Photochemical ionization device for mass spectrometry of real-time online detection of glyoxal in atmosphere

Abstract

The application belongs to the technical field of analysis and detection, and relates to a photochemical ionization device for mass spectrometry for real-time online detection of glyoxal in the atmosphere. The photochemical ionization device sequentially arranges a vacuum ultraviolet light source, an oxygen negative reagent ion generation zone and an ion molecule reaction zone according to the emission direction of the vacuum ultraviolet light. The oxygen negative reagent ion generation zone is a straight channel, bias electrodes, a first partial pressure electrode and a second partial pressure electrode are sequentially arranged in the wall of the straight channel according to the emission direction of the vacuum ultraviolet light, the direction of the electric field formed between the bias electrodes, the first partial pressure electrode and the second partial pressure electrode is opposite to the emission direction of the vacuum ultraviolet light, a pump is arranged between the bias electrodes and the first partial pressure electrode, an air source and a reagent auxiliary gas source are connected between the first partial pressure electrode and the second partial pressure electrode, and a gas source containing a target molecule to be detected is connected between the second partial pressure electrode and the ion molecule reaction zone. The application can effectively remove O3 generated by the vacuum ultraviolet light, thereby improving the sensitivity of glyoxal detection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of analytical detection technology, and relates to a photochemical ionization device for real-time online detection of mass spectrometry of glyoxal in the atmosphere. BACKGROUND

[0002] The information disclosed in this Background section is only for the purpose of increasing the understanding of the general background of the application and does not necessarily constitute an admission or a recognition that the information forms part of the prior art already known to a person of ordinary skill in the art.

[0003] Glyoxal is an important substance involved in atmospheric photochemical oxidation process, and is an important substance for oxidation reaction with volatile organic compounds in addition to traditional atmospheric oxidation indicators such as nitrogen oxides and ozone. Glyoxal is a precursor of peroxy radicals and has an important contribution to the formation of secondary organic aerosols and photochemical smog. Since glyoxal has no primary emission source, it can be used as an important indicator for evaluating atmospheric oxidation capacity.

[0004] According to the research and understanding of the inventors, at present, there is no standard method for detecting glyoxal in the atmosphere. There are two common methods for detecting glyoxal at home and abroad: spectroscopy and mass spectrometry. In the spectroscopy method, differential optical absorption spectroscopy is a common means for detecting the concentration of glyoxal in the atmosphere. However, due to the presence of particulate matter, moisture and nitrogen oxides in the atmosphere, the accuracy, sensitivity and stability of differential optical absorption spectroscopy detection will be seriously interfered. In the mass spectrometry detection, PTR-MS is a common instrument for detecting glyoxal. However, the humidity of the atmosphere will affect the detection results and cause the cracking of glyoxal. The chromatography-mass spectrometry detection method is an effective method for detecting glyoxal. However, the time of chromatography pretreatment cannot realize real-time online detection of atmospheric environment. In the field of negative ion mass spectrometry, He Shenggui uses low-energy electrons generated by laser irradiation on noble metal surfaces to realize the detection of glyoxal by electron affinity reaction. The main chemical reaction is: Metal + hv→e - and This method can realize the detection of glyoxal, but due to the large laser device, it cannot realize the on-site detection of glyoxal in the atmosphere, and the generated electrons need to go through a complex energy modulation process. In summary, there is no report on the real-time online detection of glyoxal in the atmosphere by using negative ion mode chemical ionization mass spectrometry. SUMMARY

[0005] In order to solve the problems of the prior art, the purpose of the present application is to provide a photochemical ionization device for real-time online detection of mass spectrometry of glyoxal in the atmosphere. The photochemical ionization device provided by the present application can generate ions with O2 - reagent ions as the main, and the O2 -The electron transfer reaction of the reagent ion and glyoxal ionizes glyoxal, so that glyoxal in the air is detected by mass spectrometry.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the present application is:

