Mass spectrometric detection method for protonated formaldehyde through tandem connection of association ionization and proton transfer reaction ionization

Abstract

The invention relates to a mass spectrometric detection method for associating ionization and proton transfer reaction ionization in series with protonated formaldehyde. The mass spectrometric detection method comprises the following steps: doping a certain amount of dichloromethane into a formaldehyde-containing sample gas, and generating protonated water ions in an associating ionization cavity through associating ionization reaction; then formaldehyde molecules in the sample gas are converted into protonated formaldehyde ions through a proton transfer reaction in a proton transfer reaction ionization cavity, protonated formaldehyde ion signals are analyzed and detected through a mass spectrum device, formaldehyde concentration information is obtained, the method can be used as a real-time detection method for formaldehyde pollutants in ambient air, and the method is suitable for popularization and application. The implementation device comprises a sample gas injection pipe, a Nafion pipe, a sample injection needle valve, a sample gas and dichloromethane gas mixing pipe, a dichloromethane tank, a dichloromethane gas pipe, a dichloromethane gas quantity needle valve, an association ionization cavity, a vacuum ultraviolet light source, a vacuum ultraviolet light baffle, a proton transfer reaction ionization cavity and a proton transfer reaction ionization cavity outlet. And a mass spectrum device and a molecular pump interface. The formaldehyde concentration in the air can be detected in real time, and the interference of O2 + ions in a conventional proton transfer reaction mass spectrometer on formaldehyde signals is avoided.

Description

Technical Field

[0001] The present invention relates to a mass spectrometry detection method for the tandem protonation of formaldehyde by associative ionization and proton transfer reaction ionization. In this method, a certain amount of dichloromethane is doped into the sample gas containing formaldehyde. Protonated water ions are generated through the associative ionization reaction occurring in the associative ionization chamber. Subsequently, formaldehyde molecules in the sample gas are converted into protonated formaldehyde ions through the proton transfer reaction in the proton transfer reaction ionization chamber. Finally, the signal of the protonated formaldehyde ions is analyzed and detected by a mass spectrometry device to obtain formaldehyde concentration information. This method can be used as a real-time detection method for formaldehyde pollutants in ambient air and belongs to the field of electronic technology. Background Art

[0002] Formaldehyde (HCHO) is an important indoor organic pollutant. Indoor formaldehyde mainly comes from building materials, artificial boards, various adhesives, coatings, and synthetic textiles. In addition, smoking is another important source of formaldehyde. It is measured that each cigarette can emit about 2.4 mg of formaldehyde. Formaldehyde has been determined by the World Health Organization as a carcinogenic and teratogenic substance. Long-term exposure to low-dose formaldehyde can not only cause various diseases such as chronic respiratory diseases, nasopharyngeal carcinoma, colon cancer, brain tumors, menstrual disorders, and pregnancy syndrome, but also cause memory and intelligence decline in teenagers, and even cause chromosomal abnormalities and leukemia in newborns. Therefore, it is of great significance to achieve rapid and sensitive detection of formaldehyde.

[0003] Spectrophotometry is a traditional method for detecting formaldehyde, including acetylacetone method, chromotropic acid method, MBTH method, pararosaniline method, and AHMT method. Among them, the acetylacetone method is the most common. This method utilizes the reaction of formaldehyde with a specific compound to generate a chromogenic compound, and then the formaldehyde content is quantified by colorimetry. When using spectrophotometry to detect the formaldehyde concentration in air, not only does the formaldehyde in the air need to be absorbed into the solution before step-by-step analysis, but the analysis process is also relatively complex and time-consuming.

[0004] Chromatography is the main method for detecting volatile organic compounds in air. Chromatography uses a chromatographic column to separate the organic compounds in the mobile phase one by one, and then the organic compounds are detected by a hydrogen flame (FID) or electron impact mass spectrometry. Currently, chromatography is also the main method for quantitatively measuring the formaldehyde concentration in air. The advantage of chromatography is its ability for quantitative and qualitative analysis, but the disadvantage is that it requires passing through a chromatographic column, so the analysis time for a single chromatographic method usually takes more than ten minutes.

[0005] Proton transfer reaction mass spectrometry is a real-time high-sensitivity analysis method for volatile organic compounds that emerged at the end of the last century. It uses hollow cathode discharge to generate protonated water ions (H3O +), and then use the proton transfer reaction between protonated water ions and organic molecules to generate protonated organic ions. Finally, use a mass spectrometry device to detect and analyze the organic ion signal to obtain information on the concentration and molecular weight of the organic matter. Proton transfer reaction mass spectrometry can also be used for the direct detection of formaldehyde concentration in the air. The advantages of using proton transfer reaction mass spectrometry to detect formaldehyde are fast speed and high sensitivity, and the sample does not require pretreatment, and the measurement of formaldehyde concentration in the air can be achieved within seconds. However, the disadvantage is that trace amounts of O2 are also generated while protonated water ions are generated by hollow cathode discharge. + , and O2 + will react with compounds such as methanol and ethanol to generate protonated formaldehyde ions, causing measurement errors.

