Digital electrostatic trap mass spectrometer and working method thereof

Abstract

The invention provides a digital electrostatic trap mass spectrometer and a working method thereof. The digital electrostatic trap mass spectrometer comprises a power supply, a detector and an electrostatic trap, the outer contour surface of the inner electrode is a cylindrical surface, and the ratio of the diameter D2 of the cylindrical surface to the inner diameter D1 of the outer electrode is greater than 0.45 and less than 0.75; the outer electrode comprises a plurality of ring electrodes surrounding the inner electrode, the ring electrodes are distributed in an axial symmetry mode relative to the central electrode, and the inner diameter D1 of the ring electrodes is larger than or equal to 50 mm and smaller than or equal to 70 mm; the power supply applies direct-current voltage to the plurality of ring electrodes, and the voltage amplitude Vi of the ith ring electrode arranged outwards from the central electrode meets the requirement. The invention has the advantages of simple structure, high resolution and the like.

Description

Technical Field

[0001] The invention relates to mass spectrometry technology, and in particular to a digital electrostatic trap mass spectrometer and a working method thereof. Background Art

[0002] In the field of mass spectrometry, mass spectrometry with a resolution greater than 10,000 (FWHM) is usually called high-resolution mass spectrometry (HRMS), and HRMS technology based on ion traps has developed the following technical routes: 1. Fourier transform-ion cyclotron resonance (FT-ICR); an early example was first disclosed by MB Comisarow and AG Marshall in Chem. Phys. Lett. 25, 282 (1974), which uses a superconducting coil to generate a high-intensity, high-stability uniform magnetic field to capture ions, and the ions perform a variable-diameter rotation motion inside the trap. The shortcomings of this route are: The coils were large and needed to be cooled to very low temperatures using expensive liquid nitrogen, so the instrument was very expensive to build and difficult to operate and maintain.

[0003] 2. Electrostatic orbital ion trap (Orbitrap); an early example was disclosed by Alexander Makarov in Ana1.Chem., 2000, 72(6), pp1156-1162. The central electrode is designed to be spindle-shaped and a DC high voltage is applied to generate a superlogarithmic potential inside the trap. The ions oscillate back and forth in the axial direction and rotate around the central electrode at the same time. The shortcomings of this route are: In order to maintain axial oscillation harmonics, the central electrode and outer electrodes of the orbital trap need to be processed very precisely, reaching the micron level, and extremely high DC voltage stability control requirements are required. The ion storage capacity is limited and the ion implantation technology is complex.

[0004] 3. Cassinian electrostatic trap Cassinian, such as US-8384019B2, typically has at least two central electrodes, and the ions move in the XY plane for trapping and in the Z axis for analysis. The shortcomings of this route are: Electrode processing needs to reach the micron level and the electrode structure is complex.

[0005] 4. Rotating planar electrostatic ion trap (OFA), such as WO2012116765, the core is composed of two sets of coaxially placed annular electrode arrays to generate an electrostatic electric field in the space between the arrays, and the ion movement follows a highly elliptical and precessing orbit around the central axis. The shortcomings of this route are: Due to the high-order oscillation of ions inside OFA, there is a significant problem of mixing of multiple motion frequencies, which makes spectrum analysis difficult, the algorithm complex, and requires high electrode processing accuracy. Summary of the invention

[0006] In order to solve the deficiencies in the above-mentioned prior art solutions, the present invention provides a digital electrostatic trap mass spectrometer.

[0007] The objective of the present invention is achieved through the following technical solutions: A digital electrostatic trap mass spectrometer comprises a power supply, a detector and an electrostatic trap; the electrostatic trap comprises: An inner electrode, wherein the outer contour surface of the inner electrode is a cylindrical surface, and the ratio of the diameter D2 of the cylindrical surface to the inner diameter D1 of the outer electrode is greater than 0.45 and less than 0.75; An outer electrode, the outer electrode comprising a plurality of ring electrodes surrounding the inner electrode, the plurality of ring electrodes being axially symmetrically distributed about the central electrode, and an inner diameter D1 of the ring electrodes satisfying 50 mm ≤ D1 ≤ 70 mm; The power supply applies a DC voltage to the plurality of ring electrodes, and the voltage amplitude V on the i-th ring electrode arranged outward from the central electrode i for; V i = k·U c1 ·(A i +B i )+C,A i =exp(-0.16·s i / d); B i =-0.2·sqr(d i / d max ), k is the coefficient, U c1 is the initial DC voltage of the central electrode, s i is the distance from the center of the ring electrode to the center of the center electrode, d is the thickness of each ring electrode in its axial direction, and d i is the radial distance from the inner electrode to the ith ring electrode, d max is the maximum radial distance from the inner electrode to the multiple ring electrodes, and C is the DC bias voltage.

