A three-stage atmospheric / vacuum transition mass spectrometer inlet with additional cluster separation in the third stage.

Abstract

The mass spectrometer includes an orifice plate having an orifice, a first multipole ion guide in a first chamber downstream of the orifice plate, and a second multipole ion guide in a second chamber downstream of the first chamber. The first ion lens is located between the first and second multipole ion guides. The third multipole ion guide is located in a third chamber downstream of the second chamber, and the third multipole ion guide includes a plurality of rods. The second ion lens is located between the second and third chambers. An adjustable DC voltage source applies an adjustable DC offset voltage to at least one of the ion guide and the ion lens to increase the axial kinetic energy of the ions, thereby causing at least one of de-clustering and / or fragmentation.

Description

[Technical Field]

[0001] (Related Applications) This application claims priority to U.S. Provisional Application No. 62 / 993,965, filed March 24, 2020, and entitled "Three Stage Atmosphere to Vacuum Mass Spectrometer Inlet with Additional Declustering in the Third Stage," which is incorporated herein by reference in its entirety.

[0002] (Technical field) The present teachings are directed to systems and methods for mass spectrometry in which a DC offset voltage applied between at least two components of a spectrometer is employed to promote de-clustering or fragmentation of ions. [Background technology]

[0003] Mass spectrometry (MS) is an analytical technique for determining the elemental composition of an analyte with both qualitative and quantitative applications. MS can be useful for identifying unknown compounds, determining the isotopic composition of elements within molecules, determining the structure of a particular compound by observing its fragmentation, and quantifying the amount of a particular compound in a sample. Mass spectrometers detect chemical entities as ions, whereby conversion of the analyte to a charged ion must occur during the sampling process. During the ion formation process, some adduct ions may be formed, for example, via solvation.

[0004] It is known that a voltage applied between the inlet orifice of a mass spectrometer and the first vacuum lens element (e.g., a skimmer or ion guide) can increase the internal energy of incoming ions and solvated clusters, promoting ion de-clustering or fragmentation. However, the effectiveness of such de-clustering and / or fragmentation decreases as the size of the orifice increases. For example, effective de-clustering requires a larger voltage offset for systems with larger orifice sizes.

[0005] Therefore, there is a need for improved systems and methods for mass spectrometry that allow for the utilization of large orifice sizes while at the same time allowing for effective de-clustering and / or fragmentation of ions introduced into the mass spectrometer. Summary of the Invention [Means for solving the problem]

[0006] In one aspect, a mass spectrometer is disclosed, comprising: an orifice plate having an orifice for receiving a plurality of ions; a first multipole ion guide disposed in a first chamber positioned downstream of the orifice plate; and a second multipole ion guide disposed in a second chamber positioned downstream of the first chamber. A first ion lens is disposed between the first multipole ion guide and the second multipole ion guide. A third multipole ion guide is positioned in a third chamber positioned downstream of the second chamber. A second ion lens is positioned between the second chamber and the third chamber. The mass spectrometer further includes an adjustable DC voltage source for applying an adjustable DC offset voltage to at least one of the first, second, and third multipole ion guides and / or at least one of the first and second ion lenses to increase the axial kinetic energy of ions and cause at least one of de-clustering and / or fragmentation of at least some of the ions.

[0007] In some embodiments, the first, second, and third multipole ion guides each comprise a plurality of rods arranged to allow passage of ions therebetween, hi some embodiments, the first, second, and third multipole ion guides each comprise a series of stacked rings through which ions can pass.

[0008] In some embodiments, an adjustable DC offset voltage is applied to increase the axial energy of ions in the expansion sections of the second and third multipole ion guides.

[0009] In some embodiments, the DC voltage is configured to cause de-clustering of at least some of the additional ions present in the ion bundle without causing fragmentation thereof. By way of example, in some such embodiments, the applied DC voltage may be, for example, in a range of about 0 V to about 300 V, such as in a range of about 10 V to about 200 V, such as in a range of about 20 V to about 140 V. In some embodiments, the applied DC voltage may increase the axial kinetic energy of the ions, causing fragmentation of at least some of the ions.

[0010] In some embodiments, the orifice has a diameter of at least about 0.6 mm, such as in the range of about 0.7 mm to about 3 mm, such as in the range of about 1 mm to about 1.5 mm.

[0011] In some embodiments, the adjustable voltage source is configured to vary the applied voltage in a range of 0 to about 300V, such as in a range of about 10V to about 200V, such as in a range of about 20V to about 140V.

[0012] In some embodiments, the first chamber is maintained at a pressure within a range of about 5 Torr to about 15 Torr. In some such embodiments, the second chamber is maintained at a pressure within a range of about 1 to about 5 Torr. Further, in some embodiments, the third chamber is maintained at a pressure within a range of about 3 mTorr to about 12 mTorr.

[0013] In some embodiments, in addition to the DC offset voltages described above, a DC floating voltage may be applied to any of the first, second, and third multipole ion guides, for example, in the range of about -10 V to about 10 V (this floating voltage may also range in different values, for example, on a ToF it may be up to + / - 500 V). In some embodiments, a separate voltage source is provided to apply the DC floating voltage to these ion guides.

[0014] In some embodiments, the mass spectrometer includes one or more radio frequency (RF) sources capable of applying an RF voltage to at least one of the first, second, and third multipole rods to focus ions passing therethrough.

[0015] Various ion sources may be employed to generate the ions. By way of example, in some embodiments, an atmospheric pressure ion source may be employed.

