High-sensitivity detection method for trace trimethylamine in air

Abstract

The invention belongs to the technical field of environmental monitoring, and particularly relates to a high-sensitivity monitoring method for trace trimethylamine in air. A perylene bisimide anion free radical pi-dimer is used as a probe, efficient citric acid solution absorption and an LWCC optical detection technology are combined, and accurate detection of trace trimethylamine in air is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental monitoring, and particularly relates to a highly sensitive monitoring method for trace trimethylamine in air. Background Art

[0002] Trimethylamine (N(CH 3 ) 3 ) is an organic compound with a strong pungent odor. As a typical atmospheric pollutant amine compound, trimethylamine has a significant impact on air quality and may also generate various harmful by-products through complex chemical conversion processes, posing a serious threat to the ecosystem and public health. In the atmospheric environment, trimethylamine can undergo a neutralization reaction with inorganic acidic substances such as sulfates and nitrates to form fine particulate matter (PM 2.5 ), thereby significantly promoting the formation and growth of secondary particulate matter, reducing atmospheric visibility, increasing the frequency and intensity of haze pollution events, and having a serious impact on regional air quality. In addition, during the atmospheric photochemical reaction process, trimethylamine can be further converted into harmful compounds such as nitrosamines with strong carcinogenicity and environmental persistence. These compounds have strong carcinogenicity and environmental persistence, seriously threatening public health. The emission sources of trimethylamine are extensive and complex, including industrial fields, agricultural activities, waste gas emissions from urban domestic sewage treatment plants, and emissions generated during the chemical process in chemical plants. Therefore, accurately monitoring the concentration of trimethylamine in the air is a key link in environmental protection and air pollution control.

[0003] Existing trimethylamine detection technologies (such as spectroscopy, electrochemical sensors, and wet chemical colorimetry) have met the basic requirements for trimethylamine concentration monitoring, but still have the following disadvantages.

[0004] (1) Insufficient sensitivity of spectroscopic detection technology

[0005] Spectroscopic detection technologies such as differential optical absorption spectroscopy (DOAS) quantify the concentration of trimethylamine by detecting the characteristic absorption spectrum of the gas, and have the advantages of rapid response and on-line detection. However, due to the low gas absorption coefficient and optical path limitation, its typical detection limit is in the ppb level, making it difficult to meet the detection requirements for trace trimethylamine (ppt level) in the atmosphere. In addition, the optical path stability has a greater impact on the detection accuracy, and the equipment cost is expensive. For example, the single unit price of the TRACE1310GC / ISQ 7000GC-MS developed by Thermo Fisher Scientific in the United States is close to one million, making it difficult to achieve low-cost popularization.

[0006] (2) Complexity and lifespan issues of long optical path cavity enhanced absorption technology

[0007] The long optical path cavity enhanced absorption spectroscopy (CEAS) extends the optical path through multiple reflections in the cavity, and the sensitivity can be improved to the ppb level, which is suitable for the detection of some trace gases. However, in this method, a high-reflectivity lens is used to construct the resonant cavity, which has extremely high requirements for the installation and alignment accuracy of the lens. Slight deviation will seriously affect the performance. The aging of the light source will cause the attenuation of the light intensity, affecting the detection accuracy; the cavity mirror is easily contaminated or worn, reducing the light reflection efficiency; the cavity structure may age and deform due to long-term use and temperature changes, affecting the optical path stability. Its service life is limited and it cannot meet the requirements of long-term stable monitoring.

[0008] (3) Interference and concentration-dependent defect problems of electrochemical sensors

[0009] Electrochemical sensors are based on the oxidation-reduction reaction of trimethylamine and can achieve portable or on-line monitoring. However, its selectivity is poor and it is easily interfered by other gases (such as ammonia and hydrogen sulfide). At the same time, the sensor is prone to poisoning and failure in a high-concentration environment. In a high-concentration trimethylamine environment, the sensor will show a response saturation phenomenon, resulting in inaccurate detection results; while in a low-concentration environment, the response speed may be slow, making it difficult to meet the requirements of rapid detection.

