阅读说明：本技术 质谱仪、质谱方法以及检测系统 (Mass spectrometer, mass spectrometry method and detection system ) 是由 林一明 孙文剑 于 2020-05-21 设计创作，主要内容包括：本发明涉及一种质谱仪、质谱方法以及检测系统,其中,质谱仪包括：真空室,所述真空室的工作气压P的范围为0.1Pa≤P≤10Pa；线性离子阱,设置于所述真空室内,其中,所述线性离子阱的场半径r≤5mm；以及电源,配置为向所述线性离子阱提供射频电压,所述射频电压的频率f的范围为2MHz≤f≤10MHz。由于该真空度相对较低,因此,选用粗真空泵抽真空即可实现这一真空条件,粗真空泵相比较于传统应用线性离子阱的质谱仪通常选用的由涡轮分子泵和粗真空泵构成的组合泵机组,抽速更小,体积更小,且制造成本更低,因此,本发明所提供的质谱仪,可以减小与真空室相匹配的真空泵的整体体积,进而实现质谱仪的小型化和低成本化。(The invention relates to a mass spectrometer, a mass spectrometry method and a detection system, wherein the mass spectrometer comprises: the range of the working air pressure P of the vacuum chamber is more than or equal to 0.1Pa and less than or equal to 10 Pa; the linear ion trap is arranged in the vacuum chamber, wherein the field radius r of the linear ion trap is less than or equal to 5 mm; and the power supply is configured to provide radio frequency voltage to the linear ion trap, and the frequency f of the radio frequency voltage ranges from 2MHz to 10 MHz. The vacuum degree is relatively low, so that the vacuum condition can be realized by using the rough vacuum pump for vacuum pumping, and compared with a traditional mass spectrometer using the linear ion trap, the rough vacuum pump usually uses a combined pump unit consisting of a turbo molecular pump and the rough vacuum pump, the rough vacuum pump has the advantages of lower pumping speed, smaller volume and lower manufacturing cost, so that the mass spectrometer provided by the invention can reduce the whole volume of the vacuum pump matched with the vacuum chamber, and further realize the miniaturization and the low cost of the mass spectrometer.)

1. A mass spectrometer, comprising:

the range of the working air pressure P of the vacuum chamber is more than or equal to 0.1Pa and less than or equal to 10 Pa;

the linear ion trap is arranged in the vacuum chamber, wherein the range of the field radius r of the linear ion trap is that r is less than or equal to 5 mm; and

and the power supply is configured to provide radio frequency voltage to the linear ion trap, and the frequency f of the radio frequency voltage ranges from 2MHz to 10 MHz.

2. The mass spectrometer of claim 1, further comprising:

and the vacuum pump is connected with the vacuum chamber, wherein the vacuum pump is a reciprocating vacuum pump, a rotary vane vacuum pump, a piston type vacuum pump, a vortex dry pump, a diaphragm type vacuum pump or a roots pump.

3. The mass spectrometer as defined in claim 2, wherein the pumping speed S of the vacuum pump is in the range of: s is less than or equal to 100L/min.

4. The mass spectrometer of claim 1, further comprising:

a capillary for introducing a sample into the vacuum chamber.

5. The mass spectrometer of claim 1, further comprising a membrane injector in communication with the vacuum chamber.

6. The mass spectrometer of claim 1, further comprising:

a detector disposed at an ion exit of the linear ion trap.

7. The mass spectrometer of claim 1, further comprising:

an ion source disposed between a sample inlet of the vacuum chamber and the linear ion trap.

8. The mass spectrometer of claim 7, wherein the ion source is one or a combination of a photoionization ion source, a dielectric barrier discharge ion source, a glow discharge ion source, or an electron bombardment ion source.

9. The mass spectrometer of claim 1, wherein the field radius r of the linear ion trap ranges from:

r is not more than 1mm, r is not less than 1mm and not more than 2mm, r is not less than 2mm and not more than 3mm, r is not less than 3mm and not more than 4mm, and r is not less than 4mm and not more than 5mm, or a combination thereof.

10. The mass spectrometer of claim 1, wherein the frequency f of the radio frequency voltage is in the range:

f is more than or equal to 2MHz and less than or equal to 3MHz, f is more than or equal to 3MHz and less than or equal to 4MHz, f is more than or equal to 4MHz and less than or equal to 5MHz, f is more than or equal to 5MHz and less than or equal to 6MHz, f is more than or equal to 6MHz and less than or equal to 7MHz, f is more than or equal to 7MHz and less than or equal to 8MHz, f is more than or equal to 8MHz and less than or equal to 9MHz, and f is more than or equal to 9MHz and less than or equal to 10MHz, or a combination thereof.

11. A method of mass spectrometry comprising the steps of:

providing a linear ion trap with a field radius r less than or equal to 5 mm;

providing a pressure environment with P being more than or equal to 0.1Pa and less than or equal to 10Pa for the linear ion trap; and

and providing radio frequency voltage with the frequency of 2MHz or more and f or less and 10MHz or less to the linear ion trap.

12. An online VOC monitoring device having a mass spectrometer as claimed in any one of claims 1to 10.

13. A combined gas chromatography and mass spectrometry apparatus having a mass spectrometer according to any one of claims 1to 10.

Technical Field

The invention relates to the technical field of mass spectrometry instruments, in particular to a mass spectrometer, a mass spectrometry method and a detection system.

Background

Miniaturization is one of the main trends in the development of mass spectrometers, and is a system engineering, and is severely restricted by factors such as performance requirements of various parts and processing difficulty.