[0016] In a related aspect, a mass spectrometer is disclosed that includes an orifice plate having orifices for receiving a plurality of ions, the orifices having a diameter of at least about 0.6 mm, e.g., in a range of about 0.7 mm to about 3 mm. A first multipole ion guide is disposed in a first chamber positioned downstream of the orifice plate. A second multipole ion guide is disposed in a second chamber positioned downstream of the first chamber. A first ion lens is disposed between the first multipole ion guide and the second multipole ion guide. A third multipole ion guide is disposed in a third chamber positioned downstream of the second chamber. A second ion lens is disposed between the second chamber and the third chamber, and an adjustable voltage source is provided for applying an adjustable DC offset voltage between the second multipole ion guide and the second ion lens. The adjustable voltage source may adjust the applied DC voltage to increase the axial kinetic energy of the ions, causing at least one of de-clustering and fragmentation (or both) of at least some of the ions.

[0017] In some embodiments, each of the first, second, and third ion guides may include a plurality of rods arranged to allow the passage of ions therebetween, and the rods may be arranged in a variety of different geometries, such as quadrupoles, hexapoles, decapoles, among others.

[0018] In some embodiments, the first chamber is maintained at a pressure in the range of about 5 Torr to about 15 Torr, the second chamber is maintained at a pressure in the range of about 1 Torr to about 5 Torr, and the third chamber is maintained at a pressure in the range of about 3 mTorr to about 12 mTorr.

[0019] In some embodiments, the adjustable voltage source is configured to vary the applied voltage within a range of about 0 to about 300V, for example, within a range of about 10V to about 140V.

[0020] In some embodiments, at least one of the multiple ion guides, e.g., the second ion guide, is maintained at a DC floating voltage in the range of about −200 V to about +200 V, e.g., about −100 V to about +100 V. In many embodiments, all elements positioned upstream of where de-clustering / fragmentation occurs are floated together at the same voltage. In some such embodiments, a separate voltage source is provided to apply an adjustable DC offset voltage to the multipole ion guide, the second ion lens, or any combination of ion guide and lens. In some such embodiments, the adjustable DC offset voltage can promote fragmentation of at least some of the ions.

[0021] In some embodiments, the mass analyzer may include one or more radio frequency (RF) sources to apply an RF voltage to at least one of the first, second, and third multipole ion guides to radially confine and focus ions as they pass through the ion guide.

[0022] Multipole ion guides can be implemented in a variety of different configurations. For example, they can be implemented as quadrupole, hexapole, or decadipole configurations, or geometries with any number of rods. Ion guides can also be formed by employing rings rather than rods.

[0023] In some embodiments, at least one radio frequency (RF) source applies an RF voltage to at least one of the first, second, and third multipole ion guides to focus ions passing therethrough.

[0024] In a related aspect, a method for mass spectrometric analysis of a sample using a mass spectrometer is disclosed, the spectrometer comprising an orifice plate and three chambers arranged in tandem downstream of the orifice plate, an ion guide positioned in each of the chambers, a first ion lens positioned between the first chamber and the second chamber, and a second ion lens positioned between the second chamber and the third chamber. The method includes ionizing a sample to form a plurality of ions, receiving the plurality of ions through the orifice, passing the ions through the three chambers, and applying a DC offset voltage to at least one of the ion guide and / or ion lens to cause at least one of de-clustering or fragmenting at least some of the ions. In some embodiments, at least some of the ions may be adduct ions.

[0025] In some embodiments, the pressure in the first chamber is maintained in a range from about 5 Torr to about 15 Torr, the pressure in the second chamber is maintained in a range from about 1 Torr to about 5 Torr, and the pressure in the third chamber is maintained in a range from about 3 mTorr to about 12 mTorr.