[0008] The object of the present invention is also to provide a working method of the digital electrostatic trap mass spectrometer of the present invention, and the object of the invention is achieved by the following technical solutions: A working method of a digital electrostatic trap mass spectrometer, the working method comprising: During the ion injection phase, the power supply applies a DC voltage to the outer electrode, and the ions enter between the inner electrode and the outer electrode; the voltage amplitude V i for; V i = k·U c1 ·(A i +B i)+C,A i =exp(-0.16·s i / d); B i =-0.2·sqr(d i / d max ), k is the coefficient, U c1 is the initial DC voltage of the inner electrode, s i is the distance from the center of the ring electrode to the center of the center electrode, d is the thickness of each ring electrode in its axial direction, and d i is the radial distance from the inner electrode to the ith ring electrode, d max is the maximum value of the radial distance from the inner electrode to the multiple ring electrodes, C is the DC bias voltage; During the ion compression stage, the voltage on the outer electrode is maintained constant, the voltage on the inner electrode is increased or decreased, and the trajectory of the ions is compressed toward the inner electrode.

[0009] Compared with the prior art, the present invention has the following beneficial effects: 1. Simple structure; The number of external electrodes is odd, and the amplitude of the DC voltage meets the conditions, which improves the ion injection efficiency and can optimize the design of ions in different mass ranges; 2. Simple structure; The inner electrode (such as a cylindrical electrode) and the outer electrode (multiple ring electrodes) have simple structural designs and are easy to process and install; 3. High resolution; During work, ions in a specific mass range are selected, their motion trajectories are optimized, energy compensation is performed, their motion time is increased, and AGC can be performed by the device itself to reduce the space charge effect in the trap. These methods greatly improve the resolution. BRIEF DESCRIPTION OF THE DRAWINGS The disclosure of the present invention will become easier to understand with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only used to illustrate the technical solution of the present invention and are not intended to limit the scope of protection of the present invention. In the drawings: Figure 1 is a structural schematic diagram of a digital electrostatic trap mass spectrometer according to an embodiment of the present invention; Figure 2 Schematic diagram of particle motion trajectory according to an embodiment of the present invention. DETAILED DESCRIPTION

[0010] Figure 1-Figure 2The following description describes optional specific embodiments of the present invention to teach those skilled in the art how to implement and reproduce the present invention. In order to teach the technical solution of the present invention, some conventional aspects have been simplified or omitted. Those skilled in the art will understand that variations or replacements derived from these specific embodiments will be within the scope of the present invention. Those skilled in the art will understand that the following features can be combined in various ways to form multiple variations of the present invention. Thus, the present invention is not limited to the following optional specific embodiments, but is only limited by the claims and their equivalents. Example 1

[0011] A digital electrostatic trap mass spectrometer according to an embodiment of the present invention comprises: The power supply and the detector are prior art in the art; Electrostatic trap; Figure 1 As shown, the electrostatic trap comprises: An inner electrode 1, wherein the outer contour surface of the inner electrode 1 is a cylindrical surface, and the ratio of the diameter D2 of the cylindrical surface to the inner diameter D1 of the outer electrode is greater than 0.45 and less than 0.75; An outer electrode 2, the outer electrode 2 comprising a plurality of ring electrodes surrounding the inner electrode, the plurality of ring electrodes being axially symmetrically distributed about the central electrode, and an inner diameter D1 of the ring electrodes satisfying 50 mm ≤ D1 ≤ 70 mm; The power supply applies a DC voltage to the plurality of ring electrodes, and the voltage amplitude V on the i-th ring electrode arranged outward from the central electrode i for; V i = k·U c1 ·(A i +B i )+C,A i =exp(-0.16·s i / d); B i =-0.2·sqr(d i / d max ), k is the coefficient, U c1 is the initial DC voltage of the central electrode, s i is the distance from the center of the ring electrode to the center of the center electrode, d is the thickness of each ring electrode in its axial direction, and d i is the radial distance from the inner electrode to the ith ring electrode, d max is the maximum radial distance from the inner electrode to the multiple ring electrodes, and C is the DC bias voltage.

