Sample introduction system for mass spectrometry

Abstract

A surface interaction sample introduction (SISI) system for mass spectrometers is disclosed that improves sensitivity and reduces chemical background. SISI comprises of a settling chamber with an inlet orifice that ions created by an ionization source enter the MS impinging surface that is located in front of the inlet orifice, thereby the high-speed gas jet entering the settling chamber from the inlet orifice impinges on the impinging surface resealing ions and molecules into the settling chamber. The impinging surface can be one of the settling chamber surfaces or an extra surface placed inside the settling chamber. The impinging surface can be orthogonal or angled with respect to the gas jet. The impinging surface is heated to apply thermal energy to the jet to promote the liberation of ionized particles from attached impurities. The released ions and molecules leave the settling chamber from an outlet port towards a mass spectrometer inlet.

Claims

1. An interface between an ion source and a mass spectrometer for sample introduction to the mass spectrometer, comprising: a settling chamber having an inlet orifice through which a sampling material is injected into the settling chamber, forming a jet flow inside the settling chamber, and having an outlet orifice on an outlet surface of the settling chamber to allow for a settled flow to flow from the settling chamber towards the mass spectrometer; an impinging surface configured so that the jet flow impinges on the impinging surface, and the settled flow comprising of molecules and ions is formed inside the settling chamber, wherein the impinging surface is a tube with a predefined diameter that is located in between the inlet orifice and the outlet orifice, wherein the impinging surface disturbs and heats the jet flow and heated gases and ions flow around the impinging surface and towards the outlet orifice; a heater to heat the impinging surface to heat the jet flow to prevent declustering and improve desolvation by heat dissipation, whereby the settled flow improves signal stability, reproducibility and sensitivity of the mass spectrometer.

2. The apparatus of claim 1, wherein the impinging surface is perpendicular or at an inclined angle with respect to the jet flow.

3. The apparatus of claim 1, wherein the settling chamber has 10 to 50 mm sides, and wherein the outlet orifice has a diameter in the range of 0.2-2.0 mm.

4. The apparatus of claim 1, wherein the inlet orifice and the outlet orifice are configured to control the pressure inside the settling chamber using a vacuum pump of the mass spectrometer.

5. The apparatus of claim 1, further having a secondary vacuum pump that is directly connected to the settling chamber to reduce the pressure inside the settling chamber.

6. The apparatus of claim 1, wherein the pressure inside the settling chamber is in the range of 1-20 Torr.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments herein will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the scope of the claims, wherein like designations denote like elements, and in which:

(2) FIG. 1 shows SISI Surface Interaction Sample Introduction with an orthogonal sampling and with a ring guide/Ion funnel, and with no active pumping on SISI;

(3) FIG. 2 shows SISI Surface Interaction Sample Introduction with an orthogonal sampling and a skimmer and no active pumping on SISI;

(4) FIG. 3 shows SISI Surface Interaction Sample Introduction with orthogonal sampling and an active pumping on SISI;

(5) FIG. 4 shows SISI Surface Interaction Sample Introduction with off axis sampling and no active pumping on SISI;

(6) FIG. 5 shows the fifth embodiment of the present invention with off axis sampling and active pumping on SISI;

(7) FIG. 6 shows the sixth embodiment of the present invention with a heated impinging rod set inside SISI;

(8) FIG. 7 shows the seventh embodiment of the present invention with an inclined impinging surface, and

(9) FIG. 8 shows the eighth embodiment of the present invention with an inclined impinging surface and an active pumping.