[0026] A further understanding of various aspects of the present teachings can be obtained by reference to the following detailed description in conjunction with the associated drawings, which are briefly described below. The present invention provides, for example, the following. (Item 1) 1. A mass spectrometer, comprising: an orifice plate having an orifice for receiving a plurality of ions; a first multipole ion guide disposed in a first chamber positioned downstream of the orifice plate; a second multipole ion guide disposed in a second chamber positioned downstream from the first chamber; a first ion lens disposed between the first multipole ion guide and the second multipole ion guide; a third multipole ion guide disposed within a third chamber positioned downstream from the second chamber, the third multipole ion guide comprising a plurality of rods arranged to allow passage of ions therebetween; and a second ion lens disposed between the second chamber and a third chamber; an adjustable DC voltage source for applying an adjustable DC offset voltage to at least one of the first multipole ion guide, the second multipole ion guide, the third multipole ion guide, the first ion lens, and the second ion lens; Equipped with A mass spectrometer wherein applying the adjustable DC offset voltage increases the axial kinetic energy of the ions, causing at least one of de-clustering and fragmentation of at least some of the ions. (Item 2) 2. The mass spectrometer of claim 1, wherein the adjustable DC offset voltage is applied to increase the axial kinetic energy of the ions within a gas expansion region of the second or third multipole ion guide. (Item 3) Item 10. The mass spectrometer of item 1, wherein the diameter of the orifice is at least about 0.6 mm. (Item 4) the adjustable voltage source is configured to vary the applied DC offset voltage within a range of about 0 to about 300 V; Optionally, the adjustable voltage source is configured to vary the applied DC offset voltage within a range of about 0 to about 200V. (Item 5) 2. The mass spectrometer of claim 1, wherein the first chamber is maintained at a pressure within a range of about 5 Torr to about 15 Torr. (Item 6) 6. The mass spectrometer of claim 5, wherein the second chamber is maintained at a pressure within a range of about 1 Torr to about 5 Torr. (Item 7) 7. The mass spectrometer of claim 6, wherein the third chamber is maintained at a pressure within a range of about 3 mTorr to about 12 mTorr. (Item 8) 2. The mass spectrometer of claim 1, wherein any of the first, second, and third multipole ion guides is maintained at a DC floating voltage within a range of about -500V to about 500V. (Item 9) 9. The mass spectrometer of claim 8, further comprising another voltage source for applying the adjustable DC offset voltage to any of the first multipole ion guide, the second multipole ion guide, the third multipole ion guide, and the first and second ion lenses. (Item 10) 10. The mass spectrometer of claim 1, further comprising one or more radio frequency (RF) sources, wherein the one or more RF sources apply an RF voltage to at least one of the first, second, and third multipole ion guides to focus ions passing therethrough. (Item 11) the rods of at least one of the first, second, and third multipole ion guides are arranged in one of a quadrupole, a hexapole, and a decapole configuration; Optionally, the first, second, and third multipole ion guides each comprise a series of stacked rings through which the ions can pass. (Item 12) further comprising an ion source for generating a plurality of ions; Optionally, the ion source comprises an atmospheric pressure ion source. (Item 13) 1. A method of mass spectrometric analysis of a sample using a mass spectrometer, the mass spectrometer comprising an orifice plate and three chambers arranged in tandem downstream of the orifice plate, an ion guide positioned in each of the chambers, a first ion lens positioned between the first chamber and the second chamber, and a second ion lens positioned between the second chamber and the third chamber, the method comprising: ionizing the sample to form a plurality of ions; receiving the ions through the orifice; passing the ions through the three chambers; using a DC offset voltage to increase the axial kinetic energy of said ions, thereby causing at least one of de-clustering and fragmentation of at least some of said ions; A method comprising: (Item 14) Item 14. The method of item 13, wherein the DC offset voltage is applied between the second ion lens and the third chamber. (Item 15) Item 14. The method of item 13, wherein the DC offset voltage is applied between the second ion guide and the second ion lens. (Item 16) Item 14. The method according to item 13, wherein the DC offset voltage is in the range of about 0 to about 200 V. (Item 17) Item 14. The method of item 13, wherein the ions comprise at least adduct ions. (Item 18) Item 14. The method of item 13, further comprising maintaining the first chamber at a pressure within a range of about 5 Torr to about 15 Torr. (Item 19) Item 14. The method of item 13, further comprising maintaining the second chamber at a pressure within a range of about 1 Torr to about 5 Torr. (Item 20) Item 14. The method of item 13, further comprising maintaining the third chamber at a pressure within a range of about 3 mTorr to about 12 mTorr. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a flow diagram depicting various steps in an embodiment of a method for performing mass spectrometric analysis of a sample.

[0028] [Figure 2A] 2A, 2B, and 2C schematically depict a mass spectrometer according to an embodiment of the present teachings. [Figure 2B] 2A, 2B, and 2C schematically depict a mass spectrometer according to an embodiment of the present teachings. [Figure 2C] 2A, 2B, and 2C schematically depict a mass spectrometer according to an embodiment of the present teachings.

[0029] [Figure 3A] 3A and 3B show the mass signals for the protonated codeine e-d3 ion with the acetonitrile adduct and the protonated codeine e-d3 ion, respectively. [Figure 3B] 3A and 3B show the mass signals for the protonated codeine e-d3 ion with the acetonitrile adduct and the protonated codeine e-d3 ion, respectively.

[0030] [Figure 4A] FIG. 4A shows the mass signal for the minoxidil parent ion measured on a triple quadrupole MS / MS instrument.

[0031] [Figure 4B] Figures 4B, 4C, 4D, 4E, and 4F show the mass signals for five different minoxidil daughter ions with increasing collision energy on a triple quadrupole MS / MS instrument. [Figure 4C] Figures 4B, 4C, 4D, 4E, and 4F show the mass signals for five different minoxidil daughter ions with increasing collision energy on a triple quadrupole MS / MS instrument. [Figure 4D] Figures 4B, 4C, 4D, 4E, and 4F show the mass signals for five different minoxidil daughter ions with increasing collision energy on a triple quadrupole MS / MS instrument. [Figure 4E] Figures 4B, 4C, 4D, 4E, and 4F show the mass signals for five different minoxidil daughter ions with increasing collision energy on a triple quadrupole MS / MS instrument. [Figure 4F] Figures 4B, 4C, 4D, 4E, and 4F show the mass signals for five different minoxidil daughter ions with increasing collision energy on a triple quadrupole MS / MS instrument.

[0032] [Figure 4G] FIG. 4G shows the mass signal for the minoxidil parent ion as the DC voltage to increase the axial kinetic energy of the ion is increased from 0 to 140 V.

[0033] [Figure 4H]Figures 4H, 4I, 4J, and 4K show the mass signal emergence for the four different minoxidil daughter ions, concomitant with the signal reduction for the parent ion. [Figure 4I] Figures 4H, 4I, 4J, and 4K show the mass signal emergence for the four different minoxidil daughter ions, concomitant with the signal reduction for the parent ion. [Figure 4J] Figures 4H, 4I, 4J, and 4K show the mass signal emergence for the four different minoxidil daughter ions, concomitant with the signal reduction for the parent ion. [Figure 4K] Figures 4H, 4I, 4J, and 4K show the mass signal emergence for the four different minoxidil daughter ions, concomitant with the signal reduction for the parent ion.