[0006] Vacuum ultraviolet photoionization mass spectrometry is one of the traditional methods for detecting volatile organic compounds. Vacuum ultraviolet photoionization mass spectrometers use vacuum ultraviolet light to ionize volatile organic compounds to generate organic ions, and then use a mass spectrometry device to detect and analyze the organic ion signal, and finally obtain information on the concentration and molecular weight of the organic matter. However, since the ionization threshold of formaldehyde (10.88 eV) is higher than the photon energy (10.0 eV and 10.6 eV) emitted by the krypton lamp, which is the vacuum ultraviolet light source commonly used in general vacuum ultraviolet photoionization mass spectrometry, ordinary vacuum ultraviolet photoionization mass spectrometry methods cannot detect formaldehyde. For analytes with low photoionization efficiency, reaction ions can be generated by doping reactants with high ionization efficiency (such as toluene, ionization energy 8.82 eV), and then analyte ions can be generated through the molecular ion reaction between the reaction ions and the analyte. However, the premise of this method is that the ionization energy of the analyte is close to or lower than the ionization energy of the reaction ion precursor. Therefore, the method of doping reactants with high ionization efficiency is not applicable to the measurement of formaldehyde.

[0007] The associative ionization process induced by excited dichloromethane is a new and efficient protonation phenomenon discovered in recent years. It has been found that during the vacuum ultraviolet photoionization process of oxygen-containing organic compounds, doping dichloromethane can increase the ion signal of oxygen-containing organic compounds by 2 to 3 orders of magnitude. The new associative ionization method can efficiently protonate various volatile organic compounds such as ketones, aldehydes (excluding formaldehyde), alcohols, esters, aromatic nitro compounds, organic compounds containing amino groups, nitroalkanes, nitrile compounds, thioethers, and phosphate esters. The associative ionization process induced by excited dichloromethane is a new ionization process, and its process is speculated as follows: Vacuum ultraviolet light excites dichloromethane molecules to form excited dichloromethane, and the excited dichloromethane molecules further induce water molecules (H2O) to transfer protons to other molecules to form protonated products. The reaction process is speculated as CH2Cl2 * + H2O + A → AH + + Cl -+ H2CO + HCl, where A is a water or oxygen-containing organic molecule. Formaldehyde is a product of the associative ionization process induced by excited-state dichloromethane. However, in the relevant papers, the signal of protonated water ions is very strong, while the signal of protonated formaldehyde is extremely low. The existing experimental data show that the associative ionization process induced by excited-state dichloromethane cannot be directly used for the detection of formaldehyde. Summary of the Invention

[0008] In order to overcome the deficiencies in existing formaldehyde detection technologies, the present invention provides a mass spectrometry detection method for tandem protonated formaldehyde by associative ionization and proton transfer reaction ionization. In this method, dichloromethane is doped into the sample gas containing formaldehyde. The doped dichloromethane gas is irradiated with vacuum ultraviolet light in the associative ionization chamber, and protonated water ions are generated through the associative ionization reaction induced by excited-state dichloromethane. Then, in the proton transfer reaction ionization chamber, formaldehyde molecules are ionized through a proton transfer reaction, and the generated protonated formaldehyde ions are further detected and analyzed by a mass spectrometry device, thereby obtaining the concentration information of formaldehyde.

[0009] The technical solutions adopted in this invention patent are as follows: 1. Dichloromethane is doped into the sample gas containing formaldehyde; 2. Protonated water ions are generated through the associative ionization reaction induced by excited-state dichloromethane in the associative ionization chamber; 3. Protonated formaldehyde ions are generated through the proton transfer reaction between formaldehyde and protonated water ions in the proton transfer reaction ionization chamber; 4. A light-blocking plate is provided between the associative ionization chamber and the proton transfer reaction ionization chamber to block the vacuum ultraviolet light from entering the proton transfer reaction ionization chamber; 5. The mass spectrometry device detects and analyzes the signal intensity of protonated formaldehyde ions, thereby obtaining the concentration information of formaldehyde.

