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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
  • G01N30/02—Column chromatography
  • G01N30/62—Detectors specially adapted therefor
  • G01N30/72—Mass spectrometers
  • G01N30/7206—Mass spectrometers interfaced to gas chromatograph
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J49/00—Particle spectrometers or separator tubes
  • H01J49/02—Details
  • H01J49/025—Detectors specially adapted to particle spectrometers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J49/00—Particle spectrometers or separator tubes
  • H01J49/26—Mass spectrometers or separator tubes
  • H01J49/28—Static spectrometers
  • H01J49/32—Static spectrometers using double focusing
  • H01J49/322—Static spectrometers using double focusing with a magnetic sector of 90 degrees, e.g. Mattauch-Herzog type
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J49/00—Particle spectrometers or separator tubes
  • H01J49/44—Energy spectrometers, e.g. alpha-, beta-spectrometers
  • H01J49/46—Static spectrometers
  • H01J49/48—Static spectrometers using electrostatic analysers, e.g. cylindrical sector, Wien filter

Definitions

• This disclosure generally relates to analytic instruments, and more particularly relates to gas chromatographs, and mass spectrometers and/or mass spectrographs.
• Mass spectrometry is widely used in many applications ranging from process monitoring to life sciences. Over the course of the last 60 years, a wide variety of instruments have been developed. The focus of new developments has been two fold: (1) a push for ever higher mass range with high mass resolution, and (2) on developing small, desktop mass spectrometry instruments. Mass spectrometers are often coupled with gas chromatographs for analysis of complex mixtures. This is particularly useful for analysis of volatile organic compounds (VOCs) and semi-volatile organic compounds (semi-VOCs).
• a combined gas chromatograph and mass spectrometer or spectrograph (GC/MS) instrument typically includes a gas inlet system, which may include the gas chromatograph portion of the GC/MS instrument.
• the GC/MS instrument typically also includes an electron impact (El) based ionizer with ion extractor, ion optic components to focus the ion beam, ion separation components, and ion detection components, lonization can also be carried out via chemical ionization.
• Ion separation can be performed in the time or spatial domain.
• An example for mass separation in the time domain is a time of flight mass spectrometer. Spatial separation is seen in commonly used quadrupole mass spectrometers. Here a "quadrupole filter" allows only one mass/charge ratio to be transmitted from the ionizer to the detector.
• a full mass spectrum is recorded by scanning the mass range through a "mass filter.”
• Other spatial separation approaches are based on magnetic fields, where either ion energy or magnetic field strength is varied, the mass filter allowing only one mass/charge ratio to be transmitted.
• a spectrum can be recorded by scanning through the mass range.
• One type of mass spectrometer is a mass spectrograph. In a mass spectrograph the ions are spatially separated in a magnetic field and detected with a position sensitive detector. The concept of a double focusing mass spectrograph was first introduced by Mattauch and Herzog (MH) in 1940 (J. Mattauch,
• Double focusing refers to the ability of an instrument to refocus both the energy spread as well as the spatial beam spread. Modern developments in magnet and micro-machining technologies allow dramatic reductions in the size of these instruments. The length of the focal plane in a mass spectrograph capable of VOC and semi-VOC analysis is reduced to a few centimeters.
• Electron impact ionization, Rhenium filament DC-voltages and permanent magnet Ion Energy 0.5-2.5 kV DC Mass Range: 2-200 D Faraday cup detector array or strip charge detector Integrating operational amplifier with up to 10 11 gain Duty Cycle: > 99% Read-Out time: 0.03 sec to 10 sec Sensitivity: approximately 10ppm with strip charge detector.
• the ion optic elements are mounted in the vacuum chamber floor or on chamber walls. The ion optic elements can also be an integral part of the vacuum housing. In small instruments, the ion optic elements can be built on a base plate which acts as an "optical bench" to support the ion optic elements.
• the base plate is mounted against a vacuum or master flange to provide a vacuum seal needed to operate the mass spectrometer under vacuum.
