Three-stage atmospheric to vacuum mass spectrometer inlet with additional de-clustering at the third stage

Abstract

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

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 62 / 993,965, filed March 24, 2020, entitled “Three Stage Atmospheric to Vacuum Mass Spectrometer Inlet with Additional De-clustering at Third Stage,” which is incorporated by reference herein in its entirety. TECHNICAL FIELD

[0003] The present teachings relate to systems and methods for mass spectrometry analysis in which a DC offset voltage applied between at least two components of the spectrometer is used to facilitate de-clustering or fragmentation of ions. BACKGROUND

[0004] Mass spectrometry (MS) is an analytical technique used to determine the elemental composition of a test substance, with both qualitative and quantitative applications. MS can be useful for identifying unknown compounds, determining the isotopic composition of elements in a molecule, 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, so the analyte must be converted to charged ions during the sampling process. During the ion formation process, some adduct ions can be formed (e.g., by solvation).

[0005] It is known that an applied voltage between an inlet orifice of a mass spectrometer and a first vacuum lens element (e.g., a skimmer or ion guide) can increase the internal energy of incoming ions and solvated clusters to facilitate de-clustering or fragmentation of the ions. However, the effectiveness of such de-clustering and / or fragmentation decreases as the orifice size increases. For example, for systems with larger orifice sizes, a larger voltage offset is required for effective de-clustering.

[0006] Accordingly, there is a need for improved systems and methods for mass spectrometry analysis that allow for the use of large orifice sizes and at the same time allow for effective de-clustering and / or fragmentation of ions introduced into the mass spectrometer. SUMMARY

[0007] In one aspect, a mass spectrometer is disclosed that includes an orifice plate having an orifice for receiving a plurality of ions, a first multipole ion guide disposed in a first chamber located downstream of the orifice plate, and a second multipole ion guide disposed in a second chamber located 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 located in a third chamber located downstream of the second chamber. A second ion lens is located 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 multipole ion guide, the second multipole ion guide, and the third multipole ion guide and / or at least one of the first ion lens and the second ion lens to increase an axial kinetic energy of the ions to cause at least one of de-clustering and / or fragmentation of at least a portion of the ions.

[0008] In some embodiments, each of the first multipole ion guide, the second multipole ion guide, and the third multipole ion guide includes a plurality of rods arranged to allow ions to pass therebetween. In some embodiments, each of the first multipole ion guide, the second multipole ion guide, and the third multipole ion guide includes a series of stacked rings through which ions can pass.

[0009] In some embodiments, the adjustable DC offset voltage is applied to increase an axial energy of the ions within an expanded region of the second multipole ion guide and the third multipole ion guide.

[0010] In some embodiments, the DC voltage is configured to cause de-clustering of at least some of adduct ions present in the ion stream without causing fragmentation thereof. For example, in some such embodiments, the applied DC voltage can be, for example, in a range of about 0 V to about 300 V, for example, in a range of about 10 V to about 200 V, for example, in a range of about 20 V to about 140 V. In some embodiments, the applied DC voltage can increase an axial kinetic energy of the ions to cause fragmentation of at least a portion of the ions.

[0011] In some embodiments, the orifice has a diameter of at least about 0.6 mm, for example, in a range of about 0.7 mm to about 3 mm, for example, in a range of about 1 mm to about 1.5 mm.

[0012] In some embodiments, the adjustable voltage source is configured to vary the applied DC voltage in a range of 0 to about 300 V, for example, in a range of about 10 V to about 200 V, for example, in a range of about 20 V to about 140 V.

[0013] In some embodiments, the first chamber is maintained at a pressure in a range from about 5 Torr to about 15 Torr. In some such embodiments, the second chamber is maintained at a pressure in a range from about 1 Torr to about 5 Torr. Further, in some embodiments, the third chamber is maintained at a pressure in a range from about 3 mTorr to about 12 mTorr.

[0014] In some embodiments, in addition to the DC offset voltage described above, a DC float voltage can also be applied to any of the first, second, and third multipole ion guides, e.g., in a range from about -10 V to about 10 V (this float voltage can also be a range of different values. For example, on a ToF it can be as high as + / - 500 V). In some embodiments, another voltage source is provided to apply the DC float voltage(s) to these ion guides.