For example, because the pump system has a high weight and volume ratio in a mass spectrometer, miniaturization of the pump system is one of the important directions for miniaturization development, and the miniaturization of the pump system is restricted by the performance requirements of other components. Generally speaking, reducing the volume or weight of the pump system will also reduce the vacuum performance that it can provide. Many components in the mass spectrometer system have certain requirements on vacuum performance, and if the vacuum performance provided by the pump system cannot meet the vacuum degree requirements of the components (such as the mass analyzer), the analysis performance of the mass spectrometer is reduced, and even the mass spectrometer cannot meet the requirements (such as the resolution of the mass analyzer cannot meet the requirement that the half-peak width is less than or equal to 1 Th).

In the prior art, in order to meet the resolution requirement that the half-peak width is less than or equal to 1Th in a wider mass-to-charge ratio range, such as the mass-to-charge ratio range of 20-600Th, a mass analyzer needs to work in a vacuum environment of less than 0.1Pa, thereby putting higher requirements on the vacuum performance of a pump system. Therefore, the pump system is generally required to be composed of a combination of a turbo-molecular pump and a rough vacuum pump, and the overall size and weight of the pump system are large, which not only makes miniaturization of the apparatus difficult, but also makes the manufacturing cost of the mass spectrometer high.

Patent US8525111B1 discloses a mass spectrometry system comprising an ion source, an ion trap and a detector, wherein two or more of the ion source, the ion trap and the detector are arranged in a gas pressure environment of 13.3Pa-1 atm. In this pressure range, it is difficult for the mass spectrometer to use a detector such as an electron multiplier/dynode or the like depending on a high voltage, and a faraday cup cannot generate a gain when detecting charges, and a high-power amplifier is required, so that a bandwidth is limited and a scanning speed is difficult to increase. On the other hand, the quality of the spectrogram is poor, the resolution and the signal-to-noise ratio are low, and the sensitivity and the qualitative and quantitative capability are influenced.

As disclosed by Jiang et al in Low-vacuum cylindrical ion spectrometry (Instrumentation Science & Technology,2018), a full width at half maximum FWHM of approximately 2 can be achieved using a 2.4MHz radio frequency power supply frequency at a gas pressure of 2Pa, using a Cylindrical Ion Trap (CIT). If a higher frequency rf voltage is applied, discharge occurs, which prevents further improvement of the resolution.

As disclosed in Blakeman et al, High Pressure Mass Spectrometry, The Generation of Mass Spectra at Operating Pressures Exception 1Torr in a Microcal cytological Ion Trap (Analytical Chemistry, 2016), a Cylindrical Ion Trap was used that achieved FWHM ≦ 1Th at higher RF power frequencies (6-9.5MHz) and at very High air Pressures (160 Pa). However, cylindrical ion traps have poor storage capabilities and can affect the dynamic range of mass spectra. And the CIT used by the device has a field radius of only 0.5mm, thereby further reducing the dynamic range. In addition, at such high radio frequency, the upper limit of the mass measurable by the mass spectrum is greatly reduced in order to avoid discharges.

Xu et al, in the Journal of Mass Spectrometry,2019, disclose the use of a Linear Ion Trap (LIT) that is less affected by space charge relative to a cylindrical ion trap, but at a lower resolution. The full width at half maximum FWHM of the linear ion trap is more than or equal to 1.5Th even under a lower air pressure (1.3 Pa).

Disclosure of Invention

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a mass spectrometer which can stably operate under a low vacuum condition and can maintain the resolution of mass analysis at a high level, for example, at a resolution level of 1Th or less at a half-peak width, in a wide range of mass-to-charge ratios, for example, in the range of 20 Th to 600 Th.

The mass spectrometer comprises: the range of the working air pressure P of the vacuum chamber is more than or equal to 0.1Pa and less than or equal to 10 Pa; the linear ion trap is arranged in the vacuum chamber, wherein the field radius r of the linear ion trap is less than or equal to 5 mm; and the power supply is configured to provide radio frequency voltage to the linear ion trap, and the frequency f of the radio frequency voltage ranges from 2MHz to 10 MHz.

In the technical scheme, the linear ion trap serving as the mass analyzer is arranged in the range of P being more than or equal to 0.1Pa and less than or equal to 10Pa, and the mass analyzer is basically the device with the highest requirement on vacuum performance in the mass spectrometer, so that generally, the minimum air pressure required by the mass spectrometer is within the range of P being more than or equal to 0.1Pa and less than or equal to 10Pa, and then the vacuum degree requirement of the mass spectrometer can be met by using a pump with smaller volume and lower pumping speed, thereby facilitating the miniaturization of the mass spectrometer. And, work in the linear ion trap in this atmospheric pressure scope, because ion cooling performance improves, the efficiency that ion was introduced and was evicted also promotes correspondingly, so sensitivity also can promote correspondingly.

In the course of the present invention, on the other hand, the inventors found that by limiting the field radius and voltage frequency of the linear ion trap to the above numerical ranges, the linear ion trap can be operated even in the gas pressure range of 0.1 Pa. ltoreq.P.ltoreq.10 Pa, and still a higher resolution level can be obtained. For example, a resolution level in the range of 20-600Th with a half-peak width of 1Th or less can be achieved.

If the working pressure P of the vacuum chamber is too low, for example, lower than 0.1Pa, it will be difficult to implement the vacuum pump with a low pumping speed, which is not favorable for the miniaturization of the mass spectrometer; if the operating gas pressure of the vacuum chamber is too high, e.g. above 10Pa, it is easy to cause discharge of the detector as well as of the ion trap.

