Mass analyser interface

A mass analyzer includes a desolvation chamber into which an upstream gas is injected to provide a counter-flow to said downstream flow in the chamber. The counter-flow may slow the downstream flow of solvated ionized particles in the chamber, while allowing lighter desolvated ions to travel toward an outlet aperture of the desolvation chamber.

FIELD OF THE INVENTION

The present invention relates in general to all analytical instruments and in particular to mass analysers and mass analyser interfaces that include a desolvation chamber(s) that provides a counter flow to aid in desolvation.

BACKGROUND OF THE INVENTION

Mass analysis, and more particularly mass spectrometry, has proven to be an effective analytical technique for identifying unknown compounds and for determining the precise mass of known compounds. Advantageously, compounds can be detected or analysed in minute quantities allowing compounds to be identified at very low concentrations in chemically complex mixtures. Not surprisingly, mass spectrometry has found practical application in medicine, pharmacology, food sciences, semi-conductor manufacturing, environmental sciences, security, and many other fields.

A typical mass spectrometer includes an ion source that ionizes particles of interest. The ions are passed to an analyser region, where they are separated according to their mass (m)-to-charge (z) ratios (m/z). The separated ions are detected at a detector. A signal from the detector may be sent to a computing or similar device where the m/z ratios may be stored together with their relative abundance for presentation in the format of a m/z spectrum.

Typical ion sources are detailed in “Ionization Methods in Organic Mass Spectrometry”, Alison E. Ashcroft, The Royal Society of Chemistry, UK, 1997; and the references cited therein. Conventional ion sources may, for example, create ions by electrospray or chemical ionization.

Electrospray ionization involves dispersing liquid containing analyte(s) of interest into a fine aerosol jet of solvated charged droplets. Typically, a nebulizer gas flow is involved in this dispensing process and an impinging heater gas flow assists droplet desolvation. Charged droplets are drawn by an electric field to the sampling inlet of a mass spectrometer. Liquid flows greater than 25 μL/m usually require the various gas flows to be heated for rapid desolvation.

Atmospheric pressure chemical ionization (“APCI”) relies on liquid containing analyte of interest to be discharged into a fine aerosol jet of droplets containing the analyte. Again, a nebulizer gas flow is involved and an impinging heater gas flow may assist droplet desolvation. Desolvated analyte molecules are chemically ionized by reagent ions created in close proximity by a corona current.

It has long been recognized that the sampling inlet is a major sensitivity bottleneck: typical diameters of the sampling inlet are about 0.5 mm, and space repulsion of analyte ions acts as a choke upon significant sensitivity increases. Although larger sampling diameters are desired for higher sensitivity, such apertures necessitate larger vacuum pumps. Present vacuum pumping systems are at their practical maximum in terms of size and cost.

Accordingly, alternative approaches are required.

SUMMARY OF THE INVENTION

Exemplary of an embodiment of the present invention, a mass analyzer includes a desolvation chamber into which an upstream gas is injected to provide a counter-flow to the downstream flow in the chamber. The counter flow may slow the downstream flow of solvated ionized particles in the chamber, while allowing lighter desolvated ions to travel toward an outlet aperture of the chamber. The chamber may be heated to aid in desolvation. Further, the chamber may be maintained at a low (below atmosphere) pressure.

In an embodiment, a mass analyser interface, includes a desolvation chamber having an inlet for receiving solvated analyte particles from a source of analyte particles, and an outlet aperture. An electric field source provides an electric field to urge ionized particles within the chamber from the inlet toward the outlet aperture, creating a downstream flow of ionized particles. A gas injection port injects an upstream gas proximate the outlet aperture, to provide a counter-flow to the downstream flow at the aperture, to slow the downstream flow as the ionized particles travel toward the outlet aperture. At least one evacuation port allows injected gas to escape from the desolvation chamber.

In another embodiment, a method of providing desolvated ions in a mass analyzer includes: providing solvated analyte particles from a source of analyte particles into a desolvation chamber having an inlet and an outlet aperture; providing an electric field to urge ionized particles toward the outlet aperture in a downstream flow; heating the desolvation chamber; and injecting an upstream gas proximate the outlet aperture, to provide a counter-flow to the downstream flow at the aperture, to slow the downstream flow and any solvated particles entrained therein.

