Molecular ion reaction cell for chemical ionization mass spectrometry

Abstract

The application discloses a molecular ion reaction cavity for chemical ionization mass spectrometry, which comprises a sampling module, an air inlet module, a reaction module and a power module, the sampling module is provided with a main pipeline and a drainage bypass, the air inlet module is provided with a central hole for fixing a capillary, the reaction module is internally provided with a conical cavity, an ion source air inlet channel is arranged on the side surface close to the top end of the conical cavity, and an air outlet hole is arranged at the center of the bottom surface; sampling gas enters the top end of the conical cavity through the capillary from the main pipeline, reacts with ions entering from the ion source air inlet channel in the conical cavity, and the reacted gas enters a mass spectrometer detector from the air outlet hole; and the power module provides a radial focusing electric field for the conical cavity. The drainage bypass effectively reduces the response time of the reaction cavity to organic matters, the capillary can be replaced according to different experimental conditions, the conical reaction cavity structure effectively reduces ion loss and improves ionization efficiency in a laminar flow state, and the molecular ion reaction process is effectively controlled through an external temperature adjusting device and a vacuum pump.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical ionization mass spectrometry, in particular to a molecular ion reaction chamber for chemical ionization mass spectrometry, which can be applied to chemical ionization mass spectrometry for detecting low-volatility organic matter in the presence of iodine as a reagent ion. BACKGROUND

[0002] In order to more effectively control secondary pollution, it is necessary to systematically study and master the chemical theory mechanism of atmospheric complex pollution with atmospheric oxidation as the core. The prerequisite is to accurately measure the key intermediates in the atmospheric oxidation process, which requires high accuracy and high selectivity online measurement technology.

[0003] At present, the measurement technology for atmospheric oxidation intermediates can be divided into mass spectrometry and spectroscopy. Mass spectrometry, represented by chemical ionization mass spectrometry, is widely concerned due to its high selectivity and the advantage of realizing the measurement of individual species. The principle of chemical ionization mass spectrometry is to convert the molecules to be measured into charged ions through chemical reaction with reagent ions, and then detect the charged ions by mass spectrometry to obtain their concentration information. Chemical ionization mass spectrometry usually consists of four modules, namely ion source, molecular ion reaction chamber, ion transmission system and mass analyzer. The ion source is the place where the reagent ions are generated. High-concentration reagent ions and the gas to be measured enter the reaction chamber to undergo molecular ion reaction (i.e. ionization process). Ionization efficiency is directly related to the detection efficiency of the instrument. This process is related to the properties of the measured substance and the reagent ions themselves, and is also significantly affected by operating conditions such as the structure of the reaction chamber, reaction temperature, pressure, etc. The ion transmission system is designed to enable the product ions generated by the reaction to reach the mass spectrometry system for detection, and the mass analyzer is the module for detecting product ions. It should be pointed out that the chemical ionization mass spectrometry currently used in the field of atmospheric chemistry is basically produced by foreign mass spectrometer companies, and there are few reports on the application of domestic chemical ionization mass spectrometry.

[0004] Due to the high reactivity and low concentration of oxidation intermediates in the actual atmosphere, the existing mass spectrometry detection means is still insufficient to meet the measurement needs of these species, and there are problems such as low sensitivity and high detection limit. Taking a reaction chamber designed by a Swiss Tofwerk instrument company (hereinafter referred to as a traditional reaction chamber) as an example, the results of flow field simulation and experimental testing show that the internal flow field of the traditional reaction chamber is mainly turbulent, and gas molecules are extremely easy to collide or collide with the wall, resulting in a loss, which leads to the fact that the traditional reaction chamber cannot effectively measure low-volatility organic matter in the actual atmosphere, and cannot meet the needs of exploring the chemical theory mechanism of the atmosphere. Therefore, it is of great practical significance to design a molecular ion reaction chamber and explore its reaction conditions to effectively promote the molecular ion reaction, so as to realize the measurement of ppt-level oxidation intermediates in the atmosphere. SUMMARY

[0005] The purpose of the present invention is to provide a high-efficiency molecular ion reaction chamber for chemical ionization mass spectrometry, which solves the problems of traditional reaction chambers such as large wall loss and poor detection effect caused by internal flow field turbulence, effectively controls the molecular ion reaction process, improves ionization efficiency, and realizes efficient measurement of medium and low volatile organic compounds.

