Mass spectrometer, mass spectrometry method and detection system

Abstract

The present invention relates to a mass spectrometer, a mass spectrometry method and a detection system, wherein the mass spectrometer comprises: a vacuum chamber, wherein the working gas pressure P of the vacuum chamber is in the range of 0.1Pa≤P≤10Pa; a linear ion trap, which is arranged in the vacuum chamber, wherein the field radius r≤5mm of the linear ion trap; and a power supply, which is configured to provide a radio frequency voltage to the linear ion trap, wherein the frequency f of the radio frequency voltage is in the range of 2MHz≤f≤10MHz. Since the vacuum degree is relatively low, the vacuum condition can be achieved by evacuating with a rough vacuum pump. Compared with the combined pump unit composed of a turbomolecular pump and a rough vacuum pump, which is usually used in the mass spectrometer using the traditional linear ion trap, the rough vacuum pump has a lower pumping speed, a smaller volume and a lower manufacturing cost. Therefore, the mass spectrometer provided by the present invention can reduce the overall volume of the vacuum pump matched with the vacuum chamber, thereby realizing the miniaturization and low cost of the mass spectrometer.

Description

Technical Field

[0001] The present invention relates to the technical field of mass spectrometry instruments, and in particular to a mass spectrometer, a mass spectrometry method and a detection system. Background Art

[0002] Miniaturization is one of the main trends in the development of mass spectrometers, and the miniaturization of mass spectrometers is a systematic project that is severely restricted by factors such as the performance requirements of each component and the difficulty of processing.

[0003] For example, because the pump system accounts for a large proportion of the weight and volume of the mass spectrometer, the miniaturization of the pump system is one of the important directions of miniaturization development, and the miniaturization of the pump system is constrained by the performance requirements of other components. Generally speaking, if the volume or weight of the pump system is reduced, the vacuum performance it can provide will also decrease. However, many components in the mass spectrometer system have certain requirements for vacuum performance. If the vacuum performance provided by the pump system cannot meet the vacuum requirements of these components (such as the mass analyzer), it will cause the analysis performance of the mass spectrometer to decrease, and even make it difficult for the mass spectrometer to meet the requirements (for example, the resolution of the mass analyzer cannot meet the requirement that the half-peak width is less than or equal to 1Th).

[0004] In the prior art, in order to meet the resolution requirement of half-peak width less than or equal to 1Th in a wide mass-to-charge ratio range, such as a mass-to-charge ratio range of 20-600Th, the mass analyzer needs to work in a vacuum environment less than 0.1Pa, which puts high requirements on the vacuum performance of the pump system. Therefore, the pump system usually needs to be composed of a turbomolecular pump and a rough vacuum pump. Since the overall volume and weight of the pump system are large, it not only makes it difficult to miniaturize the equipment, but also makes the manufacturing cost of the mass spectrometer high.

[0005] Patent US8525111B1 discloses a mass spectrometry system, including an ion source, an ion trap and a detector, wherein two or more of the ion source, ion trap and detector are set in an air pressure environment of 13.3Pa-1atm. Within this air pressure range, it is difficult for a mass spectrometer to use detectors that rely on high voltages, such as electron multipliers / dynodes, and when using a Faraday cup to detect charges, gain cannot be generated and a high-power amplifier is required. Therefore, the bandwidth is limited and the scanning speed is difficult to increase. On the other hand, the quality of the spectrum is poor, with low resolution and signal-to-noise ratio, which affects the sensitivity and qualitative and quantitative capabilities.

[0006] As disclosed by Jiang et al. in "Low-vacuum cylindrical ion trap mass spectrometry" (Instrumentation Science & Technology, 2018), a cylindrical ion trap (CIT) was used with a 2.4 MHz RF power frequency, and a half-peak width FWHM ≈ 2 was achieved under a gas pressure of 2 Pa. If a higher frequency RF voltage is applied, discharge will occur, hindering further improvement of resolution.

[0007] As disclosed by Blakeman et al. in "High Pressure Mass Spectrometry: The Generation of Mass Spectra at Operating Pressures Exceeding 1Torr in a Microscale Cylindrical Ion Trap" (Analytical Chemistry, 2016), a cylindrical ion trap can achieve FWHM ≤ 1Th at a higher RF power frequency (6-9.5MHz) and at a very high gas pressure (160Pa). However, the cylindrical ion trap has a weak storage capacity, which will affect the dynamic range of the mass spectrometer. Moreover, the field radius of the CIT used is only 0.5mm, which further reduces the dynamic range. In addition, at such a high RF frequency, in order to avoid discharge, the upper limit of the mass that can be measured by the mass spectrometer is greatly reduced.

[0008] Xu et al. disclosed in "Towards High Pressure Miniature Protein Mass Spectrometer: Theory and Initial Results" (Journal of Mass Spectrometry, 2019) that the use of a linear ion trap (LIT) is less affected by space charge than a cylindrical ion trap, but has a lower resolution. Even at a relatively low gas pressure (1.3 Pa), the half-peak width FWHM of this linear ion trap is ≥ 1.5 Th. Summary of the invention

[0009] The present invention is proposed to solve the above-mentioned technical problems, and its purpose is to provide a mass analyzer that can operate stably under low vacuum conditions, and in a wider mass-to-charge ratio range, such as the range of 20-600Th, the resolution of mass analysis can still be maintained at a high level, such as a mass spectrometer with a resolution level of half-peak width less than or equal to 1Th.

