Multi inlet for solvent assisted inlet ionisation

Abstract

A mass spectrometer is disclosed comprising a dual channel Solvent Assisted Inlet Ionization (“SAII”) interface.

Claims

1. A mass spectrometer comprising: an atmospheric pressure ion source; a first vacuum chamber; a first ion inlet, wherein ions from said atmospheric pressure ion source are transmitted in use through said first ion inlet into said first vacuum chamber; and a Solvent Assisted Inlet Ionisation (“SAII”) interface leading, separately from said first ion inlet, into said first vacuum chamber or a subsequent downstream vacuum chamber.

2. A mass spectrometer as claimed in claim 1, further comprising a first capillary or fluid supply device for introducing a first substance into said mass spectrometer, wherein said first capillary or fluid supply device is received within said Solvent Assisted Inlet Ionisation interface.

3. A mass spectrometer as claimed in claim 2, wherein said first substance comprises a lock mass substance.

4. A mass spectrometer as claimed in claim 2, wherein said first substance comprises a reference substance, a calibration substance, a reagent or an analyte.

5. A mass spectrometer as claimed in claim 1, further comprising one or more RF ion guides provided in a vacuum chamber downstream of said interface.

6. A mass spectrometer as claimed in claim 5, wherein said one or more RF ion guides are arranged and adapted in a mode of operation to keep ions generated by said atmospheric pressure ion source separate from ions generated by or within said Solvent Assisted Inlet Ionisation interface.

7. A mass spectrometer as claimed in claim 5, wherein said one or more RF ion guides comprise at least a first ion guiding path and a separate second ion guiding path.

8. A mass spectrometer as claimed in claim 7, wherein ions formed in said atmospheric pressure ion source are directed to said first ion guiding path, and ions formed in a said Solvent Assisted Inlet Ionisation (“SAII”) interface are directed to said second ion guiding path.

9. A mass spectrometer as claimed in claim 7, wherein said first and second ion guiding paths converge or join at a downstream section of said one or more RF ion guides.

10. A mass spectrometer as claimed in claim 7, further comprising a device which may be switched from an ion transmission mode to an ion attenuation mode thereby preventing or substantially attenuating ions from passing along or exiting said first or said second ion guiding path.

11. A mass spectrometer as claimed in claim 7, wherein ions directed into said ion guiding path are mass analysed by a first mass analyser, and ions directed into said second ion guiding path are mass analysed by a second mass analyser.

12. A mass spectrometer as claimed in claim 1, wherein said atmospheric pressure ion source comprises an Electrospray Ionisation (“ESI”) ion source, an Atmospheric Pressure Chemical Ionisation (“APCI”) ion source, an Atmospheric Pressure Photo-Ionisation (“APPI”) ion source or an Impact spray ionisation ion source.

13. A mass spectrometer as claimed in claim 1, wherein said Solvent Assisted Inlet Ionisation (“SAII”) interface comprises a single or dual channel Solvent Assisted Inlet Ionisation interface which communicates between an atmospheric pressure region and said first vacuum chamber.

14. A method of mass spectrometry comprising: providing an atmospheric pressure ion source, a first vacuum chamber and a first ion inlet; transmitting ions from said atmospheric pressure ion source through said first ion inlet into said first vacuum chamber; and providing a Solvent Assisted Inlet Ionisation (“SAII”) interface leading, separately from said first ion inlet, into said first vacuum chamber or a subsequent downstream vacuum chamber.

15. A method as claimed in claim 14, further comprising introducing a first substance into said mass spectrometer via said Solvent Assisted Inlet Ionisation (“SAII”) interface, wherein said first substance comprises a lock mass substance.

16. A mass spectrometer comprising: a vacuum chamber; a dual channel Solvent Assisted Inlet Ionisation (“SAII”) interface leading into said vacuum chamber; an RF ion guide in said vacuum chamber, wherein in the RF ion guide comprises at least a first ion guiding path and a separate second ion guiding path.

17. A mass spectrometer as claimed in claim 16, wherein ions entering said RF ion guide are directed either into said first ion guiding path or into said second ion guiding path.

18. A mass spectrometer as claimed in claim 16, further comprising a device which may be switched from an ion transmission mode to an ion attenuation mode thereby preventing or substantially attenuating ions from passing along or exiting said first ion guiding path or said second ion guiding path.

19. A mass spectrometer as claimed in claim 16, wherein said first ion guiding path and said second ion guiding path join or converge at a downstream section of said RF ion guide.

