CH3 + chemical ionization formaldehyde ionizer

Abstract

The invention relates to a CH3 + chemical ionization formaldehyde ionizer. According to the ionizer, formaldehyde components in air sample gas are subjected to photochemical and molecular ion synergistic reaction to generate CH3 + and [CH3-CH2O] + ions through the collision effect of vacuum ultraviolet light and photoelectrons. The implementation device consists of an ionizer chamber, a molecular pump interface, a vacuum ultraviolet light source, a magnesium fluoride lens, a vacuum ultraviolet light source insulating ring, a photochemical and chemical ionization synergistic reaction tube, a reaction tube insulating ring, a reaction tube cover, a photochemical and chemical ionization synergistic reaction cavity, a gas overflow port, a sample gas feeding tube, a photoelectron grid mesh and an ion outlet. The CH3 + chemical ionization formaldehyde ionizer is combined with a mass spectrum device, the concentration of formaldehyde in a sample can be detected, and the method can be used as a real-time detection method for formaldehyde pollutants in ambient air.

Description

Technical Field

[0001] This invention relates to a CH3 + Chemical ionization formaldehyde ionizer. This ionizer uses vacuum ultraviolet light and photoelectron collisions to induce a photochemical and molecular-ion synergistic reaction in an air sample containing formaldehyde, generating CH3. + and [CH3-CH2O] + Ionization. This ionizer, combined with a mass spectrometer, can detect the formaldehyde concentration in a sample. This method can be used for real-time detection of formaldehyde pollutants in ambient air and belongs to the field of electronic technology. Background Technology

[0002] Formaldehyde is a significant indoor organic pollutant that seriously endangers human health. Formaldehyde itself is a colorless gas, difficult to detect at low concentrations; however, at higher concentrations, it has a strong, pungent, and suffocating odor. The main sources of indoor formaldehyde are substandard building materials, engineered wood products, various adhesives, paints, and synthetic textiles. Formaldehyde can coagulate proteins, and skin contact can cause hardening or even necrosis of the skin. Long-term exposure to high concentrations of formaldehyde can easily lead to symptoms such as headaches, dizziness, tearing, nausea, vomiting, chest tightness, and coughing; in severe cases, it can cause cancer, leukemia, and other diseases. Furthermore, formaldehyde is an important industrial raw material, widely used in the petrochemical, energy, and transportation industries. Therefore, achieving rapid and highly sensitive detection of formaldehyde is of great importance.

[0003] Currently, there are many methods for detecting formaldehyde, among which spectroscopic methods are the most mature analytical methods for detecting formaldehyde in the air. Spectroscopic methods include differential optical absorption spectroscopy (DOAS), tunable diode laser absorption spectroscopy (TDLAS), Fourier transform infrared spectroscopy (FTIR), and Hantzsch fluorescence spectroscopy. These methods have detection limits below the ppbv level, and the detection time is typically several minutes. Fluorescence spectroscopy based on the Hantzsch reaction requires large amounts of refrigerated reagents, making it unsuitable for on-site applications. Furthermore, the analytical process of spectroscopic methods is often interfered with by humidity, ozone, and chemicals with similar absorption peaks. Chromatography offers advantages in both quantitative and qualitative analysis and is the main offline method for detecting volatile organic compounds (VOCs). However, chromatographic detection of formaldehyde requires derivatization, which is both complex and time-consuming, and does not meet the requirements for real-time analysis.

[0004] Proton transfer reaction mass spectrometry (PTR-MS) is a highly sensitive analytical instrument for real-time detection of VOCs. Formaldehyde has a proton affinity of 712 kJ / mol, slightly higher than that of water (690 kJ / mol), therefore formaldehyde can be detected via the proton transfer reaction (H₃O₂). + + CH2O → [CH2O]H +[CH2O]H is ionized by H2O and can be detected by mass spectrometry. + The method utilizes ion signals. It is rapid and sensitive, obtaining formaldehyde concentration in just seconds, and can be used for direct detection of formaldehyde in the atmosphere. Although the detection process is affected by ambient humidity and O2... + CH3O is produced by the reaction of methanol and ethanol. + While it is not affected by other factors, PTR-MS remains the only mass spectrometry method to date that enables real-time, high-sensitivity detection and analysis of gaseous formaldehyde.

