EP1819423A2 - Ion source for a mass spectrometer - Google Patents
Ion source for a mass spectrometerInfo
- Publication number
- EP1819423A2 EP1819423A2 EP05851479A EP05851479A EP1819423A2 EP 1819423 A2 EP1819423 A2 EP 1819423A2 EP 05851479 A EP05851479 A EP 05851479A EP 05851479 A EP05851479 A EP 05851479A EP 1819423 A2 EP1819423 A2 EP 1819423A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- ionization
- gas
- source
- enclosure
- region
- Prior art date
- Legal status (The legal status 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 status listed.)
- Withdrawn
Links
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
- H01J49/0431—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components for liquid samples
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J49/00—Particle spectrometers or separator tubes
- H01J49/02—Details
- H01J49/10—Ion sources; Ion guns
- H01J49/107—Arrangements for using several ion sources
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- 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
Definitions
- This invention relates to an atmospheric pressure ionization source that facilitates ionization of either a liquid or gas effluent from different sources, such as a liquid chromatograph or a gas chromatograph, to permit subsequent mass separation of the ions by a mass spectrometer.
- This invention also relates to a method, using the ionization source, of increasing the number of classes of chemical compounds that can be ionized in the effluent of a gas chromatograph by introduction of a flow of dry clean purge gas, thus minimizing low energy ionization events by reducing water and other impurities in the ionization region.
- This invention also relates to a method, using the ionization source, of enhancing analysis of a selected class of chemical compounds by introducing a reactive gas into the ionization region of the ionization source so that only compounds of interest are ionized.
- a gas chromatograph source may be either a commercially available instrument or a mini-gas chromatograph that is built into a probe assembly that forms a component of the instant ionization source.
- the probe assembly incorporating the mini-gas chromatograph can replace the interface probe assembly used in liquid chromatography/mass spectrometry (LC/MS).
- LC/MS liquid chromatography/mass spectrometry
- a single atmospheric pressure ionization mass spectrometer of any type is made capable of ionizing the effluent from either a liquid chromatograph or a gas chromatograph and of analyzing this effluent.
- GC/MS refers to a gas chromatograph (GC) interfaced to a mass spectrometer (MS).
- LC/MS refers to a liquid chromatograph (LC) interfaced to a mass spectrometer.
- the current practice in mass spectrometry is to have separate instruments for GC/MS and LC/MS operation.
- At least one manufacturer, Varian, Inc. manufactures a mass spectrometer that can be converted from atmospheric pressure LC/MS to a vacuum ionization GC/ MS by breaking vacuum and interchanging ion sources. This approach suffers the disadvantages of being time consuming, requires breaking vacuum and is only applicable on the specific Varian instrument.
- Atmospheric pressure ionization mass spectrometers currently available lack flexibility. They are either configured to receive effluent from an up-stream gas chromatograph or from an up- stream liquid chromatograph, but cannot be easily changed to accept an alternate source of effluent.
- primary ions are formed at atmospheric pressure by initiation of a gaseous electrical discharge by an electric field or by electrospray ionization (ESI) as described in US Patent 6,297,499 (Fenn) and; US Patent 5,788,166 (Valaskovic).
- the primary ions in turn ionize the gas phase analyte molecules by either an ion- molecule process as occurs in atmospheric pressure chemical ionization (APCI), by a charge transfer process, or by entraining the analyte molecules in a charged droplet of solvent produced in the electrospray process.
- APCI atmospheric pressure chemical ionization
- APCI atmospheric pressure chemical ionization
- the ionization process is the same as in electrospray ionization (ESI) because the analyte molecules are first entrained in the liquid droplets and subsequently ionized.
- Electrospray ionization is a powerful method for producing gas phase ions from compounds in solution.
- a liquid is typically forced from a small diameter tube at atmospheric pressure.
- a spray of fine droplets is generated when a potential of several thousand volts is applied between the liquid emerging from the tube and a nearby electrode.
- Charges on the liquid surface cause instability so that droplets «" ⁇ ' « bfeal ⁇ reWjels e ⁇ entMg' om the emerging liqui sur ace.
- Lvaporation of the droplets typically using a counter-current gas, leads to a state where the surface charge again becomes sufficiently high (near the Raleigh limit) to cause instability and further smaller droplets are formed.
