Method of transmitting ions for mass spectroscopy

Information

  • Patent Grant
  • 6809318
  • Patent Number
    6,809,318
  • Date Filed
    Monday, September 8, 2003
    21 years ago
  • Date Issued
    Tuesday, October 26, 2004
    20 years ago
Abstract
A system for determining the ratio of mass to charge of an ion including a pulsed ionizer, a high pressure co-linear ion guide/accelerator, and a mass analyzer. The pulsed ionizer generates intact analyte ions from a sample of matter to be analyzed. The high pressure co-linear ion guide/accelerator is interfaced with the ion source for receipt of the intact ions of the sample. The ion guide/accelerator simultaneously dampens and linearly accelerates the intact ions in the substantial absence of fragmentation of the ions to provide a substantially continuous beam of the intact ions for mass analysis. The mass analyzer is connected to the ion guide/accelerator for receipt of the beam of ions and determines the mass to charge ratio of the intact ions.
Description




BACKGROUND OF THE INVENTION




The present invention relates to the art of mass spectroscopy, and in particular, to a method and system for high sensitivity, rapid, high efficiency mass spectroscopy.




It is known in the field of mass spectroscopy to provide spectrometers with an elongated conductor having multipole conductors which act as ion transmitters. In PCT Publication WO 99/38185 (the contents of which is incorporated herein by reference), a method and apparatus are disclosed for providing ion transmission between an ion source and a spectrometer. The ion transmission device includes a multipole rod set and a damping gas which dampens spatial and energy spreads of ions generated by a pulsed ion source. The multipole rod set has the effect of guiding the ions along an ion path so that they can be directed to the inlet of a mass spectrometer.




The WO '185 publication discloses a MALDI (matrix-assisted laser desorption/ionization) ion source for producing a small jet of matrix and analyte molecules and ions and which have a wide range of energy spreads. The ion transmission device of WO '185 spreads out the generated ions along the multipole ion guide axis to provide a quasi-continuous beam while i) reducing the energy spread of ions emitted from the source and ii) at least partially suppressing unwanted fragmented analyte ions. These ions are delivered to a time-of-flight spectrometer or other spectrometers.




The apparatus described in WO '185 provides that single multiple rod sets or two or more rod sets can be used. Regardless of the number of rod sets used or the number of rods provided therein, the conductors merely provide ion guidance and possible energy damping by way of collision with a damping gas within the ion guide itself. No provision is made to enhance the efficiency or improve the speed of movement while retaining integrity of the ion beam sent to a mass spectrometer.




Another disclosure, U.S. Pat. No. 6,111,250 to Thomson, et al., discloses a mass spectrometer which includes rod sets constructed to create an axial field, e.g., a DC axial field. The Thomson, et al. '250 disclosure provides for speeding the passage of ions through an ion guide and causing the ions to be fragmented. The ion source is disclosed as being an electrospray or ion spray device such as those described in U.S. Pat. Nos. 4,935,624 and 4,861,988, or a corona discharge needle or a plasma, as shown in U.S. Pat. No. 4,861,965. The ions are directed and their speed controlled for introduction into a “time-of-flight” mass analyzer. In one embodiment, Thomson, et al. disclose the use of a set of auxiliary rods in combination with a set of quadrupole rods for the purpose of, among other things, introducing very low energy ions into a quadrupole mass analyzer. There is no disclosure by Thomson, et al. regarding transmitting intact analyte ions as a substantially continuous ion beam for highly sensitive, rapid mass analysis.




While there are numerous disclosures relating to the art of mass spectroscopy of analyte ions, there is an ever increasing demand for high speed and accurate mass spectroscopy of specimens, especially dilute specimens having only trace amounts of analyte ions. It is the purpose of the present invention to meet this and other needs in the art of mass spectroscopy.




SUMMARY OF THE INVENTION




The present invention is a method and system for determining the ratio of mass to charge of an analyte ion. According to the present invention, intact analyte ions are prepared from a sample by pulse ionizing using a pulse ionizer, e.g., preferably by matrix-assisted laser desorption/ionization (MALDI).




