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 analyzer, in particular to a prismatic linear ion trap mass analyzer.

Background technique

Mass spectrometer is a representative of modern high-end analytical instruments. It has the advantages of strong qualitative ability and high sensitivity, and is an effective tool for trace detection of low-level substances. At present, mass spectrometers have been widely used in important fields such as basic science, environmental protection, aerospace engineering and energy analysis. In order to meet the needs of the rapid development of society, the development trend of mass spectrometers in the future is mainly divided into three directions: non-magnetization, mainly for the huge weight and volume of traditional magnetic mass spectrometers, the inaccessibility of strong magnetic fields, and the high maintenance costs of magnetic fields, etc. To solve the problem, develop a high-performance non-magnetization mass spectrometer; miniaturize, take the mass spectrometer out of the laboratory, so that it can meet the needs of emergency detection and on-site in-situ analysis; simplify, the core components such as the mass analyzer in the mass spectrometer The structure is optimized to simplify its processing technology, reduce the overall cost, and improve its adaptability to harsh environments.

The mass analyzer is the core component of the mass spectrometer and determines the analytical performance of the mass spectrometer. Different kinds of mass spectrometers use different mass analyzers, and these mass analyzers achieve ion mass-to-charge ratio separation in different ways. At present, the commonly used mass analyzers are magnetic sector analyzer (magnetic sector), time-of-flight analyzer (TOF), quadrupole analyzer (QMF), ion trap analyzer (Ion Trap), Fourier analyzer Transform mass analyzer (FT-ICR) and orbital ion trap mass analyzer (Orbitrap). Among many mass analyzers, the ion trap mass analyzer has the advantages of simple structure, low requirement for vacuum, and multi-stage tandem mass spectrometry analysis. It shows unique development advantages and has strong miniaturization potential. Traditional mass analyzers are divided into three-dimensional ion traps and linear ion traps. Linear ion trap mass analyzers have higher ion storage capacity and therefore higher detection sensitivity and dynamic analysis range. Research and experiments have shown that the ion storage capacity of the linear ion trap with the same geometric size is more than 20 times that of the traditional three-dimensional ion trap under the same premise of not causing the ion space charge effect, which means that the dynamic performance of the mass spectrometer using the linear ion trap is The range is at least an order of magnitude higher than conventional 3D ion trap mass spectrometers. Further, the multi-stage mass spectrometry analysis function of the linear ion trap can greatly improve the qualitative ability of substances in the single mass spectrometry mode, especially in the case of complex matrix interference in the actual working environment, it can effectively remove chemical background interference and quickly locate. target ion and provide chemical structure information of the target ion. Miniaturized mass spectrometers have the characteristics of light weight, small size and low power consumption, and have great advantages and potential in terms of portability, timeliness, simplicity and cost. Therefore, the miniaturization of mass spectrometers has become an important trend in the development of analytical instruments. In view of the current research and development direction of mass spectrometry instruments and the demand for miniaturization, portability, high-throughput analysis methods and independent intellectual property rights, 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 hyperbolic cylindrical electrodes. The hyperboloid structure requires extremely high machining precision and assembly precision. Generally, the mechanical error is required to be within a few microns, and the cost is high. This makes the current ion trap mass spectrometer expensive and difficult to promote and popularize. In recent years, the development of miniaturized and low-cost miniaturized ion trap mass spectrometers has become a hot spot in the field of mass spectrometry, resulting in more linear ion traps with simplified electrode structures. The rectangular ion trap (RIT) proposed by Cooks et al. combines the simple structure of a cylindrical ion trap (CIT) with the advantages of a linear ion trap (LIT) with strong storage capacity. It is only surrounded by six planar electrodes, replacing the traditional hyperboloid. structure, its processing and assembly are relatively simple. The simple structure and excellent analytical performance of the rectangular ion trap make it the first choice for mass analyzers in miniaturized mass spectrometers, and it has been successfully applied to make small benchtop mass spectrometers and portable mass spectrometers. Subsequently, various mass analyzers including printed circuit board rectangular ion trap mass analyzer (PCB ion trap), PCB array ion trap, triangular trap electrode structure linear ion trap and other mass analyzers appeared, all of which have good ion storage and mass analysis capabilities. , but they are all based on the ion extraction method of resonance excitation, and this method is to open an ion extraction slot on the electrode of the linear ion trap for ion extraction. Although the ion radial extraction method has higher extraction efficiency, it requires a perfect quadrupole field in the ion trap structure, so the precision of electrode processing and assembly is higher. At the same time, there are certain shortcomings in the process of radially ejecting ions in the linear ion trap: an ion extraction slot must be opened on the ion trap electrode for ion extraction, which will cause distortion of the electric field pattern inside the ion trap, resulting in ions with other mass-to-charge ratios. At the same time, it will have a serious impact on the final ion mass resolution and weaken the mass analysis capability of the ion trap. Secondly, the radial exit method is not suitable for multiple devices to perform tandem mass spectrometry, because the radially exited ions are not easily captured by the next-stage mass analyzer for further analysis. In addition, in the radial emission mode, ions are emitted from the ion emission slots on the two electrodes respectively, and an ion detector must be installed on each side of the mass analyzer to detect the emitted ions, which not only increases the complexity of the mass spectrometer structure, but also increases the complexity of the mass spectrometer. It also increases the cost of ion mass analysis. The linear ion trap axial exit mode can effectively solve this problem.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the purpose 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 a conductive metal material or an insulating material plated with a conductive coating, and consists of four groups of working columnar The electrode structure is surrounded by two end cap electrodes: the four groups of columnar electrodes have exactly the same shape and structure, and each of the two groups of columnar electrodes is a pair, which are placed opposite each other. The end cap electrodes are respectively arranged at both ends of the columnar electrodes. All electrodes are completely symmetrically distributed around the central axis in the z-direction, and the central area surrounded by four groups of electrodes also forms a regular prism space in terms of spatial structure. Each group of working columnar electrodes is composed of three electrodes, a main electrode and two side electrodes, wherein a radio frequency voltage is applied to the main electrode, an auxiliary excitation voltage is applied to the side electrodes, and the auxiliary excitation voltage is applied to the side electrodes. The auxiliary excitation voltage is applied to the side electrodes on the two groups of working columnar electrode structures, or the auxiliary excitation voltage is applied to all side electrodes.