DETAILED DESCRIPTION

FIG. 1illustrates a mass analyser10, including a mass analyser interface20, exemplary of an embodiment of the present invention.

Mass analyser interface20guides analyte particles from a source22of analyte particles. In the analyser10, the analyte source provides ionized solvated analyte, and may for example take the form of an electrospray (ES) emitter24at a pressure of about one atmosphere (1 atm=760 torr). Interface20guides the solvated analyte from an inlet/exit opening26to a pressure less than about 4 torr, to produce desolvated ionized analyte at an outlet28, and ultimately to the remainder of mass analyser10.

Mass analyser10further includes conventional downstream mass analysis stages, including for example guide stages52a-52eto guide ionized particles along a guide axis100. Stages52a-52emay include mass quadrupole filter stages52cand52e, and collision cell52d, all leading ionized particles to a detector66. One or more pump(s)54gradually reduce the pressure from stage to stage within stages52a-52e.

Mass analyser interface20includes a desolvation chamber30having an inlet aperture33defining inlet for receiving solvated analyte particles and providing an outlet aperture34defining outlet28to a second chamber42. A low pressure interface35receives solvated ions fed to inlet aperture33at opening26of sampling inlet32, for example from ES emitter24that ionizes the solvated analyte particles. An example low pressure interface35is, for example, disclosed in U.S. Pat. No. 7,405,398, the contents of which are hereby incorporated by reference. Downstream chamber42may be in communication with desolvation chamber30directly, or indirectly, for example, by way of conduit47.

A DC voltage source (not shown) maintains a potential difference between source22and sampling inlet32to attract ions from source22to sampling inlet32of interface35. Analyte source22is typically at about atmospheric pressure (e.g. 760 torr). In alternate embodiments, pressure at source22could range from 1 atm to 10 atm or higher. Similarly, source22is depicted as a single ES emitter24, but alternatives are possible. For example, an array of ES emitters each associated with its own separate inlet aperture (like sampling inlet32) is possible. Likewise, although ES emitter24is oriented at 90° to a central axis31of chamber30, it could similarly be oriented at another angle (e.g. parallel or otherwise) to this axis. Further, as will become apparent, in other embodiments provided solvated analyte need not be ionized prior to entering interface35or chamber30, but may instead be ionized within interface35or chamber30.

As disclosed in U.S. Pat. No. 7,405,398, interface35may entrain analyte in a gas, and provide a tortuous path between sampling inlet32and aperture33, to assist in the liberation of analyte ions therein. Further, the outlet of interface35may provide a substantially laminar flow of gas and entrained analyte particles. Optionally, interface35may include a heater (not shown) and/or one or more ionizers for heating gas and analyte, and ionizing analyte in interface35.

In the depicted embodiment, interface35is a split-flow interface with gas provided by a supply38leaving interface35through inlet/exit opening26and conduit39to roughing pump41. As will become apparent, interface35may be replaced with a direct flow interface, in which substantially all gas entering the interface will exit into chamber30. As well, inlet/exit opening26is aligned with sampling inlet32, but need not be so located. Opening26is spaced from sampling inlet32by about 3 mm.

Desolvation chamber30may be formed from a generally cylindrical casing, extending along an axis31. The casing has inlet aperture33at one end and outlet aperture34at the second opposing end, formed therein. An annular shroud43encircles inlet aperture33, interior to chamber30. Other geometries are of course possible.

Chamber30is typically formed from a heat conductive material, such as metal, and may optionally be heated, by a heater58. Heater58may be configured to heat the inner cylindrical wall of chamber30to more than 100 C (e.g. 300 C or higher). Sampling inlet and outlet aperture32and34may be circular, or any other suitable shape. Inlet aperture32may alternatively, or additionally, take the form of a cylindrical or conical tube (not shown) or flat plate that may optionally be heated.

Gas flow within chamber30is influenced principally by the flow through sampling inlet32and outlet aperture34, and the introduction of gases through ports40and48, and the evacuation of gases through evacuation port44, as detailed below. Flow through sampling inlet32is largely independent of the flow from port40to conduit39, as this flow is set to be so low—and the opening26is large—that the pressure upstream of sampling inlet32is constant at about atmosphere (1 atm).

The pressure within chamber30may be measured by a pressure gauge29, in flow communication with the interior chamber30. The flow of gases through ports44and48may be electronically controlled, for example using feedback control, as described below.