[0006] To achieve the above-mentioned objectives, the present invention designs a molecular ion reaction chamber for chemical ionization mass spectrometry, comprising a sampling module, an air intake module, a reaction module and a power supply module, wherein the sampling module is provided with a main line for sampling gas to pass through and a bypass for drainage; the air intake module is a sheet-like structure with a capillary fixing hole in the center, and the capillary is fixed in the hole by a connector; the interior of the reaction module is a conical cavity, and an ion source air intake channel is opened on the side near the top of the conical cavity, and an air outlet is provided in the center of the bottom surface of the conical cavity; the sampling module, the air intake module and the reaction module are assembled together in sequence, and the main line of the sampling module and the conical cavity of the reaction module are connected through a capillary fixed in the air intake module; the sampling gas enters the conical cavity from the top of the conical cavity through the capillary from the main line of the sampling module, reacts with ions entering from the ion source air intake channel in the conical cavity, and the reacted gas enters the mass spectrometer detector from the air outlet on the bottom surface of the conical cavity; the power supply module provides a radial focusing electric field for the conical cavity.

[0007] Furthermore, the sampling module of the molecular ion reaction chamber is a columnar structure, with a main pipeline interface provided on the top of the sampling module. It is a tapered internal thread structure, which can be connected to the sampling pipeline in the form of a threaded knob using standard parts and maintain good airtightness. A drainage bypass interface is provided on the side of the sampling module. It is a small tapered internal thread hole, which can be connected to an external vacuum pump for drainage during sampling to achieve a faster response time of the instrument. The sampling module is provided with a circle of U-shaped grooves on the bottom surface for placing O-rings to ensure the sealing of the connection between the sampling module and the air intake module.

[0008] Furthermore, the air inlet module of the molecular ion reaction chamber is a disc or other shaped sheet with a capillary fixing hole in the center, and the capillary fixing hole is connected to the capillary connector in the form of a threaded knob; the capillary is preferably made of Peek material (polyetheretherketone), and a ferrule is installed at the bottom of the capillary to prevent air leakage.

[0009] Furthermore, the reaction module of the molecular ion reaction chamber is a columnar structure with a conical cavity inside. The inner wall is smooth and can be coated with Teflon or silanized to reduce the adsorption effect of organic matter. The side of the conical cavity near the top is provided with an ion source inlet channel for connecting to the ion source. The top surface of the reaction module also has a circle of U-shaped grooves for accommodating O-rings to ensure a tight seal at the connection between the inlet module and the reaction module.

[0010] Further, a plurality of through holes (such as three, four or more through holes uniformly distributed on the outer periphery of the module) are formed on the sampling module and the air inlet module, and a plurality of screw holes are formed on the top of the reaction module at corresponding positions, and screws are inserted through the through holes and screwed into the screw holes for fixing the sampling module, the air inlet module and the reaction module.

[0011] Further, the side surface of the reaction module has a protruding outer edge portion on which a plurality of threaded holes are formed for fixedly connecting the molecular ion reaction chamber of the mass spectrometry system through screws.

[0012] Further, the materials of the sampling module, the air inlet module and the reaction module of the molecular ion reaction chamber can be selected from a plurality of materials, such as 304 stainless steel, 316 stainless steel, Teflon and Peek, and the reaction module is preferably made of 304 stainless steel or 316 stainless steel.

[0013] Further, the inner diameter of the main pipeline of the sampling module is 20 mm, and a 1 / 8-1 / 2 inch Teflon pipe can be externally connected as a sampling pipe, and the 1 / 2 inch pipe is preferably selected to reduce the wall loss of organic matter.

