CN111816545A - Prismatic linear ion trap mass analyzer - Google Patents

Abstract

The invention provides a prismatic linear ion trap mass analyzer, which is formed by four groups of working columnar electrode structures and two end cover electrodes: wherein every two groups of columnar electrodes are a pair and are arranged in pairs in an opposite way; each group of working columnar electrode structure consists of three electrodes, namely a main electrode and two side electrodes, wherein only radio frequency voltage is applied to the main electrode, and auxiliary excitation voltage is applied to the side electrodes. The invention modifies the whole electrode structure of the traditional linear ion trap, adds the side electrode structure for applying auxiliary excitation, and the structure not only can realize the axial ejection of ions, but also can effectively reduce the space charge effect of the ions when more ions are injected, and improves the whole resolution capability of the mass analyzer.

Description

Prismatic linear ion trap mass analyzer

Technical Field

The present invention relates to a mass analyser, in particular a prismatic linear ion trap mass analyser.

Background

The mass spectrometer is a representative of modern high-end analytical instruments, has the advantages of strong qualitative capability, high sensitivity and the like, and is an effective tool for trace detection of low-content substances. At present, mass spectrometers have been widely used in fundamental science, environmental protection, aerospace engineering and energy analysis. In order to meet the demand of high-speed social development, the development trend of mass spectrometers in the future is mainly divided into three directions: the method is characterized in that a high-performance non-magnetized mass spectrometer is researched and developed mainly aiming at the problems of huge weight and size, difficult availability of a strong magnetic field, higher magnetic field maintenance cost and the like of the traditional magnetic mass spectrometer; the mass spectrometer is miniaturized, and can be taken out of a laboratory, so that the requirements of emergency detection and on-site in-situ analysis can be met; the mass spectrometer has the advantages that the mass spectrometer is simplified, the structures of core components such as a mass analyzer in the mass spectrometer are optimized to simplify the processing technology of the mass spectrometer, the overall cost is reduced, and meanwhile, the adaptability of the mass spectrometer to severe environments is improved.

The mass analyzer is a core component of the mass spectrometer and determines the analytical performance of the mass spectrometer. Different types of mass spectrometers use different mass analysers which also do not achieve the same way of ion mass to charge ratio separation. At present, the mass analyzers commonly used are a magnetic sector mass analyzer (magnetic sector), a time-of-flight mass analyzer (TOF), a quadrupole mass analyzer (QMF), an Ion Trap mass analyzer (Ion Trap), a fourier transform mass analyzer (FT-ICR), an orbital Ion Trap mass analyzer (Orbitrap), and the like. Among a plurality of mass analyzers, the ion trap mass analyzer has the advantages of simple structure, low requirement on vacuum degree, capability of performing multistage tandem mass spectrometry and the like, shows unique development advantages and has strong miniaturization potential. The traditional mass analyzer is divided into a three-dimensional ion trap and a linear ion trap, and the linear ion trap mass analyzer has higher ion storage capacity, thus having higher detection sensitivity and dynamic analysis range. Research and experiments show that the ion storage capacity of the linear ion trap with the same geometric dimension is more than 20 times of that of the traditional three-dimensional ion trap on the same premise of not causing the space charge effect of ions, which means that the dynamic range of a mass spectrometer adopting the linear ion trap is at least one order of magnitude higher than that of the traditional three-dimensional ion trap mass spectrometer. Furthermore, the multi-stage mass spectrometry function of the linear ion trap can greatly improve the qualitative capability of the substance in a simple substance spectrum analysis mode, particularly effectively remove the interference of chemical background, quickly position the target ions and provide the chemical structure information of the target ions under the condition of the interference of complex matrixes in the actual working environment. The miniaturized mass spectrometer has the characteristics of light weight, small volume, low power consumption and the like, and has great advantages and potentials in the aspects of portability, timeliness, simplicity and cost. Therefore, miniaturization of mass spectrometers has become an important trend in the development of analytical instruments. In view of the current development direction of mass spectrometry instruments and the demand for miniaturization, portability, high-throughput analysis methods and proprietary intellectual property, linear ion traps have become a hot spot in the research field.