20. A mass spectrometer as claimed in claim 19, wherein ions formed in a first of said dual channels are directed to said first ion guiding path, and ions formed in a second of said dual channels are directed to said second ion guiding path.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments of the present invention together with other arrangements given for illustrative purposes only will now be described with reference to the accompanying drawings in which:

(2) FIG. 1 shows a known Solvent Assisted Inlet Ionisation (“SAII”) interface;

(3) FIG. 2 shows a less preferred embodiment of the present invention wherein separate first and second capillaries are introduced into a single channel of a SAII interface;

(4) FIG. 3 shows a preferred embodiment of the present invention comprising an SAII interface having two channels, wherein first and second capillaries are positioned within different channels;

(5) FIG. 4 shows an end face of the dual channel SAII interface as shown in FIG. 3;

(6) FIG. 5 shows another embodiment of the present invention in which the SAII interface comprises two channels that are separated;

(7) FIG. 6 shows a further embodiment of the present invention wherein a dual channel SAII interface directs ions into different ion paths within a RF ion guide; and

(8) FIG. 7 shows an embodiment wherein a single channel SAII interface is provided together with a conventional Electrospray ion source and interface.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(9) A known Solvent Assisted Inlet Ionisation (“SAII”) interface arrangement will first be described.

(10) FIG. 1 shows a schematic of a known single channel SAII interface arrangement. The interface arrangement comprises a single channel 1 and is heated to a desired temperature by a heater 2. The heater is capable of heating the channel 1 to 450° C. The inlet end of the single channel 1 is at atmospheric pressure. The outlet end of the single channel 1 is within a first pumped region 3 of a mass spectrometer and is at sub-atmospheric pressure. The pressure in the first pumped region 3 is in the range 1-10 mbar.

(11) A solution comprising analyte and a solvent is introduced into the single channel 1 via a solvent inlet capillary 4 connected to a syringe pump or a liquid chromatography source (not shown). The end of the inlet capillary 4 is carefully positioned within the single channel 1 such that the solvent emerging from the capillary 4 is volatilized as it emerges. Charged droplets continue to desolvate and collide with the surfaces present as they proceed through the heated channel 1 and into the lower pressure region 3. The method of ionization involves droplet charging, desolvation and possibly ion molecule reactions and surface interaction.

(12) It has been shown that this technique is simple and sensitive and produces a range of singly and multiply charged ions with characteristics similar to Electrospray ionization.

(13) A RF ion guide 5 is located in the low pressure region 3. This is not required for operation of the Solvent Assisted Inlet Ionisation interface but allows efficient transfer of ions within this region 3.

(14) An orifice or skimmer 6 separates the first pumped region 3 from a second pumped region 7. The second pumped region 7 is differentially pumped and is maintained at a lower pressure than the first pumped region 3. The pressure of the second pumped region 7 is typically 10.sup.−2-10.sup.−3 mbar. Further stages of differential pumping may follow this region.

(15) It is known in the context of Time of Flight mass analysers to introduce an internal reference or lock mass during an analytical run. This allows mass drift to be corrected. This drift can occur because of changes in ambient temperature.

(16) Conventionally, a reference material for internal calibration or lock mass is introduced during analysis of an analyte and must be accomplished by mixing the reference material with the analyte and introducing both via the same channel 1 and using the same capillary 4. However, such an approach is problematic since signals may be suppressed due to competition for charge and/or analyte ions may be unresolved from the reference material and hence interfere with the reference material. Additionally, the reference material may require a different solvent to the analyte which cannot be accommodated by this approach.

(17) Various embodiments of the present invention address these problems and further details will now be presented.

(18) Firstly, a less preferred embodiment of the present invention will be described with reference to FIG. 2. FIG. 2 shows a method of introducing reference and analyte according to a less preferred embodiment of the present invention. The interface of FIG. 2 has a single channel 1. In this embodiment separate analyte and reference inlet capillaries 4a,4b are provided. The capillaries 4a,4b are introduced into the same heated channel 1. In this case the reference and analyte flow only mixes after volatilization in the channel 1. This has the advantage that a different solvent may be used for the analyte and reference. However, analyte and reference ions will not be separated and hence interference may occur. In addition, with two capillaries 4a,4b with possibly different flow rates and solvents it may be difficult to optimize the temperature of the channel and/or the position of the capillary within the channel to give best sensitivity and stability for both reference and analyte. Nonetheless, the embodiment shown in FIG. 2 still provides certain advantages over the prior art as shown and described above in relation to FIG. 1.