Preferably, the ion introduction direction of the prismatic linear ion trap mass analyzer is fixed so that the central area surrounded by four groups of electrodes also forms a narrow end of a regular prism space, and the end cap electrode at this position is the ion introduction electrode.

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

Preferably, the main electrodes of the four groups of columnar electrodes may have small holes or slits for ion extraction detection, or may not have small holes or slits. When there are small holes or slits on the main electrode, the position of the group of electrodes can be adjusted independently to improve the efficiency of ions ejecting in the direction of the slit.

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

Preferably, when the number of the end cap electrodes is two or more, one of them is located at one end of the linear ion trap for ion injection, and the others are arranged in sequence at the other end of the linear ion trap.

Compared with the prior art, the present invention has the following beneficial effects: First, the overall electrode structure of the traditional linear ion trap is modified, and the side electrode structure for applying auxiliary excitation is added, which gradually increases in the axial direction of the ion movement. The enlarged electrode with auxiliary excitation voltage can guide the ions to gather to the exit position in an orderly manner, thereby realizing the axial ejection of the ions. Second, the structure of gradually increasing the space in the ion exit direction can effectively reduce the ion space charge effect when more ions are injected, and improve the overall resolution capability of the mass analyzer. The third and fourth groups of electrodes are exactly the same, and the overall structure is rotationally symmetric around the central axis, which reduces the difficulty of processing and assembly, and also facilitates the adjustment of the internal space to optimize the electric field distribution in the well.