[0014] Further, the ion source, such as iodine ions and ammonium ions, is negatively charged or positively charged by applying a voltage to the reaction module through the power supply module, and a radial focusing electric field is formed in the conical cavity of the reaction module to make the product ions flow to the gas outlet hole at the bottom of the conical cavity. For example, in order to reduce the loss of negative ions (such as iodine ions) in the reaction chamber, the power supply module provides a negative voltage of -20-0V, and the power supply module is connected to the reaction module (or the sampling module and the air inlet module connected to the reaction module) through a cable, and after being powered on, the reaction chamber is negatively charged, which can effectively reduce the loss of product ions on the wall. The length of the conical cavity of the reaction module is preferably 50-53 mm, and the cone angle can be selected in the range of 13°-16°, and in an embodiment of the present application, the length of the conical cavity is 52 mm and the cone angle is 15°.

[0015] Further, the capillary tube selected for the air inlet module has an outer diameter of 1 / 16 inch and an inner diameter that can be selected in the range of 0.01 mm-1 mm, and the capillary tube with an inner diameter of 1 mm is preferably selected, which can meet the low vacuum condition of the subsequent mass spectrometry system and improve the concentration of the molecules to be tested in the reaction chamber. In order to meet different testing requirements and improve selectivity, capillary tubes with different inner diameters can be prepared in advance for easy replacement.

[0016] Further, when the chemical ionization mass spectrometry is performed, the reaction module body of the molecular ion reaction chamber is placed in a pre-designed vacuum chamber connected with a rear-end mass spectrometry detector, and is equipped with a special vacuum pump to provide the pressure condition required for the reaction, and the optimal pressure condition is 150-400 mbar.

[0017] Further, because there is a large pressure difference between the molecular ion reaction chamber and the ambient atmosphere, and the inner diameter of the capillary is small, the gas enters the reaction module in the form of high-speed injection and quickly reaches the laminar flow state; at the same time, adjusting the gas flow of the side ion source can realize the sufficient mixing of the reagent ions and the sampling gas, and effectively improve the ionization efficiency.

[0018] Further, the temperature regulation device can be installed on the periphery of the reaction module to regulate the temperature of the molecular ion reaction. On the one hand, the molecular ion reaction is an exothermic reaction, and a lower temperature is beneficial to the forward movement of the chemical equilibrium to promote the ionization process; on the other hand, the medium and low volatile organic species concerned in the present application need to be reacted in the reaction chamber in the gaseous form at a higher temperature. Finally, based on experimental tests, the optimal temperature condition is 40-45℃.

[0019] The molecular ion reaction chamber body designed in the present application is composed of three modules of sampling, gas inlet and reaction, the modules are fixedly connected, and the air tightness of the device is ensured by the O-shaped sealing ring. Among them, the sampling module is equipped with a drainage bypass to effectively reduce the response time of the instrument to organic matter; the gas inlet of the gas inlet module is designed as a replaceable capillary tube, which can be replaced according to different experimental conditions; the inside of the reaction module is a conical cavity structure, which can effectively reduce the ion loss and improve the ionization efficiency in the laminar flow state; the external temperature regulation device and vacuum pump of the reaction chamber can artificially regulate the temperature and pressure conditions to effectively control the progress of the molecular ion reaction. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a structural schematic diagram of the molecular ion reaction chamber of the present application connected with a mass spectrometry detector;

[0021] Figure 2 is an outline drawing (a) and a sectional drawing (b) of the sampling module, the gas inlet module and the reaction module of the molecular ion reaction chamber of the present application;

[0022] Figure 1 and Figure 2 In the figure: 1-sampling module, 2-gas inlet module, 3-reaction module, 4-main tube interface, 5-drainage bypass interface, 6-capillary fixing hole, 7-ion source gas inlet channel, 8-conical reaction area, 9-power module, 10-molecular ion reaction chamber fixing device, 11-vacuum air outlet, 12-mass spectrometry detector.