(19) FIG. 3 shows a particularly preferred embodiment of the present invention. According to the preferred embodiment a dual channel interface is provided comprising a tube 8 having two (or more) separate channels. The tube 8 is preferably heated with a heater element 2. An analyte capillary 4a and a reference capillary 4b are preferably independently positioned within separate channels allowing optimisation of stability and sensitivity.

(20) As there are two channels care must be taken that the conductance of the combined tube is not excessive such that a suitable operating pressure is maintained in the vacuum housing 3. Other embodiments are envisaged in which the interface comprises more than two channels.

(21) FIG. 4 shows an end on diagram of the dual channel tube shown in FIG. 3 and shows the tube 8 and the outer heater 2.

(22) FIG. 5 shows another embodiment of the invention. According to this embodiment two channels 8a,8b are provided which are physically separate from each other and may be independently heated by separate heaters 2a,2b. This allows even more flexibility in optimisation of the two inlets. For example, the analyte flow rate from analyte flow 4a may be significantly different from the reference flow rate from reference flow 4b, and may require a different temperature and or position within the channel.

(23) In the embodiments of FIGS. 2-5, the RF ion guide may be replaced with another type of ion guide, for example an RF confined ion funnel. Such an ion funnel may comprise a plurality of elements each having an aperture (or defining an aperture) through which ions travel in use. The elements may have progressively smaller apertures such that the an ion funnel is formed having an entry at the largest aperture and an exit at the smallest aperture. Alternatively, the RF ion guide may be replaced with a conjoined ion guide comprising, for example, two rows of stacked ring electrodes having parallel ion optical axes but which are radially offset from one another, wherein along the radial dimension the stacked rings are slotted to provide a path for ion movement.

(24) FIG. 6 shows a further embodiment of the present invention. According to this embodiment a dual channel inlet is provided. However, in this case ions formed by SAII from the reference material are directed to one RF ion guide whilst analyte ions are directed to another RF ion guide. The two ion guides are shown joining each other upstream of a differential pumping aperture 6. This embodiment results in the population of ions in each guide mixing together prior to passing through the orifice 6. It may be the case that the ion populations are, however, kept separate and may be directed to different mass analysers.

(25) It will be appreciated that the aspects of the embodiment shown and described above in relation to FIG. 6 including directing the outlet ends of different inlet channels to different ion guides, is not limited to the embodiment shown and could equally be applied to the embodiments of FIGS. 3-5 and FIG. 7 (described below).

(26) Moreover, the principle of keeping ions from two different channels separate as described above in relation to FIG. 6 by using independent downstream devices is equally applicable to ions formed by other sub-atmospheric or atmospheric pressure ion sources (such as Electrospray Ionisation) as well as SAII. An advantage of using SAII channels, however, is that it is easier to keep the streams of ions separate thus minimising crosstalk between the analyte streams.

(27) In the embodiment of FIG. 6, by suitable application of DC deflection voltages within the separate ion guides, or variation of RF potential, it is possible to prevent ions from either the reference material or the analyte material or from both from passing onwards to the mass analyser.

(28) In this manner, a mode of operation is envisaged where ions from the reference material are allowed to enter the mass analyser periodically to allow correction for mass drift. When ions from the reference are allowed to pass, analyte ions may be prevented from reaching the mass analyser. In this way there is no possibility of interference of the analyte with the reference causing poor mass measurement.

(29) As stated above, it should be noted that the ion populations from two channels may be kept separate beyond the first pumping region 3 and may be directed towards different mass analysers.

(30) FIG. 7 shows a further embodiment of the present invention. According to this embodiment, an atmospheric pressure ion source 45, for example an Electrospray ion source, is provided in combination with a SAII interface. An ion inlet 46 is provided in the mass spectrometer for transmitting ions from the atmospheric pressure ion source 45 into the first vacuum chamber 30 of the mass spectrometer. An inlet capillary 40 is introduced into a heated SAII channel such that a solvent solution is volatized as it emerges. The SAII interface as shown in FIG. 7 comprises a single SAII channel. Other less preferred embodiments are contemplated wherein the SAII interface may comprise a dual channel SAII interface.

(31) In the same manner as described above, an RF ion guide 50 is preferably provided in the first vacuum chamber 30 and downstream of the ion inlet 46 and SAII channel to guide ions from the first vacuum chamber 30 to a second vacuum chamber 70 of the mass spectrometer. A orifice or skimmer 60 may be provided between the first vacuum chamber 30 and the second vacuum chamber 70.