[0010] (4) Low color development efficiency of wet chemical colorimetry

[0011] Wet chemical colorimetry (such as Nessler's reagent method) relies on the reaction of the color reagent and trimethylamine for quantitative analysis. Although the operation cost is low, the color development process usually takes more than 30 minutes and is not suitable for real-time monitoring. In addition, these methods mostly use reagents with high toxicity (such as mercury iodide and phenol), which pose safety and environmental hazards, and the detection limit is only 30 ppb. Summary of the Invention

[0012] Aiming at the above defects, the purpose of the present invention is to provide a highly sensitive monitoring method for trace trimethylamine gas in air. This method uses perylene diimide anion radical π-dimer as a probe, combined with highly efficient citric acid solution absorption and long optical path liquid core waveguide capillary flow cell (LWCC) optical detection technology to achieve accurate detection of trace trimethylamine in air.

[0013] In order to achieve the above purpose, the first technical solution of the present application discloses a highly sensitive detection method for trace trimethylamine in air, which is characterized by including the following steps:

[0014] Sample the air to be measured to obtain a sample gas;

[0015] Absorb the sample gas with an aqueous citric acid solution to obtain a liquid sample;

[0016] Mix the liquid sample with the perylene diimide anion radical π-dimer probe solution, carry out a color reaction on the mixed solution in a temperature-controlled reaction tube, and perform defoaming treatment after the reaction is completed;

[0017] Optically detect the defoamed liquid using a long-path absorption cell.

[0018] Furthermore, the concentration of the citric acid aqueous solution is 0.01 mol / L.

[0019] Furthermore, the preparation method of the perylene diimide anion radical π-dimer probe solution is as follows: use a mixture of ethanol and ultrapure water in a volume ratio of 1:1 as the solvent, dissolve the perylene diimide compound, and filter it through a 0.22 μm filter membrane to obtain the perylene diimide anion radical π-dimer probe solution with a concentration of 10 μmol / L.

[0020] Furthermore, the temperature of the color reaction is 25 ± 2 °C and the time is 8 min.

[0021] Furthermore, the long-path absorption cell is LWCC.

[0022] Furthermore, the light source for the optical detection is a tungsten halogen lamp with a wavelength range of 350 - 700 nm, the detection wavelength is the absorption peak at 650 nm, and the absorbance signal is recorded using a spectrometer.

[0023] The second technical solution of the present application discloses a device for detecting trace trimethylamine in air, including:

[0024] Sampling device: used for sampling the air to be measured;

[0025] Glass spiral tube absorption device: used for absorbing the sampled gas with a citric acid aqueous solution to obtain;

[0026] Color reaction device: a temperature-controlled reaction tube, used for the color reaction of the perylene diimide anion radical π-dimer probe solution and the absorption liquid;

[0027] Defoaming device: a negative pressure vacuum pump, used for defoaming the solution after the color reaction;

[0028] Optical detection device: a long-path absorption cell, used for optically detecting the defoamed solution.

[0029] And, a method for detecting trace trimethylamine in air using the above device, using the above reagents, including the following steps:

[0030] Use the sampling device to sample the air to be measured to obtain a sample gas;

[0031] The sample gas is introduced into the glass spiral tube absorption device through a vacuum diaphragm pump. At the same time, the citric acid aqueous solution is introduced into the absorption device through a multi-channel peristaltic pump to fully contact and absorb the sample gas. The liquid sample after absorption flows from the bottom outlet of the absorption device into the color development device.

[0032] The sample gas is absorbed by the citric acid aqueous solution to obtain a liquid sample.

[0033] The liquid sample and the perylene diimide anion radical π-dimer probe solution are mixed through a three-way mixer and then enter the color development device for a color reaction. After the reaction is completed, the bubbles are removed through a defoaming device and then enter the optical detection device for detection.

[0034] Furthermore, the color development device is a Teflon pipe with a pipe length of 2 meters and an inner diameter of 1 / 16 inch.

[0035] Furthermore, the long optical path absorption cell is an LWCC with an optical path of 100 cm, a sample volume of 125 μL, and the optical signal is enhanced by total internal reflection.

[0036] The beneficial effects of the present invention are as follows:

[0037] 1. The present invention uses perylene diimide anion radical π-dimer as a probe material for the detection of trace trimethylamine in the air. This probe has an extremely high extinction coefficient (10 5 -10 6 L·mol-1·cm-1), and has excellent selectivity and sensitivity to trimethylamine ions. The color reaction conditions are mild, the temperature is controlled at 25 ± 2 °C, and the reaction time only needs 8 minutes to complete the binding of trimethylamine ions and the probe and generate a complex with characteristic absorbance. By combining with the LWCC, for low-concentration samples (ppt level), the sensitivity of this system is higher than that of existing methods, and it can accurately detect and analyze the trace concentration of trimethylamine, realizing the accurate detection of trimethylamine concentration in the range from ppt to ppm.