[0007] In one aspect, a photochemical ionization device for real-time online detection of mass spectrometry of glyoxal in the atmosphere, a vacuum ultraviolet light source, an oxygen negative reagent ion generation zone and an ion molecule reaction zone are sequentially arranged according to the emission direction of the vacuum ultraviolet light, and the ion molecule reaction zone is a region for reacting oxygen negative reagent ions with target molecules to be detected (such as glyoxal);

[0008] The oxygen negative reagent ion generation zone is a straight channel, one end of the straight channel is connected with the vacuum ultraviolet light source, the other end of the straight channel is connected with the ion molecule reaction zone, a bias electrode, a first partial pressure electrode and a second partial pressure electrode are sequentially arranged in the wall of the straight channel according to the emission direction of the vacuum ultraviolet light, the electric field direction formed between the bias electrode, the first partial pressure electrode and the second partial pressure electrode is opposite to the emission direction of the vacuum ultraviolet light, a first through hole is formed in the wall of the straight channel between the bias electrode and the first partial pressure electrode, a second through hole is formed in the wall of the straight channel between the first partial pressure electrode and the second partial pressure electrode, a third through hole is arranged between the second partial pressure electrode and the ion molecule reaction zone, the first through hole is connected with the inlet of the pump, the second through hole is used for connecting an air source and a reagent auxiliary gas source, and the third through hole is used for connecting a gas source containing target molecules to be detected.

[0009] The present application generates free electrons (e - ) by the reagent auxiliary gas under the irradiation of vacuum ultraviolet light, thereby generating O2 - reagent ions, O2 - The reagent ions and target molecules to be detected (such as glyoxal) undergo electron transfer reaction to generate target molecules to be detected, so that the target molecules to be detected are detected by mass spectrometry. However, in the presence of O2, the vacuum ultraviolet light photoionization source will inevitably generate O3, and the electron affinity (EA=2.1eV) of O3 is much stronger than that of O2 (EA=0.45eV), which leads to the free electrons released by the reagent auxiliary gas being preferentially captured by O3. Therefore, in the present application, a pump is arranged between the bias electrode and the first partial pressure electrode, which can timely remove the O3 generated by photoionization, avoid the competition of free electrons by O3 with strong electron affinity, and thus obtain a mass spectrometry ionization source with O2 - as the main reagent ion. At the same time, by constructing the electric field opposite to the emission direction of the vacuum ultraviolet light through the bias electrode, the first partial pressure electrode and the second partial pressure electrode, the free electrons released by the reagent auxiliary gas can move away from the vacuum ultraviolet lamp under the action of the electric field, further avoiding the capture of free electrons by O3, and thus increasing O2- The yield of reagent ions is increased, thereby improving the production of the target molecular ion (e.g., C2H2O2). - The yield of the target molecule is increased to achieve the detection of the target molecule.

[0010] To improve detection sensitivity, the main component in the ion-molecule reaction region is a segmented quadrupole. The radio frequency electric field generated in the segmented quadrupole region causes the generated glyoxal ions to converge towards the axis, improving the transmission efficiency of the target molecular ions and thus enhancing the overall sensitivity of the instrument.

[0011] On the other hand, a mass spectrometry system includes the aforementioned photochemical ionization device and mass spectrometer, wherein the outlet of the ion molecular reaction zone in the photochemical ionization device is connected to the inlet of the mass spectrometer.

[0012] Thirdly, the application of the aforementioned photochemical ionization device or mass spectrometry system in the detection of glyoxal.

[0013] Fourthly, a method for online detection of glyoxal, comprising providing the aforementioned mass spectrometry system, wherein after powering on the mass spectrometry system, air, reagent auxiliary gas, and air containing glyoxal are introduced into it for mass spectrometry detection.

[0014] The beneficial effects of this invention are as follows:

[0015] This invention, by placing a pump between the bias electrode and the first voltage divider electrode, can promptly remove the O3 generated by photoionization, ensuring the O2 content is maintained. - The reagent ions are generated; simultaneously, by constructing a bias electrode, a first voltage-dividing electrode, and a second voltage-dividing electrode, an electric field opposite to the emission direction of the vacuum ultraviolet light is created. This causes the free electrons released from the reagent auxiliary gas to move away from the vacuum ultraviolet lamp under the influence of the electric field, further preventing the free electrons from being captured by O3, thereby increasing the O2 concentration. - The yield of reagent ions is increased, thereby improving the production of the target molecular ion (e.g., C2H2O2). - This increases the yield of O2, enabling the detection of target molecules. Furthermore, removing O3 generated by vacuum ultraviolet light using a pump not only increases the yield of O2 but also... - The concentration of reagent ions should be reduced to minimize interference from CO3 ions. - This improves the sensitivity of mass spectrometry.