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, both the resolution and sensitivity of the mass spectrometer are severely degraded. When the frequency f is too large, for example, when the frequency f is greater than 10MHz, not only the difficulty of manufacturing the power supply is increased, but also discharge and dissociation of the sample are easily caused.

The field radius r should not be too large. For example, when the field radius r is larger than 5mm, if a voltage of a higher frequency is applied to the electrode of the linear ion trap having an excessively large field radius, discharge is easily caused, and improvement of resolution is not facilitated.

Through the mode, the mass spectrometer provided by the invention can take account of various factors such as miniaturization, processing difficulty, resolution, sensitivity, stability and the like, and the mass spectrometer can stably operate under a low vacuum condition (for example, P is more than or equal to 0.1Pa and less than or equal to 10Pa), and the resolution of mass analysis can still be kept at a higher level in a wider mass-to-charge ratio range (for example, 20-600Th range), for example, the resolution level of which the half-peak width is less than or equal to 1Th is provided.

In the preferred technical scheme, the invention also comprises a vacuum pump connected with the vacuum chamber, wherein the vacuum pump is a reciprocating vacuum pump, a rotary vane vacuum pump, a piston type vacuum pump, a vortex dry pump, a diaphragm type vacuum pump or a roots pump.

According to the preferred technical scheme, because the mass analyzer can stably operate under the condition of low vacuum (for example, P is more than or equal to 0.1Pa and less than or equal to 10Pa), the vacuum degree requirement of the mass spectrometer can be met by using the rough vacuum pump with the type of the above-mentioned type of the achievable ultimate vacuum within the range of P is more than or equal to 0.1Pa and less than or equal to 10Pa, and the vacuum pump of the type is more suitable for miniaturization treatment, thereby facilitating the miniaturization of the mass spectrometer.

In a preferred technical scheme of the invention, the range of the pumping speed S of the vacuum pump is as follows: s is less than or equal to 100L/min.

According to the preferred technical scheme, the mass analyzer can stably operate under the low vacuum condition (for example, P is more than or equal to 0.1Pa and less than or equal to 10Pa), so that the vacuum degree requirement of the mass spectrometer can be met by using the rough vacuum pump operating at the low pumping speed, and the rough vacuum pump with the low pumping speed requirement is more suitable for miniaturization treatment, thereby facilitating the miniaturization of the mass spectrometer.

In a preferred technical solution of the present invention, the method further comprises: a capillary for introducing a sample into the vacuum chamber.

The capillary can be used for the introduction of neutral samples as well as for the introduction of ions. In some technical schemes, the capillary tube is used as an atmospheric pressure connection port, and in the technical schemes, the inner diameter of the capillary tube can be set to be smaller, preferably smaller than 100um, so that a low vacuum condition that P is more than or equal to 0.1Pa and less than or equal to 10Pa can be realized by using a small vacuum pump with a lower pumping speed. In other embodiments, the mass spectrometer may also be used with a chromatograph, for example, the capillary may be configured as a capillary chromatographic column of a gas chromatograph.

In a preferred technical solution of the present invention, the method further comprises: and the film sample injector is communicated with the vacuum chamber.

According to this preferred technical scheme, the mass spectrometer that provides membrane introduction interface can conveniently ally oneself with the usefulness with VOC detection device to, because the mass spectrometer that provides is miniaturized mass spectrometer, this kind of mass spectrometer can be integrated at VOC detection device, for example by being integrated in on-line monitoring equipment's quick-witted incasement portion, improves the accurate degree that VOC detected.

In a preferred technical solution of the present invention, the method further comprises: a detector disposed at an ion exit of the linear ion trap.

According to the preferred technical scheme, the detector is arranged at the position close to the ion outlet of the linear ion trap, so that the ion intensity signal with higher resolution can be collected, the linear ion trap and the detector can be integrated in the same vacuum chamber, the internal space of the device is effectively utilized, and the mass spectrometer is convenient to miniaturize.

In a preferred technical solution of the present invention, the method further comprises: and the ion source is arranged between the sample inlet of the vacuum chamber and the linear ion trap.

In the preferred technical scheme of the 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.

The light ionization ion source, the dielectric barrier discharge ion source, the glow discharge ion source or the electron bombardment ion source and other internal ionization sources are integrated in the same vacuum chamber, so that the space of a single vacuum chamber can be effectively utilized to complete the construction of the whole mass spectrum system, and the miniaturization of a mass spectrometer is facilitated.

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

r is not more than 1mm, r is not less than 1mm and not more than 2mm, r is not less than 2mm and not more than 3mm, r is not less than 3mm and not more than 4mm, and r is not less than 4mm and not more than 5mm, or a combination thereof.

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

f is more than or equal to 2MHz and less than or equal to 3MHz, f is more than or equal to 3MHz and less than or equal to 4MHz, f is more than or equal to 4MHz and less than or equal to 5MHz, f is more than or equal to 5MHz and less than or equal to 6MHz, f is more than or equal to 6MHz and less than or equal to 7MHz, f is more than or equal to 7MHz and less than or equal to 8MHz, f is more than or equal to 8MHz and less than or equal to 9MHz, and f is more than or equal to 9MHz and less than or equal to 10MHz, or a combination thereof.

The invention provides a mass spectrum method, which comprises the following steps: providing a linear ion trap with a field radius r less than or equal to 5 mm; providing a pressure environment with P being more than or equal to 0.1Pa and less than or equal to 10Pa for the linear ion trap; and providing radio frequency voltage with the frequency of f being more than or equal to 2MHz and less than or equal to 10MHz to the linear ion trap.

