U.S. patent application number 11/833209 was filed with the patent office on 2009-11-19 for efficient atmospheric pressure interface for mass spectrometers and method.
Invention is credited to Reinhold Pesch.
Application Number | 20090283674 11/833209 |
Document ID | / |
Family ID | 39321490 |
Filed Date | 2009-11-19 |
United States Patent
Application |
20090283674 |
Kind Code |
A1 |
Pesch; Reinhold |
November 19, 2009 |
Efficient Atmospheric Pressure Interface for Mass Spectrometers and
Method
Abstract
An interface for atmospheric pressure ionization sources has an
ion transfer tube with a plurality of passageways through a
sidewall such that background gas can be pumped away before it
reaches an exit end of the ion transfer tube. A flow of the
background gas out the exit end is reduced, and a proportion of
laminar flow in the ion transfer tube may be increased. Pressure in
the ion transfer tube is also reduced and desolvation is increased.
In one embodiment, an enclosure surrounds an inner tube of the ion
transfer tube within a first vacuum chamber such that the enclosure
provides a reduced pressure region within the first vacuum chamber.
Overall, transport efficiency is increased.
Inventors: |
Pesch; Reinhold; (Weyhe,
DE) |
Correspondence
Address: |
THERMO FINNIGAN LLC
355 RIVER OAKS PARKWAY
SAN JOSE
CA
95134
US
|
Family ID: |
39321490 |
Appl. No.: |
11/833209 |
Filed: |
August 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60857737 |
Nov 7, 2006 |
|
|
|
Current U.S.
Class: |
250/288 |
Current CPC
Class: |
H01J 3/14 20130101; H01J
49/062 20130101 |
Class at
Publication: |
250/288 |
International
Class: |
H01J 49/04 20060101
H01J049/04 |
Claims
1. An interface for a mass spectrometer, comprising: an ion
transfer tube having an inlet end opening to an atmospheric
pressure chamber, an outlet end opening to a low pressure chamber,
and at least one sidewall surrounding an interior region through
which is directed a flow of gas and ions, the sidewall extending
along a central axis between the inlet end and the outlet end; at
least a portion of the sidewall being fabricated from a porous
material to permit the flow of gas from the interior region through
the sidewall to a reduced-pressure region exterior to the
sidewall.
2. The interface of claim 1, wherein the atmospheric pressure
chamber comprises an ion source chamber, and the low pressure
chamber comprises a first vacuum chamber.
3. The interface of claim 2, wherein the ion source chamber is
configured as an electrospray ionization source.
4. The interface of claim 2, wherein the ion source chamber is
configured as a chemical ionization source.
5. The interface of claim 2, wherein the reduced-pressure region is
located within an enclosure extending around the sidewall, the
enclosure being disposed within the first vacuum chamber and
communicating with a pump.
6. The interface of claim 1, further comprising a heater in thermal
contact with the ion transfer tube.
7. The interface of claim 1, wherein the porous material is at
least one of a a permeable ceramic, or a permeable polymer.
8. The interface of claim 1, wherein the porous material is a
porous metal.
9. The interface of claim 1, further comprising a skimmer lens
having an aperture positioned proximate to the outlet end.
10-17. (canceled)
Description
[0001] This application claims priority to a provisional U.S.
patent application Ser. No. 60/857,737 by Alexander A. Makarov et
al., entitled "ION TRANSFER TUBE WITH SPATIALLY ALTERNATING DC
FIELDS", filed Nov. 7, 2006, the disclosure of which is hereby
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This application is directed to ion inlet sections of mass
spectrometers, ion transfer tube assemblies, ion transfer tubes,
and methods of transporting ions from an atmospheric pressure ion
source into a vacuum chamber of a mass spectrometer.
BACKGROUND OF THE INVENTION
[0003] Various approaches have been undertaken to increase
desolvation and otherwise increase the number of ions introduced
into the ion optics of a mass spectrometer from an atmospheric
pressure ion source. One typical practice is to heat a capillary
tube to increase desolvation of sample liquid droplets and to
reduce the size of the droplets from electrospray ionization or
chemical ionization sources, for example. U.S. Pat. No. 5,245,186
to Chait et al. teaches heating the capillary tube with a wire.
U.S. Pat. No. 4,935,624 to Henion et al. teaches controlled heating
of a capillary tube. Others have utilized a counter-flow of heated
gas to increase desolvation prior to entry of the spray into the
capillary tube.