A conventional linear ion trap consists of six electrodes, including two planar end cap electrodes and four hyperboloid cylindrical electrodes. The hyperboloid structure requires extremely high machining precision and assembly precision, generally requires mechanical error within a few microns, and is high in cost, so that the current ion trap mass spectrometer is expensive and difficult to popularize. In recent years, development of a miniaturized and low-cost compact ion trap mass spectrometer has been a hotspot in the field of mass spectrometry, and thus linear ion traps with more simplified electrode structures have been generated. The Rectangular Ion Trap (RIT) proposed by Cooks and the like combines the advantages of a simple structure of a Cylindrical Ion Trap (CIT) and strong storage capacity of a Linear Ion Trap (LIT), is only surrounded by six planar electrodes, replaces the traditional hyperboloid structure, and is simple and convenient to process and assemble. The simple structure and superior analytical performance of the rectangular ion trap make it the first choice for mass analyzers in miniaturized mass spectrometers, and have been successfully applied to the fabrication of compact bench-top mass spectrometers and portable mass spectrometers. The subsequent appearance of various mass analyzers including printed circuit board rectangular ion trap mass analyzers (PCB ion trap), PCB array ion traps, triangular trap electrode structure linear ion traps and the like has good ion storage and mass analysis capabilities, but is completed based on an ion exit mode of resonance excitation, and the method is that an ion exit groove is formed in an electrode of the linear ion trap for ion exit. Although the radial ion emission mode has high emission efficiency, the quadrupole field in the ion trap structure is required to be perfect, so that the precision requirement on electrode processing and assembling is high. Meanwhile, the linear ion trap has certain disadvantages in the process of radially ejecting ions: an ion extraction groove is required to be formed in an ion trap electrode for ion extraction, which can cause distortion of an electric field pattern in the ion trap, cause ions with other mass-to-charge ratios to be extracted simultaneously, cause serious influence on final ion mass resolution and weaken the mass analysis capability of the ion trap. Secondly, the radial ejection approach is not suitable for tandem mass spectrometry with multiple devices, because the radially ejected ions are not easily captured by the next stage of mass analyzer and are analyzed in the next step. In addition, in the radial emergent mode, ions are respectively emergent from the ion emergent grooves on the two electrodes, and an ion detector is required to be respectively arranged on two sides of the mass analyzer for detecting the emergent ions, so that the complexity of the structure of the mass spectrometer is increased, and the cost of ion mass analysis is also increased. And the axial emergent mode of the linear ion trap can effectively solve the problem.

Disclosure of Invention

In order to solve the above technical problems, an object of the present invention is to provide a prismatic linear ion trap mass analyzer.

The invention provides a prismatic linear ion trap mass analyzer, which is characterized in that the material of the prismatic linear ion trap mass analyzer is conductive metal material or insulating material plated with a conductive coating, and the prismatic linear ion trap mass analyzer is enclosed by four groups of working columnar electrode structures and two end cover electrodes: the four groups of columnar electrodes have the same appearance structure, wherein each two groups of columnar electrodes are a pair and are arranged in pairs, the centers of the end cover electrodes are provided with at least one through hole, and the two end cover electrodes are respectively arranged at two ends of the columnar electrodes. All the electrodes are completely and symmetrically distributed around the central axis in the z direction, and a central area formed by four groups of electrodes in the space structure also forms a regular prism space. Each group of working columnar electrode structures consists of three electrodes, a main electrode and two side electrodes, wherein radio-frequency voltage is applied to the main electrode, auxiliary excitation voltage is applied to the side electrodes, and the auxiliary excitation voltage is applied to the side electrodes in a mode that the auxiliary excitation voltage is applied to the side electrodes on the two groups of working columnar electrode structures which are oppositely arranged or the auxiliary excitation voltage is applied to all the side electrodes.

Preferably, the ion introduction direction of the prismatic linear ion trap mass analyzer is fixed to form a narrow opening end of a regular prism space in a central area surrounded by four groups of electrodes, and the end cover electrode at the position is the ion introduction electrode.

Preferably, the internal electric field distribution can be optimized by changing the length, width and height of the four groups of columnar electrodes and the size of a central regular prism formed by the four groups of columnar electrodes.

Preferably, the main electrodes of the four groups of columnar electrodes may be provided with small holes or slits for ion extraction detection, or may not be provided with small holes or slits. When a main electrode is provided with a small hole or a slit, the positions of the electrodes can be independently adjusted, so that the efficiency of ions in the direction of the slit can be improved.