[0005] Vacuum ultraviolet photoionization mass spectrometry (PI-MS) is another mass spectrometry method for detecting VOCs. PI-MS uses a krypton lamp as the ionization source, and its structure is simpler than that of PTR-MS. For most VOCs, PI-MS exhibits superior detection performance. However, due to the limited availability of discharge gas radiation and the limited window materials, vacuum ultraviolet lamps used as photoionization sources typically employ krypton as the discharge gas and magnesium fluoride as the window material, resulting in vacuum ultraviolet light energies of 10.0 eV and 10.6 eV. Therefore, traditional PI-MS can usually only detect molecules with ionization energies below 10.6 eV through photoionization. Theoretically, lithium fluoride (LiF) windows can transmit 105 nm (11.8 eV) vacuum ultraviolet light, but the water solubility of LiF limits its practical application. Therefore, traditional PI-MS based on vacuum ultraviolet lamps cannot detect formaldehyde with an ionization energy of 10.88 eV.

[0006] CH3 + It is a very important class of gaseous carbocations, playing a crucial role in the synthesis of interstellar and organic molecules. CH3 + and protons (H) + Similar to the molecular-ionic reaction mechanism between gaseous organic molecules, H+ combines with gaseous organic molecules through electrophilic addition to form new ions. However, pure gaseous H+... + The source is not an ideal proton source for mass spectrometry analysis because of the high concentration of gaseous H₂. + Difficult to obtain and H + The reaction with organic molecules releases a large amount of heat, making the newly formed addition products easily decompose. In practical applications of proton transfer reaction mass spectrometry, hydrated hydrogen ions (H3O) are... + CH3+ is a commonly used reagent ion in proton transfer reactions, which can be generated by discharge through a hollow cathode in water vapor. Organic molecules contain CH3+. + The affinity is approximately H + Half of the affinity, which means CH3 + Specific gas phase H + It is more suitable as a reagent ion, but CH3 + Reactions with organic molecules still release a significant amount of heat. Stable CH3+ Addition products typically require a high-pressure reaction environment to dissipate excess reactive heat through intermolecular collisions. In recent years, addition reactions with CH3... + CF3 with similar spatial configuration + and CHF2 + It has been reported as a reagent ion for detecting small alkanes, but CH3... + This is not yet a commonly used reagent ion for mass spectrometry detection, possibly because high concentrations of CH3 cannot be obtained. + source. Summary of the Invention

[0007] To overcome the shortcomings of existing formaldehyde ionization technologies, this invention provides a CH3 + Chemical ionization formaldehyde ionizer. This ionizer uses a krypton lamp as a vacuum ultraviolet light source. Through the interaction of vacuum ultraviolet light and photoelectron collisions, formaldehyde in an air sample undergoes a photochemical and molecular-ion synergistic reaction to generate CH3. + and [CH3-CH2O] + ion.

[0008] The technical solution adopted in this invention patent is as follows: 1. An air sample gas containing formaldehyde enters the photochemical and chemical ionization synergistic reaction chamber through a sample gas inlet tube, forming a gas reaction environment of ~1000 Pa; 2. Vacuum ultraviolet light is irradiated into the photochemical and chemical ionization synergistic reaction chamber through a magnesium fluoride lens; 3. Part of the vacuum ultraviolet light passes through the gas overflow port and irradiates the photoelectron grid outside the photochemical and chemical ionization synergistic reaction chamber to generate photoelectrons, which enter the photochemical and chemical ionization synergistic reaction chamber under the drive of an electric field; 4. In the photochemical and chemical ionization synergistic reaction chamber, the air sample gas containing formaldehyde generates CH3 through photochemical and molecular ion synergistic reactions under the action of vacuum ultraviolet light and photoelectron collisions. + and [CH3-CH2O] + 5. The generated [CH3-CH2O] ions; + Ions fly out of the ionizer chamber under the influence of gas flow and electric field, forming an ion beam that can be detected by mass spectrometry.

[0009] The beneficial effect of this invention is to provide a CH3 + Chemical ionization formaldehyde ionizers, combined with mass spectrometry devices, can overcome the shortcomings of existing proton transfer reaction mass spectrometry and vacuum ultraviolet photoionization mass spectrometry in formaldehyde detection. Attached Figure Description

[0010] Appendix Figure 1 CH3 is the present invention +A schematic diagram of a chemical ionization formaldehyde ionizer, including: 1. Ionizer chamber; 2. Molecular pump interface; 3. Vacuum ultraviolet light source; 4. Magnesium fluoride lens; 5. Vacuum ultraviolet light source insulating ring; 6. Photochemical and chemical ionization synergistic reaction tube; 7. Reaction tube insulating ring; 8. Reaction tube cap; 9. Photochemical and chemical ionization synergistic reaction chamber; 10. Gas overflow port; 11. Sample gas inlet tube; 12. Photoelectron grating; 13. Ion outlet. Detailed Implementation

[0011] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are based on the technical solutions of the present invention, and the scope of protection of the present invention is not limited to the following embodiments.