Description of drawings

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

FIG. 1 is a schematic structural diagram of Embodiment 1 of the present invention.

FIG. 2 is a schematic diagram of the electrode voltage application method of the prismatic linear ion trap mass analyzer in the first embodiment.

3 is a schematic view of the prismatic linear ion trap mass analyzer in the first embodiment along the positive direction of the z direction.

FIG. 4 is a schematic view of the prismatic linear ion trap mass analyzer along the reverse z direction in the first embodiment.

5 is a schematic cross-sectional view of a group of electrode sheets of the prismatic linear ion trap mass analyzer in the first embodiment.

FIG. 6 is a timing diagram of the application of the radio frequency voltage and the auxiliary excitation voltage in the first embodiment.

FIG. 7 is a schematic structural diagram of Embodiment 2 of the present invention.

FIG. 8 is a schematic diagram of a front view in the z-direction of a single electrode after slotting and stretching in Example 2. FIG.

FIG. 9 is a schematic diagram of a front view in the z-direction of the two opposite electrodes after slotting and stretching in the second embodiment.

FIG. 10 is a schematic diagram of a second structure of Embodiment 2 of the present invention.

11 is a schematic cross-sectional view of a group of slotted electrode pieces of the prismatic linear ion trap mass analyzer in the second embodiment.

FIG. 12 is a schematic diagram of the specific application of the present invention to a mass spectrometer.

FIG. 13 is a second schematic diagram of the present invention being specifically applied to a mass spectrometer.

FIG. 14 is a third schematic diagram of the present invention being specifically applied to a mass spectrometer

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

The prismatic linear ion trap mass analyzer of the present invention is surrounded by four groups of working columnar electrode structures and two end cap electrodes: the electrode material is a conductive metal material or an insulating material plated with a conductive coating, and each two groups of columnar electrodes are A pair, placed opposite to each other, the center of the end cap electrode is provided with at least one through hole, and the two end cap electrodes are respectively arranged at both ends of the columnar electrode. All electrodes are completely symmetrically distributed around the central axis in the z-direction, and the central area surrounded by four groups of electrodes also forms a regular prism space in terms of spatial structure. Each group of working columnar electrode structure consists of three electrodes, the main electrode and two side electrodes, in which only radio frequency voltage is applied to the main electrode, and radio frequency voltage + auxiliary excitation voltage or only auxiliary excitation voltage is applied to the side electrodes. The main electrode may have small holes or slits for ion extraction and detection, or may not have small holes or slits.

Among them, the four groups of columnar electrodes have exactly the same shape and structure, and the length, width and height of the electrodes are adjustable, that is, by changing the length, width and height of the four groups of columnar electrodes and the relative position and voltage application method between the four groups of columnar electrodes The electric field distribution in the space enclosed by the four groups of columnar electrodes can be adjusted to obtain good ion storage and mass analysis performance.

The main electrodes of the four groups of cylindrical electrodes can have small holes or slits for ion extraction and detection, or no small holes or slits. When there are small holes or slits on the main electrodes, the group can be adjusted independently The position of the electrodes increases the efficiency of ions ejection in the direction of the slit.

A DC signal is applied to the end cap electrodes to form an axial confinement field, and a radio frequency voltage RF is applied to the cylindrical electrodes to form a radial confinement field. The radio frequency (RF) signals applied to the two groups of cylindrical electrodes opposite in the x and y directions are the same, x and y The radio frequency (RF) signals applied to the two pairs of electrodes adjacent in the direction have the same amplitude and opposite directions.