[0016] Experiments have shown that the mass spectrometry system based on photochemical ionization provided by this invention can detect glyoxal at low concentrations during online detection. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 The structure schematic diagram of photochemical ionization device in the embodiment of the present application, wherein, 1, vacuum ultraviolet lamp, 2, bias electrode, 3, partial pressure electrode 1, 4, partial pressure electrode 2, 5, skimmer 1, 6, ion molecule reaction zone, 7, skimmer 2, 8, mechanical pump, 9, reagent auxiliary gas, 10, air, 11, glyoxal sample;

[0019] Figure 2 The O3 to O2 - The impact of reagent ion generation comparison chart;

[0020] Figure 3 The air background mass spectrum and the mass spectrum of 50ppb glyoxal when the glyoxal sample is not added in the embodiment of the present application, wherein, m / z 58 is the characteristic ion peak of glyoxal (C2H2O2 - ). DETAILED DESCRIPTION

[0021] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0022] It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments consistent with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, devices, components and / or combinations thereof, but do not preclude the presence or addition of one or more other features, steps, operations, devices, components and / or combinations thereof.

[0023] In view of the problem that the existing device cannot meet the real-time online detection of glyoxal in the atmosphere, the present application provides a photochemical ionization device for real-time online detection mass spectrum of glyoxal in the atmosphere.

[0024] In a typical embodiment of the present application, a photochemical ionization device for real-time online detection mass spectrum of glyoxal in the atmosphere is provided, which comprises a vacuum ultraviolet light source, an oxygen negative reagent ion generation zone and an ion molecule reaction zone arranged in sequence according to the emission direction of the vacuum ultraviolet light, wherein the ion molecule reaction zone is a region for reacting oxygen negative reagent ions with target molecules to be detected (such as glyoxal).

[0025] The oxygen negative reagent ion generation zone is a straight channel, one end of the straight channel is connected with the vacuum ultraviolet light source, the other end of the straight channel is connected with the ion molecule reaction zone, bias electrodes, first voltage division electrodes and second voltage division electrodes are sequentially arranged in the wall of the straight channel according to the emission direction of the vacuum ultraviolet light, the electric field direction formed between the bias electrodes, the first voltage division electrodes and the second voltage division electrodes is opposite to the emission direction of the vacuum ultraviolet light, a first through hole is arranged in the wall of the straight channel between the bias electrodes and the first voltage division electrodes, a second through hole is arranged in the wall of the straight channel between the first voltage division electrodes and the second voltage division electrodes, a third through hole is arranged between the second voltage division electrodes and the ion molecule reaction zone, the first through hole is connected with the inlet of the pump, the second through hole is used for connecting the air source and the reagent auxiliary gas source, and the third through hole is used for connecting the gas source containing the target molecules to be detected.

[0026] The reagent auxiliary gas releases a large number of free electrons (Formula 1) under the irradiation of ultraviolet light, and O2 in zero gas captures these electrons to generate O2 - ions; however, O2 can also be ionized by ultraviolet light to generate O3, and the electron affinity (EA = 2.1 eV) of O3 is greater than that (EA = 0.45 eV) of O2, so that O3 - ions and reacts with CO2 to generate CO3 - ions, resulting in O2 - The yield of O2 - ions is reduced (Formulae 2-5). Therefore, the present application adds a pump at the bias electrode to timely pump away O and O3 generated below the light window, thereby avoiding the large generation of CO3 - ions, and the reagent ion yield is improved, and electron transfer reaction occurs between the reagent ion and glyoxal (EA = 0.62 eV) to generate glyoxal ions (Formula 6):

[0027] Dopant + hv → Dopant + + e- (Formula 1)

[0028] O2 + hv → O + O (Formula 2)

[0029] O2 + O → O3 (Formula 3)

[0030]

[0031]

[0032]

[0033] The generated reagent ions and glyoxal enter the ion molecule reaction zone under the action of the electric field, the highly divergent ions are collisionally cooled and focused under the action of the radio frequency electric field, further electron transfer reaction occurs to generate glyoxal ions, and the glyoxal ions enter the mass spectrometer.