[0034] [Figure 5A] FIG. 5A shows MS / MS data for ketoconazole as a function of ion energy, showing that fragmentation of ketoconazole requires ion energies of 40 eV or higher.

[0035] [Figure 5B] FIG. 5B shows the MS / MS data for two different ketoconazole daughter ions, namely m / z 489.3 and 82.2.

[0036] [Figure 5C] FIG. 5C shows the mass signal for ketoconazole ions for different DC voltages applied in accordance with the present teachings to increase the axial kinetic energy of the ions.

[0037] [Figure 5D] FIG. 5D shows the mass signals for two daughter ions of ketoconazole versus DC voltage applied in accordance with the present teachings in the range of about 40-140 V to increase the axial kinetic energy of the ions.

[0038] [Figure 6A]FIG. 6A shows MS / MS data obtained for taurocholic acid in the collision cell of a triple quadrupole mass spectrometer.

[0039] [Figure 6B] FIG. 6B shows fragmentation data obtained for taurocholic acid by increasing the DC voltage applied in accordance with the present teachings to increase the axial kinetic energy of the ions.

[0040] [Figure 7A] 7A-7D show LC / MS data for samples of taurocholic acid at various levels of cluster separation based on the level of DC voltage applied in accordance with the present teachings. [Figure 7B] 7A-7D show LC / MS data for samples of taurocholic acid at various levels of cluster separation based on the level of DC voltage applied in accordance with the present teachings. [Figure 7C] 7A-7D show LC / MS data for samples of taurocholic acid at various levels of cluster separation based on the level of DC voltage applied in accordance with the present teachings. [Figure 7D] 7A-7D show LC / MS data for samples of taurocholic acid at various levels of cluster separation based on the level of DC voltage applied in accordance with the present teachings.

[0041] [Figure 8] 8A-8C show data acquired in an LC / MS experiment performed with a sample of alprazolam at different DC voltage offsets between the IQ0 lens of the mass spectrometer and the rest of the upstream ion guide, all floated to the same DC voltage. DETAILED DESCRIPTION OF THE INVENTION

[0042] The present disclosure relates to systems and methods for mass analysis in which a DC voltage (also referred to herein as a DC offset voltage) is employed, which generally generates an electric field that can promote at least one of de-clustering or fragmenting at least some of the ions by increasing the axial kinetic energy of ions entering a mass analyzer.

[0043] 1 shows various steps in a method for mass spectrometric analysis of a sample using a mass spectrometer comprising an orifice plate and three chambers arranged in tandem downstream of the orifice plate, with an ion guide positioned in each of the chambers, a first ion lens disposed between the first and second chambers, and a second ion lens disposed between the second and third chambers. The first chamber is maintained at a pressure ranging from about 5 Torr to about 15 Torr, the second chamber is maintained at a pressure ranging from about 1 Torr to about 5 Torr, and the third chamber is maintained at a pressure ranging from about 3 mTorr to about 12 mTorr.

[0044] As depicted in the flow diagram, a sample is ionized to form a plurality of ions. In some embodiments, the plurality of ions can include one or more adduct ions (e.g., solvated ions). The ions are received through an orifice of a mass analyzer. The ions are transmitted through three chambers. Additionally, a DC voltage, e.g., an adjustable DC offset voltage, is applied to at least one of the ion guides and / or at least one of the ion lenses to cause at least one of de-clustering and fragmentation of at least some of the ions in the third chamber.

[0045] 2A and 2B schematically depict a mass spectrometer 100 according to an embodiment, which includes an ion source 22 for generating a plurality of ions 24 from a sample of interest. In this embodiment, the ion source may be an atmospheric pressure ion source. The ions 24 may travel along the general direction indicated by arrow 38 toward a vacuum chamber 26 (also referred to herein as a DJET region) in which a multipole ion guide 36 is positioned. The ions 24 may enter the vacuum chamber 26 through an inlet 28 of the vacuum chamber 26. In this embodiment, a curtain plate 10 and an orifice plate 12 are positioned in front of the inlet 28. The curtain plate 10 and the orifice plate 12 include orifices 10a / 12a through which the ions may pass to reach the vacuum chamber 26.

[0046] In this embodiment, orifices 10a / 12a are large enough to allow incoming ions to enter chamber 26. By way of example, any of orifices 10a / 12a may be substantially circular with a diameter in the range of about 0.6 mm to about 10 mm.

[0047] The ion guide 36 can have a variety of different configurations. By way of example, in some embodiments, the ion guide 36 may be in the form of a quadrupole rod set, while in other embodiments, the ion guide 36 may be in the form of a hexapole or decadupole rod set. More generally, the ion guide 36 may include any number of rods. Furthermore, in some embodiments, the ion guide may be formed by using a series of stacked rings.

[0048] A vacuum pump 42 can apply a negative pressure to chamber 26 and maintain the pressure within the chamber within a desired range. By way of example, in some embodiments, the pressure within chamber 26 can be within a range from about 5 Torr to about 15 Torr.

[0049] A power supply 40 (also referred to herein as a voltage source) applies a radio frequency (RF) voltage to the rods of the ion guide 36 to radially confine and focus the ions 24 as they pass through the ion guide 36.