[0012] In order to reduce the complexity of the structure, further, the thickness d of the plurality of ring electrodes is the same, and the inner diameters are the same or different.

[0013] The working method of the digital electrostatic trap mass spectrometer according to the embodiment of the present invention comprises: During the ion injection phase, the power supply applies a DC voltage to the outer electrode, and the ions enter between the inner electrode and the outer electrode; the voltage amplitude V i for; V i = k·U c1 ·(A i +B i )+C,A i =exp(-0.16·s i / d); B i =-0.2·sqr(d i / d max ), k is the coefficient, U c1 is the initial DC voltage of the inner electrode, s i is the distance from the center of the ring electrode to the center of the center electrode, d is the thickness of each ring electrode in its axial direction, and d i is the radial distance from the inner electrode to the ith ring electrode, d max is the maximum value of the radial distance from the inner electrode to the multiple ring electrodes, C is the DC bias voltage; During the ion compression stage, the voltage on the outer electrode is maintained constant, the voltage on the inner electrode is increased or decreased, and the trajectory of the ions is compressed toward the inner electrode. Example 2

[0014] An application example of a digital electrostatic trap mass spectrometer and a working method thereof according to embodiment 1 of the present invention.

[0015] In this application example, Figure 1 As shown, the inner electrode 1 is cylindrical, with a diameter of 45 mm and an axial length (i.e., thickness) of 67.2 mm. The outer electrode 2 includes 9 ring electrodes P1, P2, ... P9 of the same size, each with an inner diameter of 60 mm and an axial length (i.e., thickness) of 8 mm. The spacing between adjacent ring electrodes is 1.5 mm, and the length of this ion trap is 84 mm.

[0016] A working method of a digital electrostatic trap mass spectrometer according to an embodiment of the present invention includes: During the ion injection phase, the power supply applies a DC voltage to the outer electrode, and the ions enter between the inner electrode and the outer electrode; the voltage amplitude V i for; V i = k·U c1 ·(A i +B i )+C,A i=exp(-0.16·s i / d); B i =-0.2·sqr(d i / d max ), k is the logarithmic field defect correction coefficient introduced by the electrostatic trap due to the influence of processing and assembly errors, which is close to 1 and can be taken as 0.997. c1 =-2500V,s i is the distance from the center of the ring electrode to the center of the center electrode, d=8mm, d i Both are 7.5mm, d max =d i , C is a DC bias voltage freely adjustable by the user. In this embodiment, no DC bias voltage is applied, that is, C is zero; Based on this, it was concluded that: the voltage applied to P1 was -1994V, the voltage applied to P2 and P3 was -1562.7V, the voltage applied to P4 and P5 was -1206.0V, the voltage applied to P6 and P7 was -911.1V, and the voltage applied to P8 and P9 was -667.2V.

[0017] In the ion compression stage, the voltage on the outer electrode is maintained constant, and the voltage on the inner electrode is gradually reduced from -2500 V to -3500 V for 50 μs. The trajectory of the ions is compressed toward the inner electrode, as shown in Figure 2. Figure 2 As shown; During the ion oscillation stage, the inner electrode voltage is fixed at -3500V, the voltage of the ring electrodes P8 and P9 is turned off, and the grounding to floating treatment is performed. The voltage on the other ring electrodes is maintained, the voltage fluctuation is less than 10ppm, and the duration is 10ms; In the ion detection stage, differential image current detection is performed with the help of the induced signals generated by the ring electrodes P8 and P9, with a duration of 500 ms, and the mass spectrum is obtained by Fourier transform processing. Example 3