[0038] 2. The present invention uses a 0.01 mol / L citric acid solution as the absorption liquid to improve the absorption efficiency of trimethylamine gas. Trimethylamine gas generates stable trimethylamine ions through an acid-base reaction during the absorption process, and the absorption efficiency reaches more than 99.9%. Cooperating with the high borosilicate glass spiral tube absorption device, the inner diameter of the spiral tube is 2 mm, the outer diameter is 22 mm, and the number of spiral turns is 10, ensuring full contact between gas and liquid. At the same time, the working temperature of the absorption device is stably controlled at 20 ± 1 °C through a jacket water bath under low-temperature conditions, ensuring that the absorption efficiency is not affected by the ambient temperature.

[0039] 3. The present invention introduces LWCC, achieving an optical path of 100 cm through total internal reflection technology, and enhancing the sensitivity to the ppt level. The sample volume of the flow cell only needs 125 μL, greatly reducing the sample demand. The optical system is configured with a tungsten halogen lamp as the light source, with a wavelength band covering 350 - 700 nm. A high-sensitivity spectrometer model (such as NIRQuest+) is selected, and the detection wavelength is locked at the characteristic absorption peak of 650 nm of the perylene diimide-trimethylamine complex. This design can achieve real-time detection of trimethylamine concentration in the air and reduce the detection limit to the ppt level, significantly superior to the existing technology.

[0040] 4. The present invention preferably uses low-toxicity reagents (citric acid and perylene diimide probe), avoiding the use of toxic chemicals (such as mercury iodide) in traditional colorimetric methods. The reagent consumption is low (only 125 μL per detection), and the waste liquid is centrally treated through a closed system, meeting the requirements of green environmental protection and low-cost operation. Description of the Drawings

[0041] Figure 1 It is a schematic structural diagram of an on-line trimethylamine detection instrument;

[0042] Figure 2 It is a schematic diagram of a glass spiral tube absorption device;

[0043] Figure 3 It is a schematic diagram of the working principle of a trimethylamine detection device. Detailed Embodiments

[0044] The following describes the detailed embodiments of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0045] The first embodiment of the present application discloses the test of the absorption coefficient of the perylene diimide anion radical π-dimer:

[0046] Experimental method: This experiment uses the perylene diimide anion radical π-dimer as a probe to detect the sensitivity of trimethylamine (TMA). First, the perylene diimide anion radical π-dimer probe is synthesized. The core of the probe is the perylene diimide group, which is modified to enhance its selectivity and response speed to trimethylamine. Solubility and absorbance experiments are carried out in different solvents to ensure that the probe solution has efficient absorbance characteristics. The changes in absorbance and fluorescence intensity are measured through UV-Vis spectroscopy and fluorescence spectroscopy, so as to analyze its response characteristics to trimethylamine.

[0047] Experimental steps

[0048] 1. Synthesis of perylene diimide anion radical π-dimer: React the perylene diimide compound with tetrabutylammonium hydroxide (TBAOH) to prepare a stable anion radical π-dimer in dichloromethane. The specific synthesis method is as follows: React for 12 hours at 25 °C, and extract the product with sodium chloride solution and dichloromethane. Purify by column chromatography to obtain pure perylene diimide anion radical π-dimer.

[0049] 2. Sample preparation and solution preparation: Dissolve the prepared π-dimer in dichloromethane (DCM), and adjust the concentration to 20 μM to prepare a standard solution for subsequent experiments.

[0050] 3. Control and reaction of trimethylamine concentration: Pass trimethylamine gas (TMA) with different concentrations ranging from 0.1 ppb to 10 ppm into the probe solution through a gas transmission device. In each experiment, when the trimethylamine gas reacts with the π-dimer solution, the changes in absorbance and fluorescence intensity will be monitored in real time.

