A collision-induced dissociation method in an ion trap mass spectrometer

Abstract

The present invention discloses a collision-induced dissociation method for an ion trap mass spectrometer. In a continuous-injection ion trap mass spectrometer, the electric field at the ion trap entrance is altered by varying the DC voltages on the x and y electrodes of the ion trap, thereby increasing the radial displacement of ions within the trap. This energy is then converted from the radio frequency field into internal energy through collisions, leading to collision-induced dissociation. This method can rapidly switch between collision-induced dissociation and fragmentation by regulating the DC voltages on the ion trap electrodes, controlling the degree of fragmentation and obtaining information on multiple characteristic fragment ions simultaneously, thereby improving qualitative accuracy.

Description

Technical Field

[0001] The present invention relates to the field of mass spectrometry analysis methods, and more specifically, to a collision-induced dissociation method in an ion trap mass spectrometer. This method, by simply regulating the voltage difference between an aperture electrode and a front cover electrode, as well as the DC voltage difference between the front cover electrode and the x- and y-counter electrodes of the ion trap, causes ions to enter a region with a strong radio frequency field, undergo radio frequency heating, and ultimately undergo collision-induced dissociation. By regulating the pressure difference, the degree of fragmentation in collision-induced dissociation can be adjusted, and multiple levels of fragment ions can be obtained in a single test, which is beneficial for improving qualitative accuracy and enabling structural analysis of unknown compounds. Background Art

[0002] Tandem mass spectrometry is a key technique used in mass spectrometry for analyzing isomers and isobaric compounds. A key feature of ion trap mass spectrometry is its ability to perform temporal tandem mass spectrometry, primarily through collision-induced dissociation (CID). Collision-induced dissociation techniques are primarily categorized into resonant CID and non-resonant CID.

[0003] Resonant collision-induced dissociation (RCI) is achieved through ion screening, using an auxiliary resonant excitation voltage (AC) to excite ions and ultimately induce dissociation. However, the sample information obtained in a single run is relatively limited. To address this issue, Snyder et al. achieved multi-generational fragmentation in an ion trap by reversely scanning the main radio frequency (RF) amplitude during the CID process (Snyder, DT; Cooks, RG. J. Am. Soc. Mass Spectrom. 2016, 27, 1914-1921). Researchers have developed non-resonant induced dissociation methods to obtain multiple characteristic fragment ions in a single detection. For example, in a micro-ion trap, by applying a voltage to the discontinuous atmospheric pressure interface (DAPI) inlet capillary, an accelerating electric field is generated at the DAPI outlet, causing the precursor ions to undergo rapid dissociation and further accelerating and dissociating the initially formed fragments (Gao, L.; Li, G.; Cooks, RG. J. Am. Soc. Mass Spectrom. 2010, 21, 209-214). McLuckey et al. developed a dipole direct current (DDC) collision activation technique in a three-dimensional ion trap, in which a DC voltage from opposite electrodes is applied to the corresponding end cap electrodes. This causes ions to move from the center to a region of strong radio frequency field, thereby subjecting the stored ions to a wide range of radio frequency heating (Prentice, BM; McLuckey, SA Am. Soc. Mass Spectrom. 2012, 23, 736-744).

[0004] At present, the non-resonant collision-induced dissociation method based on a miniature continuous injection ion trap mass spectrometer has not been reported, and resonant collision-induced dissociation to obtain multiple characteristic fragment ions requires repeated ion screening and resonance processes, which is complicated to operate. Summary of the Invention

[0005] The present invention discloses a collision-induced dissociation method for an ion trap mass spectrometer. In a continuous-injection ion trap mass spectrometer, the electric field at the ion trap entrance is altered by varying the DC voltages on the x and y electrodes of the ion trap, thereby increasing the radial displacement of ions within the trap. This energy is then converted from the radio frequency field into internal energy through collisions, leading to collision-induced dissociation. This method can rapidly switch between collision-induced dissociation and fragmentation by regulating the DC voltages on the ion trap electrodes, controlling the degree of fragmentation and obtaining information on multiple characteristic fragment ions simultaneously, thereby improving qualitative accuracy.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The object of the present invention is to provide a collision-induced dissociation method in an ion trap mass spectrometer that is simple to operate.