[0034] In some embodiments, the main component in the ion molecule reaction zone is a fragment quadrupole. The radio frequency electric field formed by the fragment quadrupole region converges the generated glyoxal ions to the axis, improves the transmission efficiency of the target molecule ions to be detected, and further improves the overall sensitivity of the instrument.

[0035] In one or more embodiments, the fragment quadrupole is composed of four quadrupoles, which form a circumferential array along the repelling electrode axis direction; each quadrupole is coaxially fixed on an insulating rod by a circular ring electrode of the same size, and each fragment quadrupole electrode is isolated by an insulating ring of the same size.

[0036] In some embodiments, the inlet of the ion molecule reaction zone is provided as a first skimmer (skimmer 1).

[0037] In some embodiments, the outlet of the ion molecule reaction zone is provided as a second skimmer (skimmer 2).

[0038] Another embodiment of the present application provides a mass spectrometry system, which comprises the photochemical ionization device and a mass spectrometer, and the outlet of the ion molecule reaction zone in the photochemical ionization device is connected to the inlet of the mass spectrometer.

[0039] A third embodiment of the present application provides an application of the photochemical ionization device or the mass spectrometry system in detecting glyoxal.

[0040] In some embodiments, the application is in detecting the content of glyoxal in air.

[0041] A fourth embodiment of the present application provides an online method for detecting glyoxal, which provides the mass spectrometry system, and after the mass spectrometry system is powered on, air, reagent auxiliary gas, and air containing glyoxal are introduced into the mass spectrometry system for mass spectrometry detection.

[0042] In some embodiments, the absolute values of the direct current voltages applied to the bias electrode, the first voltage dividing electrode, and the second voltage dividing electrode decrease in turn. For example, the direct current voltages applied to the bias electrode, the first voltage dividing electrode, and the second voltage dividing electrode are -1170 to -1150 V, -690 to -670 V, and -250 to -230 V, respectively.

[0043] In some embodiments, the absolute value of the direct current voltage applied to the first skimmer at the inlet of the ion molecule reaction zone is lower than the absolute value of the direct current voltage applied to the second voltage dividing electrode. For example, the direct current voltage applied to the first skimmer at the inlet of the ion molecule reaction zone is -29 to -27 V.

[0044] In some embodiments, the absolute value of the direct current voltage applied to the first conical orifice body at the inlet of the ion-molecule reaction zone is higher than the absolute value of the direct current voltage applied to the second conical orifice body at the outlet of the ion-molecule reaction zone. For example, the direct current voltage applied to the second conical orifice body at the outlet of the ion-molecule reaction zone is -16 to -14 V.

[0045] In some embodiments, the absolute value of the direct current voltage applied to the first electrode of each rod of the fragment quadrupole is sequentially decreased, and the absolute value of the direct current voltage applied to the first conical orifice body at the inlet of the ion-molecule reaction zone is between the absolute value of the direct current voltage applied to the second conical orifice body at the outlet of the ion-molecule reaction zone. For example, the absolute value of the direct current voltage applied to the first electrode of each rod of the fragment quadrupole is sequentially -26 to -24 V and -21 to -19 V.

[0046] In some embodiments, in the fragment quadrupole, a radio frequency voltage with a peak-to-peak value of 290 to 310 V and a same frequency is applied to the segment electrodes of each rod through a capacitor. The radio frequency voltages applied to the radially adjacent electrodes are opposite in phase. The frequency is 1.5 to 2.0 MHz.

