Collision induced dissociation method in ion trap mass spectrometer

Abstract

The invention discloses a collision induced dissociation method in an ion trap mass spectrometer. In a continuous sample injection ion trap mass spectrometer, an electric field at an inlet of an ion trap is changed by changing direct-current voltages on an x electrode and a y electrode of the ion trap, so that the radial displacement of ions in the trap is increased, energy can be obtained from a radio-frequency field, the energy is converted into internal energy through collision, and then collision induced dissociation occurs. According to the method, the fragmentation degree can be regulated and controlled by regulating and controlling the direct-current voltage on the ion trap electrode to quickly switch collision-induced dissociation modes or not, multiple pieces of characteristic fragment ion information can be obtained at a time, and the qualitative accuracy can be improved.

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. The method allows ions to enter a region with a strong radio frequency field and undergo radio frequency heating, and finally undergo collision-induced dissociation, by simply regulating the voltage difference between an aperture electrode and a front end cover electrode, and the voltage difference between the front end cover electrode and the DC voltage on an x-pair electrode and a y-pair electrode of the ion trap. The degree of fragmentation of collision-induced dissociation can be adjusted by regulating the pressure difference, and multiple levels of fragment ions can be obtained in one detection, which is beneficial to improving the accuracy of qualitative analysis, and can perform structural analysis on unknown compounds. Background Art

[0002] Tandem mass spectrometry is an important technique used in mass spectrometry to analyze isomers and isobaric compounds. An important feature of ion trap mass spectrometry is that it can realize temporal tandem mass spectrometry, which is mainly achieved through collision-induced dissociation. Collision dissociation technology is mainly divided into resonant collision-induced dissociation and non-resonant collision-induced dissociation.

[0003] The realization of the resonant collision induced dissociation technology is through ion screening, using the auxiliary resonance excitation voltage AC to excite ions and finally achieve induced dissociation, and the sample information that can be obtained at one time is less. In order to solve this problem, Snyder et al. realized multi-generation fragmentation in the ion trap by reverse scanning the main radio frequency RF amplitude during the collision induced dissociation process (Snyder, DT; Cooks, RG. J. Am. Soc. Mass Spectrom. 2016, 27, 1914-1921.). Researchers have developed a non-resonance induced dissociation method to obtain multiple characteristic fragment ions in one detection. For example, in a micro-ion trap, by applying a voltage to the discontinuous atmospheric pressure interface inlet (DAPI) capillary, an accelerating electric field is generated at the DAPI outlet, so that the precursor ions undergo rapid dissociation, and further accelerate and dissociate the initially formed fragments (Gao, L.; Li, G.; Cooks, RGJAm. Soc. Mass Spectrom. 2010, 21, 209-214.). McLuckey et al. developed a two-pole direct current (DDC) collision activation technique based on a three-dimensional ion trap, which applies a DC voltage of opposite electrodes to the corresponding end cap electrodes. This causes the ions to move from the central position to the strong radio frequency field area, thereby performing a wide range of radio frequency heating on the stored ions (Prentice, BM; McLuckey, SAJ Am. Soc. Mass Spectrom. 2012, 23, 736-744.).

[0004] Currently, 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 in an ion trap mass spectrometer. In a continuous injection ion trap mass spectrometer, the electric field at the entrance of the ion trap is changed by changing the DC voltage on the x and y electrodes of the ion trap, so that the radial displacement of the ions in the trap increases, and the energy obtained from the radio frequency field is converted into internal energy through collision, and then collision induced dissociation occurs. This method can quickly switch the collision induced dissociation mode or not by regulating the DC voltage on the ion trap electrodes, regulate the degree of fragmentation, and obtain multiple characteristic fragment ion information at one time, which can improve the accuracy of qualitative analysis.

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

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

[0008] In order to achieve the above purpose, 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 chamber 3 and the second-stage vacuum chamber 11 are connected to the air inlet of the mechanical pump 14 through pipelines respectively, and the second-stage vacuum chamber 11 is connected to the air inlet of the molecular pump 15 through pipelines.

[0012] A vacuum ultraviolet lamp 2 and an ion transmission hexapole 4 are arranged in the first-stage vacuum chamber 3;

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

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

[0015] 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 (which is a plate-shaped electrode with a middle hole) 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 during injection is V4, and the voltage at other time periods except injection is V5; 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 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 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;

[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, 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; except for the injection, V6 is set to 50-150V in other periods.

[0024] The voltage V2 of the aperture electrode 5 is set to 0-30 V, 0-2 V when there is no collision-induced dissociation, and 2-30 V in the collision-induced dissociation mode.

[0025] 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. The amplitude of the ion transmission multipole radio frequency voltage RF1 is 200-500 Vpp.

[0026] In order to ensure the 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 samples.

[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 opening electrode and the front end cover electrode and the DC voltage difference between the front end 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 in conjunction with the accompanying drawings and embodiments:

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

[0035] Figure 2 It is the mass spectrum of styrene 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 and characteristic ion distribution changes of multiple triethyl phosphate characteristic fragment ions are obtained at one time;

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

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

[0042] A vacuum ultraviolet lamp 2 and an ion transmission hexapole 4 are arranged in the first-stage vacuum chamber 3;

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

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

[0045] The voltage applied to the ion transmission hexapole 4 is 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 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 during injection is V4, and the voltage in other time periods except injection is V5; 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 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, 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 injected, V4 is set to -2V; except for the injection, V6 is set to 100V in other periods.