[0010] The mass spectrometer includes: a vacuum chamber, wherein the working gas pressure P of the vacuum chamber is in the range of 0.1Pa≤P≤10Pa; a linear ion trap arranged in the vacuum chamber, wherein the field radius r≤5mm of the linear ion trap; and a power supply configured to provide a radio frequency voltage to the linear ion trap, wherein the frequency f of the radio frequency voltage is in the range of 2MHz≤f≤10MHz.

[0011] In the above technical solution, because the linear ion trap as a mass analyzer is set in 0.1Pa≤P≤10Pa, and the mass analyzer is basically the device with the highest vacuum performance requirements in the mass spectrometer, generally speaking, the minimum gas pressure required by the mass spectrometer can be within the range of 0.1Pa≤P≤10Pa, and then a pump with a smaller volume and lower pumping speed can be used to meet the vacuum requirements of the mass spectrometer, which facilitates the miniaturization of the mass spectrometer. In addition, the linear ion trap working in this gas pressure range can improve the sensitivity accordingly because the ion cooling performance is improved and the efficiency of ion introduction and expulsion is also improved accordingly.

[0012] On the other hand, in the process of creating the present invention, the inventors found that by limiting the field radius and voltage frequency of the linear ion trap within the above numerical range, the linear ion trap can still achieve a high resolution level even if it operates in the gas pressure range of 0.1Pa≤P≤10Pa. For example, a resolution level of half-peak width less than or equal to 1Th can be achieved in the range of 20-600Th.

[0013] Among them, if the working gas pressure P of the vacuum chamber is too low, for example, lower than 0.1Pa, it will make it difficult to use a small vacuum pump with a low pumping speed, which is not conducive to the miniaturization of the mass spectrometer; if the working gas pressure of the vacuum chamber is too high, for example, higher than 10Pa, it is easy to cause discharge of the detector and the ion trap.

[0014] The frequency f of the RF voltage should not be too large or too small. When the frequency f is too small, for example, when the frequency f is less than 2MHz, the resolution and sensitivity of the mass spectrometer are seriously reduced. When the frequency f is too large, for example, when the frequency f is greater than 10MHz, not only the difficulty of power supply production increases, but also it is easy to cause discharge and sample dissociation.

[0015] The field radius r should not be too large. For example, when the field radius r is greater than 5 mm, if a high frequency voltage is applied to the electrodes of the linear ion trap with a field radius that is too large, it is easy to cause discharge and is not conducive to improving the resolution.

[0016] Through the above approach, the mass spectrometer provided by the present invention can take into account multiple factors such as miniaturization, processing difficulty, resolution, sensitivity, stability, etc., and provide a mass analyzer that can stably operate under low vacuum conditions (for example, 0.1Pa≤P≤10Pa), and within a wider mass-to-charge ratio range, such as 20-600Th, the resolution of mass analysis can still be maintained at a high level, such as a mass spectrometer with a resolution level of half-peak width less than or equal to 1Th.

[0017] In the preferred technical solution of the present invention, it also includes: a vacuum pump, which is connected to the vacuum chamber, wherein the vacuum pump is a reciprocating vacuum pump, a rotary vane vacuum pump, a piston vacuum pump, a vortex dry pump, a diaphragm vacuum pump or a Roots pump.

[0018] According to the preferred technical solution, because the mass analyzer can operate stably under low vacuum conditions (for example, 0.1Pa≤P≤10Pa), the vacuum degree requirement of the mass spectrometer can be met by using the above-mentioned type of rough vacuum pump whose ultimate vacuum can be achieved in the range of 0.1Pa≤P≤10Pa, and the above-mentioned type of vacuum pump is more suitable for miniaturization, thereby facilitating the miniaturization of the mass spectrometer.

[0019] In a preferred technical solution of the present invention, the range of the pumping speed S of the vacuum pump is: S≤100L / min.

[0020] According to the preferred technical solution, because the mass analyzer can operate stably under low vacuum conditions (for example, 0.1Pa≤P≤10Pa), the vacuum requirement of the mass spectrometer can be met by using a rough vacuum pump operating at a low pumping speed, and a rough vacuum pump with a low pumping speed requirement is more suitable for miniaturization, thereby facilitating the miniaturization of the mass spectrometer.

[0021] In a preferred technical solution of the present invention, it also includes: a capillary tube for introducing the sample into the vacuum chamber.

[0022] The capillary can be used to introduce neutral samples or ions. In some technical solutions, the capillary is used as an atmospheric pressure interface. In these technical solutions, the inner diameter of the capillary can be set to be smaller, preferably less than 100um, so that a low vacuum condition of 0.1Pa≤P≤10Pa can be achieved by using a small vacuum pump with a lower pumping speed. In other technical solutions, the mass spectrometer can also be used in conjunction with a chromatograph, for example, the capillary can be configured as a capillary chromatographic column of a gas chromatograph.

[0023] In the preferred technical solution of the present invention, it also includes: a membrane injector connected to the vacuum chamber.

[0024] According to the preferred technical solution, a mass spectrometer providing a membrane injection interface can be conveniently used in conjunction with a VOC detection device, and because the provided mass spectrometer is a miniaturized mass spectrometer, such a mass spectrometer can be integrated into a VOC detection device, for example, integrated into the chassis of an online monitoring device, thereby improving the accuracy of VOC detection.

[0025] In a preferred technical solution of the present invention, it also includes: a detector, which is arranged at the ion outlet of the linear ion trap.

[0026] According to this preferred technical solution, a detector is set at a position near the ion outlet of the linear ion trap to collect ion intensity signals with higher resolution. The linear ion trap and the detector can be integrated in the same vacuum chamber to effectively utilize the internal space of the device, thereby facilitating the miniaturization of the mass spectrometer.