• the base plate can also function as the vacuum or master flange itself.
• a Mattauch-Herzog ion detector is a position sensitive detector. Numerous concepts have been developed over the last decades. Recent developments focus on solid state based direct ion detection as an alternative to previously used electro optical ion detection (EOID).
• EOID employs a multi-channel-plate (MCP) to convert ions into electrons, amplify the electrons, and illuminate a phosphorus film by bombarding the phosphorus film with the electrons emitted from the MCP.
• MCP multi-channel-plate
• the image formed on phosphorus film is recorded using a photo diode array, for example, via a fiber optic coupler.
• This type of EOID is described in detail in U.S. Patent 5,801 ,380.
• the EOID is intended for the simultaneous measurement of ions spatially separated along the focal plane of the mass spectrometer.
• the EOID operates by converting ions to electrons and then to photons.
• the photons form images of the ion-induced signals.
• the ions generate electrons by impinging on a micro-channel electron multiplier array.
• the electrons are accelerated to a phosphor-coated fiber-optic plate that generates photon images. These images are detected using a photo detector array such as the photo diode array.
• the EOID although highly advantageous in many ways, is relatively complicated since it requires multiple conversions. In addition, there may be complications from the use of phosphors, which may limit the dynamic range of the detector.
• the micro-channel device may also be complicated, since it may require a high-voltage, for example 1 KV, to be applied.
• the micro-channel device may be placed in a vacuum environment with a pressure of about 106 Torr. The micro-channel device may experience ion feedback and electric discharge when operating at such high pressures. Additionally, fringe magnetic fields may affect the electron trajectory. Isotropic phosphorescence emission may also affect the resolution. The resolution of the mass analyzer may therefore be compromised due to these and other effects.
• a direct charge measurement can be based on a micro-machined Faraday cup detector array (FCDA).
• FCDA micro-machined Faraday cup detector array
• an array of individually addressable Faraday cups monitors the ion beam.
• the charge collected in individual elements of the array is provided to an amplifier via a multiplexer unit.
• This layout reduces the number of amplifiers and feedthroughs needed.
• This concept is described in detail in recent publications, such as "A. A. Scheidemann, R. B. Darling, F. J. Schumacher, and A. Isakarov, Tech. Digest of the 14th Int. Forum on Process Analytical Chem. (IFPAC-2000), Lake Las Vegas, Nevada, Jan. 23-26, 2000, abstract 1-067"; "R. B. Darling, A. A.
• a flat metallic strip referred to as a strip charge detector (SCD) positioned on a grounded and insulated background can be used to monitor the ion beam.
• SCD strip charge detector
• the charge is provided to an amplifier via a multiplexer.
• Another embodiment of an ion detector array is disclosed in U.S.
• Patent 6,576,899 is referred to as a shift register based direct ion detector.
• the shift register based direct ion detector defines a charge sensing system that can be used in a GC/MS instrument, with a modification to allow direct measurement of ions in the mass spectrometer device without conversion to electrons and photons (e.g., EOID prior to measurement).
• the ion detector may use charge coupled device (CCD) technology employing metal oxide semiconductors.
• CCD charge coupled device
• the GC/MS instrument may use direct detection and collection of the charged particles using the ion detector. The detected charged particles form the equivalent of an image charge that directly accumulates in a shift register associated with a part of the CCD.
• This signal charge can be clocked through the CCD in a conventional way, to a single output amplifier. Since the CCD uses only one charge-to-voltage conversion amplifier for the entire detector, signal gains and offset variation of individual elements in the detector array are minimized.
• a Mattauch-Herzog detector array which can be composed of a FCDA, a SCD, or another type of the aforementioned detectors, is placed at the exit end of the magnet, which is commonly referred to as the "focal plane.”
• the FCDA can be made by deep reactive ion etching (DRIE).
• the SCD can be made by vapor deposition.
• a dice with an active element (FCDA or SCD) is usually cut out of a wafer with conventional techniques such as laser cutting or sawing.