DETAILED DESCRIPTION OF THE INVENTION

(10) FIG. 1 shows the first embodiment of the Surface Interaction Sample Introduction (SISI) interface with Orthogonal sampling. SISI 100 is the interface between an ionization source 110 and a mass spectrometer 120, that may be a conventional mass spectrometer, including but not limited to quadrupole mass analyzers, magnetic sectors, hybrid and stand-alone time-of-flight devices, 2- and 3-dimensional ion traps, and Fourier transform mass spectrometers. SISI is designed to enhance concentration and sensitivity and reduce chemical background while providing the appropriate gas flow to a mass spectrometer system. In the embodiment of FIG. 1, the SISI interface comprises of a settling chamber 10 that has a cavity 20, and a sampling orifice 11, through which the sampling material are injected into the chamber. The sampling orifice diameter is typically is a fraction of millimetres, for examples 0.35 mm. The settling chamber 10 can be any shape and dimension but it is much larger in size than the sampling orifice. In one embodiment, the settling chamber has 10 to 50 mm sides. The settling chamber has an impacting surface 12 and an outlet surface 14, which has an outlet orifice 15. The outlet orifice diameter depend on the pumping capacity in this region, and it is normally from 0.2-2.0 mm.

(11) Typically, the ionization source 110 is at atmospheric pressure, generating ions through different mechanisms, such as an electrospray, a MALDI, a corona discharge device, an atmospheric pressure chemical ionization device, an atmospheric pressure photo ionization device. Trace substances after ionization are injected into the interface typically with the aid of an inert gas. Ions and neutral gas molecules are transported from a high-pressure, typically an atmospheric pressure, through the sampling orifice 11, into a lower pressure of the cavity 20. When the ions and neutral gas expand into the cavity 20, a high speed jet flow is generated.

(12) As the flow from the atmospheric pressure enters the settling chamber of the interface, which is at a lower pressure, a strong flow expansion occurs, which may have a diamond shape jet flow 25 with expansion waves and Mach disks. This jet flow pattern results in a significant ion deceleration. In the zones of silence (the zones bounded by the shock waves), there is a low frequency gas-ion collision, which results in a narrow ion beam and localized decrease in the ion charge density. Downstream of the Mach disks, ions are decelerated and aggregate. The zones of silence are not beneficial for the transmission of highly charged ions of the same mass.

(13) The settling chamber is configured such that the high speed jet flow impinges on one of its surfaces, i.e., the impinging surface 12. Once the jet impinges on the impinging surface 12, the expansion waves are destroyed, the molecules and ions in the gas are bounced off the surface and are quickly settled inside the cavity 20 of the settling chamber 10, reaching settling chamber pressure and temperature. The exit orifice of the settling chamber 15 is located such that a settled flow 30 flows through the orifice 15 at the settled conditions of the settling chamber. The impinging surface 12 is heated to rapidly normalized the low temperature conditions that exists at the central regions of the expansion waves. The pressure inside the settling chamber can be in the range of 1-20 Torr. However, the system can be configured to allow for other pressure conditions. A vacuum pump 130 controls the pressure inside the settling chamber and the flow of the ions out of the settling chamber. The pumping may be for example around 10 liters/second holding the average pressure in the range of 2 Torr. Upon impingement, ions and neutrals undergo gas-surface and gas-gas interactions in the cavity of the settling chamber to liberate at least some of the ionized molecules from attached impurities, such as neutral molecules, radicals, adducts, and other ions. This increases the concentration of desired ionized molecules with characteristic m/z ratios in the flow and reduces impurities that generate chemical background. The material exiting the settling chamber 10 from the exit orifice 15, enter the mass spectrometer 120. In one embodiment as shown in FIG. 1, an ion guide 18 guides the ion flow into the MS 120. As the gases exit the settling chamber the ion guide captures the ions and guides them into the MS and the rest of the material exit from the side of the system. In another embodiment as shown in FIG. 2, a skimmer 19 is used to sample the ions through its entrance 22 and guide them into the MS 120. The system can be configured to have RF ion guides, ring guides, ion funnels, skimmers, or other types of system for controlling and containing the ions. Sampled ions and neutrals are then transported through lower pressure region 24 into mass spectrometer 120. In both embodiments of FIGS. 2 and 3, the unsampled ions and neutral flow are evacuated through evacuation port 26.