[0050] An aperture 32 disposed in an ion lens IQ00 positioned downstream of ion guide 36 allows passage of ions from chamber 26 into a downstream chamber 45 (also referred to herein as the QJET region) in which another multipole ion guide 56 is positioned. Vacuum pump 42b applies a negative pressure to chamber 45, and in some embodiments, the pressure within chamber 45 is maintained, for example, in a range from about 1 Torr to about 5 Torr.

[0051] In this embodiment, the multipole ion guide 56 has a quadrupole configuration, while in other embodiments it has other configurations such as a hexapole or decapole configuration, and in other embodiments it may comprise any number of rods or may be formed using a series of stacked rings.

[0052] Voltage source 40, or another voltage source, may apply an RF voltage to the rods of ion guide 56 to radially confine and focus ions 24 as they pass through ion guide 56. Ion lens IQ0 separates chamber 45 from chamber 46. An aperture 11 provided in ion lens IQ0 allows passage of ions 24 from chamber 45 into chamber 46.

[0053] A vacuum pump 42c may be included to apply a negative pressure to chamber 46, maintaining the pressure therein, for example, in the range of about 3 to about 8 millitorr. A multipole ion guide 60 is positioned within chamber 46. Voltage source 40 or another voltage source may apply an RF voltage to the rods of ion guide 60 to radially confine and focus ions 24 as they pass through ion guide 60. As discussed in more detail below, application of an accelerating DC voltage to one or more components positioned upstream of chamber 46 may increase the axial kinetic energy of ions 24, thereby causing de-clustering or fragmentation of at least some of the ions within chamber 45 and / or chamber 46, depending on where the voltage difference is applied.

[0054] A mass analyzer Q1 is disposed in a chamber 47 located downstream of the chamber 46. A vacuum pump 42d applies a negative pressure to the chamber 47, and a -5 The chamber 47 is maintained at a pressure below 1000 psi. In this embodiment, a stubby rod 62 is also positioned within the chamber 47. In this embodiment, the mass analyzer Q1 includes four rods arranged in a quadrupole configuration, although in other embodiments the mass analyzer may be configured according to other configurations, such as time-of-flight (ToF).

[0055] Those skilled in the art will appreciate that pump configurations other than those disclosed herein may be employed in other embodiments. For example, according to some embodiments, a single pump may be employed to eliminate multiple stages of a mass analyzer. Furthermore, in some embodiments, one or more of the vacuum pumps may be omitted entirely to eliminate pumping in a given stage. In some embodiments, pumping may be achieved in any of the stages by employing multiple pumps. For example, pumps 42c and 42d may include a combination of a roughing pump and a turbomolecular pump. It should also be understood that not all mass analyzer components are shown. For example, in some embodiments, the mass analyzer may include a triple quadrupole system with two mass analyzing quadrupoles and a collision cell between them to fragment ions.

[0056] Ion lens IQ1 is disposed between chambers 46 and 47 and focuses ions as they enter chambers 46 and 47. Like the other ion lenses employed in this embodiment, ion lens IQ1 may be formed as a metal plate with orifices provided in the metal plate to allow the passage of ions therethrough. In other embodiments, any of the ion lenses may be formed as a stacked set of plates with orifices that are substantially aligned to allow the passage of ions therethrough.

[0057] In this embodiment, a DC voltage source 50 (e.g., an adjustable DC voltage source) applies a DC voltage difference between the ion lens IQ0 and the rods of the Q0 ion guide, accelerating ions as they pass through an orifice associated with the IQ0 lens and enter the Q0 region. The acceleration of ions increases their axial kinetic energy and may therefore cause de-clustering of at least some of the additional ions present in the ion bundle, if any, and / or fragmentation of at least some of the ions as they enter a subsequent lower pressure region through gas expansion. In this embodiment, the Q0 ion guide is maintained at a floating voltage in the range of about −100 V to about +100 V, e.g., about −10 V in this embodiment (e.g., by using a separate voltage source, not shown). Thus, the DC voltage source 50 provides an additional DC offset potential above the potential applied to the Q0 electrode (which in this embodiment is about −10 V).

[0058] By way of example, the DC voltage source 50 can apply a voltage difference between the ion lens IQ0 and the rods of the Q0 ion guide in a range of about 0 to about 300 V, e.g., in a range of about 10 V to about 200 V, e.g., in a range of about 20 V to about 140 V. The applied DC voltage can be adjusted to cause de-clustering of additional ions present in the ion bundle, if any (without causing significant fragmentation of the ions). Alternatively, the applied DC voltage can be adjusted to cause fragmentation of at least some of the ions. In some such embodiments, at least some of the additional ions and ions not in the form of clusters undergo fragmentation. In some embodiments, a DC voltage applied in the range of about 0 V to about 200 V can be employed to de-cluster the additional ions, and a DC voltage applied in the range of about 0 V to about 400 V can be employed to cause fragmentation of the ions. Alternatively, ions comprising background interferences can be accelerated and fragmented as they enter the Q0 region, improving the signal-to-noise ratio for the compound of interest.

[0059] Downstream Q1 can provide mass analysis of the fragment ion products in a manner known in the art.