[0012] Step 1: The ionizer chamber (1) is connected to the molecular pump via the molecular pump interface (2) to form a vacuum environment of ~1 Pa under sample injection conditions; Step 2: The vacuum ultraviolet light source (3), magnesium fluoride lens (4), vacuum ultraviolet light source insulating ring (5), photochemical and chemical ionization synergistic reaction tube (6), reaction tube insulating ring (7), and reaction tube cap (8) are arranged as shown in the attached figure to form the photochemical and chemical ionization synergistic reaction chamber (9); Step 3: There is a small hole with a diameter of ~1.5 mm in the center of the reaction tube cap (8) as a gas overflow port (10); Step 4: The air sample gas containing formaldehyde enters the photochemical and chemical ionization synergistic reaction chamber (9) through the sample gas injection tube (11) to form a ~1000 Pa vacuum environment. Step 5: Apply voltages U1, U2, and U3 to the photochemical and chemical ionization synergistic reaction tube (6), reaction tube cap (8), and photoelectron grid (12), respectively, with the voltage set to U1>U2>U3; Step 6: Vacuum ultraviolet light generated by the vacuum ultraviolet light source (3) passes through the magnesium fluoride lens (4) to irradiate the photochemical and chemical ionization synergistic reaction chamber (9); Step 7: Part of the vacuum ultraviolet light passes through the gas overflow port (10) to irradiate the photoelectron grid (12) to generate photoelectrons; Step 8: The photoelectrons are accelerated in reverse under the driving force of voltages U1, U2, and U3 and pass through the gas overflow port (10) into the photochemical and chemical ionization synergistic reaction chamber (9); Step 9: In the photochemical and chemical ionization synergistic reaction chamber (9), the air sample gas containing formaldehyde undergoes a photochemical and chemical ionization synergistic reaction under the action of vacuum ultraviolet light and photoelectron collision to generate CH3. + Ions; Step 10: CH3 in the photochemical and chemical ionization co-reaction chamber (9) + The ions further undergo a chemical ionization reaction with formaldehyde to produce [CH3-CH2O]. + Ions; Step 11: [CH3-CH2O] + Driven by the gas flow and electric field, ions pass through the gas overflow port (10), photoelectron grid (12), and ion outlet (13) and fly out of the ionizer chamber (1) to form [CH3-CH2O].+ Ion beam.

Claims

1. CH3 + The chemical ionization formaldehyde ionizer uses vacuum ultraviolet light and photoelectron collisions to cause a photochemical and molecular ion synergistic reaction in the formaldehyde component of an air sample, generating CH3. + and [CH3-CH2O] + The device for implementing ionization consists of an ionizer chamber (1), a molecular pump interface (2), a vacuum ultraviolet light source (3), a magnesium fluoride lens (4), a vacuum ultraviolet light source insulating ring (5), a photochemical and chemical ionization co-reaction tube (6), a reaction tube insulating ring (7), a reaction tube cap (8), a photochemical and chemical ionization co-reaction chamber (9), a gas overflow port (10), a sample gas inlet tube (11), a photoelectron grid (12), and an ion outlet (13). The above components are connected according to the attached drawings in the instruction manual.

2. The CH3 according to claim 1 + A chemical ionization formaldehyde ionizer, characterized in that: Air sample containing formaldehyde enters the photochemical and chemical ionization synergistic reaction chamber through the sample gas inlet tube, forming a gas reaction environment of ~1000 Pa.

3. The CH3 according to claim 1 + A chemical ionization formaldehyde ionizer, characterized in that: Vacuum ultraviolet light passes through a magnesium fluoride lens to irradiate the photochemical and chemical ionization synergistic reaction chamber.

4. The CH3 according to claim 1 + A chemical ionization formaldehyde ionizer, characterized in that: Part of the vacuum ultraviolet light passes through the gas overflow port and irradiates the photoelectron grid to generate photoelectrons. Driven by the electric field, the photoelectrons pass through the gas overflow port and enter the photochemical and chemical ionization co-reaction chamber.

5. The CH3 according to claim 1 + A chemical ionization formaldehyde ionizer, characterized in that: In a photochemical and chemical ionization synergistic reaction chamber, an air sample containing formaldehyde undergoes a photochemical and molecular ion synergistic reaction under the influence of vacuum ultraviolet light and photoelectron collisions to generate CH3. + and [CH3-CH2O] + ion.

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