[0015] In some embodiments, the mass spectrometer can include one or more radio frequency (RF) sources for applying an RF voltage(s) to at least one of the first, second, and third multipole rods to focus ions passing therethrough.

[0016] Various ion sources can be employed to generate a plurality of ions. For example, in some embodiments, an atmospheric pressure ion source can be employed.

[0017] In one related aspect, a mass spectrometer is disclosed that includes an orifice plate having an orifice for receiving a plurality of ions, where the orifice has a diameter of at least about 0.6 mm, e.g., in a range from about 0.7 mm to about 3 mm. A first multipole ion guide is disposed in a first chamber downstream of the orifice plate. A second multipole ion guide is disposed in a second chamber 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 downstream of the second chamber. A second ion lens is disposed between the second and third chambers, and an adjustable voltage source is provided for applying an adjustable DC offset voltage offset between the second multipole ion guide and the second ion lens. The adjustable voltage source can adjust the DC voltage applied to increase the axial kinetic energy of the ions, thereby causing at least one of (or both) de-clustering and fragmentation of at least some of the ions.

[0018] In some embodiments, each of the first, second, and third ion guides can include a plurality of rods arranged to allow ions to pass therebetween. These rods can be arranged in various different geometrical configurations, e.g., quadrupole, hexapole, dodecapole, etc.

[0019] In some embodiments, the first chamber is maintained at a pressure in a range from about 5 Torr to about 15 Torr, the second chamber is maintained at a pressure in a range from about 1 Torr to about 5 Torr, and the third chamber is maintained at a pressure in a range from about 3 mTorr to about 12 mTorr.

[0020] In some embodiments, the adjustable voltage source is configured to vary the applied voltage in a range from about 0 to about 300 V, for example, in a range from about 10 V to about 140 V.

[0021] In some embodiments, at least one of the multipole ion guides (e.g., the second ion guide) is maintained at a DC floating voltage in a range from about -200 V to about +200 V (e.g., in a range from about -100 V to about +100 V). In many embodiments, all elements located upstream of the de-clustering / fragmentation occurrence are floated together at the same voltage. In some such embodiments, another voltage source is provided for applying an adjustable DC offset voltage to the multipole ion guide, the second ion lens, or any combination of ion guides and lenses. In some such embodiments, the adjustable DC offset voltage can facilitate fragmentation of at least some of the ions.

[0022] In some embodiments, the mass spectrometer can include one or more radio frequency (RF) sources for applying RF voltage(s) to at least one of the first multipole ion guide, the second multipole ion guide, and the third multipole ion guide for radially confining and focusing ions as they pass through the ion guides.

[0023] The multipole ion guides can be implemented in a variety of different configurations. For example, they can be implemented in a quadrupole, hexapole, dodecapole configuration, or a geometry with any number of rods. The ion guides can also be formed by employing rings instead of rods.

[0024] In some embodiments, at least one radio frequency (RF) source applies RF voltage(s) to at least one of the first multipole ion guide, the second multipole ion guide, and the third multipole ion guide for focusing ions passing therethrough.

[0025] In a related aspect, a method for mass spectrometric analysis of a sample using a mass spectrometer is disclosed, wherein the spectrometer comprises an orifice plate and three chambers disposed in series downstream of the orifice plate, wherein an ion guide is provided in each of the chambers, and wherein a first ion lens is disposed between the first chamber and the second chamber, and a second ion lens is disposed between the second chamber and the third chamber. The method comprises the steps of ionizing a sample to form a plurality of ions, receiving the plurality of ions through the orifice, passing ions through the three chambers, and applying a DC offset voltage to at least one of the ion guides and / or ion lenses, thereby causing at least one of de-clustering or fragmentation of at least some of the ions. In some embodiments, at least some of the ions can be adduct ions.

[0026] In some embodiments, the pressure in the first chamber can be maintained in a range from about 5 Torr to about 15 Torr, the pressure in the second chamber can be maintained in a range from about 1 Torr to about 5 Torr, and the pressure in the third chamber can be maintained in a range from about 3 mTorr to about 12 mTorr.