[0008] In order to achieve the above objectives, the technical solution adopted by the present invention is:

[0009] A collision-induced dissociation method in an ion trap mass spectrometer,

[0010] The ion trap mass spectrometer comprises an injection capillary 1, a first-stage vacuum chamber 3, and a second-stage vacuum chamber 11;

[0011] The first-stage vacuum cavity 3 and the second-stage vacuum cavity 11 are respectively connected to the air inlet of the mechanical pump 14 through pipelines, and the second-stage vacuum cavity 11 is connected to the air inlet of the molecular pump 15 through pipelines.

[0012] The first-stage vacuum chamber 3 is provided with a vacuum ultraviolet lamp 2 and an ion transmission hexapole 4;

[0013] The second-stage vacuum chamber 11 is provided with a lens electrode 6, a front cover electrode 7, an ion trap electrode 8, a rear cover electrode 9, and an ion detector 10 in sequence; the ion trap electrode 8 is composed of parallel and spaced flat x-pair electrodes 12 and parallel and spaced flat y-pair electrodes 13, and the normals of the electrode surfaces of the x-pair electrodes 12 and the y-pair electrodes 13 are perpendicular to each other; the distance between the x-pair electrodes 12 is 8-10 mm, and the distance between the y-pair electrodes 13 is 10-12 mm.

[0014] The first-stage vacuum cavity 3 and the second-stage vacuum cavity 11 are connected through the opening electrode 5 to achieve vacuum difference;

[0015] The voltages applied to the ion transmission hexapole 4 are a radio frequency voltage RF1 and a direct current voltage V1, the voltage applied to the aperture electrode (which is a plate-shaped electrode with a middle hole) 5 is a constant direct current voltage V2, the voltage applied to the lens voltage 6 is a constant direct current voltage V3, the voltage applied to the front end cover electrode 7 is a time-varying direct current voltage, the voltage is V4 during injection, and the voltage is V5 during other periods except injection; the voltage applied to the x counter electrode 12 is the auxiliary resonance excitation radio frequency voltage AC plus a direct current voltage V6, the voltage applied to the y counter electrode 13 is the main radio frequency voltage RF2 plus a direct current voltage V6 that is the same as that of the x counter electrode 12, and the voltage applied to the rear end cover electrode 9 is a constant direct current voltage V7;

[0016] The sample enters the first-stage vacuum chamber 11 through the injection capillary 1, is ionized by the vacuum ultraviolet lamp 2, is focused by the ion transmission hexapole 4, and then enters the internal space of the ion trap electrode 8 through the aperture electrode 5, the lens electrode 6, and the inner middle hole of the front cover electrode 7. Collision-induced dissociation is achieved by regulating the voltage.

[0017] Collision-induced dissociation can be achieved in one of two ways:

[0018] Keep V4 unchanged when the front cover electrode 7 is injected, reduce the DC voltage V6 on the x counter electrode 12 and the y counter electrode 13, and increase the voltage difference between V4 and V6 to more than 8V;

[0019] When the front cover electrode 7 is injected, V4 remains unchanged, the voltage difference between V4 and V6 is less than 8V, and the DC voltage V2 on the opening electrode 5 is increased, and the voltage difference between V2 and V4 is increased to greater than 10V.

[0020] The DC voltage V6 of the x counter electrode 12 and the y counter electrode 13 is set to -3 to -5 V when there is no collision-induced dissociation;

[0021] The collision-induced dissociation mode was set to -2 to -60 V, and V6 was adjusted according to the different energies required for collision-induced dissociation of different substances;

[0022] The frequency of the radio frequency voltage RF2 of the x counter electrode 12 and the y counter electrode 13 is fixed, and the amplitude of RF2 is adjustable from 200 to 400 Vpp during sample injection.