[0004] U.S. Pat. No. 4,977,320 to Chowdhury et al. and others have
relied upon the strong flow of gas that accompanies the sample
spray through the capillary tube from an atmospheric pressure
region into the vacuum region to help focus the droplets toward a
center of the capillary tube. U.S. Pat. No. 5,157,260 to Mylchreest
et al. teaches use of tube lenses at an exit end of the capillary
tube for focusing ions. Others have utilized electrodes at various
locations to focus and/or urge ions toward an orifice of a skimmer
or other ion optical element to cause ions to enter lower pressure
regions of mass spectrometers.
[0005] Various techniques for alignment and positioning of the
sample spray, capillary tube, and skimmer have been implemented to
maximize the number of ions from the source that are actually
received into the ion optics of mass spectrometers.
[0006] Nevertheless, a majority of the ions generated in the ion
source do not survive during transport from the source to the ion
optics. Rather, the majority of the ions miss an entrance of the
capillary tube, miss an entrance into the ion optics through a
narrow orifice, and/or impinge on walls of a capillary tube or
nearby plates, and are lost. Thus, there is a need to increase the
number of ions from an ambient pressure ion source that are
successfully transported through the capillary tube, reach the ion
optics, and are transported into the mass spectrometer for
analysis.
SUMMARY
[0007] In a simple form, an interface for a mass spectrometer in
accordance with embodiments of the present invention includes an
ion transfer tube having an inlet end opening to a high pressure
chamber and an outlet end opening to a low pressure chamber. The
high and low pressure chambers may be provided by any regions that
have respective higher and lower pressures relative to each other.
For example, the high pressure chamber may be an ion source chamber
and the low pressure chamber may be a first vacuum chamber. The ion
transfer tube has at least one sidewall surrounding an interior
region and extending along a central axis between the inlet end and
the outlet end. The ion transfer tube has a plurality of
passageways formed in the sidewall. The passageways permit the flow
of gas from the interior region to a reduced-pressure region
exterior to the sidewall.
[0008] In another simple form, embodiments of the present invention
include an ion transfer tube for receiving and transporting ions
from a source in a high pressure region to ion optics in a reduced
pressure region of a mass spectrometer. The ion transfer tube
includes an inlet end, an outlet end, and at least one sidewall
surrounding an interior region and extending along a central axis
between the inlet end and the outlet end. The ion transfer tube may
also include an integral vacuum chamber tube at least partially
surrounding and connected to the ion transfer tube. The integral
vacuum chamber tube isolates a volume immediately surrounding at
least a portion of the ion transfer tube at a reduced pressure
relative to the interior region. The sidewall has a structure that
provides at least one passageway formed in the sidewall. The at
least one passageway permits a flow of gas from the interior region
to the volume exterior to the sidewall. The structure and
passageway are inside the integral vacuum chamber tube. The
structure of the sidewall may include a plurality of
passageways.
[0009] In still another simple form, embodiments of the present
invention include a method of transporting ions from an ion source
region to a first vacuum chamber. The method includes admitting
from the ion source region, a mixture of ions and gas to an inlet
end of an ion transfer tube. The method also includes removing a
portion of the gas through a plurality of passageways located
intermediate the inlet end and an outlet end of the ion transfer
tube. The method further includes causing the ions and the
remaining gas to exit the ion transfer tube through the outlet end
into the first vacuum chamber. The method may also include sensing
a reduction in latent heat in the ion transfer tube due to at least
one of removal of the portion of the background gas and an
associated evaporation, and increasing an amount of heat applied to
the ion transfer tube through a heater under software or firmware
control.
[0010] The embodiments of the present invention have the advantage
of reduced flow of gas through an exit end of the ion transfer
tube. Several associated advantages have also been postulated. For
example, the reduced flow through the exit end of the ion transfer
tube decreases the energy with which the ion bearing gas expands as
it leaves the ion transfer tube. Thus, the ions have a greater
chance of traveling on a straight line through an aperture of a
skimmer immediately downstream. Also, reduction of the flow in at
least a portion of the ion transfer tube may have the effect of
increasing the amount of laminar flow in that portion of the ion
transfer tube. Laminar flow is more stable so that the ions can
remain focused and travel in a straight line for passage through
the relatively small aperture of a skimmer. With gas being pumped
out through a sidewall of the ion transfer tube, the pressure
inside the ion transfer tube is reduced. Reduced pressure can cause
increased desolvation. Furthermore, latent heat is removed when the
gas is pumped out through the sidewall. Hence, more heat may be
transferred through the ion transfer tube and into the sample
remaining in the interior region resulting in increased desolvation
and increased numbers of ions actually reaching the ion optics.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a diagrammatic view of an example mass
spectrometer with which the embodiments of the present invention
may be incorporated.