[0047] In some embodiments, the reagent auxiliary gas is benzene, toluene, xylene, acetone, or other substances that can be ionized to release electrons by vacuum ultraviolet light.

[0048] In some embodiments, the sample injection flow rate of the air headspace purging reagent auxiliary gas is 100 to 150 mL / min, and the flow rate of the air containing glyoxal is 850 to 900 mL / min.

[0049] In order for those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in conjunction with specific embodiments.

[0050] Embodiment 1

[0051] A mass spectrometry system comprises a photochemical ionization device and a mass spectrometer connected in sequence for real-time online detection of glyoxal in the atmosphere by mass spectrometry.

[0052] A photochemical ionization device for real-time online detection of glyoxal in the atmosphere by mass spectrometry, as shown in Figure 1 The photochemical ionization device comprises a vacuum ultraviolet lamp 1, an oxygen negative reagent ion generation zone, and an ion-molecule reaction zone 6 in sequence according to the emission direction of the vacuum ultraviolet light.

[0053] The main component of the ion-molecule reaction zone 6 is a fragment quadrupole. The fragment quadrupole is composed of four rods, which are arranged in a circumferential array along the repelling electrode axis. Each rod is fixed on an insulating rod by coaxial circular electrodes of the same size, and each fragment quadrupole electrode is isolated by an insulating ring of the same size.

[0054] The inlet of the ion-molecule reaction zone 6 is provided with a skimmer 1 5, and the outlet of the ion-molecule reaction zone 6 is provided with a skimmer 27.

[0055] The oxygen negative reagent ion generation zone is provided as a straight channel, and the bias electrode 2, the first voltage dividing electrode 13 and the second voltage dividing electrode 24 are sequentially arranged in the wall of the straight channel according to the emission direction of the vacuum ultraviolet light. A through hole is arranged between the bias electrode 2 and the first voltage dividing electrode 13 and is connected to the inlet of the mechanical pump 8. A through hole is arranged between the first voltage dividing electrode 13 and the second voltage dividing electrode 24 and is connected to the air source 10 and the reagent auxiliary gas source 9. The second voltage dividing electrode 24 is provided with a through hole and is connected to the glyoxal sample source 11 and the ion-molecule reaction zone 6.

[0056] The direct current voltages V1 =-1160V, V2 =-680V, V3 =-240V, S1 =-28V and S2 =-15V are respectively applied to the bias electrode, the first voltage dividing electrode, the second voltage dividing electrode, the skimmer 1 and the skimmer 2. The direct current voltages V5 =-25V and V6 =-20V are respectively applied to the first electrode and the last electrode of each pole of the fragment quadrupole. The radio frequency voltages with the same frequency (1.8MHz) and the peak-to-peak value of 300V are applied to the fragment electrodes of each pole through the capacitance (the radio frequency voltages applied to the radially adjacent electrodes are opposite in phase). Under the above conditions, the mass spectra of the closed mechanical pump and the opened mechanical pump are respectively detected, as shown in FIG. 2. Figure 2 It can be clearly seen that the signal of the O2 - reagent ion is obviously enhanced, and the signal of the CO3 - ion is obviously reduced, which indicates that the O and O3 generated under the light window can be timely pumped away by opening the mechanical pump, thereby avoiding the large generation of the CO3 ion, so that the O2 - reagent ion yield is improved.

[0057] The glyoxal sample is the air with the glyoxal concentration of 50ppb, and the detection is carried out under the above conditions. The sampling flow of the reagent auxiliary gas toluene is 100mL / min, and the flow rate of the glyoxal sample is 850mL / min. The detection result is shown in FIG. 3. Figure 3 By comparison with the air background, it can be clearly seen that the characteristic ion peak (C2H2O2 - ) of the glyoxal appears at m / z 58 in the mass spectrum of the air with the glyoxal concentration of 50ppb, which indicates that the mass spectrum detection based on the photochemical ionization device can detect the glyoxal with the concentration of 50ppb.