[0027] In a preferred technical solution of the present invention, it also includes: an ion source, which is arranged between the sample inlet of the vacuum chamber and the linear ion trap.

[0028] In a preferred technical solution of the present invention, the ion source is one of a photoionization ion source, a dielectric barrier discharge ion source, a glow discharge ion source or an electron bombardment ion source.

[0029] Integrating internal ionization sources such as photoionization ion source, dielectric barrier discharge ion source, glow discharge ion source or electron bombardment ion source in the same vacuum chamber can effectively utilize the space of a single vacuum chamber to complete the construction of the entire mass spectrometry system, facilitating the miniaturization of the mass spectrometer.

[0030] In a preferred technical solution of the present invention, the range of the field radius r of the linear ion trap is:

[0031] Any one of r≤1mm, 1mm≤r≤2mm, 2mm≤r≤3mm, 3mm≤r≤4mm and 4mm≤r≤5mm or a combination thereof.

[0032] In a preferred technical solution of the present invention, the frequency f of the radio frequency voltage is in the range of:

[0033] Any one of 2MHz≤f≤3MHz, 3MHz≤f≤4MHz, 4MHz≤f≤5MHz, 5MHz≤f≤6MHz, 6MHz≤f≤7MHz, 7MHz≤f≤8MHz, 8MHz≤f≤9MHz and 9MHz≤f≤10MHz or a combination thereof.

[0034] The present invention provides a mass spectrometry method, comprising the steps of: providing a linear ion trap with a field radius r≤5mm; providing a pressure environment of 0.1Pa≤P≤10Pa to the linear ion trap; and providing a radio frequency voltage with a frequency range of 2MHz≤f≤10MHz to the linear ion trap.

[0035] The present invention also provides a VOC online monitoring device with a mass spectrometer. Since the mass analyzer of the mass spectrometer provided by the present invention can stably operate under low vacuum conditions (for example, 0.1Pa≤P≤10Pa), and in a wide mass-to-charge ratio range, for example, in the range of 20-600Th or 20-400Th, the resolution of mass analysis can still be maintained at a high level, for example, a resolution level of half-peak width less than or equal to 1Th, high-resolution mass detection within the mass-to-charge ratio range can be well adapted to VOC (volatile organic compounds, volatile organic compounds) detection, and, because the mass spectrometer can be conveniently miniaturized, it can be placed in the cabinet of the VOC online monitoring device, occupying a small space, and the analysis accuracy of the VOC online monitoring device can be greatly improved.

[0036] The present invention further provides a chromatography-mass spectrometry device having a mass spectrometer. Because the mass spectrometer provided by the present invention can be conveniently miniaturized, it can be integrated and used in conjunction with a miniaturized chromatographic device, such as a micro gas chromatograph (micro-GC). The mass spectrometer can match the existing miniaturized chromatograph in terms of analysis speed and volume, significantly reducing the volume and weight of the chromatography-mass spectrometry device and improving the qualitative and quantitative capabilities of the mass spectrometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a partial structural schematic diagram of a mass spectrometer provided in Embodiment 1 of the present invention;

[0038] Figure 2 is a schematic structural diagram of a mass spectrometer provided in Embodiment 2 of the present invention;

[0039] Figure 3 yes Figure 2 A schematic cross-sectional view of the parallel electrodes of the linear ion trap;

[0040] Figure 4 Schematic diagram of the structure of the VOC online monitoring device provided in the third embodiment of the present invention;

[0041] Figure 5 is a schematic structural diagram of a chromatography-mass spectrometry device provided in Embodiment 3 of the present invention;

[0042] Figure 6 This is the mass spectrum obtained by mass spectrometry analysis of toluene using a linear ion trap with a field radius of r = 1 mm, a working gas pressure of P = 8.5 Pa, and a radio frequency of f = 4.14 MHz;

[0043] Figure 7This is the mass spectrum obtained by mass spectrometry analysis of toluene using a linear ion trap with a field radius of r = 1 mm, a working gas pressure of P = 8.5 Pa, and a radio frequency of f = 1.79 MHz;

[0044] Figure 8 This is the mass spectrum obtained by mass spectrometry analysis of toluene using a linear ion trap with a field radius of r = 1 mm, a working gas pressure of P = 8.3 Pa, and a radio frequency of f = 5.8 MHz;

[0045] Fig. 9 This is the simulation data of mass spectrometry analysis of reserpine using a linear ion trap with a field radius of r = 0.5 mm, a working pressure of P = 2 Pa, and a radio frequency of f = 9 MHz, with a peak at 609-611 Th;

[0046] Fig.10 This is the simulation data of mass spectrometry analysis of reserpine using a linear ion trap with a field radius of r = 1 mm, a working pressure of P = 2 Pa, and a radio frequency of f = 6 MHz, with a peak at 609-611 Th;

[0047] Fig.11 This is the simulation data of mass spectrometry analysis of reserpine using a linear ion trap with a field radius of r = 1 mm, a working pressure of P = 2 Pa, and a radio frequency of f = 5.4 MHz, with a peak at 609-611 Th;

[0048] Fig.12 This is the simulation data of mass spectrometry analysis of reserpine using a linear ion trap with a field radius of r = 2 mm, a working gas pressure of P = 2 Pa, and a radio frequency frequency of f = 4.2 MHz, with a peak at 609-611 Th.