The invention also provides VOC on-line monitoring equipment with the mass spectrometer. The mass analyzer of the mass spectrometer can stably operate under the condition of low vacuum (for example, 0.1Pa ≦ P ≦ 10Pa), the resolution of mass analysis can still be kept at a high level within a wide range of mass-to-charge ratio (for example, within the range of 20-600Th or 20-400 Th), the high-resolution mass detection within the range of mass-to-charge ratio can be well adapted to VOC (volatile organic compounds) detection, and the mass spectrometer can be conveniently miniaturized, so that the mass analyzer can be placed in a cabinet of VOC on-line monitoring equipment, occupies a small space, and the analysis accuracy of the VOC on-line monitoring equipment can be greatly improved.

The invention further provides a chromatography-mass spectrometry combined device with the mass spectrometer. The mass spectrometer provided by the invention can be conveniently miniaturized, so that the mass spectrometer can be integrated and used together with a miniaturized chromatographic device, such as a micro-gas chromatograph (micro-GC). The mass spectrometer can be matched with the existing miniaturized chromatograph in the aspects of analysis speed and volume, the volume and the weight of the chromatograph-mass spectrometer are obviously reduced, and the qualitative and quantitative capacity of the mass spectrometer is improved.

Drawings

Fig. 1 is a schematic view of a partial configuration of a mass spectrometer provided in a first embodiment of the present invention;

fig. 2 is a schematic structural diagram of a mass spectrometer provided in the second embodiment of the present invention;

figure 3 is a schematic cross-sectional view of the parallel electrodes of the linear ion trap of figure 2;

fig. 4 is a schematic structural view of an online VOC monitoring apparatus provided in the third embodiment of the present invention;

FIG. 5 is a schematic structural diagram of a chromatography-mass spectrometry apparatus provided in the third embodiment of the present invention;

fig. 6 is a mass spectrum obtained by mass spectrometry of toluene using a linear ion trap with a field radius r of 1mm, a working gas pressure P of 8.5Pa, and a radio frequency f of 4.14 MHz;

fig. 7 is a mass spectrum obtained by mass spectrometry of toluene using a linear ion trap with a field radius r of 1mm, a working gas pressure P of 8.5Pa, and a radio frequency f of 1.79 MHz;

fig. 8 is a mass spectrum obtained by mass spectrometry of toluene using a linear ion trap with a field radius r of 1mm, a working gas pressure P of 8.3Pa, and a radio frequency f of 5.8 MHz;

fig. 9 is simulation data of peak appearance at 609-611Th by performing mass spectrometry on reserpine using a linear ion trap with a field radius r of 0.5mm, a working gas pressure P of 2Pa, and a radio frequency f of 9 MHz;

fig. 10 is simulation data of peak appearance at 609-611Th by performing mass spectrometry on reserpine using a linear ion trap with a field radius r of 1mm, a working gas pressure P of 2Pa, and a radio frequency f of 6 MHz;

fig. 11 is simulation data of peak appearance at 609-611Th by performing mass spectrometry on reserpine using a linear ion trap with a field radius r of 1mm, a working gas pressure P of 2Pa, and a radio frequency f of 5.4 MHz;

fig. 12 shows simulation data of peak appearance at 609-611Th by mass spectrometry of reserpine using a linear ion trap with a field radius r of 2mm, a working gas pressure P of 2Pa, and a radio frequency f of 4.2 MHz.

Description of reference numerals:

100. 200-a mass spectrometer; 1-a sample introduction system; 2-a source of ions; 3-vacuum chamber; 4-linear ion trap, 41-parallel electrode, 411-slit, 42-end cap electrode; 5-a vacuum pump; 6-a detector; 7-sample introduction interface; 8-a power supply; 9-VOC on-line monitoring equipment, 91-a sampling device and 92-a control unit; 10-chromatographic-mass spectrometry combined equipment, 11-chromatographic equipment.

Detailed Description

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 alterations within the technical scope of the present disclosure.

Terms and explanations

It should be noted that, herein, the term "rough vacuum pump" refers to a vacuum pump with ultimate vacuum degree in the low vacuum range (P ≧ 0.1Pa), and the "rough vacuum pump" can be adopted including but not limited to: reciprocating vacuum pumps, rotary vane vacuum pumps, piston vacuum pumps, scroll dry pumps, diaphragm vacuum pumps or roots pumps, etc.

The term "VOC on-line monitoring device" is a monitoring device configured on site at a monitoring site for continuous measurement of hazardous or hazardous organic gases in an industrial environment. "VOC" is an English abbreviation for volatile organic compounds (VOLATILE organic Compounds).

Implementation mode one

Mass spectrometers using linear ion traps typically have a high vacuum requirement on the vacuum chamber, and in particular, the gas pressure in the vacuum chamber typically needs to be kept below 0.0003mbar, and since the vacuum degree under the vacuum condition is high, when only one vacuum chamber is provided in the vacuum chamber, a pumping system is required to provide a large pumping speed in order to achieve the vacuum condition, and accordingly, the space occupied by the pumping system is also large.

To further enable mass spectrometer miniaturization, as shown in fig. 1, some embodiments of the present invention provide a mass spectrometer 100 capable of operating in a low vacuum environment, comprising: the working air pressure P is within the range of 0.1 Pa-10 Pa; and the linear ion trap 4 is arranged in the vacuum chamber 3, wherein the linear ion trap 4 is a hyperboloid linear ion trap and consists of two groups of hyperboloid pole rods and two pole plates at two ends. One of the two sets of poles is applied with an alternating voltage and the other set is applied with two alternating voltages. Slits 411 are arranged on one group of pole rods, and ions are driven to be ejected from the slits 411 by changing three groups of alternating voltages.