(32) In this embodiment, the SAII channel can be used to introduce a reference material into the mass spectrometer. The SAII channel can be used as a calibration reference or “lock mass” for the Electrospray ion source 45.

(33) The embodiment shown and described with reference to FIG. 7 illustrates an example of the use of SAII when used in conjunction with another type of ion source, specifically an atmospheric pressure Electrospray ion source 45. Using a SAII interface reduces the vacuum pumping requirements of the system since using another atmospheric source as the reference (or further analyte) channel would impose extra vacuum pumping requirements.

(34) Further embodiments are also contemplated wherein no RF ion guide is provided in the first vacuum chamber 30.

(35) In all of the embodiments described above a suitably shaped or positioned impact surface (not shown) may be provided downstream of the channels to assist desolvation and or inlet ionization.

(36) The channel(s) which form the single or dual SAII interface may be made from metal or glass or quartz. Metal coated or conductive glass may also be used.

(37) The one or more channels may be heated resistively, for example by a resistive heater.

(38) In embodiments in which there are more two or more channels, multiple analyte flows can be multiplexed. For example, separate analyte substances may be introduced into separate inlet channels.

(39) According to another embodiment the RF ion guide 5; 50 may form a reaction chamber or collision or fragmentation device. For example, ETD reagent ions may be introduced via one channel and analyte ions via another. The ions may then be continuously reacted in the downstream RF confined reaction vessel. Gas phase Hydrogen Deuterium exchange (“HDx”) may also be accomplished in the same way.

(40) Substances (e.g. an analyte) may be delivered into an inlet channel via one or more separation techniques either simultaneously or sequentially. For example, techniques such as Liquid Chromatography (“LC”), Capillary Zone Electrophoresis (“CZE”), Super Critical Fluid (“SCF”) chromatography or Gas Chromatography (“GC”) may be used.

(41) When using a separation technique as described above, eluent from a separation device may be split between more than one inlet channel after separation such that different analytes are introduced into separate inlet channels. A delay in introduction time for the different analytes may be achieved, for example, by increasing the length of transfer line between the separation device (e.g. a chromatograph) and the inlet channels.

(42) Ions from one channel may then be monitored whilst ions from the other channel may be prevented from entering the mass analyser. The signal from a first channel can be used for data dependent control of the mass spectrometer for analysis of ions from a second channel. For example, transmission of ions may be alternated between analyte introduced into each channel.

(43) The signal associated with the channel for which ions appear earliest in time may be used to determine the MS-MS precursor mass set for ions from the second channel before these ions have appeared. Other data dependent functions and combinations may be envisaged e.g. control of downstream ion transmission to control space charge or detection saturation effects.

(44) Yet further embodiments are contemplated wherein other atmospheric ionisation techniques may be combined with SAII. For example, a multiple inlet interface may be provided wherein one or more inlets is a SAII interface and one or more other channels or openings accept ions produced by or generated from a different atmospheric ionisation technique e.g. example Electrospray Ionisation (“ESI”), Atmospheric Pressure Chemical Ionisation (“APCI”) or Atmospheric Pressure Photo-Ionisation (“APPI”). For example, SAII may be used as a simple lock mass interface for another API ionisation method.

(45) In addition, the principle of keeping ions from two different ionisation inlets separate using independent downstream RF devices is applicable to ions formed by sub ambient ionisation techniques (such as sub ambient Electrospray) and to atmospheric pressure ion sources as well as SAII. The advantage of SAII is that it is easier to keep the streams of ions separate thus minimising cross talk between analyte streams.

(46) Introduction of reference or calibration material and or analyte material may be discontinuous. For example, a quantity of pure solvent or gas may be introduced into the flow of sample using a switched divert valve upstream of any LC delivery system and downstream of the SAII interface. This produces a discontinuity within the sample flow. In the case of an introduced gas this discontinuity represents a gap in the column of fluid travelling towards the interface. In the case of solvent introduction the discontinuity represents a region in which analyte molecules are not present.

(47) The result of this approach is to allow the appearance of analyte or reference ions to be gated such that analyte and reference ions do not appear at the same time downstream in the mass analyser. This avoids the potential for mass interference between analyte and calibrant signals. In addition, using this approach it is possible to introduce a region of reference material into the flow of analyte allowing both reference and analyte to be introduced discontinuously via the same SAII interface. These approaches are not limited to SAII and may be used to introduce reference material into any API ion source.

(48) Although the preferred embodiment relates to SAII, embodiments of the present invention are contemplated using ESI and API sources in combination with a single channel or multiple channel SAII interface.

(49) Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the accompanying claims.