Example 1

The structure of the prismatic linear ion trap mass analyzer of the present invention is shown in FIG. 1 . The first group of electrodes is composed of the central 101 and two side electrodes 105 and 106, and the other three groups of electrodes are 102, 107, and 108 electrode groups, 103, 109, and 110 electrode groups, and 104, 111, and 112 electrode groups, respectively. The entire working area of the linear ion trap consists of the four sets of electrodes. The radio frequency voltage (RF) and the auxiliary excitation voltage (AC) are applied in the same manner as shown in FIG. 2 . The radio frequency voltage application mode is as follows: the first group of electrode body electrodes 101 and the third group of electrode body electrodes 103 are applied with equal magnitudes and the same direction. The radio frequency voltage (RF+), the second group of electrode body electrodes 102 and the fourth group of electrode body electrodes 104 are applied with the same magnitude and the same direction and the same radio frequency voltage (RF-). At the same time, the first group of electrode side electrodes 105 and 106 and the third group of electrode side electrodes 107 and 108 are connected to each other, and the auxiliary excitation voltage (AC1) is applied. The second group of electrode side electrodes 109 and 110 and the fourth group of electrode side electrodes 111 and 112 Connect to each other, and apply an auxiliary excitation voltage (AC2), wherein at least one of AC1 and AC2 is not 0, and both AC1 and AC2 are independent voltage values and adjustable in phase. Figure 3 shows the position distribution of the broad face of the four prism electrodes, where the square size of the broad face is smaller than the diameter of the internal electric field at the end, that is, L1 < 2r1; Figure 4 shows the position distribution of the narrow face of the four prism electrodes, where the size of the narrow face The size of the square is smaller than the diameter of the electric field inside the end, ie L2<2r2. Figure 5 shows a schematic cross-sectional view of the electrode, wherein 301 is the main electrode, 302 and 303 are side electrodes, and the structural parameters of 302 and 303 are identical. In this embodiment, the ions are introduced along the z-axis direction, the narrow port is in, and the wide port is out, that is, the direction indicated by the arrow in the center of the figure, as shown in Figure 6, is the same as the traditional linear ion trap analysis process. In the cooling stage, a constant RF value is applied, and the amplitude of the radio frequency voltage (RF) is scanned in the mass analysis stage; the application time of the auxiliary excitation signal (AC) is only in the mass analysis stage. Through the combined action of scanning radio frequency voltage (RF) and auxiliary excitation signal (AC), the stored ions can be detected by expelling the ordered wide-mouth end along the z-axis direction from the linear ion trap.

Embodiment 2

FIG. 7 is another structure of the prismatic linear ion trap mass analyzer of the present invention. Compared with the first embodiment, ion extraction grooves 413 and 414 are opened on the two opposite main electrodes 402 and 404. Due to the appearance of ion extraction holes, the introduction of high-order field components will inevitably lead to the introduction of high-order field components, which affects the ion extraction. Efficiency, it is necessary to improve the efficiency of ion extraction by means of electrode position adjustment. As shown in Figure 8, when the ion exit hole is opened on the main electrode of 404, the ion extraction efficiency can be improved by increasing the position of the electrode from the central axis, that is, r3>r2. The rotational symmetry axis of the electrode group composed of 411 and 412 needs to be strictly parallel to the symmetry axis of the central area and the rotational symmetry axis of the other three groups of electrodes; as shown in Fig. When exiting the small hole, the ion extraction efficiency can also be improved by increasing the position of the electrode from the central axis, that is, r3>r2, r4>r2. During the stretching process, the electrode group composed of 402, 407, and 408 The two rotational symmetry axes of the electrode group composed 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. The size relationship between r3 and r4 is uncertain, and the general ion extraction position is Larger radius, that is, if it needs to be extracted from slot 403, then r3>r4; if ion detectors are installed in both bidirectional ion extraction slots, then r3 can be the same as r4. FIG. 10 is a schematic diagram of the structure when all four electrodes are slotted, and FIG. 11 is a schematic diagram of the interface of the slotted electrode sheet.