[0023] Figure 3 is a flow field simulation diagram of an embodiment of the present application.

[0024] Figure 4 is a structural profile diagram (a) and a sectional view (b) of a conventional reaction chamber for comparison with an embodiment of the present application. DETAILED DESCRIPTION

[0025] The present patent will be further described in detail with reference to the accompanying drawings and specific implementation cases, which are merely illustrative of the present application and not limiting.

[0026] It should be noted that the following detailed description is exemplary and is intended to further illustrate the technical solutions of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0027] In addition, "up", "down", "left", "right", "top", "bottom", and the like used in the following description are merely for the convenience of explaining the structure of the present application and are not limiting.

[0028] As shown in Figure 1 , the molecular ion reaction chamber for chemical ionization mass spectrometry needs to be mounted on a matching molecular ion reaction chamber fixing device 10, the rear end of which is connected to a mass spectrometer detector 12, and the fixing device is simultaneously connected to a vacuum pump through a vacuum pumping port 11 to maintain the vacuum condition for normal operation of the reaction chamber. The molecular ion reaction chamber is divided into a sampling module 1, an air inlet module 2, a reaction module 3, and a power module 9, as shown in Figure 2 , the sampling module 1 is provided with a main pipeline for sampling gas to pass through and a bypass for flow diversion, the main pipeline interface 4 is located at the top end of the sampling module 1, and the flow diversion bypass interface 5 is located at the side of the sampling module 1; the air inlet module 2 is a flat circular disc, and a cylindrical capillary fixing hole 6 is provided at the center of the disc; the reaction module 3 has a conical reaction area 8 inside, and an ion source air inlet channel 7 is provided at the side thereof. The sampling module 1, the air inlet module 2, and the reaction module 3 are sequentially connected and assembled together to form a cylindrical structure, as shown in Figure 1 , the part of the cylindrical structure where the conical reaction area 8 is located is installed in the vacuum chamber of the molecular ion reaction chamber fixing device 10, while the ion source air inlet channel 7 and the sampling module 1, the air inlet module 2 are located outside the vacuum chamber to facilitate the connection of various pipelines. The power module 9 is connected to the reaction module 3 through a cable to provide a radial focusing electric field for the reaction chamber. A heating device and a temperature sensor are provided in the vacuum chamber of the molecular ion reaction chamber fixing device 10 to regulate the temperature of the reaction module 3.

[0029] It should be noted that the size design and application conditions of the embodiment are obtained by combining theoretical calculation and experimental test to obtain the optimal value.

[0030] The sampling module 1 is integrally formed by two cylinders, with a total length of 40 mm, and the center of the cylinder is hollowed out as a main pipeline with an inner diameter of 20 mm. The top part is a main pipeline interface 4 designed as a 1 / 2NPT threaded hole for connecting the sampling pipeline. The lower part of the side is a drainage bypass interface 5 designed as a 1 / 4NPT threaded hole for connecting the drainage pipeline. A U-shaped groove is designed on the bottom surface of the sampling module 1 for placing an O-shaped sealing ring to ensure the air tightness of the device.

[0031] The appearance of the gas inlet module 2 is a circular plate with a cylindrical groove, and the outer diameter of the central cylindrical groove is 5 mm. The inner wall of the groove is a 1 / 16NPT thread for connecting with the capillary. The capillary is placed on a 1 / 16 inch screw connector, and different inner diameter capillaries can be replaced according to actual needs.

[0032] The reaction module 3 is cylindrical in shape, with a hollow interior in the shape of a conical radial cavity, which is the molecular ion reaction area (conical reaction area 8). The side of the reaction module 3 is provided with a 1 / 8NPT threaded hole for connecting the ion source gas inlet pipeline. A U-shaped groove is designed on the top surface of the reaction module 3 for placing an O-shaped sealing ring to ensure the air tightness of the device. A small hole is provided in the center of the bottom surface of the reaction module 3, and the product ions after the reaction of the test molecules and reagent ions enter the mass spectrometer detector 12 through the small hole.