[0058] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A photochemical ionization device for mass spectrometry of real-time online detection of glyoxal in the atmosphere, characterized in that, The vacuum ultraviolet light source, the oxygen negative reagent ion generation zone and the ion molecule reaction zone are arranged in sequence according to the emission direction of the vacuum ultraviolet light, and the ion molecule reaction zone is a region for reacting the oxygen negative reagent ion with glyoxal; The oxygen negative reagent ion generation zone is a straight channel, one end of the straight channel is connected with the vacuum ultraviolet light source, the other end of the straight channel is connected with the ion molecule reaction zone, bias electrodes, first partial pressure electrodes and second partial pressure electrodes are arranged in sequence on the wall of the straight channel according to the emission direction of the vacuum ultraviolet light, the electric field direction formed between the bias electrodes, the first partial pressure electrodes and the second partial pressure electrodes is opposite to the emission direction of the vacuum ultraviolet light, a first through hole is arranged on the wall of the straight channel between the bias electrodes and the first partial pressure electrodes, a second through hole is arranged on the wall of the straight channel between the first partial pressure electrodes and the second partial pressure electrodes, a third through hole is arranged between the second partial pressure electrodes and the ion molecule reaction zone, the first through hole is connected with the inlet of the pump, the second through hole is connected with an air source and a reagent auxiliary gas source, and the third through hole is connected with a gas source containing glyoxal. The direct current voltage applied by the bias electrodes is-1170~-1150 V, the direct current voltage applied by the first partial pressure electrodes is-690~-670 V, and the direct current voltage applied by the second partial pressure electrodes is-250~-230 V.

2. The photochemical ionization device of claim 1, wherein the photochemical ionization device is configured to ionize the sample by photoionization. The main component in the ion molecule reaction zone is a fragment quadrupole.

3. The photochemical ionization device of claim 1, wherein the photochemical ionization device is configured to ionize the sample by photoionization. The inlet of the ion molecule reaction zone is provided with a first conical hole body, and the outlet of the ion molecule reaction zone is provided with a second conical hole body.

4. A mass spectrometry system characterized by, The photochemical ionization device of any one of claims 1-3 and a mass spectrometer are included, and the outlet of the ion molecule reaction zone in the photochemical ionization device is connected with the inlet of the mass spectrometer.

5. The photochemical ionization device of any one of claims 1-3 or the mass spectrometer system of claim 4 is applied to detecting glyoxal.

6. The use according to claim 5, characterized in that, The application is applied to detecting the content of glyoxal in air.

7. A method for on-line detection of glyoxal, characterized in that, The mass spectrometer system of claim 4 is provided, and after the mass spectrometer system is powered on, air, reagent auxiliary gas and air containing glyoxal are introduced into the mass spectrometer system, and mass spectrometric detection is performed.

8. The method of claim 7, wherein the online detection of glyoxal is characterized by, The absolute values of the direct current voltages applied by the bias electrodes, the first partial pressure electrodes and the second partial pressure electrodes are sequentially reduced. The absolute value of the direct current voltage applied to the first conical hole body of the inlet of the ion molecule reaction zone is lower than the absolute value of the direct current voltage applied to the second partial pressure electrodes. The absolute value of the direct current voltage applied to the first conical hole body of the inlet of the ion molecule reaction zone is higher than the absolute value of the direct current voltage applied to the second conical hole body of the outlet of the ion molecule reaction zone. The absolute values of the direct current voltages applied to the first electrode and the last electrode of each pole of the fragment quadrupole are sequentially reduced, and the absolute value of the direct current voltage applied to the first conical hole body of the inlet of the ion molecule reaction zone is between the absolute value of the direct current voltage applied to the second conical hole body of the outlet of the ion molecule reaction zone. In the fragment quadrupole, a radio frequency voltage with the same frequency and a peak-to-peak value of 290-310 V is applied to the fragment electrodes of each pole through a capacitor.

9. The method of claim 7, wherein the online detection of glyoxal is characterized by, The reagent auxiliary gas is benzene, toluene, xylene or acetone.

10. The method of claim 7, wherein the online detection of glyoxal is characterized by, The sample flow rate of air headspace purge reagent auxiliary gas is 100-150 mL / min, and the flow rate of air containing glyoxal is 850-900 mL / min.

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