- APCI atmospheric pressure chemical ionization
- APCI was initially developed by Horning, et al. using 63 Ni beta decay for ionization. See Homing, E. C; Horning, M. G.; Carroll, D. I.; Dzidic, I.; Stillwell, R. N., New Picogram Detection System Based on a Mass Spectrometer with an External Ionization Source at Atmospheric Pressure. Anal. Chem., 1973. 45: p. 936-943. A discharge ion source has since replaced the 63 Ni as the source of ionization.
- a discharge is generated when a voltage, typically applied to a metal needle, is increased to a range where electrical breakdown (formation of free electrons and ions) of the surrounding gas occurs (typically several thousand volts).
- the primary use of this ionization method has been as an ionization interface between liquid chromatography and mass spectrometry. See Dzidic, I.; Carroll, D. I.; Stillwell, R. N.; Homing, E. C, Comparison of Positive Ions formed in Nickel-63 and Corona Discharge Ion Sources using Nitrogen, Argon, ' ⁇ fiob ⁇ tb'mMmmWBmd- fflrtric Oxide as Reagents in Atmospheric Pressure Ionization Mass Spectrometry. Anal.
- Photoionization at atmospheric pressure uses an ultraviolet (UV) source for ionization of gas phase molecules.
- UV ultraviolet
- a plasma-induced discharge lamp that produces ultraviolet radiation in the range of 100 - 355 nanometers (nm) is used to generate ionization.
- a source suitable for use with LC/MS, is available from Synagen Corporation, Tustin, CA.
- liquid chromatographs interfaced with the atmospheric pressure ionization methods of ESI and APCI are in common use and frequently the mass spectrometers associated with these ionization methods have advanced analytical capabilities such as MS n (MS/MS, MS/MS/MS, etc.) and/or high mass resolution and accurate mass analysis.
- MS n MS/MS, MS/MS/MS, etc.
- LC/MS instruments do not effectively address a large di a ⁇ y'- ⁇ f " ⁇ ⁇ mjp ⁇ rt ⁇ i ⁇ 14 ⁇ 2> fit ' tfe ⁇ : a n d less polar compounds.
- atmospheric pressure ionization for gas chromatographic effluents which is capable of ionizing a large portion of this compound class with high chromatographic resolution and high sensitivity using mass spectrometers designed for LC/MS applications.
- Gas chromatography is commonly interfaced to mass spectrometers.
- the gas chromatograph is limited to volatile molecules but has higher resolving power than liquid chromatography based instruments.
- the gas chromatograph operates at atmospheric pressure and is interfaced to the mass spectrometry through a pressure drop device.
- the pressure drop device is capillary tubing or a so- called 'jet separator', both of which limit the volume of gas entering the vacuum region of the mass spectrometer.
- the interface used in these experiments couple the GC to a Ni ion source of a specially built mass spectrometer, such as from Extranuclear Laboratories, lnc.(now ABB, Inc.) (See Siegal, M. W.; McKeown, M. C, J. Chromatogr., 1976. 122: p. 397) or a Finnigan-Mat 4000 (now Thermo Finnigan) (See Mitchum, R. K.; Korfraum, W. A.; Freeman, J. P., An Atmospheric Pressure Ionization Source fora Finnigan-MAT 4000 Mass Spectrometer. Anal. Instrumentation, 1986. 15(1): p. 37-50).
- Electrospray ionization has not been discussed in the literature in relation to GC/APIMS nor have the necessary conditions for effectively transporting compounds from the gas chromatograph to the atmospheric ionization region been discussed. No work has been reported on accurate mass measurement of atmospheric pressure GC/MS produced ions, or on GC/APIMS/MS or on GC/APIMS selected or multiple ion monitoring, all of which are techniques that are not readily available in most GC/MS instrumentation.
- a wafer thermal desorption system has been described for introducing samples into APIMS (in published US patent application US2002148974).
- Several patents (for example, JP2002228636, WO2002060565, US6474136, US2003092193, US2003086826, US6032513, US6418781 , JP09015207, and JP06034616) discuss the use of GC and APIMS for the analysis and quantitation of trace gases ⁇ sfjci ⁇ ys-ih/yyfegWK ⁇ y ⁇ irti- ' argon, carbon dioxide, carbon monoxide, freons, silanes, and other compounds that are gases at ambient temperature, primarily for the semiconductor industry.