[0060] As mentioned above, the applied DC voltage employed to increase the axial kinetic energy of ions can be applied across various components of the mass analyzer positioned upstream of the QO region. By way of example, in another embodiment of the present teachings, voltage source 50 applies a DC voltage difference between the rods of the QJET ion guide (56) and ion lens IQO, accelerating ions within the QJET region and increasing their axial kinetic energy as they approach the IQO lens, thus promoting their de-clustering and / or fragmentation within the QO region or upstream QJET regions. By way of example, as with the previous embodiment, in such an embodiment, the applied DC voltage can be in the range of about 0 to about 200 V, e.g., about 10 V to about 140 V.

[0061] The following examples are provided to further elucidate various aspects of the present teachings and are not intended to limit the scope of the invention.

[0062] (Example) Example 1 - Cluster Separation Figures 3A and 3B show cluster separation data obtained for a sample of codeine e-d3 prepared in 50:50 acetonitrile:water + 5 mM ammonium acetate adjusted to pH 4.5. In addition to the protonated codeine e-d3 ion (m / z 303), an intense peak was observed for the protonated codeine with acetonitrile adduct (m / z 344). For Examples 1-5, DC offset voltages were applied as shown in Figure 2B, with the Q0 ion guide maintained at a floating potential of -10 V and adjustable DC offset potentials applied on the DJET ion guide, IQ00, QJET ion guide, and IQ0. The orifice and curtain plate potentials were optimized separately. The actual potentials applied to the DJET, IQ00, QJET, and IQ0 were -10 V + DC offset potential for analysis of the compounds in positive ion mode. In negative ion mode, the floating potential was +10 V and the potentials applied to DJET, IQ00, QJET, and IQ0 were 10 V minus a DC offset potential.

[0063] A triple quadrupole mass spectrometer similar to that depicted above, including a decadupole ion guide in the first vacuum stage, a quadrupole ion guide in the second vacuum stage, and a quadrupole ion guide in the third vacuum stage, was employed to acquire the data. The pressures in the three vacuum stages were 6 Torr, 2 Torr, and 6 mTorr. Initially, the DC offset voltage was set to 0 V, and all lens elements from the DJET to the Q0 region were maintained at the same potential. Under these conditions, no additional ion heating was expected in the interface region, resulting in a codeine adduct / protonated ion ratio of approximately 29%. At time = 1 min, the DC offset voltage was increased to 10 V, and all lenses from the DJET to the IQ0 were maintained at 0 V, while the Q0 rod was maintained at -10 V. This small offset potential applied between the IQ0 lens and Q0 was sufficient to induce the onset of cluster deconvolution, as evidenced by a decrease in the adduct signal (Figure 3A) and an increase in the signal corresponding to protonated codeine e-d3 (Figure 3B), such that the new adduct / protonated ion ratio was approximately 10.6%.

[0064] An additional 10 V increase in the DC offset potential to 20 V was introduced at time = 2 min, resulting in a further reduction in the number of cluster ions while maintaining the signal level for protonated codeine. The final ratio of clusters / protonated ions was 6.8%.

[0065] Thus, the data presented in Figures 3A and 3B show that increasing the axial kinetic energy of ions, as disclosed herein, can disrupt non-covalent clustering interactions and improve the signal / cluster ion population ratio.

[0066] Example 2 - Fragmentation of ions with low m / z As mentioned above, offset DC voltages as disclosed herein can also be used to fragment ions. Minoxidil is a small molecule and is relatively easy to fragment in an MS / MS instrument. Figures 4A-4F show MS / MS data obtained for minoxidil in the collision cell of a triple quadrupole mass spectrometer (same mass spectrometer used to collect the data presented in Example 1), and Figures 4C-4K show fragmentation data obtained by increasing the DC offset voltage between the IQ0 lens and the Q0 rod in the DJET configuration to activate ions passing into the Q0 region.

[0067] Referring to Figures 4A, 4B, 4C, 4D, 4E, and 4F, minoxidil is readily fragmented in the Q2 collision cell of a triple quadrupole mass spectrometer. Figure 4A shows the signal for the minoxidil ion measured in the Q3 region of the spectrometer. Increasing the collision energy from 5 to 10 eV causes a slight increase in the signal for the minoxidil parent ion. With collision energies higher than 10 eV, significant fragmentation of minoxidil occurs, as evidenced by a decrease in the parent ion signal, with essentially complete elimination of any parent ion signal at ion energies of 35 eV or higher.

[0068] Figures 4B-4F show the mass signals for five different minoxidil daughter ions with increasing collision energy. For the highest m / z daughter ion (m / z 193), its onset and optimal ion energies were 10 eV and 20 eV, respectively. Lower mass daughter ions were generated with higher ion energy settings, as expected. Conversely, Figure 4G shows the minoxidil parent ion as the front-end (DC offset voltage from the IQ0 lens to the Q0 ion guide) DC offset voltage was increased from 0 V to 140 V. The onset of minoxidil fragmentation occurred using a DC offset voltage of approximately 70 V, and the maximum signal for the daughter ions was measured using a DC offset voltage of 80-110 V. Figures 4H, 4I, 4J, and 4K show the onset of signals for the four different minoxidil daughter ions, concomitant with the signal reduction of the parent ion.

[0069] The data presented above in Figures 4A-4K demonstrate that the present teachings are effective in causing fragmentation of ions, such as those requiring low collision energies for dissociation in MS / MS mass spectrometers.