In the embodiment, the field radius r of the linear ion trap 4 is less than or equal to 5mm, wherein 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, wherein the frequency f of the radio frequency voltage is in the range of 2MHz ≦ f ≦ 10 MHz.

In some embodiments of the present invention, the working pressure P of the vacuum chamber 3 is in the range of 0.1Pa ≦ P ≦ 10Pa, which is set because if the working pressure P is higher than 10Pa, the voltage applied by the linear ion trap 4 and the detector is higher, the electrode spacing is small, and gas discharge is easily caused in such a pressure range; if the working pressure P is less than 0.1Pa, it is difficult for the conventional rough vacuum pump to achieve such a vacuum condition. Because the vacuum degree of the vacuum condition is relatively low, the vacuum condition can be realized by vacuumizing the vacuum chamber 3 by using the rough vacuum pump, and compared with a traditional mass spectrometer using a linear ion trap, the rough vacuum pump usually uses a combined pump unit consisting of a turbo molecular pump and the rough vacuum pump, the rough vacuum pump has the advantages of lower pumping speed, smaller volume and lower manufacturing cost, so that the mass spectrometer 100 provided by the embodiment can reduce the whole volume of the vacuum pump matched with the vacuum chamber 3, and further realize the miniaturization and the low cost of the mass spectrometer. In addition, compared with a multi-stage vacuum chamber, the design of the single vacuum chamber has the advantages of shorter ion transmission path and higher ion transmission rate, so that the quantity of ions finally available for mass spectrometry is higher, and the sensitivity of the instrument is further ensured. And compared with a mass spectrometer which is provided with a plurality of vacuum cavities and matched with a plurality of vacuum pumps, the mass spectrometer has the advantages of simpler structure, easiness in manufacturing and reduction of manufacturing cost.

In the technical scheme, the linear ion trap serving as the mass analyzer is arranged in the range of P being more than or equal to 0.1Pa and less than or equal to 10Pa, and the mass analyzer is basically the device with the highest requirement on vacuum performance in the mass spectrometer, so that generally, the minimum air pressure required by the mass spectrometer is within the range of P being more than or equal to 0.1Pa and less than or equal to 10Pa, and then the vacuum degree requirement of the mass spectrometer can be met by using a pump with smaller volume and lower pumping speed, thereby facilitating the miniaturization of the mass spectrometer. And, work in the linear ion trap in this atmospheric pressure scope, because ion cooling performance improves, the efficiency that ion was introduced and was evicted also promotes correspondingly, so sensitivity also can promote correspondingly.

In the course of the present invention, on the other hand, the inventors found that by limiting the field radius and voltage frequency of the linear ion trap to the above numerical ranges, the linear ion trap can be operated even in the gas pressure range of 0.1 Pa. ltoreq.P.ltoreq.10 Pa, and still a higher resolution level can be obtained. For example, a resolution level in the range of 20-600Th with a half-peak width of 1Th or less can be achieved.

If the working pressure P of the vacuum chamber 3 is too low, for example, lower than 0.1Pa, it will be difficult to use a small vacuum pump with a low pumping speed, which is not favorable for the miniaturization of the mass spectrometer; if the operating gas pressure of the vacuum chamber is too high, e.g. above 10Pa, it is easy to cause discharge of the detector as well as of the ion trap.

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, both the resolution and sensitivity of the mass spectrometer are severely degraded. When the frequency f is too large, for example, when the frequency f is greater than 10MHz, not only the difficulty of manufacturing the power supply is increased, but also discharge and dissociation of the sample are easily caused.

The field radius r should not be too large. For example, when the field radius r is larger than 5mm, if a voltage of a higher frequency is applied to the electrode of the linear ion trap having an excessively large field radius, discharge is easily caused, and improvement of resolution is not facilitated.

Through the mode, the mass spectrometer provided by the invention can take account of various factors such as miniaturization, processing difficulty, resolution, sensitivity, stability and the like, and the mass spectrometer can stably operate under a low vacuum condition (for example, P is more than or equal to 0.1Pa and less than or equal to 10Pa), and can still keep the resolution of mass analysis at a higher level, for example, the resolution level of which the half-peak width is less than or equal to 1Th within a wider mass-to-charge ratio range (for example, 20-600Th range).

In some embodiments, the mass spectrometer further comprises a gas supply system in communication with the vacuum chamber 3, the gas supply system being capable of supplying one or more gases, such as an inert gas, into the vacuum chamber 3.

It should be noted that fig. 1 of this embodiment shows only a part of the mass spectrometer 100 that is necessary to achieve the object of the present invention, and those skilled in the art will easily recognize that the mass spectrometer 100 has other structures such as an ion source, and the type, position, and size of the other structures such as the ion source are not limited in this embodiment.

Second embodiment

As shown in fig. 2 and 3, the mass spectrometer 200 provided in the present embodiment is mainly different from the mass spectrometer 100 provided in the first embodiment in that the mass spectrometer further includes: sample injection system 1, ion source 2, vacuum pump 5 and detector 6.

