Dual source mass spectrometry system

A dual source mass spectrometer system (10) is operable in a first mode with an LC source [LC/MS] (12) and in a second mode with a GC source [GC/MS] (18). The GC source inputs into an ion source chamber (22) for delivering the ionized output from the GC source to the mass spectrometer. The GC source comprises a GC interface probe (30) which is retractably connected to the ion source chamber to take the GC interface probe from a retracted position in which it is disengaged from the mass spectrometer (whereby the system is operable in the first LC/MS mode) into a deployed position in which the GC interface probe is operatively connected to the ion source chamber of the mass spectrometer (whereby the system is operable in said second GC/MS mode).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed generally to scientific laboratory analytical equipment, and more particularly, to the combination of Chromatography Systems and Mass Spectrometers.

2. Background of the Related Art

Scientific laboratories commonly need to analyse samples by the use of Chromatography in order to separate different constituents within the samples. Once the samples have been separated, they may need further analysis in order to identify what the different constituents are. Normally the most effective way of performing the analysis of the separated constituents is the use of mass spectrometers.

Chromatography can be performed either on gaseous samples or on liquid samples. However, the apparatus required to perform Liquid Chromatography and Gas Chromatography are rather different, so much so that different machines are required to perform the different analyses.

Mass spectrometers can be used to measure the mass of ions and analyse the structure of these ions, by studying fragmentation of the ions that may occur within the mass spectrometer. Chromatography systems typically produce molecules rather than ions, so the mass spectrometer needs to produce ions from the molecules that are delivered to it. This typically is performed in an ion source. There are many ways of ionizing the molecules that are injected into an ion source. Atmospheric Pressure Chemical Ionisation [APCI] is one of these methods. In this method, the molecules are sprayed into an ion source chamber and the spray is subjected to a corona discharge that creates ions.

APCI is a desirable fragmentation technique because it typically produces singly charged ions, and so the results of the analysis are easier to interpret. Furthermore APCI is a method of ionization that is possible to use for samples that are both liquid and gaseous.

Mass Spectrometers are complicated and precise instruments, and so are expensive and delicate. Until recently, they have always been specifically designed for one of LCMS or GCMS and not for interchangeable use. In the past also instruments have been designed to swap between GCMS and LCMS. However, the changeover has been time consuming and often the dual instruments compromised the performance on one or the other of the two techniques. This is especially true for Vacuum GCMS systems utilizing Electron Impact Ionization. The advantage of using APCI is that both LCMS and GCMS are operated at the same pressure and there is no need to change the MS other than to put an ion chamber on in place of a cone gas nozzle.

An attempt to provide a dual source mass spectrometry system comprises a mass spectrometer that has an ion source capable of being used for either LCMS or GCMS. However the design of the source is such that both an LCMS interface probe and a GCMS interface probe are permanently connected to an API source housing. This arrangement is an improvement over the use of separate LCMS and GCMS machines but is inefficient, and so cannot easily identify small quantities of analytes that may be present in the sample.

It would therefore be desirable to produce a Mass Spectrometer that is capable of efficiently analysing the output of either liquid or gas chromatography systems with easy transfer between the two different inputs, and with easy and minimal alterations required as now provided by the present invention.

It is envisaged that the dual source mass spectrometry system of the present invention has applications for example in synthetics confirmation and impurity profiling, natural products research, and in the fields of flavours and fragrances, nutraceuticals, petrochemicals, metabolomics, environmental screening, pesticide residue analysis and some forensic applications. The combination of LCMS and GCMS allows a wider range of compounds to be analyzed on a single instrument platform.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a dual source mass spectrometer system operable in a first mode with an LC source [LC/MS] and in a second mode with a GC source [GC/MS], said GC source inputting into an ion source chamber for delivering the ionized output from the GC source to the mass spectrometer and wherein the GC source comprises a GC interface probe which is retractably connected to said ion source chamber to take the GC interface probe from a retracted position in which it is disengaged from the mass spectrometer, whereby the system is operable in said first LC/MS mode, into a deployed position in which the GC interface probe is operatively connected to the ion source chamber of the mass spectrometer whereby the system is operable in said second GC/MS mode. In LCMS mode the ion chamber is not used. It is replaced with a cone gas nozzle and the corona discharge is carried out in the source enclosure on the eluent from the APCI probe.

