (en) * 1989-05-25 1990-11-20 University Of Utah Apparatus and method for sampling
EP0559089A1 (en) * 1992-02-26 1993-09-08 Varian Associates, Inc. Reagent gas flow control for an ion trap mass spectrometer used in the chemical ionization mode

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4970905A (en) * 1989-05-25 1990-11-20 University Of Utah Apparatus and method for sampling
EP0559089A1 (en) * 1992-02-26 1993-09-08 Varian Associates, Inc. Reagent gas flow control for an ion trap mass spectrometer used in the chemical ionization mode

Also Published As

Publication number Publication date
AU3040397A (en) 1998-01-05
GB9611820D0 (en) 1996-08-07

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