The sample introduction system 1 is connected to the vacuum chamber 3 via a sample introduction interface 7, for introducing a sample to be analyzed into the vacuum chamber 3. Wherein, the sample injection system 1 can be a film sample injector connected with the vacuum chamber 3 to be suitable for detecting volatile organic compounds. The sample inlet 7 is one of a taper hole, a cylindrical hole or a capillary, and the capillary can be used for introducing neutral samples and ions. In some technical schemes, the capillary tube is used as an atmospheric pressure connection port, and in the technical schemes, the inner diameter of the capillary tube can be set to be smaller, preferably smaller than 100um, so that a low vacuum condition that P is more than or equal to 0.1Pa and less than or equal to 10Pa can be realized by using a small vacuum pump with a lower pumping speed. In other embodiments, the mass spectrometer may be used with a chromatograph, for example, the capillary may be configured as a capillary chromatographic column of a gas chromatograph, and the sample inlet 7 is hereinafter described as an example of the capillary.

The linear ion trap 4 is disposed in the vacuum chamber 3 and can control the trajectory of the ion beam. The linear ion trap 4 at least includes two pairs of parallel electrodes 41 arranged in parallel and at intervals, and end cap electrodes 42 arranged at two ends of the parallel electrodes 41 in the length direction. The parallel electrodes 41 are uniformly distributed relative to the geometric central axis of the linear ion trap 4 and extend along the sampling direction of the ion beam, wherein a slit 411 for leading out ions is formed in one of the parallel electrodes 41, and the ions can be sequentially led out to the detector 6 according to the mass-to-charge ratio (m/z) under the action of a specific electric field.

The specific electric field mentioned here is usually a radial confinement electric field formed by applying a radio frequency voltage to the parallel electrodes 41 of the linear ion trap 4, an axial confinement electric field formed by applying a direct current voltage to the end cap electrode 42, and an excitation alternating current signal applied in the ion emission direction (the opening direction of the slit) to excite the ions to emit.

Preferably, in the present embodiment, the ion source 2 is disposed in the vacuum chamber 3, specifically, the ion source 2 is disposed between the sample inlet of the vacuum chamber 3 and the linear ion trap 4, the ion source 2 can ionize a sample in a photoionization mode, a dielectric barrier discharge mode, a glow discharge mode, an electron bombardment source, and the like, and the ion source 2 is disposed as an internal ionization source, so that the structure of the mass spectrometer is more compact, the space of a single vacuum chamber can be effectively utilized to complete the construction of the whole mass spectrometry system, and the mass spectrometer is convenient to be miniaturized; in some embodiments, the ion source 2 may also be provided independently, and in particular, the ion source 2 may be connected between the sample introduction system 1 and the vacuum chamber 3, for example, an electrospray ion source or an atmospheric pressure chemical ionization source, which are all within the protection scope of the present invention. After ionization of the sample by the ion source 2, an ion beam is formed consisting of ions of different mass to charge ratios (m/z).

Preferably, the mass spectrometer 100 further comprises a membrane injector (not shown) in communication with the vacuum chamber. The mass spectrometer that provides membrane introduction interface can conveniently be used with the VOC detection device to, because the mass spectrometer that provides is miniaturized mass spectrometer, this kind of mass spectrometer can be integrated at the VOC detection device, for example by being integrated in the quick-witted incasement portion of on-line monitoring equipment, improves the accurate degree of VOC detection.

The detector 6 is arranged at an ion outlet of the linear ion trap 4, and the detector 6 is arranged at a position adjacent to the ion outlet of the linear ion trap 4, so that high-resolution ion intensity signals can be collected, the linear ion trap 4 and the detector 6 can be integrated in the same vacuum chamber, the internal space of the device is effectively utilized, and the mass spectrometer is convenient to miniaturize. Specifically, the detector 6 corresponds to the position of the slit 411, and specifically, the detector 6 may be, for example, a microchannel plate detector, an electron multiplication detector, or a faraday cage.

Preferably, the detector 6 further comprises a recorder (not shown) capable of displaying the mass spectrometry results as a graph, data or a combination thereof.

Wherein the power supply 8 is capable of providing a specific electric field to the linear ion trap 4, in particular, the power supply 8 is capable of providing at least a radio frequency voltage to the linear ion trap 4.

Wherein, the vacuum pump 5 is connected with the vacuum chamber 3 and can provide a low-pressure environment for the vacuum chamber 3. The vacuum pump 5 is selected and used in relation to the vacuum condition required by the corresponding vacuum chamber 3, the working pressure P of the vacuum chamber 3 in the embodiment is in a range of 0.1Pa or more and P or less and 10Pa, and the vacuum degree of the vacuum condition is relatively low, so the vacuum pump 5 can be selected and used as a rough vacuum pump to realize the vacuum condition, and specifically, the vacuum pump 5 can be selected and used as a rough vacuum pump with a pumping speed S in a range of S or less than 100L/min, such as 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. Compared with the conventional mass spectrometer using a linear ion trap, the above various types of rough vacuum pumps generally adopt a combined pump set composed of a turbomolecular pump and a rough vacuum pump, and have the advantages of smaller pumping speed, smaller volume and lower manufacturing cost, so that the mass spectrometer 200 provided by the embodiment can reduce the overall volume of the vacuum pump 5, and further realize the miniaturization and the cost reduction of the mass spectrometer.

Considering that the analysis performance of the mass spectrometer 200 may be affected under the low vacuum condition, the analysis performance of the mass spectrometer 200 provided by the present embodiment is mainly considered from the resolution of mass spectrometry in the present embodiment.