[0027] A further understanding of the various aspects of the present teachings can be obtained by reference to the following detailed description, taken in connection with the associated drawings described briefly below. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a flowchart depicting various steps in an embodiment of a method for mass spectrometric analysis of a sample,

[0029] Figure 2A , Figure 2B and Figure 2C schematically depicts a mass spectrometer according to an embodiment of the present teachings,

[0030] Figure 3A and Figure 3B show mass signals of protonated codeine-d3 ions with acetonitrile adduct and mass signals of protonated codeine-d3 ions, respectively,

[0031] Figure 4A shows mass signals of minoxidil parent ions measured in a triple quadrupole MS / MS instrument,

[0032] Figure 4B , Figure 4C , Figure 4D , Figure 4E and Figure 4F shows mass signals of 5 different minoxidil daughter ions with increasing collision energy in a triple quadrupole MS / MS instrument,

[0033] Figure 4Gshows the onset of the mass signal of 4 different minoxidil daughter ions coinciding with the signal decrease of the parent ion,

[0034] Figure 4H , Figure 4I , Figure 4J and Figure 4K shows the onset of the mass signal of 4 different minoxidil daughter ions coinciding with the signal decrease of the parent ion,

[0035] Figure 5A shows MS / MS data of ketoconazole as a function of ion energy, indicating that fragmentation of ketoconazole requires an ion energy of 40 eV or higher,

[0036] Figure 5B shows MS / MS data of 2 different ketoconazole daughter ions (i.e. m / z 489.3 and 82.2),

[0037] Figure 5C shows the mass signal of ketoconazole ions at different DC voltages applied according to the present teachings for increasing the axial kinetic energy of the ions,

[0038] Figure 5D shows the mass signal of 2 daughter ions of ketoconazole at DC voltages applied according to the present teachings in the range of about 40 to 140 V for increasing the axial kinetic energy of the ions,

[0039] Figure 6A shows MS / MS data obtained for taurocholic acid in the collision cell of a triple quadrupole mass spectrometer,

[0040] Figure 6B shows fragmentation data obtained for taurocholic acid by increasing the DC voltage applied according to the present teachings for increasing the axial kinetic energy of the ions,

[0041] Figures 7A-7D shows LC / MS data of a taurocholic acid sample at different de-clustering levels based on the level of the DC voltage applied according to the present teachings, and

[0042] Figures 8A-8C shows data obtained in an LC / MS experiment with an alprazolam sample at different DC voltage offsets between the IQ0 lens and the rest of the upstream ion guide of the mass spectrometer, which are both floated to the same DC voltage. DETAILED DESCRIPTION

[0043] The present disclosure relates generally to systems and methods for mass spectrometry analysis in which a DC voltage (also referred to herein as a DC offset voltage) is used to generate an electric field that can increase the axial kinetic energy of ions entering a mass spectrometer in order to facilitate at least one of de-clustering or fragmentation of at least a portion of the ions.

[0044] Figure 1 The flow diagram illustrates various steps in a method for mass spectrometry analysis of a sample using a mass spectrometer comprising an orifice plate and three chambers disposed in series downstream of the orifice plate, wherein an ion guide is provided in each of the chambers, and wherein a first ion lens is disposed between the first chamber and the second chamber, and a second ion lens is disposed between the second chamber and the third chamber. The first chamber is maintained at a pressure in a range from about 5 Torr to about 15 Torr, the second chamber is maintained at a pressure in a range from about 1 Torr to about 5 Torr, and the third chamber is maintained at a pressure in a range from about 3 mTorr to about 12 mTorr.

[0045] 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 the mass spectrometer. The ions are transmitted through the three chambers. Further, 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, thereby causing at least some of the ions to undergo at least one of de-clustering and fragmentation within the third chamber.

[0046] Figure 2A and Figure 2B A mass spectrometer 100 according to an embodiment is schematically depicted, which includes an ion source 22 for generating a plurality of ions 24 from a sample of interest. In the present embodiment, the ion source can be an atmospheric pressure ion source. The ions 24 can travel in a general direction indicated by arrow 38 toward a vacuum chamber 26 (also referred to herein as a DJET region) provided with a multipole ion guide 36. The ions 24 can enter the vacuum chamber 26 through an inlet 28 of the vacuum chamber 26. In the present 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 can pass to reach the vacuum chamber 26.

[0047] In the present embodiment, the orifices 10a / 12a are large enough to allow the incoming ions to enter the chamber 26. By way of example, any of the orifices 10a / 12a can be substantially circular with a diameter in a range from about 0.6 mm to about 10 mm.