Gas introduced proximate sampling inlet32through port40may be introduced into chamber30by way of interface35, effectively positioned upstream of inlet aperture33.

Gas injection port48injects a drying gas from a gas source50, by way of a gas flow controller51, into chamber30proximate outlet aperture34, and is located on the cylindrical wall of chamber30, axially proximate outlet aperture34. Typical gas types from source50are again air or nitrogen—clean and dry. An annular manifold80, located exterior to chamber30may ensure gas entering through port48enters chamber30uniformly around axis31, with a flow generally toward axis31. Manifold80may have evenly spaced openings on its inner wall to ensure even distribution of gas from flow controller51. An inline heater (not shown) may additionally heat gas from gas source50, prior to the gas entering chamber30.

In general, forces on desolvated ions and charged droplets are different in a viscous flow and in an electric field. For the same flow and electric field, droplets experience the force of viscous flow more than that of electric fields, and vice-versa for desolvated ions. As such, gas injected through gas injection port48provides a counter flow that maintains droplets within chamber30, while allowing desolvated ions to travel to outlet aperture34and thus aids in desolvation. The average axial electric field and counter flow in chamber30may be adjusted to enable desolvated ions to travel to outlet aperture34in chamber30, but prevent droplets from so travelling.

The length of the desolvation chamber may thus be chosen to be inversely proportional to ion transit time and can be selected to allow a sufficient number of energy transferring collisions for effective desolvation, for a given temperature, pressure and counter flow. The pressure and temperature can be selected to produce a number density and heat effect sufficient for desolvation while also optimizing the effect of DC and RF confining electric fields.

In an embodiment, desolvation chamber30may be about 20 cm in length and 8 cm in diameter, with sampling inlet32of interface35having a diameter of about 0.5 mm. The typical diameter of inlet aperture33may range from about 4 mm to 8 mm, providing minimal flow impedance between sampling inlet32and inlet aperture33. Depending on the desired gas flow through outlet aperture34, the diameter of outlet aperture34can typically range from 1 mm to 5 mm.

Evacuation port44for chamber30is shown terminating in an annular port extending through an outer cylindrical wall of chamber30, in close axial proximity to inlet aperture33. Evacuation port44, may extend from, or be part of an evacuation conduit45that extends from the interior of chamber30, proximate its central axis to roughing pump46. Evacuation port44(like typical roughing pump ports) may be a series of apertures, but in general, may be reasonably symmetric about and proximate the central axis of chamber30. In this way, the flow via port44from chamber30will be flowing roughly parallel to the central axis31of chamber30.

Roughing pump46evacuates gases from chamber30through evacuation port44, and thereby regulates the pressure in chamber30. Roughing pump46may be adjustable, so that its flow rate may be adjusted and electronically controlled. Roughing pump46may, for example, be a variable frequency pump.

Optionally an adjustable flow restrictor49with pressure sensors immediate upstream and downstream of it, may be placed in conduit45between roughing pump46and chamber30to maintain a desired dry gas flow in chamber30. Again, flow restrictor49could be electronically controlled.

Annular wall43on the interior of chamber30further shape the direction of flow of gases leaving chamber30through port44.

A multi-polar (e.g. quadrupolar, hexapolar, octopolar, etc) multi-stage RF ion guide36is disposed in desolvation chamber30. RF ion guides are known to those of ordinary skill. A possible ion guide36is for example disclosed in U.S. Pat. No. 7,932,488, the contents of which are hereby incorporated by reference. Ion guide36will typically be low capacitance in order to allow application of a voltage from a voltage source (not shown) at high RF frequencies and voltages, e.g., 2 MHz at 1 kVpp. In addition, ion guide36will typically create a large average axial electric field: for example, inFIG. 1, a 5 kV electrostatic drop from one end of ion guide36of length 10 cm and constant interior diameter and equally spaced stages, may produce a 500 V/cm field. Different geometries and voltages on ion guide36could be used to achieve a different field pattern. For example, a cone section of ion guide36could generate a hemispherical electric field that has an electric field strength that rises rapidly and focuses ions toward outlet aperture34as ions proceed along the cone section of ion guide36. Average electric fields in excess of 5000 V/cm may thus be possible. Alternatively, a voltage pulsed ion guide may be employed, to generate electrodynamic fields, having similar average axial fields.FIG. 1illustrates an example shape for ion guide36. Other shapes are of course possible, an ion guide cone with an inner angle usually ranging from 5° to more than 90° is possible; or a non-conical design may be possible. In addition, ion guide36shown inFIG. 1, could be configured to as a ring ion guide, as known to those of ordinary skill. As well, the axial field could be produced otherwise without use of an ion guide or ring ion guide.