The rf voltage applied by the power supply 8 to the linear ion trap 4 is Vcos ω t, the amplitude of the rf voltage is V, the frequency is f (f ═ ω/2 π), 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 referred to as the field radius r of the linear ion trap 4, according to the empirical formula: m/Δ m ∈ ω/P,the resolution m/am of the linear ion trap decreases as the operating gas pressure P increases. In order to increase the resolution, the oscillation frequency ω, i.e., the rf frequency f, needs to be increased. According to the Mashao equation, q is 4eV/m omega²r²(where e is the charge of the ion, and m is the mass of the ion), when the ion emission condition q is fixed, the higher the rf frequency f, the higher the amplitude V of the rf voltage, and the discharge phenomenon may occur when the amplitude V of the rf voltage is too high. To avoid discharges, the amplitude V of the rf voltage cannot be too high, so that, under the condition of ensuring a high rf frequency f, the field radius r needs to be correspondingly reduced.

The effect 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 below: according to the masha equation, when the radio frequency f is too high, the amplitude V of the applied radio frequency voltage also increases correspondingly, which will result in an increased risk of discharge; on the other hand, too high frequency f can cause ion dissociation and affect the quality of a spectrogram. To reduce the risk of discharges, the ion trap field radius r may be reduced appropriately to reduce the required radio frequency voltage V. However, if the field radius r is too small, the parallel electrode 41 will be difficult to machine. In addition, the discharge phenomenon is easily generated even if the electrode spacing is too close. Too small a field radius r also limits the capacity of the linear ion trap 4. Therefore, the values of the rf frequency f and the field radius r need to be chosen properly to maintain good analytical performance of the mass spectrometer.

Specifically, in view of the above considerations, in the present embodiment, the range of the field radius r of the linear ion trap 4 is designed to be r ≦ 5 mm; the frequency f of the radio frequency voltage applied to the linear ion trap 4 is designed to be in the range of 2MHz or less and f 10MHz or less.

Further, the field radius r of the linear ion trap 4 ranges from:

r is not more than 1mm, r is not less than 1mm and not more than 2mm, r is not less than 2mm and not more than 3mm, r is not less than 3mm and not more than 4mm, and r is not less than 4mm and not more than 5mm, or a combination thereof.

Further, the frequency f of the rf voltage ranges from:

f is more than or equal to 2MHz and less than or equal to 3MHz, f is more than or equal to 3MHz and less than or equal to 4MHz, f is more than or equal to 4MHz and less than or equal to 5MHz, f is more than or equal to 5MHz and less than or equal to 6MHz, f is more than or equal to 6MHz and less than or equal to 7MHz, f is more than or equal to 7MHz and less than or equal to 8MHz, f is more than or equal to 8MHz and less than or equal to 9MHz, and f is more than or equal to 9MHz and less than or equal to 10MHz, or a combination thereof.

It should be noted that, when the radio frequency f exceeds a specific value, for example, 5MHz or 6MHz, the power supply is difficult to manufacture and consumes more power. And the ion dissociation is serious under the too high frequency, and the mass spectrogram noise is increased to cause space charge effect, so that the resolution ratio is reduced, and the spectrogram quality is deteriorated. 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 3MHz ≦ f ≦ 6MHz or 4MHz ≦ f ≦ 5 MHz.

The mass spectrometer 200 provided by the embodiment designs the ranges of the field radius r and the radio frequency voltage frequency f of the linear ion trap 4, so that the mass spectrometer 200 realizes the miniaturization of the instrument while ensuring good resolution.

Preferably, the present embodiment provides a mass spectrometry method including the steps of: providing a linear ion trap with a field radius r less than or equal to 5 mm; providing a pressure environment with P being more than or equal to 0.1Pa and less than or equal to 10Pa for the linear ion trap; and providing radio frequency voltage with the frequency range of f being more than or equal to 2MHz and less than or equal to 10MHz to the linear ion trap.

Third embodiment

The embodiment provides a detection system, specifically, the detection system is a detection system with a VOC on-line monitoring device 9 or a chromatography-mass spectrometry combined device 10, and more specifically, both the VOC on-line monitoring device and the chromatography-mass spectrometry combined device can adopt the mass spectrometer provided in the first embodiment or the second embodiment. Hereinafter, the mass spectrometer 200 provided in the second embodiment is used as an example of both the VOC on-line monitoring apparatus 9 and the combined chromatography-mass spectrometry apparatus 10.

As shown in fig. 4, the VOC on-line monitoring apparatus 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 on-line monitoring apparatus 9.

Since the mass analyzer (linear ion trap 4) of the mass spectrometer 200 can operate stably under low vacuum conditions (e.g., 0.1 Pa. ltoreq. P.ltoreq.10 Pa), and the resolution of mass analysis can be maintained at a high level, e.g., a resolution level of 1Th or less at a half-peak width, over a wide range of mass-to-charge ratios, e.g., 20-600Th, high resolution mass detection over this range of mass-to-charge ratios can be well adapted to VOC detection, and since the mass spectrometer can be conveniently miniaturized, it can be placed in a cabinet of an on-line VOC monitoring apparatus, occupies a small space, and can greatly improve the analysis accuracy of the on-line VOC monitoring apparatus.

As shown in fig. 5, when the mass spectrometer 200 is applied to the combined chromatography-mass spectrometer 10, the mass spectrometer 200 can be conveniently miniaturized, so that it can be integrated and used with a miniaturized chromatographic apparatus 11, such as a micro-gas chromatograph (micro-GC), and in particular, the micro-gas chromatograph can be integrated inside the mass spectrometer 200, so that the combined chromatography-mass spectrometer 10 can be further miniaturized. The mass spectrometer 200 can be matched with the existing miniaturized chromatographic equipment in the aspects of analysis speed and volume, the volume and the weight of the chromatographic-mass spectrometry combined equipment are obviously reduced, and in addition, the qualitative and quantitative capacity of the mass spectrometer 200 is greatly enhanced by being combined with the chromatographic equipment.