Preferably, a direct current signal is applied to the end cap electrode to form an axial bound field in the z direction, and a radio frequency voltage is applied to the columnar electrode to form a radial bound field in the x and y directions.

Preferably, when the number of the end cover electrodes is more than two, one of the end cover electrodes is located at one end of the linear ion trap for ion sampling, and the rest of the end cover electrodes are sequentially arranged at the other end of the linear ion trap.

Compared with the prior art, the invention has the following beneficial effects: firstly, the whole electrode structure of the traditional linear ion trap is modified, an edge electrode structure for applying auxiliary excitation is added, and the electrodes with auxiliary excitation voltage which gradually increase in the axial direction of ion movement can guide ions to orderly gather to an outlet position, so that the ions are axially ejected. And secondly, the structure with the space gradually increasing in the ion emergent direction can effectively reduce the space charge effect of ions when more ions are injected, and the overall resolution capability of the mass analyzer is improved. And the four groups of electrodes are completely the same, the whole structure is in a rotational symmetry state around the central shaft, the processing and assembling difficulty is reduced, the adjustment of the internal space is conveniently realized, and the purpose of optimizing the distribution of the electric field in the trap is achieved.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

fig. 1 is a schematic structural diagram of a first embodiment of the present invention.

Fig. 2 is a schematic diagram illustrating an electrode voltage application manner of a prismatic linear ion trap mass analyzer according to an embodiment.

Fig. 3 is a schematic view of a prismatic linear ion trap mass analyzer in a positive z-direction view according to an embodiment.

Fig. 4 is a schematic view of a prismatic linear ion trap mass analyzer in an opposite z-direction according to an embodiment.

Fig. 5 is a schematic cross-sectional view of one set of electrode slices of a prismatic linear ion trap mass analyzer according to an embodiment.

FIG. 6 is a timing diagram illustrating the application of the RF voltage and the auxiliary trigger voltage according to an embodiment.

Fig. 7 is a schematic structural diagram of a second embodiment of the present invention.

Fig. 8 is a schematic view of the positive z-direction of the stretched single-electrode slot in the second embodiment.

Fig. 9 is a schematic view of the positive z-direction after stretching the two opposing electrodes in the second embodiment.

Fig. 10 is a second structural diagram according to a second embodiment of the present invention.

Fig. 11 is a schematic cross-sectional view of a set of slotted electrode plates of a prismatic linear ion trap mass analyzer according to a second embodiment.

Figure 12 is a schematic diagram of the invention as applied to a mass spectrometer.

Figure 13 is a second schematic diagram of the invention as applied to a mass spectrometer.

FIG. 14 is a third schematic diagram of the invention as applied to a mass spectrometer

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.

The invention relates to a prismatic linear ion trap mass analyzer, which is formed by four groups of working columnar electrode structures and two end cover electrodes: the electrode material is conductive metal material or insulating material plated with conductive coating, every two groups of columnar electrodes are paired and oppositely arranged, the center of the end cover electrode is provided with at least one through hole, and the two end cover electrodes are respectively arranged at two ends of the columnar electrodes. All the electrodes are completely and symmetrically distributed around the central axis in the z direction, and a central area formed by four groups of electrodes in the space structure also forms a regular prism space. Each group of working columnar electrode structure consists of three electrodes, a main electrode and two side electrodes, wherein only radio frequency voltage is applied to the main electrode, radio frequency voltage + auxiliary excitation voltage or only auxiliary excitation voltage is applied to the side electrodes, and the four main electrodes can be provided with small holes or slits for ion extraction detection or not.

The four groups of columnar electrodes have the same appearance structure, and the length, width and height of the electrodes can be adjusted, namely, the electric field distribution in the space enclosed by the four groups of columnar electrodes can be adjusted by changing the relative positions of the four groups of columnar electrodes and the voltage application mode, so that good ion storage and mass analysis performances are obtained.

The main electrodes of the four groups of columnar electrodes can be provided with small holes or slits for ion extraction detection, or can not be provided with small holes or slits, and when the main electrodes are provided with the small holes or slits, the positions of the groups of electrodes can be independently adjusted, so that the efficiency of ions in the direction of the slits in popping up is improved.

The end cover electrodes are applied with direct current signals to form an axial bound field, the columnar electrodes are applied with radio frequency voltage RF to form a radial bound field, Radio Frequency (RF) signals applied to two groups of columnar electrodes opposite to each other in the x and y directions are the same, and the Radio Frequency (RF) signals applied to two pairs of electrodes adjacent to each other in the x and y directions are equal in amplitude and opposite in direction.