[0070] Example 3 - Fragmentation of ions with intermediate m / z Figures 5A / 5B show MS / MS fragmentation data obtained for ketoconazole in the collision cell of a triple quadrupole mass spectrometer by increasing the collision energy and activating ions passing through the Q2 region. Figure 5A shows that fragmentation of ketoconazole requires ion energies of 40 eV or higher. Figure 5B shows signals for two different ketoconazole daughter ions, namely, daughter ions with m / z of 489.3 and 82.2. The emerging ion energies for m / z 489.3 and m / z 82.2 were 30 eV and 40 eV, respectively.

[0071] 5C / 5D show fragmentation data for ketoconazole when a DC offset voltage was applied between the IQ0 lens and Q0 in accordance with the present teachings. The onset for fragmentation of ketoconazole was approximately 40 V DC offset voltage, and the parent ion signal was essentially eliminated using voltage values ​​above 90 V. Elimination of the parent ion signal, accompanied by an increase in signals associated with two daughter ions, was monitored for this compound. The maximum daughter ion signal was observed with an applied DC offset voltage of approximately 40-110 V.

[0072] Example 4 - Fragmentation of ions requiring high internal energy to dissociate Figures 6A and 6B show MS / MS data obtained for taurocholic acid in the collision cell of a triple quadrupole mass spectrometer and fragmentation data obtained by increasing the potential difference between the IQ0 lens and the Q0 ion guide to activate ions passing into the Q0 region, which was maintained at a pressure of approximately 7 mTorr.

[0073] Referring to Figure 6A, the onset for fragmentation of taurocholic acid occurs at approximately 60 eV, as evidenced by the signal reduction in the black trace. The gray trace shows the signal for the very low m / z daughter ion (m / z = 80), with threshold and optimal collision energies of 60 eV and 130 eV, respectively. The onset for the generation of the m / z 80 daughter ion using the methods disclosed herein was 80 V (Figure 6B), with the maximum daughter ion signal observed using a 100 V DC offset voltage. When the DC offset voltage was increased to 140 V, an approximately two-fold reduction in the parent ion signal was observed for taurocholic acid. Similar to the MS / MS data, the m / z 80 daughter ion requires substantial internal energy to form.

[0074] Example 5 - Cluster Separation to Improve Signal-to-Noise (S / N) Ratio for LC / MS Liquid chromatography-mass spectrometry (LC / MS) experiments were performed using a 1 pg / µL sample of taurocholic acid. The data are presented in Figures 7A-7D. LC / MS experiments were performed at a flow rate of 500 µL / min using a 2.1 mm LC column (C18). All parameters were kept constant for the data in Figures 7A-7D, except that the applied DC offset voltage, between 0 V and 140 V, was adjusted to provide various levels of cluster separation. DC offset voltage settings were 0 V (Figure 8A), 50 V (Figure 8B), 65 V (Figure 8C), and 90 V (Figure 7D).

[0075] When the DC offset voltage was set to 0 V, the peak height for deprotonated taurocholic acid was 75,000 cps and the background continuum was relatively high, resulting in an S / N ratio of 67.5. The DC offset voltage was then increased to 50 V, as shown in Figure 7B. When the DC offset voltage was set to 50 V, there was no significant effect on the intensity of deprotonated taurocholic acid (i.e., the peak height was within 2% of the value measured using a 0 V DC offset voltage). However, there was a substantial reduction in the level of the background continuum, resulting in an S / N ratio of 251.1. These data indicate that improved cluster separation can provide a substantial improvement in detectability for this compound. The DC offset voltage was further increased to 65 V, as shown in Figure 7C. At a DC offset voltage of 65 V, some fragmentation of the parent ion peak appeared. The peak intensity decreased by approximately 34%. However, the background was reduced by a larger margin, resulting in a further improved signal-to-noise ratio. Finally, the applied DC offset voltage was increased to 90 V, as shown in Figure 7D, to induce more fragmentation of the deprotonated taurocholate ion. Under these conditions, the peak intensity decreased by more than 13-fold, resulting in a poor signal-to-noise ratio of 41.

[0076] The data presented in Figures 7A-7D demonstrate that additional improvements in signal-to-noise ratio can be achieved by controlling the DC offset voltage, which causes an increase in the axial kinetic energy of the ions. As shown in Table 1 below, this approach produces reproducible results for repeated LC / MS analyses performed with the DC offset voltage set at either 0 V or 65 V. Use of the cluster separation approach according to the present teachings resulted in an average improvement in signal-to-noise ratio of approximately 3.8 times. [Table 1]

[0077] Example 6 - Fragmentation to reduce / remove interfering peaks for LC / MS For the data presented in Example 6, a DC offset potential was applied, as shown in FIG. 2C, with the IQ0 and Q0 ion guides maintained at a floating voltage of −10 V. DC offset voltages were applied to the DJET ion guide, IQ00, and QJET ion guides, and the curtain plate and orifice plate potentials were optimized separately. The actual potentials applied to the DJET ion guide, IQ00, and QJET ion guides were −10 V + DC offset voltage. Liquid chromatography-mass spectrometry (LC / MS) experiments were performed using a sample of alprazolam at different DC offset voltages between the QJET and IQ0 lenses. In this case, a DC offset voltage was applied after the chamber with the QJET ion guide to increase the axial energy. For this embodiment, the magnitude of the DC offset voltage may need to be increased compared to the previous embodiment, in which a DC offset voltage was applied between IQ0 and Q0. DC offset voltages were applied to the DJET, IQ00, and QJET. The orifice potential was controlled separately and maintained at a more positive potential than the DJET for analysis of ions. The data are depicted in Figures 8A-8C. The shaded peak in the chromatogram is alprazolam, while the peak with an asterisk is an interference. When there is no DC offset between the QJET and IQO (Figure 8A), the interference peak is significantly larger than alprazolam, and under different chromatographic conditions, it may overlap with the alprazolam peak and negatively affect its limit of quantitation. Figures 8B and 8C show the effect of applying 45 V and 50 V DC offset potentials, respectively, between the QJET and IQO. Under these conditions, the interference peak is virtually eliminated, and there is no longer any risk to successful quantitation of alprazolam.