• FCDA or SCD dice is placed in front of the magnet and electrically connected to the multiplexer and amplifier unit, which is referred to as a "FARADAY CUP DETECTOR ARRAY” - "INPUT/OUTPUT” - "PRINTED CIRCUIT BOARD” (FCDA-I/O-PCB), to read out the charge collected with the detector elements.
• Patents discussing mass spectrometers and gas chromatographs include U.S. Patent 5,317,151 , U.S. Patent 5,801 , 380, U.S. Patent 6, 182,831 , U.S. Patent 6,191 ,419, U.S. Patent 6,403,956, and U.S. Patent 6,576,899.
• Figure 1 shows a double focusing Mattauch-Herzog mass spectrometer assembly 10 with a gas chromatograph assembly 12.
• the gas chromatograph assembly 12 comprises a sample injector valve V, which has an entry port S for introduction of the sample, an exit port W for the waste after the sample has been vaporized and/or decomposed, typically by heat.
• the sample to be analyzed (referred to as analyte) is carried by a carrier gas to a column M (capillary tube, usually coated with polymeric materials).
• the carrier gas may be inert (e.g., helium), or may not be inert.
• the constituents of the analyte are separated by different absorption rates on the wall of the column M, which has a rather small inside diameter, for example on the order of about 50 - 500 ⁇ m.
• the carrier gas flows typically at 2-5 atm. cm 3 /sec.
• the constituents of the analyte are received by the ionizer 14 of the mass spectrometer 10 for further spectrometric analysis.
• a larger bore of the capillary tube corresponds to a larger bore of the vacuum pump in the mass spectrometer core.
• a smaller bore of the capillary tube causes narrower peaks of the effluent to be even more narrow, which is indicative of a large loss of signal. A compromise for this problem is addressed by U.S.
• the double focusing mass spectrometry assembly 10 comprises an ionizer 14, a shunt and aperture 16, an electrostatic energy analyzer 18, a magnetic section 20, and a focal plane section 22.
• the ion optics are placed on the vacuum chamber wall, and the position sensitive ion detector is mounted on the exit flange of the ion flight path. This arrangement is required as a result of having the magnet outside of the vacuum.
• the multiplexer and amplifier unit is also positioned outside of the vacuum chamber in the case of traditional Mattauch- Herzog instruments.
• the separate units have separate power supplies, separate, input/output devices, as well as other components, making them heavier and cumbersome.
• the analyte has to be transferred from the gas chromatograph to the mass spectrometer, necessitating special handling of the capillary tube, which is very sensitive, and therefore difficult to connect between the two separate instruments.
• This disclosure relates to a GC/MS system that includes a master flange comprising a vacuum feed-through, the master flange having a first side and a second side; a holder board integrally connected to the second side of the master flange; a base plate integrally connected to the first side of the master flange; a chromatograph supported on the holder board; and an mass spectrometry assembly of an ionizer, shunt and aperture group, electrostatic energy analyzer, magnetic section, and a focal plane section comprising an ion detector, all supported on the base plate.
• a gas chromatograph and a mass spectrometer are assembled into one unit where all parts of the gas chromatograph are placed on a holder board and all the parts of the mass spectrometer are placed on a base plate. Both the holder board and the base plate are integral parts of a vacuum or master flange.
• an analytic instrument in another aspect, includes a master flange comprising a first side, a second side, and a vacuum feed-through passage extending between the first side and the second side; a holder board coupled to the second side of the master flange; a base plate coupled to the first side of the master flange; a gas chromatograph coupled to the holder board; and a mass spectrometer assembly supported by the base plate, the mass spectrometer assembly having an ionizer, a shunt and aperture group, an electrostatic energy analyzer, a magnetic section, and a focal plane section, which includes an ion detector, wherein the ionizer receives an analyte via the vacuum feed-through passage of the master flange.