[0023] When the front cover electrode 7 is injected, V4 is set to -10-0V; and V6 is set to 50-150V in other periods except injection.

[0024] The voltage V2 of the aperture electrode 5 was set to 0-30 V, 0-2 V in the absence of collision-induced dissociation, and 2-30 V in the collision-induced dissociation mode.

[0025] In order to ensure smooth ion transmission, the DC voltage V1 on the ion transmission hexapole 4 is greater than the voltage V2 applied to the aperture electrode 5. The amplitude of the ion transmission multipole radio frequency voltage RF1 is 200-500 Vpp.

[0026] In order to ensure smooth transmission of ions, the DC voltage V3 on the lens electrode 6 is smaller than the DC voltage V4 on the aperture electrode 5 .

[0027] The voltage V7 applied to the rear end cover electrode 9 is equal to the voltage V5 applied to the front end cover electrode 7 during other periods except when injecting a sample.

[0028] The injection capillary 1 can be one or more of a metal capillary, a PEEK capillary and a quartz capillary.

[0029] The advantages of the present invention are:

[0030] 1. The outstanding advantage of the present invention is that the collision-induced dissociation of ions is achieved by adjusting the voltage difference between the aperture electrode and the front cover electrode and the DC voltage difference between the front cover electrode and the x-pair electrode and the y-pair electrode, and the operation is simple.

[0031] 2. The degree of fragmentation of collision-induced dissociation can be controlled by changing the voltage difference.

[0032] 3. Multiple characteristic fragment ions can be obtained in one detection, which is beneficial to improve the accuracy of qualitative analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0034] Figure 1 It is a structural schematic diagram of the present invention;

[0035] Figure 2 The mass spectrum of styrene is tested by changing the voltage difference between the front cover electrode and the x-counter electrode and the y-counter electrode;

[0036] Figure 3 The mass spectra of multiple triethyl phosphate characteristic fragment ions and characteristic ion distribution changes are obtained at one time;

[0037] Figure 4 is the trend of the fragmentation degree changing with the voltage difference between the opening electrode and the front cover electrode.

[0038] Among them, 1 is the injection capillary, 2 is the vacuum ultraviolet lamp, 3 is the first-stage vacuum chamber, 4 is the ion transmission hexapole, 5 is the opening electrode, 6 is the lens electrode, 7 is the front cover electrode, 8 is the ion trap electrode, 9 is the rear cover electrode, 10 is the ion detector, 11 is the second-stage vacuum chamber, 12 is the x-counter electrode, and 13 is the y-counter electrode. DETAILED DESCRIPTION

[0039] A collision-induced dissociation method in an ion trap mass spectrometer,

[0040] The ion trap mass spectrometer comprises an injection capillary 1, a first-stage vacuum chamber 3, and a second-stage vacuum chamber 11;

[0041] The first-stage vacuum cavity 3 and the second-stage vacuum cavity 11 are respectively connected to the air inlet of the mechanical pump 14 through pipelines, and the second-stage vacuum cavity 11 is connected to the air inlet of the molecular pump 15 through pipelines.

[0042] The first-stage vacuum chamber 3 is provided with a vacuum ultraviolet lamp 2 and an ion transmission hexapole 4;

[0043] The second-stage vacuum chamber 11 is provided with a lens electrode 6, a front cover electrode 7, an ion trap electrode 8, a rear cover electrode 9, and an ion detector 10 in sequence; the ion trap electrode 8 is composed of x-pair electrodes 12 and y-pair electrodes 13 arranged in parallel and spaced apart, and the normals of the electrode surfaces of the x-pair electrodes 12 and the y-pair electrodes 13 are perpendicular to each other; the distance between the x-pair electrodes (12) is 8 mm, and the distance between the y-pair electrodes (13) is 10 mm.