[0049] Description of reference numerals:

[0050] 100, 200-mass spectrometer; 1-injection system; 2-ion source; 3-vacuum chamber; 4-linear ion trap, 41-parallel electrodes, 411-slit, 42-end cap electrode; 5-vacuum pump; 6-detector; 7-injection interface; 8-power supply; 9-VOC online monitoring equipment, 91-sampling device, 92-control unit; 10-chromatography-mass spectrometry equipment, 11-chromatographic device. DETAILED DESCRIPTION

[0051] Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, but includes various changes, substitutions, and modifications within the technical scope of the present disclosure.

[0052] Terminology and Explanation

[0053] It should be noted that, in this article, the term "rough vacuum pump" refers to a vacuum pump whose ultimate vacuum degree is within the low vacuum range (P≥0.1Pa). According to the operating principle or structural type, the "rough vacuum pump" can include but is not limited to: reciprocating vacuum pump, rotary vane vacuum pump, piston vacuum pump, scroll dry pump, diaphragm vacuum pump or Roots pump and other types.

[0054] The term "VOC online monitoring equipment" refers to monitoring equipment that is deployed at the monitoring point to continuously measure harmful organic gases in hazardous or industrial environments. "VOC" is the abbreviation of volatile organic compounds.

[0055] Implementation Method 1

[0056] Mass spectrometers using linear ion traps usually have high requirements for the vacuum degree of the vacuum chamber. Specifically, the gas pressure in the vacuum chamber usually needs to be maintained below 0.0003 mbar. Due to the high vacuum degree of this vacuum condition, when only one vacuum cavity is provided in the vacuum chamber, in order to achieve this vacuum condition, the pump system needs to provide a higher pumping speed. Accordingly, the space occupied by the pump system is also larger.

[0057] In order to further miniaturize the mass spectrometer, Figure 1 As shown, some embodiments of the present invention provide a mass spectrometer 100 capable of operating in a low vacuum environment, including: a vacuum chamber 3 with a working gas pressure P in the range of 0.1Pa≤P≤10Pa; a linear ion trap 4 arranged in the vacuum chamber 3, wherein the linear ion trap 4 is a hyperbolic linear ion trap, consisting of two groups of hyperbolic poles and two pole plates at both ends. One group of the two groups of poles is applied with an alternating voltage, and the other group is applied with two alternating voltages. A slit 411 is opened on one group of poles, and ions are driven to be ejected from the slit 411 by changing the three groups of alternating voltages.

[0058] In this embodiment, the field radius r≤5mm of the linear ion trap 4, where r is the radius of the inscribed circle of the two pairs of parallel electrodes of the linear ion trap 4; and a power supply 8 configured to provide a radio frequency voltage to the linear ion trap 4, where the frequency f of the radio frequency voltage is in the range of 2MHz≤f≤10MHz.

[0059] In some embodiments of the present invention, the range of the working pressure P of the vacuum chamber 3 is 0.1Pa≤P≤10Pa. The reason for such setting is that if the working pressure P is higher than 10Pa, the voltage applied by the linear ion trap 4 and the detector is relatively high, and the electrode spacing is small, which is easy to cause gas discharge under such a pressure range; if the working pressure P is less than 0.1Pa, it is difficult for the existing rough vacuum pump to achieve this vacuum condition. Since the vacuum degree of this vacuum condition is relatively low, the vacuum condition can be achieved by using a rough vacuum pump to evacuate the vacuum chamber 3. Compared with the conventional mass spectrometer using a linear ion trap, which is usually composed of a turbomolecular pump and a rough vacuum pump, the rough vacuum pump has a lower pumping speed, a smaller volume, and a lower manufacturing cost. Therefore, the mass spectrometer 100 provided in this embodiment can reduce the overall volume of the vacuum pump matched with the vacuum chamber 3, thereby realizing the miniaturization and low cost of the mass spectrometer. In addition, compared with the multi-stage vacuum chamber, the design of the single vacuum chamber has a shorter ion transmission path and a higher ion transmission rate, so that the number of ions available for mass spectrometry analysis is higher, thereby ensuring the sensitivity of the instrument. Moreover, compared with a mass spectrometer with a multi-stage vacuum chamber and matched with multiple vacuum pumps, the structure is simpler, easier to manufacture, and the manufacturing cost is reduced.

[0060] In the above technical solution, because the linear ion trap as a mass analyzer is set in 0.1Pa≤P≤10Pa, and the mass analyzer is basically the device with the highest vacuum performance requirements in the mass spectrometer, generally speaking, the minimum gas pressure required by the mass spectrometer can be within the range of 0.1Pa≤P≤10Pa, and then a pump with a smaller volume and lower pumping speed can be used to meet the vacuum requirements of the mass spectrometer, which facilitates the miniaturization of the mass spectrometer. In addition, the linear ion trap working in this gas pressure range can improve the sensitivity accordingly because the ion cooling performance is improved and the efficiency of ion introduction and expulsion is also improved accordingly.

[0061] On the other hand, in the process of creating the present invention, the inventors found that by limiting the field radius and voltage frequency of the linear ion trap within the above numerical range, the linear ion trap can still achieve a high resolution level even if it operates in the gas pressure range of 0.1Pa≤P≤10Pa. For example, a resolution level of half-peak width less than or equal to 1Th can be achieved in the range of 20-600Th.

[0062] Among them, if the working gas pressure P of the vacuum chamber 3 is too low, for example, lower than 0.1Pa, it will make it difficult to use a small vacuum pump with a low pumping speed, which is not conducive to the miniaturization of the mass spectrometer; if the working gas pressure of the vacuum chamber is too high, for example, higher than 10Pa, it is easy to cause discharge of the detector and the ion trap.