The present invention further includes simultaneously damping and linearly accelerating intact ions in a co-linear ion guide/accelerator to reduce the energy spread of the ions without fragmenting them and to linearly accelerate the ions to provide a substantially continuous beam of intact ions. This dual functionality step of the process in the system is implemented by co-linearly arranged multipole rods and accelerator rods which define an axial ion path along which the continuous ion beam travels. This step of the process and the system also includes a damping gas which acts to reduce the energy spread of the ions. While the pressure of the damping gas can range from 0.1 mTorr to 10 Torr, it is preferably from about 10 mTorr to about 1000 mTorr, and most preferably from about 50 mTorr to about 100 mTorr.




In a preferred embodiment of the present process and system, an additional ion guide can be provided for receipt of the ion beam resulting from the simultaneous damping and linear acceleration and further directing such beam to mass analysis. Preferably the additional ion guide is provided with a multipole ion guide having at least about eight ion guide rods.




Finally, the present invention includes a determination of mass to charge ratio of the substantially intact analyte ions provided from the previous step(s). In a preferred embodiment the determination of mass to charge ratio is conducted in an ion trap spectrometer. The invention is ideally suited for high-efficiency rapid ion trap spectroscopy.




The present invention provides a highly sensitive instrument for detection of analyte ions, e.g., peptides, in a concentration at the subfemtomole level. The present invention provides true MSMS capabilities which enable one to perform multiple MSMS experiments within very short periods of time. Moreover, the process and system of the present invention provide a high degree of accuracy even at extremely diluted levels and at unexpectedly high speed.




For a better understanding of the present invention, together with other and further objects, reference is made to the following description, taken in conjunction with the accompanying drawings, and its scope will be pointed out in the claims which follow.











BRIEF DESCRIPTION OF THE DRAWINGS




Preferred embodiments of the invention have been chosen for purposes of illustration and description and are shown in the accompanying drawings, wherein:





FIG. 1

illustrates a block diagram of a system for mass spectroscopy in accordance with the present invention;





FIG. 2

is a schematic diagram of a first embodiment of the present invention;





FIG. 3

is an exploded view of the ionguide/accelerator of the present invention;





FIG. 4

is a cross sectional view taken along line


4





4


in

FIG. 3

showing a multipole rod set and an accelerator rod set;





FIG. 5

is a plan view of a sample introduction system for use with the present invention;





FIG. 6

is a schematic diagram of a second embodiment of the present invention;





FIG. 7

is an exploded schematic diagram showing the quadrupole positioned between the ion trap and the detector of the second embodiment of the present invention;





FIG. 8

illustrates a mass spectra of a six peptide mixture acquired in about 2 seconds for a sample amount of 100 fmole;





FIG. 9

illustrates a mass spectra of a six peptide mixture acquired in about 2 seconds for a sample amount of 10 fmole;





FIG. 10

illustrates a mass spectra of a six peptide mixture acquired in about 2 seconds for a sample amount of 1 fmole; and





FIG. 11

illustrates a MS/MS spectrum of an ion at m/z 1956.7 selected from the spectrum of the 1 fmole peptide mixture corresponding to

FIG. 10

that was acquired in about 2 seconds.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




Referring now to

FIG. 1

, a system for mass spectroscopy


10


in accordance with the present invention is illustrated as a block diagram. The system for mass spectroscopy


10


includes a pulsed ionizer


12


, an ionguide/accelerator


14


, and a mass analyzer


16


. The pulsed ionizer


12


is preferably a matrix assisted laser desorption device that ionizes a sample to form analyte ions. The ionguide/accelerator


14


is interfaced with the pulsed ionizer


12


for receiving desorbed intact analyte ions from the sample to simultaneously dampen and linearly accelerate the intact ions in the substantial absence of fragmentation of the ions to provide a substantial continuous beam of the intact ions for mass analyses. Preferably the ionguide/accelerator


14


includes a multipole rod set


18


and an accelerator rod set


20


in a collinear arrangement in the presence of high pressure gas. The mass analyzer


16


is connected to the ionguide/accelerator


14


for receiving the beam of ions and to determine the mass charge ratio of the intact ions.