[0078] The present teachings have demonstrated de-clustering and fragmentation using potential offsets between QJET and IQO, and between IQO and QO. It will be apparent to those skilled in the art in view of the present teachings that any means of increasing the axial energy of ions within the QO region can achieve de-clustering and fragmentation as discussed herein. For example, increasing the axial kinetic energy of ions can be achieved by using DC offset potentials between various components of the system.

[0079] Those skilled in the art will appreciate that various modifications can be made to the above-described embodiments without departing from the scope of the present invention.

Claims

1. 1. A mass spectrometer, comprising: an orifice plate having a large sized orifice for receiving a plurality of ions; a first multipole ion guide disposed in a first chamber positioned downstream of the orifice plate; a second multipole ion guide disposed in a second chamber located downstream from the first chamber; a first ion lens disposed between the first multipole ion guide and the second multipole ion guide; a third multipole ion guide disposed in a third chamber located downstream from the second chamber, the third multipole ion guide comprising a plurality of rods arranged to allow the passage of the ions therebetween; and a second ion lens disposed between the second chamber and a third chamber; a mass analyzer disposed in a fourth chamber downstream of the third chamber; at least one DC voltage source configured to apply a DC offset voltage between the second multipole ion guide and the second ion lens, or between the second ion lens and the third multipole ion guide, to increase the axial kinetic energy of the plurality of ions in the third chamber, thereby causing at least one of de-clustering and fragmentation of at least some of the plurality of ions; Equipped with the first chamber is maintained at a pressure within a range of 5 Torr to 15 Torr, the second chamber is maintained at a pressure within a range of 1 Torr to 5 Torr, and the third chamber is maintained at a pressure within a range of 3 mTorr to 12 mTorr; A mass spectrometer wherein the large size orifice has a diameter of at least 0.6 mm.

2. 10. The mass spectrometer of claim 1, wherein the DC offset voltage is applied to increase the axial kinetic energy of the ions within a gas expansion section of the second multipole ion guide or the third multipole ion guide.

3. 2. The mass spectrometer of claim 1, wherein the voltage source is configured to vary the applied DC offset voltage within a range of 0V to 300V.

4. 4. The mass spectrometer of claim 3, wherein the voltage source is configured to vary the applied DC offset voltage within a range of 0V to 200V.

5. 10. The mass spectrometer of claim 1, wherein any of the first multipole ion guide, the second multipole ion guide, and the third multipole ion guide is maintained at a DC floating voltage in the range of −500V to 500V.

6. 6. The mass spectrometer of claim 5, further comprising another voltage source for applying the DC offset voltage to any of the first multipole ion guide, the second multipole ion guide, the third multipole ion guide, the first ion lens, and the second ion lens.

7. 10. The mass spectrometer of claim 1, further comprising one or more radio frequency (RF) sources for applying an RF voltage to at least one of the first, second and third multipole ion guides to focus ions passing through the first, second and third multipole ion guides.

8. 10. The mass spectrometer of claim 1, wherein the plurality of rods of at least one of the first, second and third multipole ion guides are arranged in one of a quadrupole configuration, a hexapole configuration and a decapole configuration.

9. 9. The mass spectrometer of claim 8, wherein the first, second and third multipole ion guides each comprise a series of stacked rings through which the ions can pass.

10. The mass spectrometer of claim 1 , further comprising an ion source for generating a plurality of ions.

11. The mass spectrometer of claim 10 , wherein the ion source comprises an atmospheric pressure ion source.

12. 1. A method for mass spectrometric analysis of a sample using a mass spectrometer, the mass spectrometer comprising an orifice plate and a first chamber, a second chamber and a third chamber arranged in tandem downstream of the orifice plate, the orifice plate having a large sized orifice, a first ion guide, a second ion guide and a third ion guide positioned within the first chamber, the second ion guide and the third ion guide, respectively, a first ion lens positioned between the first chamber and the second chamber, and a second ion lens positioned between the second chamber and the third chamber, the method comprising: maintaining the first chamber at a pressure within a range of 5 Torr to 15 Torr; maintaining the second chamber at a pressure within a range of 1 Torr to 5 Torr; maintaining the third chamber at a pressure within a range of 3 mTorr to 12 mTorr; ionizing the sample to form a plurality of ions; receiving the plurality of ions through the large size orifice; passing the plurality of ions through the first chamber, the second chamber, and the third chamber; applying a DC offset voltage between the second ion guide and the second ion lens or between the second ion lens and the third ion guide to increase the axial kinetic energy of the ions in the third chamber, thereby causing at least one of de-clustering and fragmentation of at least some of the ions; passing at least a portion of the plurality of ions from the third chamber to a mass analyzer downstream of the third chamber; Including, The large size orifice has a diameter of at least 0.6 mm.

13. The method of claim 12, wherein the DC offset voltage is in the range of 0V to 200V.

14. The method of claim 12 , wherein the plurality of ions includes at least an adduct ion.

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