A second chamber42is in flow communication with the desolvation chamber30, by way of outlet aperture34connecting the desolvation chamber30to the second chamber42. Chamber42is shown to principally transport analyte, but chamber42could further provide ion mobility selection, as for example discussed in “Ion Mobility-Mass Spectrometry”, JOURNAL OF MASS SPECTROMETRY, J. Mass Spectrom. 2008; 43: 1-22.

In operation, pressure within chamber30may be maintained below 1 atm—for example at about 76 torr (or 1/10 atm), but could easily be chosen to range from 1/100 atm to 1 atm. To maintain a fixed pressure in chamber30as measured by pressure gauge29while accommodating different dry gas flows from flow controller51, the flow rate of roughing pump46may be adjusted, by way of a controller or otherwise.

As noted, the pressure at source22is typically at about atmosphere. Analyte particles are solvated at ES emitter24. Solvated ions and charged liquid droplets from source22are drawn to sampling inlet32by electric fields. The flow through sampling inlet32further transports the mixture through inlet aperture33. Ion guide36contains the ionized particles proximate axis31, and provides an axial electric field to urge ions from inlet aperture33to outlet aperture34generally along axis31.

The axial electric field extends throughout the length of chamber30, to urge charged particles from inlet aperture33to outlet aperture34.

Gas flow introduced from gas source38through interface35splits into two flow portions: one portion flows through opening26—acting as an exit—opposing the flow of charged droplets from source22/ES emitter24, while the other portion flows through sampling inlet32due to the pressure difference between the region of source22and chamber30—with the pressure at sampling inlet32and inlet aperture33being marginally above the pressure in chamber30. The portion that flows through sampling inlet32and ultimately into chamber30entrains charged droplets and transports them through inlet aperture33and toward outlet aperture34.

The temperature of the gas flow from source38and the temperature of the analyte path defined by interface35assist in determining the degree of ES droplet desolvation through inlet aperture33. Typical gas type from source38is clean and dry air or nitrogen. The gas pressure from gas source38may be adjusted to provide sufficient flow.

As shown approximately by the solid arrows, the flow of charged droplets through aperture33slows, expands, reverses direction, and folds back toward aperture(s)44leading to roughing pump46. This pumping design is intended to slow the velocity of droplets from source22, allowing the droplet time to absorb heat from the surrounding hot gas, as well as absorbing the black body radiation from the heated walls of chamber30, resulting in desolvated ions.

Adjustable flow restrictor49can also be adjusted to ensure a reasonably constant gas flux through roughing pump46, thereby adjusting residence time of entrained droplets within chamber30. Without roughing pump46—or other pumping system—all gas entering chamber30through inlet aperture33will exit through outlet aperture34. If this gas containing droplets with or without high salt and protein content (and the like) enters outlet aperture34, the droplets alone can cause electrical discharge in chamber42, or conduit47leading thereto (or subsequent lower pressure regions—e.g.), and the salt and protein can be deposited on downstream components of mass analyser10, causing sensitivity degradation.

Proximate outlet34, gas flow into chamber30through gas injection port48from gas source50splits into two flows: one portion—a counter flow that flows away from outlet aperture34opposing the flow of charged droplets emanating from inlet aperture33—and another portion that flows in the direction of outlet aperture34, caused by the pressure difference between chamber30and conduit47. The counter flow further slows and desolvates the downstream flow of solvated ionized particles entrained therein, as the solvated ionized particles travel through the desolvation chamber30from inlet aperture33toward outlet aperture34.

The flow toward outlet aperture34entrains now desolvated ions and transports them through outlet aperture34into conduit47and onto chamber42. The temperature of the counter gas flow from source50greatly determines the degree of ES droplet desolvation. For example, a temperature of 200° C. or higher may be used.