Referring now to

FIGS. 2 through 5

, a first preferred embodiment of the system for mass spectroscopy


10


according to the present invention is illustrated. The first embodiment includes a matrix assisted laser desorption ionization (MALDI) pulsed ionizer


12


and ionguide/accelerator


14


configured to cooperate with a mass analyzer


16


, such as the mass analyzer of a commerically available Finnigan LCQ ion trap mass spectrometer as shown in FIG.


2


. While, the Finnigan LCQ mass spectrometer is generally equipped with an electro spray ionization device (ESI) when sold to consumers, in the first embodiment shown herein the ESI device was removed to accomodate the pulsed ionizer


12


and ionguide/accelerator


14


. It is also possible to configure the device to accommodate both ESI and MALDI.




Referring now to

FIG. 2

, the MALDI pulsed ionizer


12


includes a laser


21


configured to pulse a sample located on a substrate


22


. Any pulsed laser that can produce ions from a sample for mass spectrometry can be used. The laser


21


is preferably a nitrogen laser. As known in the art, the laser may be focused at the sample on the substrate


22


by various optical components, examples of which are shown in

FIGS. 2 and 6

. A suitable laser is the VSL-337 Nitrogen Laser manufactured by Laser Science, Inc. of Franklin, Mass. which operates at a repletion rate of 10-20 Hz. The laser


21


can also be a Nd: YAG laser. In

FIG. 2

, the laser


21


is focused on the sample through a lens


24


and a mirror


26


. Preferably the lens collimates the laser beam and has a focal length of about 1 mm to about 1 meter, preferably about 50 cm. The mirror


26


directs the collimated laser beam through a window


25


towards the surface of the substrate


22


at an angle of about 10 degrees to about 80 degrees, preferably about 60 degrees to the normal of the substrate


22


. Preferably the laser beam has a laser spot diameter on the surface of a sample from about 0.3 mm to about 0.5 mm. Preferably the power density of laser radiation in the spot is about 10


7


W/cm


2


. The mirror


26


is preferably configured to be “wobbled” in order to scan the sample with the laser beam. Alternatively as shown in

FIG. 6

, the laser


21


can be focused on the sample located on the substrate


22


through an optical fiber


28


.




The sample is supported on a substrate


22


. Various substrates are known in the art to be useful. For example, the substrate may be made of a plastic material, preferably a polycarbonate surface such as that found in a commercially available compact disc.




Referring now to

FIGS. 2 and 5

, preferably the first embodiment of the mass spectroscopy system


10


includes a sample introduction system


30


such as that disclosed in Andrew Krutchinsky's and Brian Chait's co-pending U.S. patent application Ser. No. 09/737,660 entitled “High Capacity and Scanning Speed System for Sample Handling and Analysis” filed on Dec. 15, 2000, the disclosure of which is incorporated herein by reference. The sample introduction system


30


generally includes a support plate


27


configured to support a substrate in the form of a compact disc


32


for holding a plurality of samples


34


as shown in FIG.


5


. The sample introduction system


30


preferably includes a video camera


36


for monitoring the sample during the pulsed ionizing by the laser


21


as shown in FIG.


2


. Preferably the sample introduction system


30


is connected to a pump (not shown herein) via vacuum line


38


which maintains a vacuum lock between the pump and the system


30


such as by use of an o-ring


40


shown in FIG.


5


.




Referring to

FIG. 5

, the plurality of samples


34


located on the compact disc


32


are preferably formed by dissolving a compound to be analyzed in a solution containing a large molar excess of a matrix forming material that efficiently absorbs the light of the laser


21


. A small amount of the solution is then deposited on the compact disc


32


and dried to form a sample


34


. The samples


34


can be deposited on the compact disc


32


in a variety of known methods including spraying as an aerosol, ultrasonically, or by using a micropipette or fine needle. Preferably, the plurality of samples


34


are discretely deposited over the surface of the compact disc


32


as shown in FIG.