[0048] The ion guide 36 can have various different configurations. For example, in some embodiments, the ion guide 36 can be in the form of a quadrupole rod set, while in other embodiments, the ion guide 36 can be in the form of a hexapole rod set or a dodecapole rod set. More generally, the ion guide 36 can include any number of rods. Also, in some embodiments, the ion guide can be formed by using a series of stacked rings.

[0049] The vacuum pump 42 can apply a negative pressure to the chamber 26 to maintain the pressure in the chamber within a desired range. For example, in some embodiments, the pressure within the chamber 26 can be in the range of about 5 Torr to about 15 Torr.

[0050] The power supply 40 (also referred to herein as a voltage supply) applies radio frequency (RF) voltage(s) to the rods of the ion guide 36 for radially restricting and focusing the ions 24 as they pass through the ion guide 36.

[0051] The aperture 32 disposed in the ion lens IQO located downstream of the ion guide 36 allows ions to pass from the chamber 26 into a downstream chamber 45 (also referred to herein as a QJET region) in which another multipole ion guide 56 is disposed. The vacuum pump 42b can apply a negative pressure to the chamber 45 such that, in some embodiments, the pressure within the chamber 45 is maintained in the range of, for example, about 1 Torr to about 5 Torr.

[0052] While in the present embodiment, the multipole ion guide 56 has a quadrupole configuration, in other embodiments, it can have other configurations, such as a hexapole configuration or a dodecapole configuration. In other embodiments, it can include any number of rods or can be formed by using a series of stacked rings.

[0053] The voltage supply 40 or another voltage supply can apply RF voltage(s) to the rods of the ion guide 56 for radially restricting and focusing the ions 24 as they pass through the ion guide 56. The ion lens IQO separates the chamber 45 from the chamber 46. The aperture 11 disposed within the ion lens IQO allows the ions 24 to pass from the chamber 45 into the chamber 46.

[0054] A vacuum pump 42c can be included to apply a negative pressure to the chamber 46, thereby maintaining a pressure within the chamber in a range of, for example, about 3 to about 8 millitorr. A multipole ion guide 60 is located within the chamber 46. The voltage source 40, or another voltage source, can apply RF voltage(s) to the rods of the ion guide 60 for radially confining and focusing the ions 24 as they pass through the ion guide 60. As discussed in greater detail below, application of acceleration DC voltage(s) to one or more components located upstream of the chamber 46 can increase the axial kinetic energy of the ions 24, thereby causing at least a portion of the ions to de-cluster or fragment within the chamber 45 and / or the chamber 46, depending on where the voltage difference is applied.

[0055] A mass analyzer Ql is disposed in a chamber 47 located downstream of the chamber 46. A vacuum pump 42d applies a negative pressure to the chamber 47, thereby maintaining the chamber 47 at a pressure of less than 5e-5 torr. In the present embodiment, a short, stubby rod 62 is also located within the chamber 47. In the present embodiment, the mass analyzer Ql includes four rods arranged in a quadrupole configuration, while in other embodiments, the mass analyzer can be arranged according to other configurations, such as time-of-flight (ToF).

[0056] Those skilled in the relevant art will appreciate that different pumping configurations than those disclosed herein can be employed in other embodiments. For example, a single pump can be employed to pump down multiple stages of the mass spectrometer, according to some embodiments. Further, one or more of the vacuum pumps can be entirely excluded in some embodiments, to eliminate pumping of a given stage. In some embodiments, pumping can be achieved at any stage by use of multiple pumps. For example, the pumps 42c and 42d can comprise a combination of a roughing pump and a turbo-molecular pump. It will also be appreciated that not all mass spectrometer components are shown. For example, in some embodiments, the mass analyzer can comprise a triple quadrupole system having two mass analyzing quadrupoles and a collision cell therebetween for fragmenting ions.

[0057] An ion lens IQl is disposed between the chamber 46 and the chamber 47 to focus ions as they enter the chamber 47 from the chamber 46. Like the other ion lenses employed in the present embodiment, the ion lens IQl can be formed as a metal plate having an aperture disposed therein to allow ions to pass therethrough. In other embodiments, any of the ion lenses can be formed as a stack of plates having apertures that are substantially aligned to allow ions to pass therethrough.