In typical operation, gas flows through sampling inlet32from atmosphere through aperture33into chamber30at about 0.1 atm, and subsequently through aperture34into a conduit47at roughly 0.01 atm. With no drying gas flow from gas flow controller51and no flow through aperture44, a typical inlet aperture of 0.5 mm diameter requires an outlet aperture34diameter of 1.6 mm, i.e., the gas flux of about 36 atm-cc/s flows through both apertures. Adding drying gas flow from flow controller51will increase the pressure in chamber30from 0.1 atm, and therefore the pumping speed through aperture44can be increased—usually by increasing the frequency of the roughing pump46—to maintain the pressure in chamber30at 0.1 atm.

Conveniently, outlet aperture34feeding the remainder of mass spectrometer10is larger than a typical inlet aperture at or above atmospheric pressure found in conventional mass spectrometers. That is, in conventional mass spectrometers, desolvated ions are provided through an aperture at atmospheric pressure through a sampling orifice. The typical sampling orifice is, for example, about 0.5 mm in diameter.

In interface20, solvated ions enter desolvation chamber30and desolvate therein. Droplets remain, on average, resident in chamber for a longer time due to the counter flow introduced through gas injection port48. Desolvated ions then exit at lower pressure (e.g. at 1/10th atmospheric pressure) through a outlet orifice34having a 1.6 mm diameter. Provided the desolvated ion densities are reasonably similar to those of a conventional mass spectrometer, and are extracted at a similar velocity, the ion flux through outlet aperture34in interface20will be correspondingly larger than the usual ion flux through a conventional sampling orifice. For example, if the area of outlet aperture34is ten times larger than a conventional sampling orifice, the ion flow will increase by a factor of ten, as will the sensitivity.

Although inlet aperture33is shown on axis31of chamber30, it could be located off-axis. In addition, although the direction of flow through sampling inlet32is shown as parallel axis31, alternatives are also possible. Although not shown, reactive gases may also be introduced into chamber30are also possible for ion-gas reaction manipulation. Likewise, although source22has been described as an ES emitter, ions drawn toward sampling inlet32need not originate from an ES emitter: any approximately atmospheric ion source that produces ions will suffice.

In an alternate embodiment illustrated inFIG. 2, a mass analyser interface20′ is depicted. Mass analyser interface20′ is generally the same as mass analyser interface20(FIG. 1) but also includes a jet disrupter102, located on the interior of chamber30, proximate its center. Jet disrupter102may be used to further desolvate the largest droplets in the droplet mixture entering through sampling inlet32. Typical jet disruptors102disturb the incoming jet flow by their physical presence and an applied voltage. An example jet disruptor102may, for example, take the form of a 1 mm thick, 5 mm cylindrical disc, or a 5 mm sphere. Example jet disruptors are detailed in U.S. Pat. No. 7,671,344.

In another alternate embodiment illustrated inFIG. 3, a mass analyser interface20″ is depicted. Mass analyser interface20″ is generally the same as mass analyser interface20′ (FIG. 2), except that the jet disrupter104provides a gas flow component opposing the flow through inlet sampling inlet32′, along axis31, and that interface35′ is unlike interface35, in that interface35′ is not a split flow interface, but instead is a direct flow interface. Gas provided by gas supply38primarily exits interface35′ into desolvation chamber30through inlet aperture33′. In this case, jet disruptor104can affect the incoming jet(s) from sampling inlet32′ by gas flow from another source, provided to jet disruptor104as well as its physical and electrical characteristics. As required, a conduit106in flow communication with jet disruptor104may extend from the exterior of chamber30′ to a gas source (now shown). The gas pressure from the disruptor104is relative to the pressure in chamber30, sufficient to create the counter flow. For example, flow through disruptor104may be about one half the flow through sampling inlet32′.

In a further alternate embodiment illustrated inFIG. 4, a mass analyser interface20″′ is depicted. Mass analyser interface20″′ is generally the same as mass analyser interface20″ (FIG. 3), except that two gas jet disrupters108are used. In this embodiment, the two gas jet disrupters108are on either side of the central axis31of chamber30. The gas flow from these two gas jet disruptors108performs the principal function of jet disruption from sampling inlet32′. Again, a gas source (not shown) may feed jet disruptors108. Although two gas jet disruptors are shown at 180°, a multiplicity of such disruptors, such as four equally spaced at 90° are possible. Jet disruptors108may be located at chosen locations within chamber30, and may be located in/along the flow from sampling inlet32′ to outlet aperture34, for example along axis31. Some may likewise be located off axis, away from the downstream flow and central axis31.