According to a feature of the invention the GC interface probe and a housing of the ion source chamber may have complementary docking means so that they can be releasably engaged to allow operation with a GC ion source chamber in said second mode. Preferably, the docking means comprises a docking port in the GC ion source housing to receive the GC interface probe and complementary locking means by which the probe can be progressively drawn into the docking port and releasably locked in position. The GC interface probe docks on the ion source housing such that the end of the transfer line positions in the back of the chamber which is open. It is also preferred that the docking port comprises a screw-threaded nozzle incorporating sealing means and the GC interface probe comprises a complementary screw-threaded locking lever to releasably engage the nozzle whereby the probe can be sealingly coupled with the nozzle.

According to another feature of the invention the GC interface probe may be carried by a gas chromatography unit which is retractably connectable to a mass spectrometer of the system when a GC ion source chamber is present. Preferably, the gas chromatography unit is slidably connectable to the mass spectrometer of the system. It is further a preferred feature that the gas chromatography unit incorporates a lockable rail system to allow slidable movement of the unit over the rail system so that it can be offered up to, and retracted from, the mass spectrometer of the system.

Another aspect of the invention provides a method of operating a dual source mass spectrometer system in a first mode with an LC source [LC/MS] and in a second mode with a GC source [GC/MS], said GC source inputting into an ion source chamber for delivering the ionized output from the GC source to the mass spectrometer and wherein the GC source comprises a GC interface probe, the method comprising the steps of taking the GC interface probe from a retracted position in which it is disengaged from the ion source chamber, whereby the system is operable in said first LC/MS mode, into a deployed position in which the GC interface probe is operatively connected to the ion source chamber whereby the system is operable in said second GC/MS mode.

According to another feature of this aspect of the invention, complementary docking means provided between the GC interface probe and a housing of the ion source chamber may be actuated so that the probe and the housing can be releasably engaged to allow operation with a GC ion source chamber in said second mode and substitution of the GC ion source housing by an LC ion source housing to allow operation with the LC ion source chamber in said first mode. Preferably, the docking means comprises a docking port and the complementary locking means is actuated such that the probe is progressively drawn into the docking port and releasably locked in position. It is further preferred that the docking port comprises a screw-threaded nozzle incorporating sealing means and the GC interface probe comprises a complementary screw-threaded locking lever and wherein the locking lever is manipulated to releasably engage the nozzle whereby the probe can be sealingly coupled with the nozzle.

According to a still further feature of this aspect of the invention, the GC interface probe may be carried by a gas chromatography unit, and wherein the gas chromatography unit is retractably connected to a mass spectrometer of the system when a GC ion source chamber is present. Still more preferably, where this feature is adopted the gas chromatography unit is slidably connected to the mass spectrometer of the system. Even more preferably, the gas chromatography unit incorporates a lockable rail system the method comprising slidable movement of the unit over the rail system so that it is offered up to and retracted from the mass spectrometer of the system.

SPECIFIC DESCRIPTION

Referring to the drawings there is shown a dual source mass spectrometry system10which comprises a liquid chromatography [LC] unit12, a mass spectrometer [MS] unit14, an ion source housing16which may be suitable for use with the LC unit or with the GC unit and a gas chromatography [GC] unit18.

When it is required for the system to operate in LC/MS mode, the ion source housing16is one which is appropriate for use with a LC column of the LC unit12in which case the GC unit18is disengaged and refracted from the MS unit14. In order to operate the system in GC/MS mode, the LC ion source housing (not shown) is substituted by a GC ion source housing and the GC unit18is put into a deployed position in which it is operatively connected to the MS unit.

Referring now toFIG. 2of the drawings, the GC ion source housing16incorporates an ion source chamber22. The chamber22has at least one outlet port24, at least one gas inlet (not shown), a sample port26, and at least one corona pin port28.

The housing16is made of a structural material such as plastics, metal, glass or ceramic. A preferred metal is stainless steel, titanium, aluminium, copper, brass and other alloys.

The sample port26is constructed and arranged to receive a GC interface probe30comprising a gas chromatographic column32. The column is surrounded by a heated sheath gas tube34. The gas chromatographic column32is for placing the analyte molecules in the chamber22. The analyte molecules are suspended or dissolved in gas. The column has a mobile phase and a stationary phase and is used to separate components based upon their vapour pressure. When compounds elute from the column into the chamber they are in the vapour phase. Gas chromatographic columns are known in the art and are available from several venders. For example, without limitation, gas chromatographic columns are sold by Varian, Inc. (Palo Alto, Calif., USA) under several trademarks including FactorFour™, CP-Sil, and Select™

Referring toFIG. 2A, the sample port26receives the inner tube27of a transfer line29and transfer line tip31from which the column32protrudes. It is not a close fit but has a reasonable clearance with the transfer line to prevent the chamber from grounding on the metal transfer line. The outside wall of the column32and the inner diameter of the sample port cooperate to form a close fit. However, the fit need not be airtight. A gap allows excess gas in chamber22to vent and be carried off by a vent structure of the atmospheric pressure ionization housing. Thereby the chamber is swept out in the timescale of a chromatographic peak.