[0051] 4. Spectral testing and data recording: Use a UV-Vis spectrometer and a fluorescence spectrometer to record the changes in absorbance and fluorescence intensity respectively. The test wavelength range is from 350 nm to 800 nm, and 650 nm is used as the main detection wavelength.

[0052] The experimental results are shown in Table 1.

[0053] Table 1 Absorbance change data (TMA concentration and absorbance)

[0054]

[0055] The experimental results show that as the concentration of trimethylamine increases, the absorbance gradually increases at 773 nm and gradually decreases at 545 nm. It indicates that the perylene diimide anion radical π-dimer can effectively respond to trimethylamine gas at a level as low as ppb, and the reaction becomes more obvious with the increase in concentration.

[0056] Result analysis: Absorbance change: In the presence of trimethylamine at different concentrations, the perylene diimide anion radical π-dimer shows significant absorbance changes. Especially when the trimethylamine concentration reaches 0.1 ppm, a significant absorption peak appears at 773 nm, and the absorption peak at 545 nm weakens significantly. As the concentration of trimethylamine increases, the absorbance gradually increases, indicating that the probe can respond at a concentration as low as ppb.

[0057] Fluorescence intensity change: Experimental results show that the addition of trimethylamine causes attenuation of the fluorescence intensity of the perylene diimide anion radical π-dimer solution. The fluorescence intensity decreases significantly with the increase in trimethylamine concentration. Especially at a concentration of 0.5 ppm, the fluorescence signal almost completely disappears.

[0058] Limit of detection (LOD): By establishing a standard curve, the limits of detection (LOD) of this system were calculated as follows: TMA: 0.049 ppb; Putrescine (Put): 0.13 ppb; Cadaverine (Cad): 0.46 ppb;

[0059] Dimethylamine (DMA): 0.02 ppb. These results indicate that the perylene diimide anion radical π-dimer probe has extremely high sensitivity and can detect multiple amines at extremely low concentrations.

[0060] Reaction rate and stability: Experiments show that at 25 °C, the color reaction can be completed in only 8 minutes, significantly improving the detection efficiency. Through multiple cycle experiments, it was found that the probe can still maintain a stable response in different cycles, with good repeatability.

[0061] Therefore, it can be seen that when the perylene diimide anion radical π-dimer is used to detect trimethylamine in this application, it has the following advantages.

[0062] Extremely low limit of detection: According to experimental data, the perylene diimide anion radical π-dimer can achieve highly sensitive detection of trimethylamine at the ppt (parts per trillion) level. The experimental data show that the perylene diimide anion radical π-dimer probe significantly reduces the limit of detection when detecting trimethylamine and has higher sensitivity compared to other traditional methods.

[0063] Rapid color reaction: In the experiment, the perylene diimide anion radical π-dimer probe can quickly react with trimethylamine to form a complex with characteristic absorbance. The color reaction can be completed in only 8 minutes at 25 ± 2 °C, which significantly improves the detection efficiency compared to other detection methods.

[0064] Excellent extinction coefficient: The perylene diimide anion radical π-dimer has an extremely high extinction coefficient (105 - 106 L·mol -1 ·cm -1 ), making it show extremely high sensitivity in the detection of trace trimethylamine in the air.

[0065] The second embodiment of this application discloses an experiment with citric acid solution as the absorption liquid

[0066] Experimental method: In this experiment, a 0.01 mol / L citric acid solution was used as the absorption liquid. Through its acid-base reaction with trimethylamine gas, trimethylamine was absorbed as stable trimethylamine ions (NH(CH 3 ) 3 + ), and combined with a perylene diimide anion radical π-dimer probe for a color reaction. Finally, optical detection was carried out through a long optical path liquid waveguide capillary flow cell (LWCC). The experiment aimed to verify the absorption effect of the citric acid solution and its application in the detection of low-concentration trimethylamine. Experimental steps

[0067] Air sampling: A sampling device was used to sample the air to be tested. The sampled gas was introduced at a flow rate of 1.0 L / min by a vacuum diaphragm pump.

[0068] Absorption process: The collected air was introduced into the 0.01 mol / L citric acid solution through a glass spiral tube. The inner diameter of the spiral tube was 2 mm, the outer diameter was 22 mm, and the number of spiral turns was 10. By precisely controlling the flow rate ratio of the absorption liquid and the gas, sufficient contact between the gas and the absorption liquid was ensured to achieve the maximum absorption effect.