- An ionization source useful with an atmospheric pressure mass spectrometer capable of ionizing either liquid or gaseous effluent from a preceding separation apparatus, such as a gas chromatograph or a liquid chromatograph, and capable of introducing the ions from the atmospheric pressure region into the vacuum region of the mass spectrometer for mass analysis of the ions
- the source comprising: an ionization arrangement for generating an electric discharge, such ionization arrangement being connected to a high voltage source, or a photoionization arrangement employing an ultraviolet (UV) lamp for p od t rr if ⁇ ri s " ph t ⁇ ld zation; and an enclosure for enclosing the ionization arrangement thereby defining an ionization region, the enclosure having at least one port for introducing an effluent, from either a source of liquid effluent or a source of gaseous effluent, and an aperture for introducing ions into the
- the enclosure further comprises a port for introducing a purge gas or a reactive gas and a vent for venting excess purge gas from the enclosure.
- a heater is provided for heating the gas.
- the at least one port for introducing an effluent may be configured as multiple ports, each port being configured to accept an interface probe from a respective preceding separation apparatus, which supplies a liquid effluent or gaseous effluent.
- the ionization arrangement for generating an electric discharge comprises a sharp-edged or pointed electrode onto which a high voltage is applied to generate a Townsend or corona discharge.
- the ionization arrangement for generating an electric discharge may comprise a solvent- filled capillary or wick structure, whereby an electrospray ionization is generated by application of a high voltage.
- the photoionization arrangement may comprise a suitable lamp for generating ionizing radiation, such as a plasma induced discharge (PID) lamp.
- PID plasma induced discharge
- the present invention also provides a method of increasing the scope of compounds that can be analyzed at atmospheric pressure by the introduction of a dry, clean purge gas, preferably nitrogen, into the ionization region to help exclude air and water.
- Gas chromatographic columns made of fused silica typically have a polyimide coating, which can be a source of contaminant ions that originate from thermal breakdown of the polyimide coating at typical operating temperatures used in the interface between the GC and the APIMS.
- Removal of the polyimide coating along a section of the GC column adjacent to the exit end may be performed by either: flame removal; chemical removal by use of liquid acids, bases, or solvents; or by high temperature pre-conditioning of that section of the column for a sufficient time interval. Such removal or pre-conditioning minimizes the observation of contaminant ions in the mass spectrometer and improves the signal to noise.
- the present invention also provides a method for adding reactive gases to the dual ion source region to limit the kinds of compounds that can be ionized by GC/APIMS.
- addition of ammonia gas allows only compounds more basic than ammonia or those that form stable Jl ga ⁇ p7t ⁇ se ⁇ n Clusters with NH 4 + to be ionized. This can be advantageous when the compounds of interest are highly basic compounds in a matrix of less basic compounds that are not of interest.
- An example would be ionization of amine containing compounds in, for example, fuel oil without ionization of aromatic hydrocarbons and oxygen containing compounds.
- the present invention also provides a method of heating the capillary column to its tip without cool spots. This is necessary with atmospheric pressure GC/MS in order to maintain chromatographic resolution for less volatile compounds.
- the preferred method involves heating a gas, typically nitrogen, by passing it through tubing that runs through the GC oven into the heated GC to MS transfer line and through a sheath tube that is coaxial with the GC column and extending to or near the exit tip of the GC column.
- the hot gas passing over the GC column prevents any cool spots even to the very tip of the capillary and in addition may provide a focusing gas stream that guides the analyte toward the MS entrance aperture.
- resistive heating may be used to heat a thermally conductive sheath that snugly fits over the GC column.
- the material may be made of any thermally conductive material, such as ceramic or metal to conduct heat from the resistive heater to the GC capillary column.
- thermally conductive material such as ceramic or metal to conduct heat from the resistive heater to the GC capillary column.
- fused silica GC columns coated with an electrically conductive material, such as metal or carbon, can be resistively heated by passage of an electric current through the conductive coating.