In an alternate embodiment illustrated inFIG. 5, a mass analyser interface20(iv)is similar to mass analyser20″′ ofFIG. 4except that ES emitter24has been replaced with a sprayer122′. Sprayer122′ volatilizes liquid analyte at atmospheric pressure by, for example by mixing heated, eluted analyte at relatively high temperatures (e.g. above 400 degrees Celsius) with a high flow rate nebulising gas. Some or all of this aerosol cloud is introduced into chamber30, at sub-atmospheric pressure. In chamber30, the aerosol is subjected to a corona discharge by corona emitter124′, as shown. Example sprayers and corona emitter are thus similar to those used in APCI interfaces, but separated from another and operating in different pressure regimes, as will be appreciated by those of ordinary skill. Sprayer122′ is also similar to an ES emitter without an electric field at the tip of the liquid tube: that is, it nebulizes a flowing liquid to create droplets and solvated molecules. In this configuration, solvated analyte molecules and droplets from sprayer122′ are entrained within gas flowing through sampling inlet32′. Again, these solvated analyte molecules and droplets in chamber30desolvate due to the counter flow of dry gas and the elevated temperature of heated chamber30, and are chemically ionized by reagent ions originating from the corona emitter124′ within chamber30, at pressures less than 1 atm. As such, this configuration provides a sub-atmospheric pressure chemical ionization source. As droplets from sprayer122′ are not charged, they will not be electrically attracted to sampling inlet32. Instead, droplets are directed to aperture32, and gas flow through sampling inlet32′ will entrain such droplets and guide them to the interior of chamber30.

Although not shown inFIG. 5, further analyte ionization may be provided for in chamber30—either directly or chemically—such as photo-ionization—could be used within desolvation chamber30on its own or in conjunction with an atmospheric ES emitter, or emitters.

Although not shown in the embodiments ofFIGS. 1 to 5, it should be understood that an atmospheric ES emitter, or emitters, could be used in conjunction with a sprayer and corona emitter in chamber30, or sprayers and corona emitters, simultaneously or consecutively.

In another alternate embodiment illustrated inFIG. 6, a mass analyser interface20(v)is depicted. In analyser interface20(v)an ES emitter22″ provides electrospray droplets to an inlet/exit opening26″ of an interface35″ along the side wall of chamber30. An inlet aperture33(as inFIGS. 1 to 5) in an end wall of chamber30may thus be eliminated, and replaced by an inlet aperture33″ on the side wall of chamber30″. A gas jet disruptor flow emanates from gas jet disruptor tube112is roughly axially aligned with inlet aperture110, creating jet disruption opposing the flow from inlet aperture110, as illustrated. Again, a gas source feeds disruptor tube112. Of course, additional jet disrupters (not shown), like gas jet disrupter104or108(FIGS. 3 and 4), may be included in interface20(v).

In another alternate embodiment illustrated inFIG. 7, a mass analyser interface20(vi)that is the same as mass analyser interface20(v)inFIG. 6except that the ES emitter22″ has been replaced by a sprayer122″ (like sprayer122′—FIG. 5) to feed solvated molecules and droplets into chamber30through aperture110. A corona emitter124″ inside chamber30, proximate aperture110, completes ionization of the desolvated molecules.

In another alternate embodiment illustrated inFIG. 8, a mass analyser interface200that is similar to mass analyser interface20inFIG. 1. However, sampling inlet32and inlet aperture33have combined become a single aperture232. A gas distribution manifold270includes two parallel plates274aand274b. Plate274bdefines inlet aperture232, and plate274bdefines opening226to gas manifold270. Opening226is aligned with inlet aperture232to desolvaton chamber230. Plates274aand274bare spaced from each other by about 3 mm to define region278. An annular passage276is formed adjacent the region defined by plates274aand274b. The inlet to annular passage276extends from the outer wall defining the annular passage276, and is connected with gas supply238. Evenly spaced openings on the inner wall of annular passage276ensure that gas from supply238enters region278with a flow toward axis231, in a generally axial direction of chamber230. A ring ion guide326guides ions within chamber230to outlet aperture234, while a dry gas creating a counter-flow is injected through port248from gas supply250.