[0069] Mixing and color reaction: The absorbed liquid sample was mixed with the perylene diimide anion radical π-dimer probe solution in a 1:1 ratio and entered a temperature-controlled reaction tube. The reaction was carried out at 25 ± 2 °C for 8 minutes. The trimethylamine ions reacted with the probe to form a complex with characteristic absorbance.

[0070] Defoaming treatment: The reacted liquid passed through an annular PTFE membrane microfluidic defoaming device with a negative pressure value of -20 kPa to remove residual bubbles and ensure accurate optical measurement results.

[0071] Optical detection: The defoamed solution entered the long optical path liquid waveguide capillary flow cell (LWCC). The optical path was set to 100 cm, and the sample volume was 125 μL. The optical signal was enhanced by total internal reflection, and the absorbance signal was recorded at a wavelength of 650 nm using a spectrometer.

[0072] Experimental results: A standard curve was established by relating the absorbance to the known concentration of trimethylamine. The formula for the standard curve is: A = S·C + B; where: A is the absorbance (the value measured at a specific wavelength), C is the trimethylamine concentration (unit: ppb or ppm), S is the slope (i.e., the change in absorbance corresponding to a unit change in concentration), and B is the intercept, usually representing the absorbance background value when there is no trimethylamine.

[0073] The experimental data (concentration and absorbance) were substituted into the above formula for linear regression analysis to obtain the values of the slope S and the intercept B. Then, the lowest detection limit (LOD) was calculated using them. When calculating the LOD, the slope S of the standard curve and the standard deviation (σ) were used to determine: Where: σ is the standard deviation of background noise or measurement error, usually estimated through multiple background measurements; S is the slope in the standard curve; finally, the LOD of trimethylamine is obtained as 0.049 ppb, that is, when the concentration of trimethylamine is as low as 0.049 ppb, the measured change in absorbance is still significant.

[0074] Absorption efficiency: In a 0.01 mol / L citric acid solution, the absorption efficiency of trimethylamine is as high as 99.9%. Through an acid-base reaction, citric acid combines with trimethylamine gas to form stable trimethylamine ions. Compared with traditional solvents (such as 0.1 mol / L dilute sulfuric acid solution), the citric acid solution exhibits a higher absorption efficiency. At a low temperature environment (20 ± 1 °C), the absorption efficiency of dilute sulfuric acid is usually 70% - 85%, while the citric acid solution maintains a stable absorption effect of over 99.9% under the same conditions.

[0075] Color reaction: The color reaction is completed within 8 minutes, which is significantly better than traditional wet chemical colorimetry, which usually takes more than 30 minutes to complete the reaction. In addition, this method avoids the use of toxic chemical reagents such as mercury iodide and phenol, ensuring the safety and environmental friendliness of the experimental process.

[0076] Detection sensitivity: The detection limit (LOD) of this experiment is 0.3 ppb, and the quantification limit (LOQ) is 1.0 ppb, which enables this method to detect trace amounts of trimethylamine in the air. Compared with traditional equipment such as GC-MS, the detection method combining the citric acid solution and the perylene diimide probe can achieve a sensitivity as low as the ppt level.

[0077] Comparison experiment: The comparison experiment with a 0.1 mol / L dilute sulfuric acid solution shows that the absorption efficiency of the citric acid solution at low temperature is significantly higher than that of dilute sulfuric acid. The absorption efficiency of dilute sulfuric acid drops to below 60% at 20 ± 1 °C, while the citric acid solution can be stably maintained above 99.9%. In addition, the citric acid solution has stronger environmental friendliness and does not produce toxic waste.

[0078] Result analysis: The results of this experiment show that the citric acid solution exhibits extremely high absorption efficiency when absorbing trimethylamine gas, reaching an efficiency of over 99.9%. Compared with traditional solvents (such as dilute sulfuric acid solution), the absorption efficiency of the citric acid solution is significantly improved, especially in a low temperature environment (20 ± 1 °C). The absorption efficiency of the dilute sulfuric acid solution is usually between 70% - 85%, and the absorption effect significantly decreases under low temperature conditions, while the citric acid solution can maintain a stable high absorption efficiency both at room temperature and low temperature. This indicates that the citric acid solution has stronger stability and higher efficiency in the process of absorbing trimethylamine gas.