- the present invention can use any commercially available GC, GC to mass spectrometer interface, and any commercially available mass spectrometer designed for liquid chromatography using atmospheric pressure ionization.
- the GC may be a mini GC that is sufficiently small to fit into a hand-held probe that can be inserted into the standard LC ESI/APCI probe inlet adjacent to the ion region.
- a second inlet may be provided, allowing simultaneous insertion of both an LC probe and a GC probe into the ionization region.
- the present invention allows GC/MS analysis to incorporate all of the potential of the mass spectrometer, known to those skilled in the art, m ⁇ ti ⁇ lig' i ⁇ 'iT-moriitoring, for accurate mass measurement, for cone voltage fragmentation, for MS n experiments, and the like.
- any LC/MS instrumentation can be converted to a dual LC/APIMS and GC/APIMS configuration.
- the effluent from the GC or from the LC is ionized at atmospheric pressure, thus facilitating rapid switching between the two separation methods.
- the dual ion source described herein when compared to LC/MS stand-alone instrumentation, has higher chromatographic resolution and higher sensitivity for many volatile compounds when they are separated using gas chromatography.
- some chemical compound types that cannot be ionized by LC/APIMS can be ionized by GC/APIMS and many other chemical compound types can be ionized with greater sensitivity.
- GC/APIMS also has advantages over GC/ vacuum MS. Many LC/MS instruments are capable of accurate mass measurement and selected ion fragmentation (i.e., MS/MS) whereas few GC/MS instruments have such capabilities. Conversion of LC/MS instrumentation having such features to the dual ion source of the present invention described herein also provides these features to GC/APIMS operation.
- the present invention permits higher linear carrier gas velocity and shorter GC columns, which in turn permits higher boiling compounds to be analyzed, since GC/APIMS is not deleteriously affected by high GC carrier gas flow as is GC/ vacuum MS.
- the present invention is a device that enables interfacing gas chromatographs (GC) to commercially available atmospheric pressure ionization mass spectrometers (APIMS) which are designed to interface to liquid separation methods such a liquid chromatography (LC) or capillary electrophoresis (CE).
- GC gas chromatographs
- AIMS atmospheric pressure ionization mass spectrometers
- LC liquid chromatography
- CE capillary electrophoresis
- the present invention provides a mass spectrometry apparatus that provides both GC/APIMS and LC/APIMS operation on the same instrument.
- the primary ionization process for the occurs at atmospheric pressure using a Townsend or Corona discharge, using photoionization or optionally using electrospray ionization.
- GC/APIMS include simple inter-conversion between LC/APIMS and GC/APIMS operation, extended range of compounds that can be analyzed by APIMS by use of a dry purge gas, higher chromatographic resolution than obtainable with LC/MS, and no vacuum limitation of the GC flow rate allowing faster separations and separation of less volatile compounds.
- a mini GC built into a probe or flange that inserts into the probe position used for the LC interface is demonstrated to be a facile method for switching between LC/MS and GC/APIMS operation.
- the present invention is also useful for the analysis of compounds that have sufficient volatility, or that can be made sufficiently volatile by using derivatization methods known in the art, to pass through a gas chromatograph while excluding saturated hydrocarbon compounds that cannot be ionized under, atmospheric pressure conditions.
- GC/APIMS is useful for the analysis of environmental pollutants, synthetic products, off-gas products from polymers and other solid or liquid materials, lipids, fatty acids, alcohols, aldehydes, amines, amino acids, contaminants, drugs, metabolites, esters, ethers, halogenated compounds, certain gases, glycols, isocyanates, ketones, nitriles, nitroaromatics, pesticides, phenols, phophorus compounds, polymer additives, prostaglandins, steroids, and sulfur compounds.
- FIG. 1 is a sectional view of an embodiment of an atmospheric pressure ionization (API) source region showing replacement of the liquid chromatograph (LC) interface probe with a probe containing a gas chr ⁇ rhat ⁇ gfa ⁇ h CGG ⁇ eVerFand sample injector interfaced with the atmospheric pressure ionization region;
- API atmospheric pressure ionization
- Figure 2 is a sectional view of a second embodiment of an atmospheric pressure ion (API) source region showing incorporation of both an LC interface probe and a GC interface;
- API atmospheric pressure ion
- Figure 3 is a modified embodiment of the API ion source shown in Figure 1 showing a L)V lamp as the source of ionization.