[0063] The frequency f of the RF voltage should not be too large or too small. When the frequency f is too small, for example, when the frequency f is less than 2MHz, the resolution and sensitivity of the mass spectrometer are seriously reduced. When the frequency f is too large, for example, when the frequency f is greater than 10MHz, not only the difficulty of power supply production increases, but also it is easy to cause discharge and sample dissociation.

[0064] The field radius r should not be too large. For example, when the field radius r is greater than 5 mm, if a high frequency voltage is applied to the electrodes of the linear ion trap with a field radius that is too large, it is easy to cause discharge and is not conducive to improving the resolution.

[0065] Through the above methods, the mass spectrometer provided by the present invention can take into account multiple factors such as miniaturization, processing difficulty, resolution, sensitivity, stability, etc., and provide a mass analyzer that can operate stably under low vacuum conditions (for example, 0.1Pa≤P≤10Pa), and in a wider mass-to-charge ratio range, such as 20-600Th, the resolution of mass analysis can still be maintained at a high level, for example, a mass spectrometer with a resolution level of half-peak width less than or equal to 1Th.

[0066] In some embodiments, the mass spectrometer further includes a gas replenishment system communicated with the vacuum chamber 3 , and the gas replenishment system can replenish one or more gases, such as an inert gas, into the vacuum chamber 3 .

[0067] It should be noted that the appendix of this embodiment Figure 1 Only the necessary structures of the mass spectrometer 100 that can help achieve the purpose of the present invention are shown. Those skilled in the art can easily imagine that the mass spectrometer 100 also has other structures such as an ion source. In this embodiment, the type, position and size of other structures such as the ion source are not limited.

[0068] Implementation Method 2

[0069] like Figure 2 and Figure 3 As shown, the main difference between the mass spectrometer 200 provided in this embodiment and the mass spectrometer 100 provided in the first embodiment is that it also includes: an injection system 1, an ion source 2, a vacuum pump 5 and a detector 6.

[0070] Wherein, the injection system 1 is connected to the vacuum chamber 3 via the injection interface 7, so as to introduce the sample to be analyzed into the vacuum chamber 3. Wherein, the injection system 1 can be a membrane injector connected to the vacuum chamber 3, so as to be suitable for the detection of volatile organic compounds. The injection interface 7 is one of a conical hole, a cylindrical hole or a capillary, and the capillary can be used for the introduction of neutral samples or for the introduction of ions. In some technical schemes, the capillary is used as an atmospheric pressure interface. In these technical schemes, the inner diameter of the capillary can be set to be smaller, preferably less than 100um, so that a low vacuum condition of 0.1Pa≤P≤10Pa can be achieved by using a small vacuum pump with a lower pumping speed. In other technical schemes, the mass spectrometer can also be used in conjunction with a chromatograph, for example, the capillary can be configured as a capillary chromatographic column of a gas chromatograph. In the following, the injection interface 7 is described as an example of a capillary.

[0071] The linear ion trap 4 is arranged in the vacuum chamber 3 and can control the trajectory of the ion beam. The linear ion trap 4 includes at least two pairs of parallel electrodes 41 which are arranged in parallel and spaced apart and end cap electrodes 42 which are arranged at both ends of the length direction of the parallel electrodes 41. The parallel electrodes 41 are evenly distributed relative to the geometric center axis of the linear ion trap 4 and extend substantially along the injection direction of the ion beam. A slit 411 for ion extraction is provided on one of the parallel electrodes 41. Under the action of a specific electric field, the ions can be sequentially extracted to the detector 6 according to the mass-to-charge ratio (m / z).

[0072] It should be noted that the specific electric field mentioned here is usually to apply a radio frequency voltage to the parallel electrodes 41 of the linear ion trap 4 to form a radial confinement electric field, and to apply a DC voltage to the end cover electrode 42 to form an axial confinement electric field, and to apply an excitation AC signal in the direction of ion emission (the direction of the slit opening) to stimulate ion emission.

[0073] Preferably, in the present embodiment, the ion source 2 is arranged in the vacuum chamber 3, specifically, the ion source 2 is arranged between the sample inlet of the vacuum chamber 3 and the linear ion trap 4, and the ion source 2 can ionize the sample by means of photoionization, dielectric barrier discharge, glow discharge, electron bombardment source, etc., and the ion source 2 is set as an internal ionization source, which can make the structure of the mass spectrometer more compact, and can effectively use the space of a single vacuum chamber to complete the construction of the entire mass spectrometry system, which is convenient for the miniaturization of the mass spectrometer; in some embodiments, the ion source 2 can also be independently arranged, specifically, the ion source 2 can be connected between the sample injection system 1 and the vacuum chamber 3, for example, using an electrospray ion source or an atmospheric pressure chemical ionization source, and the above embodiments are all within the protection scope of the present invention. After the sample is ionized by the ion source 2, an ion beam composed of ions of different mass-to-charge ratios (m / z) is formed.

[0074] Preferably, the mass spectrometer 100 further includes a membrane injector (not shown) connected to the vacuum chamber. A mass spectrometer providing a membrane injector interface can be conveniently used with a VOC detection device, and because the provided mass spectrometer is a miniaturized mass spectrometer, such a mass spectrometer can be integrated into a VOC detection device, for example, integrated into a chassis of an online monitoring device, thereby improving the accuracy of VOC detection.

[0075] The detector 6 is arranged at the ion outlet of the linear ion trap 4. The detector 6 is arranged at a position adjacent to the ion outlet of the linear ion trap 4 to collect ion intensity signals with high resolution, so that the linear ion trap 4 and the detector 6 can be integrated in the same vacuum chamber to effectively utilize the internal space of the device, which is convenient for miniaturization of the mass spectrometer. Specifically, the detector 6 corresponds to the position of the slit 411. Specifically, the detector 6 can be, for example, a microchannel plate detector, an electron multiplier detector, or a Faraday cage.