[0079] In terms of the color reaction, the reaction rate after the citric acid solution combines with the perylene diimide anion radical π-dimer probe is significantly higher than that of the traditional wet chemical colorimetric method. The color reaction can be completed in only 8 minutes, while the traditional method usually takes more than 30 minutes to achieve the same reaction effect. This advantage not only improves the experimental efficiency but also avoids the use of toxic chemicals, ensuring the environmental protection and safety of the experiment. In addition, the citric acid solution also shows excellent sensitivity in the detection of low-concentration trimethylamine. The experimental results show that the method of combining the citric acid solution with the perylene diimide probe can accurately detect trimethylamine at the ppb (parts per billion) level, with a detection limit of 0.3 ppb and a quantification limit of 1.0 ppb. This is comparable to existing high-precision equipment such as GC-MS, and compared with other detection methods, the sensitivity and detection limit have been significantly improved.

[0080] In summary, the experimental results of this study show that the citric acid solution can not only efficiently absorb trimethylamine but also exhibits strong stability, short reaction time, and low detection limit during the experiment, with obvious technical advantages. Through comparative experiments with traditional solvents, the superiority of the citric acid solution as an absorption solution in the detection of trimethylamine is further verified, providing a new solution for the efficient monitoring of low-concentration air pollutants. Through experimental comparison, the citric acid solution shows significant superiority. When using the citric acid solution (concentration of 0.01 mol / L), trimethylamine gas is converted into stable trimethylamine ions through an acid-base reaction, and the absorption efficiency is over 99.9%. In addition, the citric acid solution can also maintain a stable absorption efficiency under low-temperature conditions (20 ± 1°C), while traditional solvents such as dilute sulfuric acid solution (concentration of 0.1 mol / L) usually have an absorption efficiency between 70% - 85% when absorbing trimethylamine gas, and its absorption efficiency often drops below 60% in a low-temperature environment (20 ± 1°C). In addition, the dilute sulfuric acid solution is more sensitive to changes in environmental temperature, and when the temperature rises, the absorption efficiency may decrease due to the increased volatility of the gas.

[0081] The third embodiment of this application discloses a device for detecting trace trimethylamine in the air and a method for detecting trace trimethylamine in the air through this device, as Figures 1 - 3 shown, the device includes:

[0082] Sampling device: a vacuum pump and a spiral tube (as Figure 1 shown) for sampling the air to be measured;

[0083] Glass spiral tube absorption device: as Figure 2 shown, located on the left side of the Figure 3 peristaltic pump, for absorbing the sampled gas with an aqueous citric acid solution;

[0084] Color display device: ( Figure 3The reaction chamber is a temperature-controlled reaction tube used for the color reaction of the perylene diimide anion radical π-dimer probe solution and the absorbent solution.

[0085] Defoaming device: a negative pressure vacuum pump ( Figure 3 including the defoamer and the vacuum pump in it), used to defoam the solution after the color reaction.

[0086] Optical detection device: a long optical path absorption cell ( Figure 3 including the long optical path flow cell, the flowing optical cavity chamber, the light source, and the spectrometer in it), used to perform optical detection on the defoamed solution.

[0087] It should be noted that in addition to the above, it also includes a peristaltic pump: used for liquid transportation, with precise flow control and pollution-free characteristics; MFC: used to precisely control the gas flow rate to ensure that the gas entering the device passes through the system at a stable flow rate.

[0088] In the above embodiments, the sampling device can also be equipped with a temperature and humidity compensation sensor, which can monitor the changes in environmental conditions in real time and automatically adjust the sampling flow rate and gas concentration compensation. Under environmental conditions where the humidity fluctuation range is 20%-90%, the system automatically adjusts the sampling conditions to ensure that even in a high humidity environment (such as in a sewage treatment plant or an industrial park), the collected gas sample still accurately represents the on-site gas concentration.

[0089] In the above embodiments, a high borosilicate glass spiral tube (inner diameter 2mm, number of spiral turns 10) is used as the absorption device to increase the gas-liquid contact area and extend the gas-liquid contact time. The flow rates of the absorbent solution and the sample gas are precisely controlled to achieve the optimal flow rate ratio. Further, the outside of the absorption device can also include a water bath jacket temperature control device (20±1°C), which can still maintain high absorption performance in a low temperature and high humidity environment. This device enables a 0.01mol / L citric acid solution to absorb trimethylamine and converts trimethylamine into a stable ionic form (NH(CH3)3 + ) through an acid-base reaction, and the absorption efficiency reaches more than 99.9%.