- Figure 4 is a sectional view of the exit tip of the GC interface showing use of an inert gas flow to heat the capillary column to the exit tip;
- Figures 5A- 5C are chromatograms of a commercial calibration mixture separated by GC and ionized by atmospheric pressure chemical ionization (APCI) where time is plotted along the X-axis and the total ion current registered by the mass spectrometer is plotted along the Y-axis.
- Figure 5A shows results without a purge gas
- Figure 5B shows results using nitrogen as a purge gas
- Figure 5C shows the API mass spectrum from a compound in the calibration mixture eluting from the GC.
- FIG. 1 shows a sectional view, in greater detail, of the interface tube of Figures 1 , 2 or 3.
- GC gas chromatograph
- AP-LC/MS atmospheric pressure liquid chromatograph/mass spectrometer
- Figure 1 shows an atmospheric pressure ionization source 10 comprising an enclosure or housing 11 , for receiving a gas chromatography probe 30 and for interfacing an associated gas chromatograph oven 40 to an associated mass spectrometer 50.
- the enclosure 11 has an outlet aperture 54 for introducing ions into a vacuum region 53 of the mass spectrometer 50.
- the outlet aperture 54 communicates directly and merges into the entrance aperture (also known as a skimmer aperture) of tHe ' nri si sfcefcfrdrn'e ' te? 50?
- Figure 2 shows an enclosure 11' that has a port 13' for receiving an LC probe 20 and a port 13" for receiving the GC probe 30.
- Other embodiments using these basic components can be envisioned.
- the ionization source 10 comprises at least one port 13 for receiving the GC probe 30.
- An inlet port 14 and one or more gas vent(s) 15 extend through the wall of the enclosure 11.
- An electrode 16 supported by an electrically insulating sleeve 17 is mounted on the enclosure 11.
- the electrode 16 extends through the wall of the enclosure and is connected to a source of high voltage HV (typically from one thousand to ten thousand volts, preferably from two thousand to six thousand volts)
- a counter electrode 18, shown grounded to the enclosure 11 is used in conjunction with the electrode 16.
- HV high voltage
- a counter electrode 18 shown grounded to the enclosure 11 , is used in conjunction with the electrode 16.
- an electric discharge is generated between the electrode 16 and the counter electrode 18.
- the volume within the enclosure 11 adjacent to the electrode 16 and the counter electrode 18 defines an ionization region 19.
- the GC probe 30 includes a heated tubular interface device 32 ( Figures 1 - 3) that interfaces the gas chromatograph oven 40 to the mass spectrometer 50.
- the GC oven 40 has a heater element 36, a thermocouple 37. and an injector 38.
- a helium carrier gas illustrated by the flow arrow 35, supplies the GC column 42.
- the length of the tubular interface 32 may vary from as short as about one centimeter for micro-GC's to as long as about one meter for conventional GCs.
- This tubular interface 32 can be fabricated from a commercially available GC/MS interface in which the temperature inside the tubular device is maintained high by resistive heating.
- a downstream portion of the coiled capillary GC column 42 extends through the heated tubular interface 32 in a coaxial manner.
- the capillary GC column 42 has an exit tip 44 at its exit end within the enclosure 11.
- the capillary GC column 42 may have an electrically conductive-coating (not shown).
- An inert gas entrance port 43 allows the gas to flow through a metal or fused silica tube heated by a heat source 36 before passing through a sheath tube 46 and over the downstream portion of the capillary GC column 4 ⁇ r' TH ⁇ 1 'iMe : f l fa ' ce l! ttjtii 1 3 : 2' c from the GC can be adjusted in position to be as close as one millimeter or as far as twenty-five millimeters from the aperture 54 of the mass spectrometer 50.
- the electrode 16 is typically located within five centimeters of the aperture 54.
- the direction of flow of the GC effluent relative to the flow of gas into the mass spectrometer is between ninety degrees, as shown in Figure 1 , and one-hundred-eighty degrees, as shown in Figure 2.
- the GC column 42 is heated along its length from the injector 38, through the GC oven 40, all the way to the exit tip 44.