[0076] Preferably, the detector 6 further comprises a recorder (not shown), which can display the mass spectrometry results in the form of graphs, data or a combination thereof.

[0077] The power supply 8 can provide a specific electric field for the linear ion trap 4 . Specifically, the power supply 8 can at least provide a radio frequency voltage to the linear ion trap 4 .

[0078] Among them, the vacuum pump 5 is connected to the vacuum chamber 3 and can provide a low-pressure environment for the vacuum chamber 3. The selection of the vacuum pump 5 is related to the vacuum conditions required by the corresponding vacuum chamber 3. In this embodiment, the range of the working gas pressure P of the vacuum chamber 3 is 0.1Pa≤P≤10Pa. Since the vacuum degree of the vacuum condition is relatively low, the vacuum pump 5 can achieve this vacuum condition by selecting a rough vacuum pump. Specifically, the vacuum pump 5 can select a reciprocating vacuum pump, a rotary vane vacuum pump, a piston vacuum pump, a vortex dry pump, a diaphragm vacuum pump or a roots pump, etc., with a pumping speed S in the range of S≤100L / min. Compared with the mass spectrometer using the traditional linear ion trap, the above various types of rough vacuum pumps usually use a combined pump unit composed of a turbomolecular pump and a rough vacuum pump, which has a smaller pumping speed, a smaller volume, and a lower manufacturing cost. Therefore, the mass spectrometer 200 provided in this embodiment can reduce the overall volume of the vacuum pump 5, thereby realizing the miniaturization and low cost of the mass spectrometer.

[0079] Considering that the analysis performance of the mass spectrometer 200 may be affected under low vacuum conditions, in this embodiment, the analysis performance of the mass spectrometer 200 provided in this embodiment is mainly considered from the resolution of mass spectrometry analysis.

[0080] The radio frequency voltage applied by the power supply 8 to the linear ion trap 4 is Vcosωt, the amplitude value of the radio frequency voltage is V, the frequency is f (f = ω / 2π), and the shortest distance between each parallel electrode 41 and the geometric center axis of the linear ion trap 4 (the radius of the inscribed circle of the two pairs of parallel electrodes 41) is also called the field radius r of the linear ion trap 4. According to the empirical formula: m / Δm∝ω / P, the resolution m / Δm of the linear ion trap decreases as the working gas pressure P increases. In order to improve the resolution, it is necessary to increase the oscillation frequency ω, that is, to increase the radio frequency frequency f. According to the Marshall equation: q = 4eV / mω 2 r 2 (where e is the charge of the ion and m is the mass of the ion). When the ion emission condition q is constant, the higher the RF frequency f, the higher the RF voltage amplitude V. When the RF voltage amplitude V is too high, discharge will occur. In order to avoid discharge, the RF voltage amplitude V cannot be too high. Therefore, under the condition of ensuring a high RF frequency f, the field radius r needs to be reduced accordingly.

[0081] Below, the influence of the field radius r of the linear ion trap 4 and the frequency f of the radio frequency voltage applied to the linear ion trap 4 on the analytical performance of the mass spectrometer 200 is explained: According to the Marshall equation, when the radio frequency frequency f is too high, the amplitude V of the applied radio frequency voltage also needs to be increased accordingly, which will increase the risk of discharge; on the other hand, too high a frequency f will cause ion dissociation and affect the quality of the spectrum. In order to reduce the risk of discharge, the ion trap field radius r can be appropriately reduced to reduce the required radio frequency voltage V. However, if the field radius r is too small, the parallel electrodes 41 will be difficult to process. In addition, discharge is also likely to occur if the distance between the electrodes is too close. A field radius r that is too small also limits the capacity of the linear ion trap 4. Therefore, it is necessary to appropriately select the values ​​of the radio frequency frequency f and the field radius r in order to enable the mass spectrometer to maintain good analytical performance.

[0082] Specifically, considering the above, in this embodiment, the field radius r of the linear ion trap 4 is designed to be in the range of r≤5 mm; and the frequency f of the radio frequency voltage applied to the linear ion trap 4 is designed to be in the range of 2 MHz≤f≤10 MHz.

[0083] Further, the range of the field radius r of the linear ion trap 4 is:

[0084] Any one of r≤1mm, 1mm≤r≤2mm, 2mm≤r≤3mm, 3mm≤r≤4mm and 4mm≤r≤5mm or a combination thereof.

[0085] Furthermore, the frequency f of the radio frequency voltage is in the range of:

[0086] Any one of 2MHz≤f≤3MHz, 3MHz≤f≤4MHz, 4MHz≤f≤5MHz, 5MHz≤f≤6MHz, 6MHz≤f≤7MHz, 7MHz≤f≤8MHz, 8MHz≤f≤9MHz and 9MHz≤f≤10MHz or a combination thereof.

[0087] It should be noted that when the radio frequency f exceeds a specific value, such as 5MHz or 6MHz, at present, the power supply is difficult to manufacture and the power consumption is high. Moreover, the ion dissociation is serious at too high a frequency, and the increase in mass spectrum noise causes a space charge effect, which reduces the resolution and deteriorates the spectrum quality. Therefore, it is further preferred that the frequency range of the radio frequency voltage is 2MHz≤f≤5MHz or 2MHz≤f≤6MHz, and it is further preferred that it is 3MHz≤f≤6MHz or 4MHz≤f≤6MHz or 4MHz≤f≤5MHz.