[0090] In the above embodiments, the color development device is a temperature-controlled reaction tube, preferably a Teflon pipe, with a pipe length of 2 meters and an inner diameter of 1 / 16 inch, ensuring that the color reaction is completed while the reaction liquid flows in the pipe. A constant temperature control module is equipped outside the circuit to ensure that the temperature inside the pipe remains at 25±2°C, and the color reaction time is 8 minutes. After the reaction is completed, the solution passes through the defoamer to remove residual bubbles and ensure the stability of the detection signal. This color reaction does not require complex pretreatment and can be completed in only 8 minutes under the condition of 25±2°C, significantly shortening the detection time. The high selectivity of the probe ensures that the color reaction to trimethylamine is not interfered by common gases (such as CO 2 and H 2 O).

[0091] In the above embodiments, the defoamer adopts an annular PTFE membrane microfluidic defoaming device, the negative pressure of which is provided by a vacuum pump, and the negative pressure value is set to -20 kPa to ensure that the bubbles in the solution are completely removed. The defoamed sample solution enters the LWCC (or other long optical path absorption cells) through a Teflon pipe for optical detection. The optical path of the LWCC is 100 cm, the sample volume is 125 μL, and the optical signal is enhanced by total internal reflection. The light source is a tungsten halogen lamp with a wavelength band covering 350 - 700 nm, and the spectrometer records the absorbance signal. The detection wavelength is 650 nm, which is the characteristic absorption peak of the perylene diimide-trimethylamine complex.

[0092] It should be noted that after the optical detection, the spectral signal is processed by Oceanview 2.0 software. The absorbance value is converted into the trimethylamine concentration using a pre-established standard curve, and the result is output in ppt or μg / m 3 and automatically recorded in the system database. The waste liquid contains trimethylamine salt formed by the reaction of trimethylamine and citric acid, so special treatment is required. It enters a waste liquid barrel with a closed volume of 10 L through the liquid path outlet. First, it undergoes preliminary neutralization treatment (such as adding an alkaline solution) to adjust the pH value. The waste liquid is centrally treated by a professional waste liquid treatment agency with ISO 14001 environmental management certification to ensure safety and environmental protection requirements.

[0093] Example 1 On-site Detection of Trimethylamine Concentration in the Air around an Industrial Park and a Sewage Treatment Plant

[0094] 1. Detection Environmental Conditions

[0095] (1) Detection Location

[0096] Industrial Park: To verify the detection ability under relatively mild environmental conditions.

[0097] Sewage Treatment Plant: To verify the stability of the method in a high-humidity (78% RH) and complex environment.

[0098] (2) Real-time Environmental Parameters:

[0099] Temperature: 22 - 23.5 °C (monitored and recorded in real time by a temperature and humidity sensor);

[0100] Relative Humidity: 55% - 78% (to verify the anti-interference ability and adaptability of the method in a high-humidity environment);

[0101] Atmospheric Pressure: 101.3 kPa;

[0102] Wind Speed: 1.0 - 1.2 m / s (to calibrate the sampling flow rate with a portable anemometer).

[0103] 2. Detection Steps

[0104] Sampling and Absorption: Start the vacuum diaphragm pump to collect air samples at a flow rate of 1.0 L / min. Synchronously record the real-time temperature and humidity data of the environment, and automatically adjust the sampling flow rate and gas concentration compensation through the temperature and humidity compensation module. The sampled gas contacts the 0.01 mol / L citric acid solution countercurrently in a glass spiral tube (trimethylamine is converted into ionic NH(CH3)3 + ), and the absorption efficiency is verified to be 99.9%. The absorption liquid flows into the colorimetric pipeline through the bottom outlet to ensure the stability and accuracy of the absorption process.

[0105] Colorimetric Reaction: The absorption liquid is mixed with the perylene diimide anion radical π-dimer probe solution in a ratio of 1:1 and enters a constant temperature reaction pipeline at 25°C. The reaction lasts for 8 minutes, and trimethylamine ions specifically bind to the probe to form a complex (the change in absorbance <0.5%).