- the heating prevents cold spots along the capillary GC column 42 which degrade analytical resolution, especially for less volatile components.
- the heating may be accomplished by either arranging a resistive heater along the tubular interface 32 (as shown in Figure 4) or by resistively heating the electrically conductive-coated GC column (not shown).
- a heated dry clean inert gas illustrated by the flow arrow 60 may be passed through the sheath tube 46 that surrounds the GC column 42 in a coaxial manner.
- the heated dry, clean inert gas is supplied from a gas source 6OG and flows through the sheath tube 46 to the exit tip 44.
- the sheath tube 46 may be electrically conductive or non-conductive.
- the inert gas may be heated by a heat source 62 upstream of sheath tube 46.
- An optional purge gas (flow arrow 64) from gas source 64G, preferably clean, dry nitrogen, can pass through the interface 32 and exit at end 39.
- the purge gas is warmed by the heat from the interface heater 34.
- the interface heater 34 applies heat directly to a heat transfer tube 47 which in turn heats the sheath tube 46 and the inert gas flowing therein.
- the exit tip 44 of the GC column ( Figure 4) is positioned near the outlet aperture 54 ( Figure 1 ). Ionization is initiated using a Townsend or corona gaseous discharge (as seen in Figures 1 and 2) or by photoionization (as seen in Figure 3), or by an ESI probe 22 shown in Figure 2.
- the effluent from the GC column 42 is swept out of the ionization region 19 by a flow of a clean dry purge gas illustrated by the flow arrow 64. Nitrogen vapor, typically from a liquid nitrogen supply 64G ( Figures 2 and 4), may be used as the purge gas.
- the ionization region 19 preferably is enclosed such that a dry clean purge gas (flow arrow 64 shown in alternate locations in Figures 2, 3 and 4), preferably nitrogen, can be continuously added to the ionization region 19 through the gas inlet 14 ( Figure 3) or through the interface 32 ( Figure 4) to minimize the presence of water vapor and contamination within the ionization region 19.
- a dry clean purge gas flow arrow 64 shown in alternate locations in Figures 2, 3 and 4
- nitrogen can be continuously added to the ionization region 19 through the gas inlet 14 ( Figure 3) or through the interface 32 ( Figure 4) to minimize the presence of water vapor and contamination within the ionization region 19.
- a dry clean purge gas flow arrow 64 shown in alternate locations in Figures 2, 3 and 4
- nitrogen preferably nitrogen
- This invention produces a more universal ion source than has previously been available to mass spectrometry.
- a typical LC/MS ion source that has interchangeable ESI and APCI probes can be modified for GC/APIMS operation by replacing either the ESI or the APCI probe with the GC to MS interface probe 30, as shown in Figure 1 and Figure 3.
- a separate introduction device for the GC to mass spectrometry interface can be built into the source so that the GC oven 40 is always interfaced to the mass spectrometer 50 as shown in Figure 2.
- the source is capable of ionizing either liquid or gaseous effluent from a preceding separation apparatus and of introducing the ions from the atmospheric pressure region into the vacuum region of the mass spectrometer for mass analysis of the ions.
- the GC can be a micro GC that is built into the ion source region or is part of the probe assembly ( Figures 1 and 3).
- probe refers to a device for introducing compounds into a mass spectrometer ionization region and is well known to those experienced in the practice of mass spectrometry.
- ionization is initiated by an electric discharge and can use the same high voltage electronics and discharge electrode 16, usually in the form of a metal needle, that is available with commercial APCI ion sources designed for interface with a LC.
- an ESI source is ⁇ aVail ⁇ BliV ⁇ nF'felect ' Hci 'a'is ⁇ i ' arge can be initiated by placing an electrically conductive material such as a needle or a drawn metal-coated capillary in place of the electrospray capillary 23 ( Figure 2). With a sharp tip discharges are generated in the voltage range used by the ESI source.
- the primary ionization processes involves stripping of electrons from abundant gaseous species for positive ionization, or for negative ionization electron resonant or dissociative electron attachment to the most electronegative gaseous components.
- the electron stripping process produces positive ions that undergo further reactions during collisions and result in charge transfer where thermodynamically favored.