[0018] The application example of a digital electrostatic trap mass spectrometer and its working method according to embodiment 1 of the present invention is different from embodiment 2 in that: The working method of the digital electrostatic trap mass spectrometer also includes: Ion AGC stage: scheduled to be performed every 10 seconds. Taking positive ion detection as an example, the DC voltage amplitude of the outer electrode P8 is instantly lowered to -10000V, used as a charge detection collector, and the charge detection gain is 10 10 -10 11 V / Coulomb, the integration frequency of the ion current is 5MHz, and the integration period is 50ms. This process is always carried out regularly to control the ion injection time in mass spectrometry detection, so that the number of ions in the trap is maintained at an optimal level, ensuring the high mass resolution and high mass accuracy of the electrostatic trap The above embodiment only takes 9 electrodes as an example for the outer electrode. Of course, there may be 13, 15 or more ring electrodes, and the inner diameter or outer diameter of the ring electrodes may be inconsistent. The inner electrode may be composed of multiple short columnar electrodes instead of a single long columnar electrode.

Claims

1. A digital electrostatic trap mass spectrometer, comprising a power supply, a detector and an electrostatic trap; characterized in that: The electrostatic trap comprises: An inner electrode, wherein the outer contour surface of the inner electrode is a cylindrical surface, and the ratio of the diameter D2 of the cylindrical surface to the inner diameter D1 of the outer electrode is greater than 0.45 and less than 0.75; An outer electrode, the outer electrode comprising a plurality of ring electrodes surrounding the inner electrode, the plurality of ring electrodes being axially symmetrically distributed about the central electrode, and an inner diameter D1 of the ring electrodes satisfying 50 mm ≤ D1 ≤ 70 mm; The power supply applies a DC voltage to the plurality of ring electrodes, and the voltage amplitude V on the i-th ring electrode arranged outward from the central electrode i for; V i =k·U c1 ·(A i +B i )+C,A i =exp(-0.16·s i / d);B i =-0.2·sqr(d i / d max ), k is the coefficient, U c1 is the initial DC voltage of the central electrode, s i is the distance from the center of the ring electrode to the center of the center electrode, d is the thickness of each ring electrode in its axial direction, and d i is the radial distance from the inner electrode to the ith ring electrode, d max is the maximum radial distance from the inner electrode to the multiple ring electrodes, and C is the DC bias voltage.

2. A digital electrostatic trap mass spectrometer according to claim 1, characterized in that: The thickness d of the plurality of ring electrodes is the same, and the inner diameters are the same or different.

3. A digital electrostatic trap mass spectrometer according to claim 1, characterized in that: The inner electrode includes one electrode or a plurality of electrodes.

4. The working method of the digital electrostatic trap mass spectrometer according to any one of claims 1 to 3, the working method comprising: During the ion injection phase, the power supply applies a DC voltage to the outer electrode, and the ions enter between the inner electrode and the outer electrode; The voltage amplitude V on the i-th ring electrode arranged outward from the central electrode i for; V i =k·U c1 ·(A i +B i )+C,A i =exp(-0.16·s i / d);B i =-0.2·sqr(d i / d max ), k is the coefficient, U c1 is the initial DC voltage of the inner electrode, s i is the distance from the center of the ring electrode to the center of the center electrode, d is the thickness of each ring electrode in its axial direction, and d i is the radial distance from the inner electrode to the ith ring electrode, d max is the maximum value of the radial distance from the inner electrode to the multiple ring electrodes, C is the DC bias voltage; During the ion compression stage, the voltage on the outer electrode is maintained constant, the voltage on the inner electrode is increased or decreased, and the trajectory of the ions is compressed toward the inner electrode.

5. The working method according to claim 4, characterized in that: The working method also includes: During the ion oscillation stage, the voltage of the symmetrical outer electrode outside the ion oscillation range is turned off, and the grounding to floating ground processing is performed to maintain the voltage stability of the inner electrode and the outer electrode adjacent to the ion oscillation range; In the ion detection stage, the induced signal generated by the electrode with the voltage turned off in the ion oscillation stage is used to perform differential image current detection, and the mass spectrum is obtained by Fourier transform processing.

6. The working method according to claim 4, characterized in that: The working method also includes: In the ion automatic gain control stage, the DC voltage amplitude of the outer electrode at the edge end is reduced. The outer electrode is used as an ion collecting plate, and the ion current intensity inside the electrostatic trap is detected by an integral amplifier circuit.

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