[0058] In this embodiment, DC voltage source 50 (e.g., a tunable DC voltage source) applies a DC voltage difference between the rods of ion lens IQ0 and Q0 ion guide, so as to accelerate ions as they pass through the orifice associated with IQ0 lens into the Q0 region. Acceleration of the ions can increase their axial kinetic energy and thus cause de-clustering of at least some of the adduct ions, if any, present in the ion stream and / or fragmentation of at least some of the ions as they pass through the gas expansion into the subsequent lower pressure region. In this embodiment, Q0 ion guide is held at a floating voltage in the range of about -100 V to about +100 V, e.g., at a floating voltage of about -10 V in this embodiment, (e.g., by use of another voltage source not shown in the figure). Thus, DC voltage source 50 provides an additional DC offset potential above the potential applied to the Q0 electrode (about -10 V in this embodiment).

[0059] For example, DC voltage source 50 can apply a voltage difference between the rods of ion lens IQ0 and Q0 ion guide in the range of about 0 to about 300 V, e.g., in the range of about 10 V to about 200 V, e.g., in the range of about 20 V to about 140 V. The applied DC voltage can be adjusted to cause de-clustering of adduct ions, if any, present in the ion stream without causing significant fragmentation thereof. 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 ions and adduct ions in non-clustered form can undergo fragmentation. In some embodiments, an applied DC voltage in the range of about 0 V to about 200 V can be employed to de-cluster adduct ions, and an applied DC voltage in the range of about 0 V to about 400 V can be employed to fragment ions. Alternatively, ions comprising background interference can be accelerated and fragmented as they enter the Q0 region to improve the signal-to-noise ratio of compounds of interest.

[0060] Downstream Q1 can provide mass analysis of fragment ion products in a manner known in the art.

[0061] As noted above, an applied DC voltage for increasing the axial kinetic energy of ions can be applied across various components of the mass spectrometer located upstream of the Q0 region. For example, in another embodiment of the present teachings, voltage source 50 applies a DC voltage difference between the rods of QJET ion guide (56) and ion lens IQ0, thereby accelerating ions in the QJET region as they approach the IQ0 lens to increase their axial kinetic energy and thus facilitate their de-clustering and / or fragmentation within the Q0 region or upstream QJET region. For example, similar to the foregoing embodiment, in this embodiment the applied DC voltage can be in the range of about 0 to about 200 V, e.g., in the range of about 10 V to about 140 V.

[0062] The following examples are provided to further illustrate various aspects of the present teachings and are not intended to limit the scope of the application.

[0063] Example

[0064] Example 1 - De-clustering

[0065] Figure 3A and Figure 3B De-clustering data obtained for codeine-d3 samples prepared in 50:50 acetonitrile: water + 5 mM ammonium acetate adjusted to pH 4.5 are shown. In addition to the protonated codeine-d3 ion (m / z 303), a strong peak of protonated codeine with acetonitrile adduct (m / z 344) was observed. For Examples 1-5, a DC offset voltage was applied as shown, where the Q0 ion guide was held at a floating potential of -10 V and adjustable DC offset potentials were applied on the DJET ion guide, IQ00, QJET ion guide, and IQ0. The orifice plate potential and curtain plate potential were optimized separately. The actual potentials applied to DJET, IQ00, QJET, and IQ0 were -10 V + DC offset potential for analyzing 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 - DC offset potential. Figure 2B

[0066] A triple quadrupole mass spectrometer similar to the one described above comprising a twelve electrode 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 obtain the data. The pressures in the three vacuum stages were 6 Torr, 2 Torr, and 6 mTorr, respectively. Initially, the DC offset voltage was set to 0 V so that all lens elements from DJET to Q0 region were held at the same potential. Under these conditions, no additional ion heating in the interface region was expected, resulting in a ratio of codeine adduct / protonated ion of about 29%. At time = 1 min, the DC offset voltage was increased to 10 V so that all lenses from DJET to IQ0 were held at 0 V while the Q0 rod was held at -10 V. This small offset potential applied between the IQ0 lens and Q0 was sufficient to initiate de-clustering as evidenced by a decrease in the adduct signal (m / z 344) and an increase in the signal corresponding to protonated codeine-d3 (m / z 303), resulting in a new ratio of adduct / protonated ion of about 10.6%. Figure 3A Figure 3B

[0067] At time = 2 min, the DC offset potential was further increased to 20 V, resulting in a further decrease in the number of cluster ions while maintaining the signal level of protonated codeine. The final ratio of cluster / protonated ion was 6.8%. ​​​

[0068] Thus, Figure 3A and Figure 3B The data presented in Example 2 show that the increase in axial kinetic energy of the ions as disclosed herein can break the non-covalent cluster interactions to increase the ratio of signal / cluster ion population.