• an analytic system includes a gas chromatograph assembly; a vacuum housing; a mass spectrometer assembly at least partially received within the vacuum housing; a flange having a first side, a second side opposed to the first side, and a passage extending from the first side to the second side to permit the transfer of an analyte from the gas chromatograph assembly to the mass spectrometer assembly; a first extension securely connected to the first side of the flange and supportingly engaging the gas chromatograph assembly; and a second extension securely connected to a second side of the flange and supportingly engaging the mass spectrometer assembly.
• a method of assembling a gas chromatograph assembly and mass spectrometer assembly includes securely coupling a first extension to a first side of a flange, the flange having the first side, a second side, and a passage extending from the first side to the second side to permit the transfer of an analyte from the gas chromatograph assembly to the mass spectrometer assembly; supporting the gas chromatograph assembly on the first extension; securely coupling the second extension to the second side of the flange; supporting the mass spectrometer assembly on the second extension; and affixing a vacuum housing to the flange, the vacuum housing configured to encompass the mass spectrometer assembly and the second extension.
• the master flange can include electrical connectors for electrical transfer between the first side and the second side of the master flange.
• a vacuum housing is supported on the first side of the master flange so that a vacuum can be applied to the mass spectrometry assembly.
• One or more pumps, in series or in parallel, may be connected to the vacuum housing.
• the GC/MS assembly includes a GC controller disposed under the holder board and may further include a MCP/CCD controller.
• the GC/MS assembly includes a valve block (sample injector valve) and a transfer line, which is aligned with the vacuum feed-through.
• FIG. 1 is a schematic view of a Mattauch Herzog spectrometer connected to a gas chromatograph according to the prior art, wherein the two instruments are separate units.
• Figure 2 is a perspective view of a GC/MS instrument according to one illustrated embodiment, where a gas chromatograph and a vacuum housing are integrally connected to a master flange.
• Figure 3 is an isometric view of a portion of the mass spectrometer within the vacuum housing including a base plate, an ionizer, an electrostatic energy analyzer, and a magnetic section.
• the GC/MS instrument 1 comprises a master flange 26 with a first side 26A, a second side
• a holder board 28B having a support side extension 28C is integrally connected to the second side 26B of the master flange 26.
• a base plate 28A is integrally connected to the first side 26A of the master flange 26.
• a gas chromatograph assembly 12 ( Figure 2) is supported on the holder board 28B, and a mass spectrometry assembly 10 ( Figure 3) is supported on the base plate 28A, in very well defined and predetermined positions.
• a sample injector valve V with a lid 13 is attached to the exterior of the gas chromatograph assembly 12.
• a microbore column or capillary tube (not shown) originates at the sample injector valve V and ends into a transfer line 2.
• the transfer line 2 is aligned with the vacuum feed-through 4, and is coupled to the vacuum feed-through 4, at least during operation.
• the vacuum feed-through 4 is connected to an inlet of the ionizer 14 of the mass spectrometry assembly 10 on the other side of the master flange 26.
• the gas chromatograph assembly 12 can also include a means for stabilizing the temperature of the microbore column (not shown) within a desired range.
• the master flange can include electrical connectors 5 for electrical power transfer between the first side 26A and the second side 26B of the master flange 26.
• a vacuum housing 27 may be supported on the first side 26A of the master flange, so that a vacuum can be applied to the components of the mass spectrometry assembly 10.
• the GC/MS instrument 1 may further include a gas chromatograph controller 6 disposed under the holder board 28B and/or an MCP/CCD controller 7, as previously described.
• One or more pumps (not shown for purposes of clarity), connected in series or in parallel, may be connected to a bottom region of the vacuum housing 27 on the side of the MCP/CCD controller 7.
• the major components or the Mattauch-Herzog Sector of a miniaturized mass spectrometer assembly 10 are shown to be located on the first side 26A of the master flange 26 according to the illustrated embodiment.
• the base plate 28A is supported on the first side 26A of the master flange 26.
• the vacuum housing 17 covers the vacuum space within which the major components of the mass spectrometer assembly 10 are residing. Using the base plate 28A to support the components of the mass spectrometry assembly 10 results in a sturdy and accurate configuration.