[0053] The voltage V2 of the aperture electrode 5 is set to 0-30 V, 0-2 V when there is no collision-induced dissociation, and 2-30 V in the collision-induced dissociation mode.

[0054] 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. The amplitude of the ion transmission multipole radio frequency voltage RF1 is 400 Vpp.

[0055] In order to ensure the 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 samples.

[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 transmission hexapole 4, and then enters the internal space of the ion trap electrode 8 through the opening electrode 5 and the internal middle hole of the lens electrode 6 and the front cover electrode 7, and 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, is ionized by the vacuum ultraviolet lamp 2, is focused by the ion transmission hexapole 4, and enters the internal space of the ion trap electrode 8 through the opening electrode 5, the lens electrode 6, and the inner middle hole of the front cover electrode 7, and realizes collision induced dissociation by regulating the voltage. The first fragmentation method is used to realize collision induced dissociation, that is, V1 is 2V, V2 is 2V, V3 is 0V, V4 is -2V, V5 is 100V, and V7 is 100V. The amplitude of RF1 is 400Vpp, the frequency is 2.4MHz, and the amplitude of RF2 is 300Vpp, and the frequency is 914kHz. Styrene is detected when V6 is -5V and -20V, that is, the voltage difference between V4 and V6 is 3V and 18V. When the voltage difference between V4 and V6 is 3V, no fragment ions are generated, while a large number of fragment ions are generated when the voltage difference is 18V.

[0065] Example 2

[0066] Obtaining 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, is ionized by the vacuum ultraviolet lamp 2, and is focused by the ion transmission hexapole 4. It enters the internal space of the ion trap electrode 8 through the opening electrode 5, the lens electrode 6, and the internal middle hole of the front cover electrode 7, and realizes collision-induced dissociation by regulating the voltage. The first fragmentation method is used to realize collision-induced dissociation, that is, V1 is 2V, V2 is 2V, V3 is 0V, V4 is -2V, V5 is 100V, and V7 is 100V. The amplitude of RF1 is 400Vpp, the frequency is 2.4MHz, and the amplitude of RF2 is 300Vpp, and the frequency is 914kHz. V6 is adjusted to -5V, -10V, -15V, -20V, and -25V, that is, 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, 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 opening electrode 5, the lens electrode 6, and the internal middle hole of the front cover electrode 7. The collision-induced dissociation is achieved by regulating the voltage. The second fragmentation method is used to achieve collision-induced dissociation, that is, V1 is 2V, V3 is 0V, V4 is -2V, V5 is 100V, V6 is -5V, and V7 is 100V. The amplitude of RF1 is 400Vpp, the frequency is 2.4MHz, and the amplitude of RF2 is 300Vpp, and the frequency is 914kHz. V2 is adjusted to 2V, 6V, 10V, 14V, and 18V, that is, 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 chamber (3), and a second-stage vacuum chamber (11); The first-stage vacuum chamber (3) and the second-stage vacuum chamber (11) are respectively connected to the air inlet of the mechanical pump (14) through pipelines, and the second-stage vacuum chamber (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 arranged in the first-stage vacuum chamber (3); A lens electrode (6), a front cover electrode (7), an ion trap electrode (8), a rear cover electrode (9), and an ion detector (10) are sequentially arranged in the second-stage vacuum chamber (11); the ion trap electrode (8) is composed of a pair of x electrodes (12) arranged in parallel and at intervals and a pair of y electrodes (13) arranged in parallel and at intervals, and the normals of the electrode surfaces of the pair of x electrodes (12) and the pair of y electrodes (13) are perpendicular to each other; The first-stage vacuum cavity (3) and the second-stage vacuum cavity (11) are connected via an opening electrode (5) to achieve vacuum difference; 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 sample injection, and the voltage is V5 during other time periods except sample injection; the voltage applied to the x pair of electrodes (12) is the auxiliary resonance excitation radio frequency voltage AC plus a direct current voltage V6, the voltage applied to the y pair of electrodes (13) is the main radio frequency voltage RF2 plus a direct current voltage V6 that is the same as that of the x pair of electrodes (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 (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 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; Collision-induced dissociation can be 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 greater than 8V; When the front end cover electrode (7) is kept constant for sample injection, 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.

2. The method according to claim 1, characterized in that: 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 sample injection is 200 to 400V. 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, characterized in that: When the front cover electrode (7) is injected, V4 is set to -10-0V; except for the injection period, V6 is set to 50-150V.

4. The method according to claim 1, characterized in that: The voltage V2 of the aperture electrode (5) is set to 0-30 V, 0-2 V when there is no collision-induced dissociation, and 2-30 V in the collision-induced dissociation mode.

5. The method according to claim 1, characterized in that: 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 to the aperture electrode (5). The amplitude of the ion transmission multipole radio frequency voltage RF1 is 200-500V. pp .

6. The method according to claim 1, characterized in that: 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).

7. The method according to claim 1, characterized in that: 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 samples.

8. The method according to claim 1, characterized in that: The injection capillary (1) can be one or more of a metal capillary, a PEEK capillary and a quartz capillary.

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