[0069] Example 2 - Fragmentation of ions with low m / z

[0070] As mentioned above, the offset DC voltage as disclosed herein can also be used for ion fragmentation. Minoxidil is a small molecule that is relatively easy to fragment in MS / MS instruments. Figures 4A-4F 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) is shown, and Figures 4C-4K Fragmentation data obtained by increasing the DC offset voltage in the DJET configuration between the IQ0 lens and the Q0 rod to activate ions into the Q0 region is shown.

[0071] Referring to Figure 4A , Figure 4B , Figure 4C , Figure 4D , Figure 4E and Figure 4F Minoxidil is easy to fragment in the q2 collision cell of a triple quadrupole mass spectrometer. Figure 4A The signal of minoxidil ions measured in the Q3 region of the spectrometer is shown. Increasing the collision energy from 5 eV to 10 eV results in a slight increase in the signal of the minoxidil parent ion. When the collision energy is higher than 10 eV, significant fragmentation of minoxidil occurs, as evidenced by the decrease in the parent ion signal, essentially eliminating any parent ion signal at 35 eV or higher ion energies.

[0072] Figures 4B-4F The mass signal of 5 different minoxidil daughter ions as the collision energy is increased is shown. In the case of the highest m / z daughter ion (m / z 193), the onset ion energy and the optimal ion energy are 10 eV and 20 eV, respectively. As expected, using higher ion energy settings generates daughter ions of lower mass. Conversely, Figure 4G The minoxidil parent ion as the front-end (DC offset voltage from the IQ0 lens to the Q0 ion guide) DC offset voltage is increased from 0 V to 140 V is shown. The onset of minoxidil fragmentation is evident at a DC offset voltage of about 70 V, and the maximum signal of the daughter ions is measured at a DC offset voltage of 80-110 V. Figure 4H , Figure 4I , Figure 4J and Figure 4K The onset of the signal of 4 different minoxidil daughter ions is shown, occurring simultaneously with the decrease in the signal of the parent ion.

[0073] above Figures 4A-4K The data presented demonstrate that this teaching is effective in inducing ion fragmentation (such as those requiring low collision energies for dissociation in MS / MS mass spectrometry).

[0074] Example 3 - (Fragmentation of ions with moderate m / z)

[0075] Figure 5A / Figure 5B MS / MS fragmentation data for ketoconazole were obtained in the collision cell of a triple quadrupole mass spectrometer by increasing the collision energy to activate ions passing through the Q2 region. Figure 5A This indicates that the fragmentation of ketoconazole requires ionic energies of 40 eV or higher. Figure 5B The signals for two different ketoconazole daughter ions (i.e., the daughter ion with m / z 489.3 and the daughter ion with m / z 82.2) are shown. The starting ion energies for m / z 489.3 and m / z 82.2 are 30 eV and 40 eV, respectively.

[0076] Figure 5C / Figure 5D The fragmentation data of ketoconazole when a DC offset voltage is applied between the IQ0 lens and Q0, according to this teaching, are shown. Ketoconazole fragmentation begins at approximately 40V DC offset voltage, and the precursor ion signal is essentially eliminated when the voltage value exceeds 90V. The elimination of the precursor ion signal and the increase in the signal associated with the two seed ions monitored for this compound occur simultaneously. The maximum seed ion signal is observed when a DC offset voltage of approximately 40–110V is applied.

[0077] Example 4 - (Fragmentation of ions requiring high internal energy for dissociation)

[0078] Figure 6A and Figure 6B MS / MS data for taurocholic acid obtained in the collision cell of a triple quadrupole mass spectrometer are shown, along with fragmentation data obtained by increasing the potential difference between the IQ0 lens and the Q0 ion director to activate ions entering the Q0 region. The Q0 region was maintained at a pressure of approximately 7 mTorr.