[0033] The sampling module 1 and the gas inlet module 2 are provided with through holes, and the two can be fixed in the threaded holes on the reaction module 3 by using M4 type screws passing through the through holes. The reaction module 3 is provided with a heating device and a temperature sensor on the outside to realize the regulation of the reaction temperature, so as to promote the volatilization of organic matter and reduce the wall loss as much as possible.

[0034] Table 1

[0035]

[0036] In this embodiment, the reaction module 3 serves as the place for molecular ion reaction, and its design parameters and application conditions are the key to affecting the efficiency of molecular ion reaction. Table 1 lists the key parameters and application conditions of this embodiment based on experimental tests.

[0037] Figure 3 Based on the related parameters described in Table 1, the flow field simulation diagram of the conical reaction area 8 of this embodiment is shown in Figure 1. Figure 3As shown, the sampling gas flow enters the reaction chamber through the capillary and is disturbed by the ion source gas flow from the side, and the gas molecules in the sampling gas flow rapidly react with the reagent ions of the ion source gas flow, which is part of the mixing reaction area; After the mixed gas flow is transmitted for a distance, it gradually reaches a laminar flow state and almost does not collide with the inner wall of the reaction chamber, and part of the gas flow enters the mass spectrometer through the axial outlet for detection, and the remaining gas flow is pumped out by the vacuum pump. Figure 3 It is shown that the molecular ion reaction chamber designed in the present application effectively realizes the laminar flow state of the reaction area, and better avoids the loss caused by the collision of the gas flow with the wall. The calculation obtains that the sampling gas inlet flow rate in the present example is about 360 m / s, and the average residence time is 0.3 milliseconds.

[0038] To more intuitively reflect the advantages of the present example in reducing molecular ion loss and improving molecular ion reaction efficiency, the measurement effects of the traditional reaction chamber and the reaction chamber of the present example on measuring medium and low volatile organic substances are compared below. As a supplement, Figure 4 The basic structure of the traditional reaction chamber is shown. The flow field simulation results of the traditional reaction chamber show that the internal gas flow is relatively turbulent, and most of the gas flow will directly contact the wall, which will cause a large amount of ion loss, but its advantage is that it has a converging outlet, which can focus the gas flow. The structure of the reaction chamber in the present example is optimized to reduce ion loss, and the gas flow is focused by an external DC power supply.

[0039] Table 2

[0040]

[0041] Table 2 is the measurement effect of the present example and the traditional reaction chamber on medium and low volatile organic substances. The specific implementation method of the comparative experiment is: using the same standard gas generation system to provide standard substance gas with the same concentration, and the gas in this group passes through the same pipeline and enters the chemical ionization mass spectrometer equipped with the present example and the traditional reaction chamber respectively, and the performance indicators of the rear-end mass spectrometer are completely consistent, and the detection signal intensity (i.e. sensitivity) of the same substance by the present example and the traditional reaction chamber is compared. The main test species are products generated in the gas-phase oxidation process of aromatic hydrocarbons, which are substances that need to be focused on in the field of atmospheric chemistry research, such as 2,4-hydroxytoluene (C7H8O2), 4-nitrophenol (C6H5NO3), 2-methyl-4-nitrophenol (C7H7NO3), products generated by oxidation of natural source organic matter, such as pipemidic acid (C 10 H 16 O3), and volatile relatively high formic acid (CH2O2). The experimental results show that the detection sensitivity of the present example for these species is obviously better than that of the traditional reaction chamber. Among them, C6H5NO3, C7H7NO3, C 10 H16 O3 is a low volatile organic matter with high relative molecular mass and special functional groups, which is easy to be deposited and thus leads to gas phase loss. However, in the present embodiment, the loss of these substances in the reaction and transmission stages is reduced by optimizing the structure of the reaction chamber, temperature adjustment, electric field focusing and other measures, and the optimization effect of the detection sensitivity is more than 50%. CH2O2 and C7H8O2 have relatively high volatility, and it can be found that the detection effect of the present example and the traditional reaction chamber has little difference. Overall, the present embodiment can better optimize the molecular ion reaction efficiency and improve the detection effect.