• the ionizer 14 is secured on the base plate 28A, close to the vacuum flange 26, with a shunt and aperture combination 16 in front of the ionizer 14. Further from the flange 26 is an electrostatic energy analyzer 18, which is also secured on the base plate 28.
• a magnetic sector or magnetic section 20 is also secured on the base plate 28.
• the magnetic sector 20 comprises a yoke 20B and magnets 20A attached to the yoke 20B.
• the yoke has magnetic flux saturation value in the range of about 15,000 G to 20,000 G.
• the yokes 20B can be made from a hyperco-51A VNiFe alloy.
• the volume and mass of a magnet is typically inversely proportional to the energy product value of the magnetic material.
• a typical magnetic material is AINiCo V (Aluminum Nickel Cobalt), which has an energy product of about 5-6 MGOe.
• Other materials include, but are not limited to Sm-Co (Samarium Cobalt) alloys and Nd-B-Fe (Neodymium Boron Iron) alloys. Some of these materials, in particular Nd-B-Fe, may be sensitive to temperature variations.
• the analyte then passes through the transfer line 2 and the vacuum feed-through 4 to the ionizer 14 where it is bombarded by electrons to produce ions.
• the ions are focused in the shunt and aperture section 16 to form an ion beam 24.
• the ions are then separated according to their charge/mass ratio as the ion beam travels through the electrostatic energy analyzer 18 and the magnetic section 20.
• the ions with a desired charge/mass ratio are then detected by the focal plane section 22.
• the focal plane section 22 is described in U.S. Patent 5,801 ,380.
• the operation takes place under vacuum of the order of about 10 "5 Torr with a use of a vacuum pump (not shown).
• the GC/MS instrument 1 is a single integral unit with the mass spectrometer assembly 10 under vacuum and the gas chromatograph assembly 12 under atmospheric pressure.
• the close proximity of all the components produces a robust system and substantially reduces a considerable amount of electronic and electromagnetic noise that two separate units present.
• the GC/MS instrument 1 described herein may include other advantages, such as: (1) The system may be more compact than two combined systems; (2) The system may be lighter in weight; (3) If the mass spectrometry assembly is taken out of the vacuum housing, the gas chromatograph assembly does not need to be separated from the mass spectrometry assembly; (4) It may be possible to check the location of the column after the entire GC/MS instrument 1 is put together; (5) The GC/MS instrument 1 is easy to assemble and disassemble; (6) Low cost; (7) The electronics to drive the gas chromatograph function are located directly under the gas chromatograph assembly.
• the cables are short, and noise pick-up (e.g., from the sensitive thermo-sensors) will be limited; (8) Tests of the gas chromatograph functionality (such as heat on/off, gas chromatograph lid open/close, valve(s) open/close, can be tested while the has chromatograph assembly is outside the GC/MS instrument 1.
• gas chromatograph functionality such as heat on/off, gas chromatograph lid open/close, valve(s) open/close
• the only cable connector needed may be an extension cable for supply of the inputs to the gas chromatograph driver, and main power (e.g., 24 V); (9)
• the entire gas chromatograph assembly 12 can readily be exchanged: a) Open vacuum feed-through 10; and b) Separate the gas chromatograph-holder board (6) from the master flange (two screws), c) Such an exchange maintains the gas chromatograph and gas chromatograph electronics together during removal and replacement, which permits easy service and reduces assembly cost.
• the following devices and/or assemblies may be combined with the disclosed embodiments in a variety of ways.

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• 2005
  • 2005-03-04 WO PCT/US2005/007197 patent/WO2005088671A2/en not_active Ceased
  • 2005-03-04 WO PCT/US2005/007128 patent/WO2005088672A2/en not_active Ceased
  • 2005-03-04 EP EP05732599A patent/EP1721330A2/en not_active Withdrawn
  • 2005-03-04 JP JP2007502023A patent/JP4931793B2/ja not_active Expired - Lifetime
  • 2005-03-04 US US11/071,992 patent/US20060011829A1/en not_active Abandoned
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