[0079] refer to Figure 6A The fragmentation of taurocholic acid begins at approximately 60 eV, as evidenced by the signal decrease in the black trace. The gray trace shows the signal for very low m / z daughter ions (m / z = 80), where the threshold collision energy and the optimum collision energy are 60 eV and 130 eV, respectively. The method disclosed herein produces daughter ions with an m / z of 80 starting at 80 V (… Figure 6B), the maximum daughter ion signal was observed at a DC offset voltage of 100 V. When the DC offset voltage was increased to 140 V, the parent ion signal of taurocholic acid was observed to decrease by about a factor of 2. Similar to the MS / MS data, a large amount of internal energy was required to produce the m / z 80 daughter ion.

[0080] Example 5 - De-clustering to improve the signal-to-noise (S / N) ratio of LC / MS

[0081] A sample of 1 pg / μL taurocholic acid was used for liquid chromatography-mass spectrometry (LC / MS) experiments. The data are presented in Figures 7A-7D . The LC / MS experiments were performed using a 2.1 mm LC column (C18) at a flow rate of 500 μL / min. All parameters were kept constant for the data in Figures 7A-7D except that the DC offset voltage applied between 0 V and 140 V was adjusted to provide different levels of de-clustering. The DC offset voltage was set to 0 V Figure 8A ), 50 V Figure 8B ), 65 V Figure 8C ), and 90 V Figure 7D .

[0082] When the DC offset voltage was set to 0 V, the peak height of the deprotonated taurocholic acid was 75000 cps, and the background continuum was relatively high, resulting in an S / N ratio of 67.5. Then, as shown in Figure 7B , the DC offset voltage was increased to 50 V. When the DC offset voltage was set to 50 V, there was no significant effect on the intensity of the deprotonated taurocholic acid (i.e., the peak height was within 2% of the value measured at a 0 V DC offset voltage). However, the level of the background continuum was substantially decreased, resulting in an S / N ratio of 251.1. These data indicate that improved de-clustering can provide a significant improvement in detectability for this compound. As shown in Figure 7C , the DC offset voltage was further increased to 65 V. At a DC offset voltage of 65 V, some fragmentation of the parent ion peak was evident. The peak intensity decreased by about 34%; however, the background decreased by a greater amount, further improving the S / N ratio. Finally, as shown in Figure 7D , the applied DC offset voltage was increased to 90 V to induce more fragmentation of the deprotonated taurocholic acid ion. Under these conditions, the peak intensity decreased by more than a factor of 13, resulting in a difference S / N ratio of 41.

[0083] Figures 7A-7DThe data presented indicate that an additional improvement in the S / N ratio can be achieved by controlling the DC offset voltage, which leads to an increase in the ionic axial kinetic energy. As shown in Table 1 below, this method yields reproducible results from repeated LC / MS analyses performed with the DC offset voltage set to 0V or 65V. The use of the declustering method according to this teaching results in an average improvement in the S / N ratio of approximately 3.8-fold.

[0084] Table 1

[0085] Number of injections DC offset voltage = 0 V DC offset voltage = 65 V 1 73.1 286 2 78.2 316 3 82.5 306 4 89.8 309 Average 81+ / -7 304+ / -13

[0086] Example 6 - (Fragmentation to reduce / remove interfering peaks in LC / MS)

[0087] For the data presented in Example 6, such as Figure 2C The diagram shows the application of a DC offset potential, with the IQ0 and Q0 ion directors maintained at a floating voltage of -10V. A DC offset voltage was applied to the DJET ion director, IQ00, and QJET ion director, and the curtain plate potential and orifice plate potential were optimized, respectively. The actual potential applied to the DJET ion director, IQ00, and QJET ion director was -10V + DC offset voltage. Liquid chromatography-mass spectrometry (LC / MS) experiments were performed with alprazolam samples at different DC offset voltages between the QJET and IQ0 lenses. In this case, the DC offset voltage was applied to the rear of the chamber with the QJET ion director to increase the axial energy. For this embodiment, it may be necessary to increase the magnitude of the DC offset voltage compared to the previous embodiment where 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 individually controlled and maintained at a potential more positive than that of the DJET for ion analysis. Data is plotted in... Figures 8A-8C In the chromatogram, the shaded peak is alprazolam, while the asterisked peaks are interferences. When there is no DC offset between QJET and IQ0 ( Figure 8A The interfering peak is significantly larger than that of alprazolam; under different chromatographic conditions, it may overlap with the alprazolam peak and have a negative impact on its quantitative limit. Figure 8B and Figure 8C The effects of applying 45V and 50V DC offset potentials between QJET and IQ0 are shown, respectively. Under these conditions, the interfering peaks are effectively removed and no longer pose a risk to the accurate quantification of alprazolam.