- hydronium ions are produced which undergo further collisions resulting in production of protonated water clusters, ( i.e. [(HkO) x ]H + ). Because these gas phase reactions are diffusion controlled and at atmospheric pressure collisions occur on a very short time scale, the ionization cascade causes all of the available charge to reside on the most basic molecules.
- a dry clean purge gas such as nitrogen gas obtained from vaporization of liquid nitrogen (previously described)
- nitrogen gas obtained from vaporization of liquid nitrogen can be used to reduce the amount of water and other basic contaminant gases in the ionization region 19 so that higher energy species are available for ionization.
- compounds such as methylcyclohexanone, naphthalene, dimethylphenol, dinitrobenzene, and chloromethylphenol, which do not ionize or ionize poorly under positive ion LC/API conditions, will ionize readily under GC elution with the inert purge gas. !
- ionization may also be generated using a UV lamp with photo-energy output between about eight and twelve electron volts (eV). In photoionization, ionization occurs by stripping an electron from those molecules in which the ionization potential is below the eV output of the UV lamp source.
- Photoionization light sources are described in a number of patents, for example US5,338,931 , US5,808,299, US5,393,979, US5.338.931 , and US5,206,594. Even though the molecules of interest are ionized directly, they can lose charge by ion-molecule reactions, as described above, to water and other contaminants in the ionization region.
- a photoionization lamp 68 is mounted on the enclosure 11 and has a connector V for application of a voltage to power the lamp. Also shown is an electrode 70 connected to a source of high voltage HV that operates in a voltage range between zero to five hundred volts to help focus ions on the aperture 54 to the mass spectrometer.
- ionization can be produced from an ESI capillary or wick as described in U.S. Patent 6,297,499. Sensitivity may be enhanced by use of lower flow rates of liquid through the capillary or by use of small diameter wicks. Therefore, nanospray, as described in U.S. patent 5,788,166 (Valaskovic, et al.) appears to produce the most sensitive results using this method of ionization.
- a commercially available nanospray needle that can operate for many hours with just a few microliters of solvent, is a simple solution for production of primary ions.
- the gas phase analyte molecules from a GC or other source become entrained in the liquid droplets and are ionized by the electrospray process described above.
- This ionization mode is more selective as to the types of compounds that can be ionized and generally produces only quasi- molecular ions with little or no fragmentation.
- the advantage of this ionization process is that typically only [M + H] + ions are produced in the positive ion mode from polar compounds that are sufficiently basic to accept a proton from the liquid media used to produce the primary 'Pib-ftierrnal fragmentation.
- the ionization can be influenced by addition of an additive to either the solvent being used in the nanospray process or into the gas phase. For example, addition of NH 3 gas into the ionization region will cause only molecules more basic than ammonia gas to be ionized by protonation, but cationization by NH 4 + addition will occur with a wider variety of compounds. This allows the ionization process to be tailored to the analytical problem.
- fragmentation is needed for structural elucidation it can be generated in the region on vacuum side 53 of the entrance aperture 54 ( Figures 1 - 3) of atmospheric pressure ion sources by application of a voltage that increases the collision energy of ions in this intermediate pressure region.
- so called MS/MS or MS ⁇ mass spectrometers can be used to select an ion of a specific mass using one mass analyzer for fragmentation by gas or surface collisions and then using a second mass analyzer to obtain a mass spectrum of the fragment ions.
- gas flow through the GC column is not limited by the ionization source as it is with GC/MS using vacuum ionization.
- Low boiling compounds can be made to pass through a GC column by using a thin stationary phase, a shorter column and higher gas flow through the column. for compound separation from a mixture of compounds with subsequent ionization of volatile and semi-volatile components. Compounds ionized with these methods will have all of the analytical benefits of the mass spectrometer being employed as to generation of fragmentation and making accurate mass measurements.
- Reduction of contaminants generated by heating the polyimide coated GC column can be accomplished by flame removal of the coating over the area of the column that comes in direct contact with the external inert gas flow or by conditioning at high temperature in the interface probe for several hours.
- FIGS 5A, 5B and 5C are chromatograms of a commercial calibration mixture separated by GC and ionized by APCI where time is plotted along the X- axis and the total ion current registered by the mass spectrometer is plotted along the Y-axis.
- Figure 5A shows a resulting chromatogram with no purge gas.