[0088] The mass spectrometer 200 provided in this embodiment designs the field radius r of the linear ion trap 4 and the range of the radio frequency voltage frequency f, so that the mass spectrometer 200 can achieve miniaturization of the instrument while ensuring good resolution.

[0089] Preferably, the present embodiment provides a mass spectrometry method, comprising the steps of: providing a linear ion trap with a field radius r≤5 mm; providing a pressure environment of 0.1Pa≤P≤10Pa to the linear ion trap; and providing a radio frequency voltage with a frequency range of 2MHz≤f≤10MHz to the linear ion trap.

[0090] Implementation Method 3

[0091] This embodiment provides a detection system. Specifically, the detection system is a detection system having a VOC online monitoring device 9 or a chromatography-mass spectrometry device 10. More specifically, the VOC online monitoring device and the chromatography-mass spectrometry device can both use the mass spectrometer provided in Embodiment 1 or Embodiment 2. Hereinafter, the VOC online monitoring device 9 and the chromatography-mass spectrometry device 10 both use the mass spectrometer 200 provided in Embodiment 2 as an example.

[0092] like Figure 4 As shown, the VOC online monitoring device 9 further includes a sampling device 91 connected to the mass spectrometer 200 and a control unit 92 for controlling the operation of the VOC online monitoring device 9 .

[0093] Since the mass analyzer (linear ion trap 4) of the mass spectrometer 200 can operate stably under low vacuum conditions (for example, 0.1Pa≤P≤10Pa), and within a wider mass-to-charge ratio range, such as 20-600Th, the resolution of the mass analysis can still be maintained at a high level, such as a resolution level of half-width less than or equal to 1Th, high-resolution mass detection within this mass-to-charge ratio range can be well adapted to VOC detection. Furthermore, because the mass spectrometer can be conveniently miniaturized, it can be placed in the cabinet of the VOC online monitoring equipment, occupying a smaller space, thereby significantly improving the analysis accuracy of the VOC online monitoring equipment.

[0094] like Figure 5 As shown, when the mass spectrometer 200 is applied to the chromatography-mass spectrometry device 10, the mass spectrometer 200 can be conveniently miniaturized, so it can be integrated and used with a miniaturized chromatography device 11, such as a micro gas chromatograph (micro-GC). Specifically, the micro gas chromatograph can be integrated inside the mass spectrometer 200, so that the chromatography-mass spectrometry device 10 is further miniaturized. The mass spectrometer 200 can match the existing miniaturized chromatography device in terms of analysis speed and volume, significantly reducing the volume and weight of the chromatography-mass spectrometry device. In addition, the qualitative and quantitative capabilities of the mass spectrometer 200 are greatly enhanced when used in conjunction with the chromatography device.

[0095] Experimental analysis

[0096] Figure 6-Figure 12 The figure shows the resolution of the mass spectrometer 100 in the first embodiment of the present invention in the range of 20-600 Th, that is, the half-peak width FWHM parameter measurement or simulation result.

[0097] Figure 6-Figure 8 This is a mass spectrum obtained by measuring toluene at a concentration of 10 ppm using a linear ion trap with a field radius of 1 mm.

[0098] Depend on Figure 6 It can be seen that under the conditions of field radius r = 1 mm, working gas pressure P = 8.5 Pa, and radio frequency f = 4.14 MHz, the half-peak width FWHM = 0.9 Th, and the resolution is relatively high.

[0099] Depend on Figure 7 It can be seen that when other parameter conditions such as field radius and working gas pressure are controlled to be basically the same, the RF frequency is set to f=1.79 MHz, and the half-peak width changes accordingly to FWHM=1.8 Th.

[0100] Depend on Figure 8It can be seen that under the conditions of field radius r = 1mm, working gas pressure P = 8.3Pa, and RF frequency f = 5.8MHz, the half-peak width FWHM = 1.5Th, and a noise signal is generated. It can be seen that when the frequency increases, ions are prone to generate noise due to dissociation, affecting the quality of the spectrum.

[0101] according to Figure 6-Figure 8 From the experimental results, it can be seen that the setting value of the frequency should not be too high or too low. If it is set too high, ions are prone to generate noise due to dissociation, affecting the quality of the spectrum; if it is set too low, the resolution and sensitivity of the mass spectrometer will decrease to a certain extent. Taking the above factors into consideration, when the field radius is configured within 1-2mm and the working pressure is configured within 8-10Pa, the radio frequency is preferably configured within the range of 3-5MHz, and more preferably within the range of 3.5-4.5MHz, so as to improve the resolution and sensitivity of the mass spectrometer and make the resolution reach a level where the half-peak width is less than or equal to 1Th within 20-600Th.

[0102] Figure 9-12 In order to simulate the linear ion traps with different structures and working states, the spectral resolution data of reserpine peaking at 609-611Th were obtained.

[0103] Fig. 9 The mass spectrum peak resolution data in the range of 609-611Th obtained under the conditions of working gas pressure P=2Pa, field radius r=0.5mm, RF frequency f=9MHz, and scanning speed of 850Th / s are shown. The half-peak width FWHM of the mass spectrum peak in the figure is in the range of: 0.67Th≤FWHM≤0.75Th.

[0104] Fig.10 The mass spectrum peak resolution data in the range of 609-611Th obtained under the conditions of working gas pressure P=2Pa, field radius r=1mm, RF frequency f=6MHz, and scanning speed of 900Th / s are shown. The half-peak width FWHM of the mass spectrum peak in the figure is in the range of: 0.8Th≤FWHM≤0.89Th.