(14) The settling chamber has several purposes. One that the expansion waves impinge on a surface and are destroyed. Also, the settling chamber allows the mixture of neutral molecules and ions forming a constant flow inside the settling chamber, stabilizes ion to gas ratio for greater sensitivity and reproducibility. The outlet orifice 15 of the settling chamber allows the flow of neutral gas and entrained ions exit into the next stage of the mass spectrometer with a constant flow and minimum turbulent. The advantages of the settling chamber are as follows: Avoiding sampling from the free jet expansion by destruction of free jet expansion by a hot surface; low temperature of expansion rises to ambient temperature avoiding declustering; effective desolvation by heat dissipation from the hot surface; continuous flow of ions and natural gas improving signal stability, reproducibility and sensitivity; avoiding photons and meta-stable neutrals enter the mass analyzer; and greatly reducing instability of the MS device, which is highly susceptive to contamination.

(15) In the embodiments shown in FIGS. 1 and 2 the pressure inside the settling chamber is less than 20 torr. However, in another embodiment, as shown in FIG. 3, a lower pressure settling chamber is disclosed, in which the pressures inside the settling chamber is less than 5 torr. In this embodiment, a secondary vacuum pump 135 is directly connected to the settling chamber 60. The secondary vacuum pump may be located at a position with a minimum influence on the settled flow 30. In some embodiments, the background pressure is between 1.0 to 50 Torr, but system with other pressures can be designed.

(16) In configuration of FIG. 3, a settled flow of ions and neutral gas molecules 30 are transported from high-pressure settling chamber 31 (typically 1-5 Torr) through the orifice 33 to the second chamber 32 that is at a lower pressure (typically 50-200 mTorr). In the present system, the settling chamber 31 allows for the gas and ions to settle. The settling chamber 31 may have different shapes, however, it is significantly larger than the jet. The chamber (settling chamber) may be 4-10 mm. The expansion jet impinges on the front surface of the chamber and deflect downwardly towards the chamber exit hole at the bottom of the chamber. The impingement of the jet on the surface causes that the flow is disturbed and loses its shock structure. The flow becomes smoother with less turbulence before exiting the chamber. The ions and molecules may flow inside the chamber and settle down through mixing. Ions and neutrals undergo gas-surface and gas-gas interactions inside the chamber 31 to liberate at least some of the ionized molecules from attached impurities, such as neutral molecules, radicals, adducts, and other ions. This increases the concentration of desired ionized molecules with characteristic m/z ratios in the flow and reduces impurities that generate chemical background.

(17) FIG. 4 shows another embodiment of the current surface interaction sample introduction with off axis sampling and no active pumping. In this case, the injection point 41 is on the top of the settling chamber body 40. The jet 42 impinges on the bottom surface 43 of the settling chamber 40 and exits from an orifice 44 on the same plane 43. This is off-axis sampling. The ion guide 18 takes the ions into the mass spectrometer 120. In this embodiment of FIG. 4, the impinging surface 43 is heated by a heater.

(18) In another embodiment as shown in FIG. 5, the inlet 51 to the settling chamber 50 is at the top and substantially aligned with the exit orifice 52. A heating tube (or surface) 54 is located in front of the jet 55. The tube disturbs the jet as well as heating it. The heated gases and ions flow around the tube and towards the exit 52. Again, an ion guide 18 carries the ions towards the MS 120.

(19) FIG. 6 shows another embodiment of the surface interaction sample introduction 60 with off axis sampling, using active pumping on the settling chamber. A secondary vacuum pump 135 is connected to the settling chamber 60 to reduce the pressure inside the settling chamber.

(20) FIG. 7 shows another embodiment of the Surface Interaction Sample Introduction with an angled impinging surface. The inlet orifice 71 of the settling chamber 70 is at the top of the settling chamber. The jet 72 impinges of an angle impinging surface 73 and the settled flow 74 is directed towards the exit orifice 75 The impinging surface angel is 45° but it can be configure to be any other angle. The settling chamber may have no active pumping as in FIG. 7 or have active pumping 135 as in FIG. 8.

(21) Other advantage of the present interface are that it improves desolvation; reduces background chemical noise; is entirely flow dominant, and there is nothing to adjust; requires no optimization; accommodates Liquid Chromatography (LC) flow rate of 100 to 3000 μl/min with equal respond; is a self cleaning interface, since the settling chamber is continuously hit by a jet that cleans it, and is easy to maintain and simple to operate.