5


. The location of each sample


34


can be tracked for use with a high speed compact disc drive to enable the analysis of an extremely large number of samples within a short period of time. During the analysis, the matrix absorbs the energy from the laser pulse resulting in the vaporization and ionization of the sample.




Referring now to

FIGS. 3 and 4

, the ionguide/accelerator


14


preferably includes a multipole rod set


18


and an accelerator rod set


20


in a collinear arrangement in the presence of high pressure gas. That is, both the multipole rod set


18


and an accelerator rod set


20


are preferably symmetrically arranged about an axis


54


of the ionguide/accelerator


14


as shown in FIG.


4


. The high pressure gas is maintained generally from about 0.1 mTorr to about 10 Torr by a pump represented as arrow


45


in FIG.


2


. Preferably the high pressure gas is maintained from about 10 m Torr to about 1000 m Torr, and most preferably from about 50 m Torr to about 100 m Torr. The presence of the high pressure gas provides collisional damping for reducing the energy spread of the desorbed ions without substantial fragmentation. Preferably the ionguide/accelerator


14


is arranged spatially at a distance, A, of not greater than about 2.0 cm from the source of ions for entry of analyte ions, which is generally measured from the substrate


22


as shown in FIG.


2


. Preferably the spatial distance is from about 0.1 mm to about 1 cm, and most preferably from about 0.8 mm to about 1.2 mm. Referring to

FIG. 3

, preferably the ionguide/accelerator


14


includes a plate


44


at an opposite end of the source of ions formed with an aperture


46


having a dimension, e.g., a diameter, from about 0.1 cm and to about 2 cm. Preferably the dimension of the aperture


46


is from about 0.2 cm to about 1.0 cm, and most preferably is about 0.3 cm. Preferably the aperture


46


is circular. The ionguide/accelerator


14


preferably includes an ion guide screen


48


.




The multipole rod set


18


confines the ions and preferably includes at least four (4) ion guide rods


40


symmetrically arranged about the axis


54


. The multipole rod set


18


can be configured to include more than four (4) ion guide rods


40


. For example, the multipole rod set


18


could include eight (8) ion guide rods


40


to be configured in a similar manner as an octopole. Preferably each ion guide rod


40


has a length in a range from about 1 cm to about 100 cm and has a largest cross-sectional dimension, e.g., a diameter, in a range from about 0.1 cm to about 2 cm. The length of each ion guide rod


40


is preferably from about 10 cm to about 40 cm and most preferably from about 18 cm to about 22 cm. The cross-sectional dimension of each ion guide rod


40


is preferably from about 0.2 cm to about 1 cm and most preferably from about about 0.50 cm to about 0.8 cm. Preferably each ion guide rod


40


has a circular cross section.




The accelerator rod set


20


provides an electrical force to drag the ions towards the exit of the ion guide


14


and preferably includes at least four (4) accelerator rods


42


symmetrically arranged about the axis


54


. The accelerator rod set


20


can be configured to include more than four (4) accelerator rods


42


. For example, the accelerator rod set


20


could include eight (8) accelerator rods


42


. The accelerator rods


42


are arranged closer to the axis


54


of the ion guide


14


at the entrance


50


and further from the axis


54


at the ion guide


14


exit


52


. Preferably each accelerator rod


42


has a length in a range from about 1 cm to about 100 cm and has a largest cross-sectional dimension, e.g., diameter, in a range from about 0.1 mm to about 2 cm. The length of each accelerator rod


42


is preferably from about 10 cm to about 40 cm and most preferably from about 16 cm to about 20 cm. The cross-sectional dimension of each accelerator rod


42


is preferably from about 0.1 cm to about 1 cm and most preferably from about 0.25 cm to about 0.5 cm. Preferably each accelerator rod


42


has a circular cross section.