Embodiment 3

Fig. 12, Fig. 13, Fig. 14 show the specific application of the prismatic linear ion trap mass analyzer in the mass spectrometer. In Figure 12, 501 is the ion source, used to generate ions to be analyzed; 502 is the atmospheric pressure interface, used for the introduction of the sample from the outside; 503 is the vacuum chamber, used for the vacuum environment guarantee for mass spectrometry analysis; 504 is the ion guide, It is used for focusing, cooling, guiding and transporting ions to the next stage; 505 is the working electrode body of the prismatic linear ion trap mass analyzer, and 506 and 507 are the front and back cover electrodes respectively, which together constitute the mass analyzer, which is used to complete different 508 is an ion detector, which is used for the collection of ions separated by the mass analyzer and supplies the next signal processing and analysis; 509 is a vacuum pump responsible for maintaining the vacuum inside the vacuum chamber. The mass analysis process is that the ion source converts the sample to be analyzed into gas-phase ions, enters the vacuum chamber through the atmospheric pressure interface, and is focused, cooled, and guided by the ion guide, and then transferred to the next stage, and enters the prismatic linear ion trap through the front cover. Inside the mass analyzer, the ions are trapped by the radio frequency (RF) applied to the main electrode, and the ions are stored in the prismatic linear ion trap after collision cooling. Under the combined action of the electrode-assisted excitation signal (AC), it is separated along the central region and ejected along the rear end cap in an orderly manner, and is captured by the ion detector. The prismatic linear ion trap mass analyzer structure in Figure 12 can be the first embodiment and any structure of the second embodiment. Fig. 13 shows the usage method of radial extraction. The difference from Fig. 12 is that the installation position of the ion detector 608 is facing the ion extraction slot. In this method, the prismatic linear ion trap mass analyzer structure must be an embodiment Two main body electrode slotted structure. Figure 14 shows the usage method when both axial exit and radial exit are provided. Similarly, in this method, the structure of the prismatic linear ion trap mass analyzer must be the main electrode slotted structure of the second embodiment.

The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and those skilled in the art can make various variations or modifications within the scope of the claims, which do not affect the essential content of the present invention.

Claims (8)

1. a prismatic linear ion trap mass analyzer, it is characterized in that, the material of described prismatic linear ion trap mass analyzer is conductive metal material or is the insulating material that is plated with conductive coating, and is composed of four groups of working columnar electrode structures. Surrounded by two end cap electrodes: the four groups of columnar electrodes have exactly the same shape and structure, wherein each two groups of columnar electrodes are a pair, and they are placed opposite each other. The cover electrodes are arranged on both ends of the columnar electrodes, respectively. 2. The prismatic linear ion trap mass analyzer according to claim 1, wherein all electrodes are completely symmetrically distributed around the central axis of the z-direction, and the central area surrounded by four groups of electrodes also forms a regular prism on the spatial structure space. 3. The prismatic linear ion trap mass analyzer according to claim 1, wherein each group of working columnar electrodes is composed of three electrodes, the main electrode and two side electrodes, and the three electrodes together form a regular prism Structure. 4 . The prismatic linear ion trap mass analyzer according to claim 1 , wherein the ion introduction direction is fixed so that the central region surrounded by four groups of electrodes also forms a narrow mouth end of a regular prism space, and the end at the position The cover electrode is an ion introduction electrode. 5 . The prismatic linear ion trap mass analyzer according to claim 3 , wherein the voltage application mode on each group of working columnar electrode structures is as follows: RF voltage is applied to the main electrode, and auxiliary excitation voltage is applied to the side electrodes. 6 . 6. The prismatic linear ion trap mass analyzer according to claim 3, wherein the four main electrodes can have small holes or slits for ion extraction detection, or can not have small holes or slits . 7 . The prismatic linear ion trap mass analyzer according to claim 5 , wherein the auxiliary excitation voltage is applied to the side electrodes by applying auxiliary excitation voltage to the side electrodes on the oppositely placed two groups of working columnar electrode structures. 8 . Or apply auxiliary excitation voltage to all side electrodes. 8 . The prismatic linear ion trap mass analyzer according to claim 6 , wherein when there are small holes or slits on the main electrode, the position of the group of electrodes can be adjusted independently to increase the ions in the slit direction. 9 . Efficiency when popping.

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