[0044] The first-stage vacuum cavity 3 and the second-stage vacuum cavity 11 are connected through the opening electrode 5 to achieve vacuum difference;

[0045] The voltages applied to the ion transmission hexapole 4 are a radio frequency voltage RF1 and a direct current voltage V1, the voltage applied to the aperture electrode 5 is a constant direct current voltage V2, the voltage applied to the lens voltage 6 is a constant direct current voltage V3, the voltage applied to the front end cover electrode 7 is a time-varying direct current voltage, the voltage is V4 during injection, and the voltage is V5 during other periods except injection; the voltage applied to the x counter electrode 12 is an auxiliary resonance excitation radio frequency voltage AC plus a direct current voltage V6, the voltage applied to the y counter electrode 13 is a main radio frequency voltage RF2 plus a direct current voltage V6 that is the same as that of the x counter electrode 12, and the voltage applied to the rear end cover electrode 9 is a constant direct current voltage V7;

[0046] Collision-induced dissociation can be achieved in one of two ways:

[0047] Keep V4 unchanged when the front cover electrode 7 is injected, reduce the DC voltage V6 on the x counter electrode 12 and the y counter electrode 13, and increase the voltage difference between V4 and V6 to more than 8V;

[0048] When the front cover electrode 7 is injected, V4 remains unchanged, the voltage difference between V4 and V6 is less than 8V, and the DC voltage V2 on the opening electrode 5 is increased, and the voltage difference between V2 and V4 is increased to greater than 10V.

[0049] The DC voltage V6 of the x counter electrode 12 and the y counter electrode 13 is set to -3 to -5 V when there is no collision-induced dissociation;

[0050] The collision-induced dissociation mode was set to -2 to -60 V, and V6 was adjusted according to the different energies required for collision-induced dissociation of different substances;

[0051] The frequency of the radio frequency voltage RF2 of the x counter electrode 12 and the y counter electrode 13 is fixed, and the amplitude of RF2 is 400 Vpp during sample injection.

[0052] When the front cover electrode 7 is injecting a sample, V4 is set to -2V; and V6 is set to 100V during other periods except the injection.

[0053] The voltage V2 of the aperture electrode 5 was set to 0-30 V, 0-2 V in the absence of collision-induced dissociation, and 2-30 V in the collision-induced dissociation mode.

[0054] In order to ensure smooth ion transmission, the DC voltage V1 on the ion transmission hexapole 4 is greater than the voltage V2 applied to the aperture electrode 5. The amplitude of the ion transmission multipole radio frequency voltage RF1 is 400 Vpp.

[0055] In order to ensure smooth transmission of ions, the DC voltage V3 on the lens electrode 6 is smaller than the DC voltage V4 on the aperture electrode 5 .

[0056] The voltage V7 applied to the rear end cover electrode 9 is equal to the voltage V5 applied to the front end cover electrode 7 during other periods except when injecting a sample.

[0057] The injection capillary 1 is a metal capillary.

[0058] The sample enters the first-stage vacuum chamber 11 through the injection capillary 1, is ionized by the vacuum ultraviolet lamp 2, is focused by the ion transfer hexapole 4, and then enters the internal space of the ion trap electrode 8 through the inner hole of the opening electrode 5, the lens electrode 6, and the front cover electrode 7. Collision-induced dissociation is achieved by regulating the voltage.

[0059] The first fragmentation mode: V1 is 2V, V2 is 2V, V3 is 0V, V4 is -2V, V5 is 100V, V6 is -5V when there is no fragmentation, V6 is -20V when there is fragmentation, V7 is 100V. RF1 amplitude is 400V pp , frequency is 2.4MHz, RF2 amplitude is 300V pp , the frequency is 914kHz.

[0060] The second fragmentation mode: V1 is 2V when there is no fragmentation, V1 is 18V when there is fragmentation, V2 is 2V when there is no fragmentation, V2 is 18V when there is fragmentation, V3 is 0V, V4 is -2V, V5 is 100V, V6 is -5V, and V7 is 100V.

[0061] RF1 amplitude is 400V pp , frequency is 2.4MHz, RF2 amplitude is 300V pp , the frequency is 914kHz.

[0062] Example 1

[0063] The DC voltage difference between the front cover electrode and the x-counter electrode and the y-counter electrode is adjusted to detect styrene.