In operating the ionguide/accelerator


14


, the multipole rod set


18


is preferably driven by an independent RF power supply to generate a sine wave amplitude from about 1 V to about 10,000 V. Preferably the amplitude is in the range from about 100 V to about 1000 V, and most preferably from about 300 V to about 500 V. The power supply can include a 500 kHz crystal oscillator-controlled sine wave generator and a power amplifier such as Model No. 240L of ENI, Rochester, N.Y. The multipole rod set


18


can also be operated as a mass filter by applying DC voltages from about −50 V to about +50 V while providing the necessary offset from about 15 V to about 25 V. Both the plate


44


and ion guide screen


48


are grounded as shown in FIG.


3


. The voltage applied to the accelerator rod set


20


creates a small electrical field along the axis


54


of the ion guide


14


because of the changing proximity of the accelerator rods


42


to the axis


54


of the ion guide


14


that drags the desorbed ions along the axis


54


. Preferably, a constant voltage is applied to the accelerator rod set


20


from about 1 V to about 10,000 V. The accelerator rod set voltage can be in the range from about of 100 V to about 1000 V, and preferably is about 100 V. Although MALDI spectra can be obtained when the substrate


22


is isolated and no potential is applied to the support plate


27


, preferably about 200 V is applied to the support plate


27


for the optimum recording of MALDI spectra.




Referring now to

FIG. 2

, the mass analyzer


16


preferably includes an ion trap


56


and a detector


58


. In the first embodiment of the present invention, the mass analyzer


16


utilizes the ion trap


56


and the detector


58


configuration of the commerically available Finnigan LCQ ion trap mass spectrometer (hereinafter “Finnigan mass spectrometer”). The Finnigan mass spectrometer also includes an octopole


60


which interfaces with the ionguide/accelerator


14


.





FIGS. 8 through 10

, illustrate the MALDI spectra of samples obtained from a mixture of six peptides at an equimolar concentration of 100 fmol/μl in a solution of 60/35/5 MeOH/water/acetic acid as well as dilutions thereof at respectively 10 fmol/μl and 1 fmol/μl. The sample analyzed for

FIGS. 8

,


9


, and


10


respectively contained 100, 10 and 1 fmole of each peptide. The sample matrix solutions were prepared by depositing the solution onto the polycarbonate surface of the compact disc


32


and allowed to dry. The samples were bombarded with a collimated nitrogen laser beam having a diameter between 0.3 and 0.5 mm and a power density of about 10


7


W/cm


2


while applying about 200 V to the support plate


27


. The desorbed ions were introduced into the ion guide/accelerator


14


for simultaneously damping by high pressure gas at about 65 mTorr and dragging the ions with the accelerator rod set


20


. A constant voltage of about 100 V was applied to the accelerator rod set


20


, and about 400 V was applied to the multipole rod set


18


. The mass analyzer


16


of the Finnigan LCQ was operated in substantially the traditional intended manner for analyzing the ions. The MALDI spectra reproducibly exhibited ion signals from all six components of the peptide mixture, even for the sample having only 1 fmole of each peptide. All spectra were acquired in about 2 seconds.




Referring now to

FIG. 11

, the MS/MS spectrum of the peptide at 1956.7 m/z selected from the MALDI spectrum of the 1 fmole peptide mixture shown in

FIG. 10

is shown. This fragmentation spectrum was also acquired in about 2 seconds. Almost all major peaks in the spectrum can be identified as b or y-type fragments of the peptide.




Referring now to

FIGS. 6 and 7

, a second preferred embodiment of the system for mass spectroscopy


100


according to the present invention is illustrated. The second embodiment includes a matrix assisted laser desorption ionization (MALDI) pulsed ionizer


112


, an ionguide/accelerator


114


, and a mass analyzer


116


all in a substantially collinear arrangement. Both the ionguide/accelerator


114


, and a mass analyzer


116


are subjected to a vacuum as represented by arrows


145


in FIG.