[0012] FIG. 2 is a diagrammatic view of an inlet assembly in
accordance with an embodiment of the present invention.
[0013] FIG. 3 is a diagrammatic view of an inlet assembly in
accordance with another embodiment of the present invention.
[0014] FIG. 4 is a diagrammatic partial perspective view of an ion
transfer tube in accordance with the embodiment of FIG. 3.
[0015] Like reference numerals refer to corresponding parts
throughout the several views of the drawings.
DETAILED DESCRIPTION OF EMBODIMENTS
[0016] As has been discussed, conventional inlet sections having
atmospheric pressure ionization sources suffer from a loss of a
majority of the ions produced in the sources prior to the ions
entering ion optics for transport into filtering and analyzing
sections of mass spectrometers. It is believed that high gas flow
at an exit end of the ion transfer tube is a contributing factor to
this loss of high numbers of ions. The neutral gas undergoes an
energetic expansion as it leaves the ion transfer tube. The flow in
this expansion region and for a distance upstream in the ion
transfer tube is typically turbulent in conventional inlet
sections. Thus, the ions born by the gas are focused only to a
limited degree in the ion inlet sections of the past. Rather, many
of the ions are energetically moved throughout a volume of the
flowing gas. It is postulated that because of this energetic and
turbulent flow and the resultant mixing effect on the ions, the
ions are not focused to a desirable degree and it is difficult to
separate the ions from the neutral gas under these flow conditions.
Thus, it is difficult to separate out a majority of the ions and
move them downstream while the neutral gas is pumped away. Rather,
many of the ions are carried away with the neutral gas and are
lost. On the other hand, the hypothesis associated with embodiments
of the present invention is that to the extent that the flow can be
caused to be laminar along a greater portion of an ion transfer
tube, the ions can be kept focused to a greater degree. One way to
provide the desired laminar flow is to remove the neutral gas
through a sidewall of the ion transfer tube so that the flow in an
axial direction and flow out the exit end of the ion transfer tube
is reduced. Also, by pumping the neutral gas out of the sidewalls
to a moderate degree, the boundary layer of the gas flowing axially
inside the ion transfer tube becomes thin, the velocity
distribution becomes fuller, and the flow becomes more stable.
[0017] One way to increase the throughput of ions or transport
efficiency in atmospheric pressure ionization interfaces is to
increase the conductance by one or more of increasing an inner
diameter of the ion transfer tube and decreasing a length of the
ion transfer tube. As is known generally, with wider and shorter
ion transfer tubes, it will be possible to transport more ions into
the ion optics downstream. However, the capacity of available
pumping systems limits how large the diameter and how great the
overall conductance can be. Hence, in accordance with embodiments
of the present invention, the inner diameter of the ion transfer
tube can be made relatively large and at the same time flow out of
the exit end of the ion transfer tube can be reduced to improve the
flow characteristic for keeping ions focused toward a center of the
gas stream. In this way, the neutral gas can be more readily
separated from the ions, and the ions can be more consistently
directed through the orifice of a skimmer into the ion optics and
analyzer sections downstream. The result is improved transport
efficiency and increased instrument sensitivity.
[0018] Even if it is found in some or all cases, that turbulent
flow results in increased ion transport efficiency, it is to be
understood that decreased pressure in a downstream end of the ion
transfer tube and increased desolvation due to the decreased
pressure may be advantages accompanying the embodiments of the
present invention under both laminar and turbulent flow conditions.
Furthermore, even with turbulent flow conditions, the removal of at
least some of the neutral gas through the sidewall of the ion
transfer tube may function to effectively separate the ions from
the neutral gas. Even in turbulent flow, the droplets and ions with
their larger masses will most likely be distributed more centrally
during axial flow through the ion transfer tube. Thus, it is
expected that removal of the neutral gas through the sidewalls will
effectively separate the neutral gas from the ions with relatively
few ion losses under both laminar and turbulent flow conditions.
Still further, the removal of latent heat by pumping the neutral
gas through the sidewalls enables additional heating for increased
desolvation under both laminar and turbulent flow conditions.