[0105] It can be seen that compared with the condition of field radius r=1mm, the resolution is better when the field radius r=0.5mm. However, on the one hand, as the field radius decreases, the manufacturing cost will gradually increase. On the other hand, a field radius that is too small also limits the capacity of the linear ion trap 4. Therefore, preferably, the field radius r has a lower limit, which can be selected from the following values, for example: 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm or 0.9mm.

[0106] Fig.11It shows that under the conditions of working gas pressure P=2Pa, field radius r=1mm, RF frequency f=5.4MHz, and scanning speed of 1200Th / s, the range of half-peak width FWHM is: 0.96Th≤FWHM≤1.13Th.

[0107] Fig.12 It shows that under the conditions of working gas pressure P=2Pa, field radius r=2mm, radio frequency f=4.2MHz, and scanning speed 2000Th / s, the range of half-peak width FWHM is: FWHM>1Th.

[0108] Depend on Fig.12 It can be seen that the field radius r should not be too high, otherwise it is easy to cause discharge and the resolution is difficult to meet the requirements. Therefore, the field radius r needs to have an upper limit, for example, the field radius r should be less than or equal to 5mm. Preferably, the field radius r≤4mm; r≤3mm; or r≤2mm.

[0109] In some embodiments of the present invention, the effect of working pressure on resolution at a specified field radius and radio frequency is further studied. At a scanning speed of 10000 Th / s, a linear ion trap with a field radius r = 1 mm and a radio frequency f = 6 MHz is used, and the effect of working pressure P on half peak width is simulated by adjusting the working pressure.

[0110] The simulation results show that when the working gas pressure P = 5Pa, the half-peak width FWHM = 1Th; when the working gas pressure P = 10Pa, the half-peak width FWHM = 1.5Th. From the above results, it can be seen that when the field radius r and the RF frequency f remain constant, the half-peak width tends to increase with the increase of the working gas pressure P. Therefore, the working gas pressure P should not be too large or too small. In the embodiment of the present invention, the appropriate working gas pressure P can be reasonably selected within the range of 0.1Pa≤P≤10Pa according to the actual situation, so as to take into account the miniaturization of the pump system, the discharge problems of the detector and the ion trap, and the resolution.

[0111] Those skilled in the art will appreciate that, in the above-mentioned embodiments, many technical details are provided in order to enable readers to better understand the present application. However, even without these technical details and various changes and modifications based on the above-mentioned embodiments, the technical solutions claimed for protection in the claims of the present application can be basically realized. Therefore, in practical applications, various changes can be made to the above-mentioned embodiments in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A mass spectrometer, characterized in that include: A vacuum chamber, wherein the working pressure P of the vacuum chamber is in the range of 0.1Pa≤P≤10Pa; A linear ion trap is disposed in the vacuum chamber, wherein a field radius r of the linear ion trap is in the range of r≤5 mm; and The power supply is configured to provide a radio frequency voltage to the linear ion trap, and the frequency f of the radio frequency voltage is in the range of 2 MHz≤f≤10 MHz.

2. The mass spectrometer according to claim 1, characterized in that Also includes: A vacuum pump is connected to the vacuum chamber, wherein the vacuum pump is a reciprocating vacuum pump, a rotary vane vacuum pump, a piston vacuum pump, a scroll dry pump, a diaphragm vacuum pump or a Roots pump.

3. The mass spectrometer according to claim 2, characterized in that The range of the pumping speed S of the vacuum pump is: S≤100L / min.

4. The mass spectrometer according to claim 1, characterized in that Also includes: A capillary tube is used to introduce the sample into the vacuum chamber.

5. The mass spectrometer according to claim 1, characterized in that Also included is a membrane injector in communication with the vacuum chamber.

6. The mass spectrometer according to claim 1, characterized in that Also includes: The detector is arranged at the ion outlet of the linear ion trap.

7. The mass spectrometer according to claim 1, characterized in that Also includes: The ion source is arranged between the sample inlet of the vacuum chamber and the linear ion trap.

8. The mass spectrometer according to claim 7, characterized in that The ion source is one of a photoionization ion source, a dielectric barrier discharge ion source, a glow discharge ion source or an electron bombardment ion source or a combination thereof.

9. The mass spectrometer according to claim 1, characterized in that The range of the field radius r of the linear ion trap is: Any one of r≤1mm, 1mm≤r≤2mm, 2mm≤r≤3mm, 3mm≤r≤4mm and 4mm≤r≤5mm or a combination thereof.

10. The mass spectrometer according to claim 1, wherein The frequency f of the radio frequency voltage is in the range of: Any one of 2MHz≤f≤3MHz, 3MHz≤f≤4MHz, 4MHz≤f≤5MHz, 5MHz≤f≤6MHz, 6MHz≤f≤7MHz, 7MHz≤f≤8MHz, 8MHz≤f≤9MHz and 9MHz≤f≤10MHz or a combination thereof.

11. A mass spectrometry method, characterized in that: Includes steps: Provide a linear ion trap with a field radius r≤5mm; Providing a pressure environment of 0.1Pa≤P≤10Pa to the linear ion trap; as well as A radio frequency voltage with a frequency of 2 MHz≤f≤10 MHz is provided to the linear ion trap.

12. A VOC online monitoring device, characterized in that: The VOC online monitoring device has a mass spectrometer as described in any one of claims 1-10.

13. A gas chromatography-mass spectrometry device, characterized in that: The gas chromatography-mass spectrometry device comprises a mass spectrometer as claimed in any one of claims 1 to 10.

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