Example one

The structure of the prismatic linear ion trap mass analyzer of the present invention is shown in fig. 1. Wherein the first group of electrodes consists of a center 101 and two side electrodes 105 and 106, the same other three groups of electrodes are respectively 102, 107 and 108 electrode groups, 103, 109 and 110 electrode groups, 104, 111 and 112 electrode groups, and the working area of the whole linear ion trap consists of the four groups of electrodes. The application modes of the radio frequency voltage (RF) and the auxiliary excitation voltage (AC) are as shown in fig. 2, and the application modes of the radio frequency voltage specifically include: radio frequency voltages (RF +) with the same magnitude and the same direction are applied to the first group of electrode main body electrodes 101 and the third group of electrode main body electrodes 103, radio frequency voltages (RF-) with the same magnitude and the same direction are applied to the second group of electrode main body electrodes 102 and the fourth group of electrode main body electrodes 104, and the two groups of radio frequency voltages have the same amplitude and have a phase difference of 180 degrees. Meanwhile, the first group of electrode side electrodes 105 and 106 are communicated with the third group of electrode side electrodes 107 and 108, an auxiliary excitation voltage (AC1) is applied, the second group of electrode side electrodes 109 and 110 are communicated with the fourth group of electrode side electrodes 111 and 112, and an auxiliary excitation voltage (AC2) is applied, wherein at least one of AC1 and AC2 is not 0, and AC1 and AC2 are both independent in voltage value and adjustable in phase. FIG. 3 shows the distribution of the positions of the broad faces of four prismatic electrodes, wherein the square size of the broad faces is smaller than the internal electric field diameter of the end, namely L1 < 2r 1; FIG. 4 shows the distribution of the narrow face positions of four prismatic electrodes, wherein the square size of the narrow face is smaller than the internal electric field diameter of the end, namely L2 < 2r 2. Fig. 5 shows a schematic cross-sectional view of the electrode, wherein 301 is a main electrode, 302 and 303 are side electrodes, and 302 and 303 have the same structural parameters. In this embodiment, ions are introduced along the z-axis direction, enter from a narrow port, exit from a wide port, i.e., the direction indicated by the central dashed arrow in the figure, as shown in fig. 6, and as in the conventional linear ion trap analysis process, in the ionization and cooling phases, an RF value with a constant amplitude is applied, and in the mass analysis phase, the amplitude of the radio frequency voltage (RF) is scanned; the application time of the auxiliary excitation signal (AC) is only the mass analysis phase. The stored ion order can be detected by the combined action of a scanning radio frequency voltage (RF) and an auxiliary excitation signal (AC) by driving the wide-mouth end along the z-axis direction out of the linear ion trap.

Example two

Figure 7 is another configuration of a prismatic linear ion trap mass analyzer of the present invention. Compared with the first embodiment, the ion exit grooves 413 and 414 are formed in the two opposite main body electrodes 402 and 404, and the introduction of high-order field components is inevitably caused due to the occurrence of the ion extraction aperture, so that the ion exit efficiency is affected, and the ion exit efficiency needs to be improved by means of electrode position adjustment. As shown in fig. 8, when the main body electrode 404 is provided with the ion emitting apertures, the ion emitting efficiency can be improved by increasing the distance between the electrode and the central axis, that is, r3 is greater than r2, and during the stretching process, the rotational symmetry axis of the electrode group consisting of 404, 411 and 412 needs to be strictly parallel to the symmetry axis of the central region and the rotational symmetry axes of the other three groups of electrodes; as shown in fig. 9, when the ion emitting apertures are formed in the two main electrodes 402 and 404, the ion emitting efficiency can be similarly improved by increasing the positions of the electrodes from the central axis, that is, r3 > r2 and r4 > r2, in the stretching process, two rotational symmetry axes of the electrode group consisting of 402, 407 and 408 and the electrode group consisting of 404, 411 and 412 need to be strictly parallel to the symmetry axis of the central area and the rotational symmetry axes of the other two groups of electrodes, wherein the size relationship between r3 and r4 is not fixed, the ion extraction position is generally a larger radius, that is, if the ion extraction from the 403 slot is needed, r3 > r 4; r3 may be the same as r4 if both ion detectors are installed for the bi-directional ion exit slots. Fig. 10 is a schematic structural diagram of the case where four electrodes are all slotted, and fig. 11 is a schematic interface diagram of a slotted electrode sheet.