[0042] The above is the preferred embodiment of the present application, and any changes made according to the present embodiment, as long as the resulting functional effects do not exceed the scope of the technical solutions of the present application, are within the protection scope of the present application.

[0043] Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

Claims

1. A molecular ion reaction chamber for chemical ionization mass spectrometry comprising a sampling module, a gas inlet module, a reaction module and a power module, wherein, The sampling module is provided with a main pipeline for sampling gas to pass through and a bypass for flow guiding; the air inlet module is a sheet structure with a capillary tube fixing hole in the center, and the capillary tube is fixed in the hole through a connecting piece; the reaction module is internally a conical cavity, and an ion source air inlet channel is arranged on the side close to the top end of the conical cavity, and an air outlet hole is arranged in the center of the bottom surface of the conical cavity; the sampling module, the air inlet module and the reaction module are assembled together in sequence, and the main pipeline of the sampling module and the conical cavity of the reaction module are communicated through the capillary tube fixed in the air inlet module; the sampling gas enters the conical cavity from the top end of the conical cavity through the capillary tube from the main pipeline of the sampling module, and reacts with the ions entering from the ion source air inlet channel in the conical cavity, and the reacted gas enters the mass spectrometer detector from the air outlet hole in the bottom surface of the conical cavity; the power module provides a radial focusing electric field for the conical cavity.

2. The molecular ion reaction cell of claim 1, wherein, The sampling module is a columnar structure, and a main pipeline interface is arranged on the top of the sampling module, which is a conical internal thread structure and is connected with the sampling pipeline in a threaded screwing manner; a flow guiding bypass interface is arranged on the side of the sampling module, which is a conical internal thread hole and is connected with an air pump for flow guiding during sampling; a U-shaped groove is arranged on the bottom surface of the sampling module, and an O-shaped sealing ring is arranged in the U-shaped groove to seal the connection between the sampling module and the air inlet module.

3. The molecular ion reaction cell of claim 1, wherein, The air inlet module is a circular sheet with a capillary tube fixing hole in the center, and the capillary tube fixing hole is connected with the capillary tube connecting piece in a threaded screwing manner.

4. The molecular ion reaction cell of claim 1, wherein, The reaction module is a columnar structure, and internally a conical cavity is provided, and the inner wall is coated with a Teflon film or is subjected to silanization treatment; a U-shaped groove is arranged on the top surface of the reaction module, and an O-shaped sealing ring is arranged in the U-shaped groove to seal the connection between the air inlet module and the reaction module.

5. The molecular ion reaction cell of claim 1, wherein, A plurality of through holes are arranged on the sampling module and the air inlet module, a plurality of screw holes are arranged on the top of the reaction module, a screw is inserted into the screw hole through the through hole, and the sampling module, the air inlet module and the reaction module are fixed together.

6. The molecular ion reaction cell of claim 1, wherein, The side surface of the reaction module has a protruding outer edge portion, a plurality of threaded holes are arranged on the outer edge portion, and a screw is inserted into the threaded hole to fix and connect the molecular ion reaction chamber with a molecular ion reaction chamber fixing device of a mass spectrometry system.

7. The molecular ion reaction cell of claim 1, wherein, The material of the sampling module, the air inlet module and the reaction module of the molecular ion reaction chamber is selected from 304 stainless steel, 316 stainless steel, Teflon and Peek.

8. The molecular ion reaction cell of claim 1, wherein, The inner diameter of the capillary tube is in the range of 0.01mm to 1mm; the length of the conical cavity is 50mm to 53mm, and the taper angle is 13° to 16°.

9. The molecular ion reaction cell of claim 1, wherein, A temperature control device is mounted on the periphery of the reaction module to control the temperature of the molecular ion reaction.

10. The molecular ion reaction cell of claim 1, wherein, The part of the conical cavity of the reaction module is located in a vacuum chamber.

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