[0064] Styrene enters the first-stage vacuum chamber 11 through the injection capillary 1. It is ionized by the vacuum ultraviolet lamp 2 and focused by the ion transfer hexapole 4. It then passes through the aperture electrode 5, the lens electrode 6, and the inner hole of the front cover electrode 7 into the interior space of the ion trap electrode 8. Collision-induced dissociation is achieved by voltage regulation. Collision-induced dissociation is achieved using the first fragmentation method, with V1 set to 2V, V2 to 2V, V3 to 0V, V4 to -2V, V5 to 100V, and V7 to 100V. RF1 has an amplitude of 400Vpp and a frequency of 2.4MHz, while RF2 has an amplitude of 300Vpp and a frequency of 914kHz. Styrene is detected when V6 is set to -5V and -20V, or when the voltage difference between V4 and V6 is 3V and 18V. No fragment ions are generated when the voltage difference between V4 and V6 is 3V, while a large number of fragment ions are generated when the voltage difference is 18V.

[0065] Example 2

[0066] Obtain multiple mass spectra of triethyl phosphate characteristic fragment ions and characteristic ion distribution changes at one time

[0067] Triethyl phosphate enters the first-stage vacuum chamber 11 through the injection capillary 1. It is ionized by the vacuum ultraviolet lamp 2 and focused by the ion transfer hexapole 4. It then passes through the aperture electrode 5, the lens electrode 6, and the inner hole of the front cover electrode 7 into the interior space of the ion trap electrode 8. Collision-induced dissociation (CID) is achieved by voltage regulation. The first fragmentation mode is used for CID, with V1 set to 2V, V2 to 2V, V3 to 0V, V4 to -2V, V5 to 100V, and V7 to 100V. RF1 has an amplitude of 400Vpp and a frequency of 2.4MHz, while RF2 has an amplitude of 300Vpp and a frequency of 914kHz. V6 is adjusted to -5V, -10V, -15V, -20V, and -25V, i.e., the voltage difference between V4 and V6 is adjusted to 3V, 8V, 13V, 18V, and 23V. Triethyl phosphate has no fragments when the pressure difference is 3V. As the pressure difference increases, fragments gradually appear and the proportion of fragments gradually increases. At the same time, the proportion of fragments with 3 ethyl groups removed gradually increases and eventually becomes the main fragment ion.

[0068] Example 3

[0069] Variation trend of styrene fragmentation degree with the voltage difference between the opening electrode and the front cover electrode

[0070] Styrene enters the first-stage vacuum chamber 11 through the injection capillary 1. It is ionized by the vacuum ultraviolet lamp 2 and focused by the ion transfer hexapole 4. It then passes through the aperture electrode 5, the lens electrode 6, and the inner hole of the front cover electrode 7 into the interior space of the ion trap electrode 8. Collision-induced dissociation (CID) is achieved by voltage regulation. The second fragmentation method is used for CID, with V1 set to 2V, V3 to 0V, V4 to -2V, V5 to 100V, V6 to -5V, and V7 to 100V. RF1 has an amplitude of 400Vpp and a frequency of 2.4MHz, while RF2 has an amplitude of 300Vpp and a frequency of 914kHz. V2 is adjusted to 2V, 6V, 10V, 14V, and 18V, i.e., the voltage difference between V2 and V4 is 4V, 8V, 12V, 16V, and 20V. As the voltage difference increases, the fragmentation rate of styrene gradually increases.