6


. Preferably the second embodiment of the system


10


also includes at least one additional multipole


118


located between the ionguide/accelerator


114


and the mass analyzer


116


. The multipole


118


can be any type including a quadrupole or an octopole. The matrix assisted laser desorption ionization (MALDI) pulsed ionizer


112


and the ionguide/accelerator


114


are preferably configured in a similar manner as described above with respect to the first embodiment


10


. The ionguide/accelerator


114


can be configured as a flexible device built from metallic springs or flexible metallized rods for use as a “sniffing” type of a sample scanning system as disclosed in U.S. application Ser. No. 09/737,660. The details of the mass analyzer


116


are shown in FIG.


7


and will now be described below.




Referring now to

FIG. 7

, the mass analyzer


116


preferably includes a quadrupole ion trap


156


and a detector


158


interfaced by a second ionguide/accelerator


162


. The detector


158


includes a conversion plate


159


for converting ions to secondary charged particles received from the exit end


164


of the second ionguide/accelerator


162


. The secondary charged particles include electrons and ions. The second ionguide/accelerator


162


is configured in a similar manner as the first ionguide/accelerator


14


and includes a first end


166


that is preferably coupled to the exit of the quadrupole ion trap


156


. In this embodiment, the second ionguide/accelerator


162


provides for the efficient transport of ions from the quadrupole ion trap


156


to the detector


158


. The second ionguide/accelerator


162


can also be operated as a mass filter as described above with respect to the first ionguide/accelerator


14


for selecting a subset of ions ejected from the quadrupole ion trap


156


to the detector


158


.




The operation and advantages of the second ionguide/accelerator


162


will now be explained with reference to

FIG. 7

where the flow of ions is depicted by arrows. The ion trap


156


operates in its original mode admitting the injected ions and collisionally cooling them. After some time, the ejection process from the ion trap


156


starts. The ejection of ions from the trap


156


is usually achieved by changing the amplitude of RF potential applied to the trap (by using a so called instability scan). The increased RF field inside of an ion trap makes the trajectory of some ions with a particular mass-to-charge ratio unstable such that these ions are caused to hit the walls or leave through one of the holes in the ion trap electrode. The process of ion ejection also causes the kinetic energy of the ejected ions to increase so that there is a greater chance that the ejected ions will fragment upon collision with buffer gas molecules present in the ion trap. With the second ionguide/accelerator


162


it is possible to select some particular fragment of the ejected ions. In this way only those ejected ions that produce a particular fragment will be capable of going through the second ionguide/accelerator


162


to the detector


158


using the well known “linked scan” mode of detection. Thus it may be possible to measure the spectrum of only those ions that undergo a particular fragmentation, but with very high efficiency.




Different types of so-called “link scans” can be performed with this instrument, including neutral ion losses scan, parent ion scan etc. In the proposed device, these types of scans can be performed with much greater efficiency compared with those carried out on existing instruments (e.g., the triple quadrupole mass spectrometer). Because only particular ions are ejected from the ion trap at a given ejection time, other ions are left in the ion trap to be ejected at different time. Thus no losses are expected because all ions undergo the same linked scan analysis during the total ion ejection analysis scan.




Thus, while there have been described what are presently believed to be the preferred embodiments of the invention, those skilled in the art will realize that changes and modifications may be made thereto without departing from the spirit of the invention, and is intended to claim all such changes and modifications as fall within the true scope of the invention.