[0019] Accordingly, FIG. 1 shows an example mass spectrometer 12
having an ion source 15 in a source chamber 16 and an interface 18
between the high pressure source chamber 16 and a lower pressure
first vacuum chamber 19. The ion source 15 may be, without
limitation, an electrospray ionization source, a chemical
ionization source, another liquid sample based atmospheric pressure
ionization source, or any other source. The interface 18 may
include an ion transfer tube portion 21 and an ion guide portion 24
with separate or shared pumping stages. Ions from the source 15 are
introduced into the transfer tube portion 21 and move along an ion
path generally on a central axis 25 through one or more additional
sections to a detector 27. The sections may include one or more of
each of ion guides, filters, collision cells, and analyzers, as
indicated by q0, Q1, q2, and Q3. The devices in each of these
sections may be operated by an electronic controller 30 under
software and/or firmware control to perform the needed functions
for analysis of sample ions in the mass spectrometer 12.
[0020] In the more detailed diagrammatic view of FIG. 2, a skimmer
lens 33 separates the ion transfer tube portion 21 from the ion
guide portion 24 of the interface 18. As shown, an ion transfer
tube 36 may be supported near its entrance end 39 on a chamber wall
42 between the source chamber 16 and the first vacuum chamber 19.
While FIG. 2 shows the ion transfer tube 36 with an inlet or
entrance end opening in direct communication with the ion source
15, it is to be understood that one or more reduced pressure
chambers may be placed intermediate the ion source 15 and the ion
transfer tube 36. The one or more reduced pressure chambers may or
may not have one or more additional ion transfer tubes therein.
[0021] As shown in FIG. 2, sidewall 45 of the ion transfer tube
extends axially from the entrance end 39 to an exit end 48 and is
surrounded by a heater 51. The heater 51 may be placed in direct
contact or otherwise in any kind of thermal contact with the ion
transfer tube 36. The skimmer lens 33 may have an aperture
positioned proximate to the outlet or exit end 48 of the ion
transfer tube 36. A tube lens or other focusing lens 52 may be
disposed between the exit end 48 of the ion transfer tube 36 and
the skimmer lens 33. An ion guide 54 may be located in a second
vacuum chamber 57 downstream from the first vacuum chamber 19. It
is to be understood that "vacuum chamber" as used herein may
include any reduced pressure chamber or region that has a pressure
that is lower than atmospheric pressure. High pressure and low
pressure as used herein denote relative pressures in respective
regions and are not to be limited to pressures relative to
atmospheric or any other threshold pressure. Each of the first and
second vacuum chambers 19, 57 may be pumped by the same or separate
vacuum pumps as indicated by arrows 58, 59.
[0022] Alternatively, an interface 62 in accordance with another
embodiment of the invention may include a third vacuum chamber 65
formed integrally as a unit with an ion transfer tube 68, as shown
in FIG. 3. Walls create an enclosure that forms the third vacuum
chamber 65 and at least partially surrounds an inner tube 71 that
may be structurally analogous to the ion transfer tube 36 described
with regard to the embodiment of FIG. 2 above. As indicated by
arrow 75, a separate pump or a pump in common with pump(s) of one
or more of the first and second vacuum chambers 19, 57 may be
operably connected with the third vacuum chamber 65 in order to
pump gas from within an interior region 74 inside the ion transfer
tube 68 out through a sidewall 77 of the ion transfer tube 68. As
with the embodiment of FIG. 2, the sidewall 77 of the ion transfer
tube 68 extends axially from an entrance end 78 to an exit end 79.
Also, the sidewall 77 is surrounded by a heater 51. The heater 51
may be placed in direct contact or otherwise in any kind of thermal
contact with the ion transfer tube, as described with regard to the
embodiment of FIG. 2.
[0023] FIG. 4 is a diagrammatic partial perspective view of the ion
transfer tube 68 of FIG. 3. As shown, the inner tube 71 and the
interior region 74 may be substantially the same as the ion
transfer tube 36 and an interior region thereof, in accordance with
the embodiment of FIG. 2. The sidewall 77 has one or more
passageways 80 for fluid communication between the interior region
74 and an exterior region within the enclosure created by an
enclosure sidewall 83 and enclosure end walls 86, 87, which walls
form the third vacuum chamber 65. As shown by arrows 90, neutral
gas is pumped from within the interior region 74 and out through
the passageways 80 of the sidewall 77 into the third vacuum chamber
65 where it is pumped away. The third vacuum chamber 65 encompasses
a reduced-pressure region that is located within the enclosure and
extends around the sidewall 77. As may be appreciated by referring
back to FIG. 3, the enclosure is disposed within the first vacuum
chamber 19 and communicates with a pump 91 that may be separate or
in common with other pumps in the system.