Claims

1. A collision-induced dissociation method in an ion trap mass spectrometer, characterized in that: The ion trap mass spectrometer comprises an injection capillary (1), a first-stage vacuum cavity (3), and a second-stage vacuum cavity (11); The first-stage vacuum cavity (3) and the second-stage vacuum cavity (11) are respectively connected to the air inlet of the mechanical pump (14) through pipelines, and the second-stage vacuum cavity (11) is connected to the air inlet of the molecular pump (15) through a pipeline; A vacuum ultraviolet lamp (2) and an ion transmission hexapole (4) are provided in the first-stage vacuum chamber (3); The second-stage vacuum chamber (11) is provided with a lens electrode (6), a front cover electrode (7), an ion trap electrode (8), a rear cover electrode (9), and an ion detector (10) in sequence; the ion trap electrode (8) is composed of a parallel and spaced-apart flat-plate x pair electrode (12) and a parallel and spaced-apart flat-plate y pair electrode (13), and the normals of the electrode surfaces of the x pair electrode (12) and the y pair electrode (13) are perpendicular to each other; The first-stage vacuum cavity (3) and the second-stage vacuum cavity (11) are connected via the opening electrode (5) to achieve vacuum differential; The voltages applied to the ion transmission hexapole (4) are radio frequency voltage RF1 and direct current voltage V1, the voltage applied to the aperture electrode (5) is a constant direct current voltage V2, the voltage applied to the lens electrode (6) is a constant direct current voltage V3, the voltage applied to the front end cover electrode (7) is a time-varying direct current voltage, the voltage is V4 during injection, and the voltage is V5 during other periods except injection; the voltage applied to the x counter electrode (12) is the auxiliary resonance excitation radio frequency voltage AC plus direct current voltage V6, the voltage applied to the y counter electrode (13) is the main radio frequency voltage RF2 plus the same direct current voltage V6 as the x counter electrode (12), and the voltage applied to the rear end cover electrode (9) is a constant direct current voltage V7; The sample enters the first-stage vacuum chamber (3) through the injection capillary (1) and is ionized by the vacuum ultraviolet lamp (2). After being focused by the ion transmission hexapole (4), the sample enters the internal space of the ion trap electrode (8) through the opening electrode (5) and the inner middle hole of the lens electrode (6) and the front cover electrode (7), and collision-induced dissociation is achieved by regulating the voltage. When the front cover electrode (7) is injected, V4 is set to -10-0V; except when injecting, V6 is set to 50-150V; The voltage V2 of the aperture electrode (5) is set to 0-30 V, 0-2 V in the absence of collision-induced dissociation, and 2-30 V in the collision-induced dissociation mode; Collision-induced dissociation is achieved in one of two ways: Keeping V4 unchanged when injecting the sample through the front cover electrode (7), reducing the DC voltage V6 on the x counter electrode (12) and the y counter electrode (13), and increasing the voltage difference between V4 and V6 to more than 8V; When the front cover electrode (7) is kept constant when injecting the sample, the voltage difference between V4 and V6 is less than 8V, and the DC voltage V2 on the opening electrode (5) is increased, and the voltage difference between V2 and V4 is increased to more than 10V.

2. The method according to claim 1, wherein: The DC voltage V6 of the x counter electrode (12) and the y counter electrode (13) is set to -3 to -5 V when there is no collision-induced dissociation; The collision-induced dissociation mode was set to -2 to -60 V, and V6 was adjusted according to the different energies required for collision-induced dissociation of different substances; The frequency of the radio frequency voltage RF2 of the x counter electrode (12) and the y counter electrode (13) is fixed, and the amplitude of RF2 during injection is 200 to 400 V. pp Adjustable; The distance between the x-pair electrodes (12) is 8-10 mm, and the distance between the y-pair electrodes (13) is 10-12 mm.

3. The method according to claim 1, wherein: In order to ensure the smooth transmission of ions, the DC voltage V1 on the ion transmission hexapole (4) is greater than the voltage V2 applied on the aperture electrode (5), and the RF voltage RF1 of the ion transmission multipole is 200-500V. pp .

4. The method according to claim 1, wherein: In order to ensure smooth transmission of ions, the DC voltage V3 on the lens electrode (6) is smaller than the DC voltage V4 on the aperture electrode (5).

5. The method according to claim 1, wherein: The voltage V7 applied to the rear end cover electrode (9) is equal to the voltage V5 applied to the front end cover electrode (7) during other periods except when injecting a sample.

6. The method according to claim 1, wherein: The injection capillary (1) is one or more of a metal capillary, a PEEK capillary and a quartz capillary.

Images