Analysis of experiments

Fig. 6-12 show mass spectrometer 100 in a first embodiment of the invention, with resolution in the range of 20-600Th, i.e. full width at half maximum FWHM parametric measurements or simulation results.

FIGS. 6 to 8 are mass spectra obtained by measurement of toluene at a concentration of 10ppm using a linear ion trap with a field radius of 1 mm.

As can be seen from fig. 6, under the conditions that the field radius r is 1mm, the operating pressure P is 8.5Pa, and the radio frequency f is 4.14MHz, the full width at half maximum FWHM is 0.9Th, and the resolution is high.

As can be seen from fig. 7, when other parameter conditions such as the field radius and the operating gas pressure are controlled to be substantially the same, the rf frequency is set to 1.79MHz, and the full width at half maximum is changed to 1.8Th as FWHM.

As can be seen from fig. 8, under the conditions that the field radius r is 1mm, the working gas pressure P is 8.3Pa, and the radio frequency f is 5.8MHz, the full width at half maximum FWHM is 1.5Th, and a noise signal is generated, and thus it is known that ions are easily dissociated to generate noise when the frequency is increased, which affects the spectrum quality.

From the experimental results of fig. 6-8, it can be seen that the set value of the frequency is neither too high nor too low. If the setting is too high, ions are easy to generate noise due to dissociation, and the quality of a spectrogram is affected; if the setting is too low, the resolution and sensitivity of the mass spectrometer will be reduced to some extent. Combining the above factors, when the field radius is configured in 1-2mm and the working gas pressure is configured in 8-10Pa, the radio frequency is preferably configured in the range of 3-5MHz, and more preferably in the range of 3.5-4.5MHz, so as to improve the resolution and sensitivity of the mass spectrometer, and the resolution reaches the level that the half-peak width is less than or equal to 1Th in 20-600 Th.

Fig. 9-12 show spectral resolution data of reserpine peaks at 609-611Th obtained by simulation of linear ion traps with different structures and working states.

Fig. 9 shows mass spectrum peak resolution data of 609-channel 611Th range obtained under the conditions of operating pressure P2 Pa, field radius r 0.5mm, radio frequency f 9MHz, scanning speed 850Th/s, where the range of full width at half maximum FWHM of the mass spectrum peak is: FWHM is not less than 0.67Th and not more than 0.75 Th.

Fig. 10 shows mass spectrum peak resolution data of 609-fold 611Th range obtained under the conditions of operating pressure P of 2Pa, field radius r of 1mm, radio frequency f of 6MHz, scanning speed of 900Th/s, where the range of full width at half maximum FWHM of the mass spectrum peak is: 0.8Th or more and FWHM or less and 0.89 Th.

From this, it can be seen that the resolution is better when the field radius r is 0.5mm compared to the condition of 1mm, but on one hand, the manufacturing cost is gradually increased as the field radius is reduced, and on the other hand, the capacity of the linear ion trap 4 is limited because the field radius is too small, and therefore, the field radius r preferably 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 0.9 mm.

Fig. 11 shows that under the conditions of an operating gas pressure P of 2Pa, a field radius r of 1mm, a radio frequency f of 5.4MHz, and a scanning speed of 1200Th/s, the range of the full width at half maximum FWHM is: 0.96Th or more and FWHM or less and 1.13 Th.

Fig. 12 shows that the range of the full width at half maximum FWHM is, under the conditions of operating pressure P2 Pa, field radius r 2mm, radio frequency f 4.2MHz, and scanning speed 2000 Th/s: FWHM > 1 Th.

As can be seen from fig. 12, the field radius r should not be too high, otherwise discharge is easily caused, and the resolution is difficult to satisfy. Therefore, the field radius r needs to have an upper limit, for example, the field radius r should be 5mm or less. Preferably, the field radius r is less than or equal to 4 mm; r is less than or equal to 3 mm; or r is less than or equal to 2 mm.

The effect of operating gas pressure on resolution at a specified field radius and radio frequency was further investigated in some embodiments of the present invention. At a scanning speed of 10000Th/s, a linear ion trap with a field radius r of 1mm and a radio frequency f of 6MHz is used to simulate the effect of the working pressure P on the half-peak width by adjusting the working pressure.

The simulation result shows that when the working air pressure P is 5Pa, the full width at half maximum FWHM is 1 Th; when the working air pressure P is 10Pa, the full width at half maximum FWHM is 1.5 Th. From the above results, when the field radius r and the rf frequency f are kept constant, the half-peak width tends to increase as the operating air pressure P increases. Therefore, the working pressure P is not suitable to be too large or too small, and in the embodiment of the invention, the suitable working pressure P can be reasonably selected according to the actual situation in the range of 0.1Pa ≦ P ≦ 10Pa, so as to take the miniaturization of the pump system, the discharge problem of the detector and the ion trap and the resolution into consideration.

It will be appreciated by those of ordinary skill in the art that in the embodiments described above, numerous technical details are set forth in order to provide a better understanding of the present application. However, the technical solutions claimed in the claims of the present application can be basically implemented without these technical details and various changes and modifications based on the above-described embodiments. Accordingly, in actual practice, various changes in form and detail may be made to the above-described embodiments without departing from the spirit and scope of the invention.