[0010] The beneficial effect of the present invention is to provide a new method for the real-time detection of formaldehyde, which can overcome the deficiencies of existing proton transfer mass spectrometry, vacuum ultraviolet photoionization mass spectrometry, and associative ionization mass spectrometry in the detection of formaldehyde. Description of the Drawings

[0011] The attached drawing is a schematic structural diagram of the implementation device of the mass spectrometry detection method for tandem protonated formaldehyde by associative ionization and proton transfer reaction ionization of the present invention. Among them: 1. Sample gas inlet tube, 2. Nafion tube, 3. Injection needle valve, 4. Sample gas and dichloromethane gas mixing tube, 5. Dichloromethane tank, 6. Dichloromethane gas tube, 7. Dichloromethane gas volume needle valve, 8. Associative ionization chamber, 9. Vacuum ultraviolet light source, 10. Vacuum ultraviolet light baffle, 11. Proton transfer reaction ionization chamber, 12. Proton transfer reaction ionization chamber outlet, 13. Mass spectrometry device, 14. Molecular pump interface. Detailed Embodiments

[0012] 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 solution of the present invention, and the protection scope of the present invention is not limited to the following embodiments.

[0013] Step 1: The sample gas containing formaldehyde is sampled through the sample gas inlet tube (1); Step 2: The sample gas is dehumidified through the Nafion tube (2); Step 3: The dehumidified sample gas enters the sample gas and dichloromethane gas mixing tube (4) through the appropriately opened injection needle valve (3); Step 4: The dichloromethane gas in the dichloromethane tank (5) enters the sample gas and dichloromethane gas mixing tube (4) through the dichloromethane gas tube (6), and its flow rate is controlled by the appropriately opened dichloromethane gas volume needle valve (7); Step 5: The mixed sample gas and dichloromethane gas enter the association ionization chamber (8); Step 6: In the association ionization chamber (8), the dichloromethane gas and the trace water vapor in the sample gas undergo an association ionization reaction under the irradiation of the vacuum ultraviolet light source (9) to generate ionized water ions; Step 7: The vacuum ultraviolet light is blocked by the vacuum ultraviolet light baffle (10) and cannot irradiate into the proton transfer reaction ionization chamber (11); Step 8: The sample gas containing ionized water ions bypasses the vacuum ultraviolet light baffle (10) and enters the proton transfer reaction ionization chamber (11); Step 9: In the proton transfer reaction ionization chamber (11), the formaldehyde molecules in the sample gas and the ionized water ions generate protonated formaldehyde ions through a proton transfer reaction; Step 10: The generated protonated formaldehyde ions flow out of the proton transfer reaction ionization chamber outlet (12) with the sample gas and enter the mass spectrometry device (13); Step 11: The mass spectrometry device (13) obtains the concentration of formaldehyde in the sample gas through the signal intensity of the protonated formaldehyde ions; Step 12: The detected sample gas is pumped away by an external vacuum device through the molecular pump interface (14).

Claims

1. A mass spectrometry detection method for ionizing and tandem protonating formaldehyde by associative ionization and proton transfer reaction. A certain amount of dichloromethane is doped into the sample gas containing formaldehyde. Protonated water ions are generated by the associative ionization method in the associative ionization chamber. Then, formaldehyde molecules in the sample gas are converted into protonated formaldehyde ions through a proton transfer reaction in the proton transfer reaction ionization chamber. The signal of the protonated formaldehyde ions is analyzed and detected by a mass spectrometry device, and the formaldehyde concentration information in the sample gas can be obtained in real time. The implementation device is composed of a sample gas inlet tube (1), a Nafion tube (2), an injection needle valve (3), a sample gas and dichloromethane gas mixing tube (4), a dichloromethane tank (5), a dichloromethane gas tube (6), a dichloromethane gas volume needle valve (7), an associative ionization chamber (8), a vacuum ultraviolet light source (9), a vacuum ultraviolet light baffle (10), a proton transfer reaction ionization chamber (11), a proton transfer reaction ionization chamber outlet (12), a mass spectrometry device (13), and a molecular pump interface (14). The above components are connected according to the attached drawings of the specification.

2. The mass spectrometry detection method for ionizing and protonating formaldehyde in series by association ionization and proton transfer reaction according to claim 1, wherein: The ionizer is composed of an associative ionization chamber and a proton transfer reaction ionization chamber.

3. The mass spectrometry detection method for the ionization of tandem protonated formaldehyde by associative ionization and proton transfer reaction according to claim 1, characterized in that: A light baffle is provided between the associative ionization chamber and the proton transfer reaction ionization chamber.

4. The method for mass spectrometry detection of ionized formaldehyde in an associated ionization and proton transfer reaction ionization tandem protonation according to claim 1, characterized in that: A certain amount of dichloromethane is doped during the injection of the sample gas.

5. The method for mass spectrometry detection of ionized formaldehyde in an association ionization and proton transfer reaction ionization tandem protonation according to claim 1, characterized in that: Protonated formaldehyde ions are generated by the proton transfer reaction between protonated water ions and formaldehyde molecules.

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