[0024] Like the embodiment of FIGS. 3 and 4, the ion transfer tube
36 of the embodiment of FIG. 2 may have similar structure in which
the sidewall 45 has passageways 80, and the neutral gas is pumped
away by a pump in fluid communication with the first vacuum chamber
19. As shown in FIG. 4, a sensor 93 may be connected to the ion
transfer tube 68 and to the controller 30 for sending a signal
indicating a temperature of the sidewall 77 or some part of the ion
transfer tube 68 back to the controller 30. It is to be understood
that a plurality of sensors may be placed at different positions to
obtain a temperature profile. Thus, the sensor(s) 93 may thus be
connected to the ion transfer tube 68 for detecting a reduction in
heat as gas is pumped through the plurality of passageways 80 in
the sidewall 77 of the ion transfer tube 68. The sensor(s) 93 may
also be connected to the ion transfer tube 36 and controller 51 in
the embodiment of FIG. 2 for heat reduction detection and
control.
[0025] With further reference to the embodiment of FIGS. 3 and 4,
the third vacuum chamber 65 may be utilized to introduce a flow of
gas through the sidewall 71 and into an interior region 74 of the
ion transfer tube 68 instead of removing the background gas, as
described above. This may be achieved by adjusting the pressure in
the third chamber 65 to be between atmospheric pressure and the
pressure in the interior region 74. By introducing a flow of gas
through passageways 80 into the interior region 74, more turbulent
flow conditions may be created in which sample droplets are
disrupted. The more turbulent flow conditions may thus cause the
sample droplets to be broken up into smaller droplets. This
disruption of the droplets is an external force disruption, as
opposed to a coulomb explosion type disruption which also breaks up
the droplets.
[0026] In an application of both external force and coulomb
explosion disruption, both removal and addition of gas may be
applied in one ion transfer tube. For example, the chamber 65 could
be divided into plural regions with respective removal and addition
of gas in a series of the plural regions. Thus, an alternating
series of external force and coulomb explosion disruptions can be
implemented to break up the droplets of the sample.
[0027] The sidewall 45 of the ion transfer tube 36 and the sidewall
77 that forms at least a part of the inner tube 71 in the
embodiments of FIGS. 1-4 may be formed from a material that
includes one or more of a metal frit, a metal sponge, a permeable
ceramic, and a permeable polymer. The passageways 80 may be defined
by the pores or interstitial spaces in the material. The pores or
interstices in the material of the sidewalls may be small and may
form a generally continuous permeable element without discrete
apertures. Alternatively, the passageways may take the form of
discrete apertures or perforations formed in the sidewalls 45, 77
of ion transfer tubes 36, 68. The passageways may be configured by
through openings that have one or more of round, rectilinear,
elongate, uniform, and non-uniform configurations.
[0028] Embodiments of the present invention include a method of
transporting ions from a source region into a vacuum region, a
method of separating and removing a background gas from a mixture
of the background gas and sample ions, and a method of desolvating
a sample in an interface. One or more of the methods may include
heating the ion transfer tube to promote evaporation of residual
liquid solvent admitted into the ion transfer tube. The methods may
include the step of removing at least a portion of the gas by
providing a reduced-pressure region exterior to an inner tube of
the ion transfer tube. The methods may also include sensing a
reduction in latent heat in the ion transfer tube due to at least
one of removal of the portion of the background gas and an
associated evaporation. A subsequent step to sensing may be the
step of increasing an amount of heat applied to the ion transfer
tube through a heater under software or firmware control.
[0029] The methods may include reducing a pressure in at least a
portion of the ion transfer tube interior region such that
desolvation is increased. The methods may include reducing the
energy of a free jet expansion of the gas leaving the outlet or
exit end of the ion transfer tube. The methods may also include
reducing a velocity of a second downstream portion of the
background gas that moves axially out an outlet or exit end of the
ion transfer tube relative to a velocity of a first upstream
portion of the background gas entering the ion transfer tube. The
method may also include increasing a proportion of laminar flow
along a length of the ion transfer tube.
[0030] The embodiments and examples set forth herein were presented
in order to best explain the present invention and its practical
application and to thereby enable those of ordinary skill in the
art to make and use the invention. However, those of ordinary skill
in the art will recognize that the foregoing description and
examples have been presented for the purposes of illustration and
example only. The description as set forth is not intended to be
exhaustive or to limit the invention to the precise form disclosed.
Many modifications and variations are possible in light of the
teachings above without departing from the spirit and scope of the
forthcoming claims.
* * * * *