The gas inlet is constructed and arranged to be placed in fluid communication with a source of an inert gas [not shown] for placing the inert gas into the chamber22. Inert gases comprise any substantially non-reactive gas, such as nitrogen. Such gases are sold by numerous venders under pressure in tanks.

The outlet port24is constructed and arranged to be received on or about an opening36of a vacuum region38of a mass spectrometer generally designated by the numeral40. The opening36normally interfaces between the vacuum region38and an atmospheric pressure region of the atmospheric pressure ionization housing16. The atmospheric region may deviate slightly from atmospheric but is substantially near atmospheric pressure.

Opening36is formed in an inlet cone42which substantially fills the outlet port24to form a substantially closed chamber22. The chamber22has a volume of 0.5 to 5.0 cc when the outlet port24is received on or about the opening36of the vacuum region38.

The opening36of the vacuum region38defines a sample axis. A preferred sample port24is constructed and arranged to introduce analyte molecules33within sixty degrees of a line perpendicular to the sample axis.

The corona pin port28is constructed and arranged for receiving a corona discharge pin for discharging electrons. The discharged electrons place a charge on analyte molecules33(FIG. 2) as the analyte molecules leave the gas chromatographic column32. These charged and uncharged analyte molecules are circulated around the chamber22by the gas introduced through the gas inlet and received in the opening36of the vacuum region for mass analysis.

Preferably, the corona discharge port is constructed and arranged to place the corona discharge pin within the flow of the sample discharged from the gas chromatographic column32. Usually, the corona discharge port is aligned with the sample axis allowing gases to circulate around the corona discharge pin. Plasma formed by corona discharge into a gas consists of the carrier gas in combination with make-up gas supplied through the transfer inner tube27through a connecting line35.

In the case of N2 make-up gas N2+and N4+are formed in the plasma then
N2++M>M++N2
N4++M>M++2N2
In addition with trace amounts of moisture H30+, then
H30++M>MH++H20
With higher concentrations of water H+(H20)n, then
H+(H20)n+M>MH++nH20
Selective ionization can also be performed by photo-ionization.

The removal of the GC ion source housing16allows the mass spectrometer to receive liquid samples from an LC atmospheric pressure ionization source [not shown] in a conventional manner.

Referring toFIGS. 2,3and4, the GC ion source housing16includes a nozzle42which forms part of complementary docking means for detachably receiving the GC interface probe30which incorporates the GC column32. The nozzle includes a sealing O-ring44(FIG. 2) by which the GC interface probe is sealingly engaged in the nozzle. Referring back toFIGS. 3 and 4, the GC interface probe30has another part of the complementary docking means which includes a rotatable screw-threaded locking lever46which co-operates with a mating screw-threaded portion48of the docking nozzle such that when the probe is offered up to the nozzle, engagement of the complementary screw-threaded parts by manipulation of the locking level causes the probe, and hence the GC column, to be progressively docked in the chamber22of the GC ion source housing16.

In order to take the GC interface probe30from a retracted position in which it is disengaged from the GC ion source chamber, whereby the system is operable in a first LC/MS mode, into a deployed position in which the GC interface probe30is operatively connected to the GC ion source chamber, whereby the system is operable in a second GC/MS mode, as shown inFIG. 5, the GC unit is slidably mounted on a rail system.

Referring now toFIGS. 6 and 7of the drawings, details of the GC unit rail system are shown. The GC unit18(seeFIGS. 1 to 5) is received in a carriage50which includes a floor52having a keel portion54and end walls56,58respectively by which the GC unit18is secured to the carriage50. End wall56includes an opening60through which the GC interface probe extends from the GC unit. The keel portion54is furnished with a pair of parallel rails62,64(which operate in a manner similar to those found in office filing cabinets) which have runners fixed to opposed walls66,68of a channel70formed in the upper face of a base unit72so that the keel portion sits with clearance in the channel. Thus the carriage (together with the GC unit18) can slide to and fro with respect to the base unit. A locking handle74is provided by the carriage to assist in the sliding movement of the carriage but also for manipulation to lock the rail66against the channel to prevent movement of the carriage relative to the base unit.

The travel of the carriage relative to the base unit is such that when the GC unit is retracted, the GC transfer probe is drawn clear of the MS unit and, at the extremity of its travel in the opposite direction, the GC transfer probe is presented to the docking nozzle so that the complementary docking means can progressively draw in the probe and hence the GC column for operative connection to the chamber.