Claims
  • 1. A method of transmitting ions along an axis located between a length defined by a first mass spectroscopy device and a second mass spectroscopy device, said method comprising the steps of:(a) receiving the ions from the first mass spectroscopy device; (b) guiding the ions along the axis; (c) accelerating the ions along the entire length; (d) damping the ions along the entire length; and (e) delivering a substantially continuous beam of ions to the second mass spectroscopy device.
  • 2. A method of transmitting ions as defined in claim 1, wherein step (d) is perfonned by maintaining the ions under high pressure.
  • 3. A method of transmitting ions as defined in claim 2, wherein said high pressure is maintained at a range from 0.1 mTorr to 10 Torr.
  • 4. A method of transmitting ions as defined in claim 2, wherein said high pressure is maintained at a range from about 10 mTorr to about 1000 mTorr.
  • 5. A method of transmitting ions as defined in claim 2, wherein said high pressure is maintained at a range from about 50 m Torr to about 100 m Torr.
  • 6. A method of transmitting ions as defined in claim 2, wherein said high pressure is maintained by pumping.
  • 7. A method of transmitting ions as defined in claim 1, wherein step (b) is performed by providing a plurality of ion guide rods about the axis.
  • 8. A method of transmitting ions as defined in claim 7, wherein said plurality of ion guide rods are symmetrically arranged about the axis along the length.
  • 9. A method of transmitting ions as defined in claim 8, wherein said plurality of ion guide rods includes at least about four (4) ion guide rods.
  • 10. A method of transmitting ions as defined in claim 1, wherein step (c) is performed by providing a plurality of accelerator rods about the axis.
  • 11. A method of transmitting ions as defined in claim 10, wherein said plurality of accelerator rods are symmetrically arranged about the axis along the length.
  • 12. A method of transmitting ions as defined in claim 11, wherein said plurality of accelerator rods are arranged closer to the axis at the first mass spectroscopy device than the second mass spectroscopy device.
  • 13. A method of transmitting ions as defined in claim 12, wherein said plurality of accelerator rods includes at least about four (4) accelerator rods.
  • 14. A method of transmitting ions along an axis located between a length defined by a first mass spectroscopy device and a second mass spectroscopy device, said method comprising the steps of:(a) receiving the ions from the first mass spectroscopy device at an entrance; (b) guiding the ions along the axis with at least one ion guide rod; (c) accelerating the ions along the entire length with at least one accelerator rod; (d) damping the ions along the entire length; and (e) delivering a substantially continuous beam of ions through an exit to the second mass spectroscopy device.
  • 15. A method of transmitting ions as defined in claim 14, wherein step (d) is performed by maintaining the ions under high pressure.
  • 16. A method of transmitting ions as defined in claim 15, wherein said high pressure is maintained at a range from 0.1 mTorr to 10 Torr.
  • 17. A method of transmitting ions as defined in claim 15, wherein said high pressure is maintained at a range from about 10 mTorr to about 1000 mTorr.
  • 18. A method of transmitting ions as defined in claim 15, wherein said high pressure is maintained at a range from about 50 m Torr to about 100 m Torr.
  • 19. A method of transmitting ions as defined in claim 18, wherein said plurality of accelerator rods are arranged closer to the axis at the entrance than the exit.
  • 20. A method of transmitting ions as defined in claim 19, wherein said plurality of accelerator rods includes at least about four (4) accelerator rods.
  • 21. A method of transmitting ions as defined in claim 15, wherein said high pressure is maintained by pumping.
  • 22. A method of transmitting ions as defined in claim 14, wherein said at least one ion guide rod is a plurality of ion guide rods located about the axis.
  • 23. A method of transmitting ions as defined in claim 22, wherein said plurality of ion guide rods are symmetrically arranged about the axis between said entrance and said exit.
  • 24. A method of transmitting ions as defined in claim 23, wherein said plurality of ion guide rods includes at least about four (4) ion guide rods.
  • 25. A method of transmitting ions as defined in claim 14, wherein said at least one accelerator rod step is a plurality of accelerator rods located about the axis.
  • 26. A method of transmitting ions as defined in claim 25, wherein said plurality of accelerator rods are symmetrically arranged about the axis between said entrance and said exit.
Parent Case Info

This application is a continuation application of U.S. patent application Ser. No. 09/835,943 filed on Apr. 16, 2001, now U.S. Pat. No. 6,617,577, which is incorporated herein by reference.

GOVERNMENTAL SUPPORT

The research leading to the present invention was supported, at least in part, by NIH Grant No. RR 00862. Accordingly, the Government may have certain rights in the invention.

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Continuations (1)
Number Date Country
Parent 09/835943 Apr 2001 US
Child 10/657580 US