[0088] The present teachings have demonstrated de-clustering and fragmentation using QJET and IQ0, as well as a potential offset between IQ0 and Q0. In view of the present teachings, one of ordinary skill in the art will appreciate that any means of increasing the axial energy of ions into the Q0 region can achieve de-clustering and fragmentation as discussed herein. For example, the increase in axial kinetic energy of the ions can be achieved by using DC offset potentials between various components of the system.

[0089] One of ordinary skill in the art will appreciate that various changes can be made to the above-described embodiments without departing from the scope of the present application.

Claims

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 downstream of the orifice plate, a second multipole ion guide disposed in a second chamber downstream of 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 downstream of the second chamber, the third multipole ion guide comprising a plurality of rods arranged to allow the plurality of ions to pass therebetween, a second ion lens disposed between the second chamber and the third chamber, a mass analyzer disposed in a fourth chamber downstream of the third chamber, the mass analyzer comprising a collision cell for fragmenting ions, and at least one adjustable DC voltage source configured to apply an adjustable 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, thereby increasing an axial kinetic energy of the plurality of ions to cause at least one of de-clustering and fragmentation of at least a portion of the plurality of ions in the third chamber, wherein the first chamber is maintained at a pressure in a range of 5 Torr to 15 Torr, the second chamber is maintained at a pressure in a range of 1 Torr to 5 Torr, and the third chamber is maintained at a pressure in a range of 3 mTorr to 12 mTorr.

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

3. The mass spectrometer of claim 1, wherein, A diameter of the orifice is at least 0.6 mm.

4. The mass spectrometer of claim 1, wherein, The at least one adjustable DC voltage source is configured to vary the adjustable DC offset voltage applied in a range of 0 to 300 V.

5. The mass spectrometer of claim 1, wherein, The at least one adjustable DC voltage source is configured to vary the adjustable DC offset voltage applied in a range of 0 to 200 V.

6. 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 a range of -500 V to 500 V.

7. The mass spectrometer of claim 6, wherein, The at least one adjustable DC voltage source comprises a first voltage source for applying the adjustable DC offset voltage between the second multipole ion guide and the second ion lens and a second voltage source for applying the adjustable DC offset voltage between the second ion lens and the third multipole ion guide.

8. The mass spectrometer of claim 1, further comprising one or more radio frequency (RF) sources for applying one or more RF voltages to at least one of the first multipole ion guide, the second multipole ion guide, and the third multipole ion guide for focusing the plurality of ions passing therethrough.

9. The mass spectrometer of claim 1, wherein, The plurality of rods of at least one of the first multipole ion guide, the second multipole ion guide, and the third multipole ion guide are arranged in any one of a quadrupole configuration, a hexapole configuration, and a dodecapole configuration.

10. The mass spectrometer of claim 1, wherein, Each of the first, second, and third multipole ion guides includes a series of stacked rings through which ions can pass.

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

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

13. A method for mass spectrometric analysis of a sample using a mass spectrometer comprising an orifice plate and first, second, and third chambers disposed in series downstream of the orifice plate, wherein first, second, and third ion guides are located in the first, second, and third chambers, respectively, and wherein a first ion lens is disposed between the first and second chambers and a second ion lens is disposed between the second and third chambers, the method comprising: maintaining the first chamber at a pressure in the range of 5 to 15 Torr, maintaining the second chamber at a pressure in the range of 1 to 5 Torr, maintaining the third chamber at a pressure in the range of 3 to 12 mTorr, ionizing the sample to form a plurality of ions, receiving the plurality of ions through an orifice of the orifice plate, passing the plurality of ions through the first, second, and third chambers, 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 plurality of ions to cause at least one of de-clustering and fragmentation of at least some of the plurality of ions within the third chamber, and passing at least a portion of the plurality of ions from the third chamber to a mass analyzer downstream of the third chamber, the mass analyzer comprising a collision cell for fragmenting ions.

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

15. The method of claim 13, wherein, The plurality of ions comprises at least one adduct ion. The DC offset voltage is in the range of 0 and 200 V. The plurality of ions comprises at least one adduct ion.

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