- Figure 5B shows a resulting chromatogram using nitrogen as a purge gas.
- Figure 5C shows the API mass spectrum of a compound in the calibration mixture eluting from the GC.
- reactive gases such as ammonia in the positive ion mode or methylene chloride in the negative ion mode
- ammonia gas increases the specificity of the ionization.
- Either positive or negative ions can be used for the analysis of compounds eluting from the gas chromatograph or liquid chromatograph.
- methylene chloride is an additive gas that can be used to enhance the ionization process for certain compound types. The sensitivity of this method is comparable to that of currently available ionization methods used with gas chromatography or liquid chromatography and frequently superior.
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
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US62616104P | 2004-11-09 | 2004-11-09 | |
US68749705P | 2005-06-03 | 2005-06-03 | |
PCT/US2005/040632 WO2006060130A2 (en) | 2004-11-09 | 2005-11-09 | Ion source for a mass spectrometer |
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EP1819423A2 true EP1819423A2 (en) | 2007-08-22 |
EP1819423A4 EP1819423A4 (en) | 2010-11-03 |
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DE102006050136B4 (en) * | 2006-10-25 | 2016-12-15 | Leibniz-Institut für Analytische Wissenschaften-ISAS-e.V. | Method and device for generating positive and / or negative ionized gas analytes for gas analysis |
FR2918753B1 (en) * | 2007-07-09 | 2010-06-18 | Renault Sas | METHOD FOR DETERMINING THE FUEL CONTENT IN A COMBUSTION ENGINE LUBRICATING OIL. |
US8642952B2 (en) | 2009-11-10 | 2014-02-04 | Waters Technologies Corporation | Apparatus and methods for gas chromatography-mass spectrometry |
US8378293B1 (en) * | 2011-09-09 | 2013-02-19 | Agilent Technologies, Inc. | In-situ conditioning in mass spectrometer systems |
WO2013112680A1 (en) * | 2012-01-26 | 2013-08-01 | University Of The Sciences In Philadelphia | Ionization at intermediate pressure for atmospheric pressure ionization mass spectrometers |
WO2013122745A1 (en) * | 2012-02-13 | 2013-08-22 | Waters Technologies Corporation | Ionization of analyte molecules comprised in a flow of gas |
US9153427B2 (en) | 2012-12-18 | 2015-10-06 | Agilent Technologies, Inc. | Vacuum ultraviolet photon source, ionization apparatus, and related methods |
US11662340B1 (en) * | 2018-07-31 | 2023-05-30 | InspectIR Systems, Inc. | Techniques for rapid detection and quantitation of volatile organic compounds (VOCS) using breath samples |
US11841359B1 (en) | 2018-07-31 | 2023-12-12 | Inspectir Systems, Llc | Techniques for portable rapid detection and quantitation of volatile organic compounds (VOCS) using breath samples |
US11721533B1 (en) | 2018-07-31 | 2023-08-08 | Inspectir Systems, Llc | Techniques for rapid detection and quantitation of volatile organic compounds (VOCS) using breath samples |
US11874270B1 (en) | 2018-07-31 | 2024-01-16 | Inspectir Systems, Llc | Techniques for rapid detection and quantitation of volatile organic compounds (VOCs) using breath samples |
US11841372B1 (en) | 2018-07-31 | 2023-12-12 | Inspectir Systems, Llc | Techniques for rapid detection and quantitation of volatile organic compounds (VOCs) using breath samples |
US11879890B1 (en) | 2018-07-31 | 2024-01-23 | Inspectir Systems, Llc | Techniques for rapid detection and quantitation of volatile organic compounds (VOCS) using breath samples |
EP3998624A4 (en) * | 2019-07-10 | 2023-03-29 | Hitachi High-Tech Corporation | Mass spectrometer |
CN115116819A (en) * | 2022-07-04 | 2022-09-27 | 广东智普生命科技有限公司 | Electrospray extraction ionization source |
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EP1819423A4 (en) | 2010-11-03 |
WO2006060130A2 (en) | 2006-06-08 |
JP2008519985A (en) | 2008-06-12 |
JP4782796B2 (en) | 2011-09-28 |
WO2006060130A3 (en) | 2007-04-26 |
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