EXAMPLE III

Fig. 12, 13 and 14 show a method of using the prismatic linear ion trap mass analyser in a mass spectrometer. In fig. 12, 501 is an ion source for generating ions to be analyzed; 502 is an atmospheric pressure interface for the introduction of a sample from the outside; 503 is a vacuum chamber for vacuum environment guarantee of mass spectrometry; 504 is ion guide for focusing, cooling, guiding and transporting ions to the next stage; 505 is a working electrode main body of the prismatic linear ion trap mass analyzer, 506 and 507 are front and rear end cover electrodes respectively, which jointly form the mass analyzer and are used for completing different mass analyses; 508 is an ion detector for collecting the ions separated by the mass analyzer and providing them for further signal processing and analysis; 509 is responsible for the maintenance of a vacuum inside the vacuum chamber for the vacuum pump. The mass analysis process is that an ion source converts a sample to be analyzed into gas-phase ions, the gas-phase ions enter the vacuum chamber through an atmospheric pressure interface, the gas-phase ions are transmitted to the next stage through focusing, cooling and guiding of ion guiding, the gas-phase ions enter the mass analyzer of the prismatic linear ion trap through a front end cover, the gas-phase ions are captured by radio frequency voltage (RF) applied to a main body electrode, the gas-phase ions are stored in the prismatic linear ion trap through collision cooling, and in the mass analysis stage, the ions are separated along a central area under the combined action of the radio frequency voltage (RF) of the main body electrode and auxiliary excitation signals (AC) of side electrodes, are orderly ejected along a rear end cover and are captured by an ion detector. Fig. 13 shows the method of use in radial extraction, and unlike fig. 12, the ion detector 608 is mounted directly opposite the ion extraction slot, in this method the prismatic linear ion trap mass analyzer structure must be the body electrode slot structure of the second embodiment. Fig. 14 shows the method of use with both axial and radial extraction, and as such, in this method, the prismatic linear ion trap mass analyzer structure must be the body electrode slotted structure of the second embodiment.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims (8)

1. A prismatic linear ion trap mass analyzer is characterized in that the material of the prismatic linear ion trap mass analyzer is conductive metal material or insulating material plated with conductive coating, and the prismatic linear ion trap mass analyzer is defined by four groups of working columnar electrode structures and two end cover electrodes: the four groups of columnar electrodes have the same appearance structure, wherein each two groups of columnar electrodes are a pair and are arranged in pairs, the centers of the end cover electrodes are provided with at least one through hole, and the two end cover electrodes are respectively arranged at two ends of the columnar electrodes.

2. A prismatic linear ion trap mass analyser as claimed in claim 1 wherein all electrodes are distributed completely symmetrically about a central axis in the z direction and the central region bounded by four sets of electrodes in the spatial configuration also forms a regular prismatic space.

3. The prismatic linear ion trap mass analyzer of claim 1, wherein each set of working cylindrical electrode structures consists of three electrodes, a main electrode and two side electrodes, the three electrodes together forming a regular prismatic structure.

4. A prismatic linear ion trap mass analyser as claimed in claim 1 wherein the central region bounded by the four sets of electrodes in the ion introduction direction also forms a narrow end of a right prismatic space, the end cap electrode at that location being the ion introduction electrode.

5. The prismatic linear ion trap mass analyzer of claim 3, wherein the voltages on each set of working cylindrical electrode structures are applied in a manner such that: radio frequency voltage is applied to the main electrode, and auxiliary excitation voltage is applied to the side electrode.

6. A prismatic linear ion trap mass analyser as claimed in claim 3 wherein said four body electrodes may or may not be apertured or slit for ion extraction detection.

7. The prismatic linear ion trap mass analyzer of claim 5, wherein the auxiliary excitation voltage is applied to the side electrodes in such a way that the auxiliary excitation voltage is applied to the side electrodes of the two oppositely disposed sets of working cylindrical electrode structures or to all the side electrodes.

8. The prismatic linear ion trap mass analyzer of claim 6, wherein when there is a small aperture or slit in the bulk electrode, the efficiency of ion ejection in the direction of the slit can be improved by independently adjusting the position of the set of electrodes.

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