[0106] Debubbling and Optical Detection: The mixed liquid removes microbubbles through a PTFE membrane debubbler (negative pressure -20 kPa) and enters the LWCC flow cell. The LWCC technology enhances the optical signal through total internal reflection, and the spectrometer records the absorbance signal at 650 nm for concentration calculation.

[0107] 3. Data Analysis and Detection Results (see Table 2)

[0108] Table 2 Measured Data

[0109] Detection parameter Value Absorbance (A) 0.218 Background-corrected absorbance 0.215 Standard curve equation y = 0.042x + 0.003 (x: ppb, y: A) Trimethylamine concentration 5.0 ppb Relative standard deviation (RSD, n = 3) 1.80％

[0110] Spiked Recovery Verification:

[0111] Add 5.0 ppb of trimethylamine standard gas to the sample. The measured recovery rate is between 98.6% - 102.3%, verifying the accuracy and reliability of the method. At the same time, the detection limit (LOD, 3σ) is 0.3 ppb, and the quantification limit (LOQ, 10σ) is 1.0 ppb, indicating that this method can sensitively detect trimethylamine concentrations as low as the ppb level. In addition, the results of synchronous detection with GC-MS show that the trimethylamine concentration is 4.9 ppb, and the relative error is less than 3%, further verifying the high accuracy and comparability of this method.

[0112] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A highly sensitive detection method for trace trimethylamine in air, characterized in that: The steps include: Sampling the air to be tested to obtain sample gas; Utilize citric acid aqueous solution to absorb sample gas to obtain liquid sample; Mixing the liquid sample and the perylene imide anion radical π-dimer probe solution, subjecting the mixed solution to a color reaction in a temperature-controlled reaction tube, and performing a defoaming treatment after the reaction is completed; The debubbled liquid is optically detected using a long optical path absorption cell.

2. The detection method according to claim 1, characterized in that: The concentration of the citric acid aqueous solution is 0.01 mol / L.

3. The detection method according to claim 1, characterized in that: The preparation method of the perylene imide anion free radical π-dimer probe solution is as follows: ethanol and ultrapure water are mixed in a volume ratio of 1:1 as a solvent, the perylene imide compound is dissolved, and the solution is filtered through a 0.22 μm filter membrane, wherein the solubility of the perylene imide anion free radical π-dimer probe solution is 10 μmol / L.

4. The detection method according to claim 1, characterized in that: The color development reaction temperature is 25±2° C. and the reaction time is 8 minutes.

5. The detection method according to claim 1, characterized in that: The long optical path absorption cell is LWCC.

6. The detection method according to claim 1, characterized in that: The light source of the optical detection is a 350-700nm halogen tungsten lamp, the detection wavelength is an absorption peak of 650nm, and a spectrometer is used to record the absorbance signal.

7. A device for detecting trace trimethylamine in air, characterized in that: include: Sampling device: used to sample the air to be tested; Glass spiral tube absorption device: used to absorb the sample gas with citric acid aqueous solution to obtain; Color development device: a temperature-controlled reaction tube used for the color development reaction of the perylene imide anion free radical π-dimer probe solution and the absorption liquid; Debubbling device: negative pressure vacuum pump, used to debubble the solution after the color development reaction; Optical detection device: long optical path absorption cell, used for optical detection of the debubbled solution.

8. A method for detecting trace trimethylamine in air using the device according to claim 7, characterized in that: Using the reagent according to claim 1, comprising the following steps: The air to be tested is sampled by using a sampling device to obtain sample gas; The sample gas is introduced into the glass spiral tube absorption device through a vacuum diaphragm pump, and the citric acid aqueous solution is introduced into the absorption device through a multi-channel peristaltic pump to fully contact and absorb the sample gas. After the absorption is completed, the liquid sample flows into the color development device from the bottom outlet of the absorption device. Utilize citric acid aqueous solution to absorb sample gas to obtain liquid sample; The liquid sample and the perylene imide anion radical π-dimer probe solution are mixed through a three-way mixer and then enter a color development device for color development reaction. After the reaction is completed, the bubbles are removed through a debubbling device and the liquid sample enters an optical detection device for detection.

9. The method according to claim 8, characterized in that: The color developing device is a Teflon pipe with a length of 2 meters and an inner diameter of 1 / 16 inch.

10. The method according to claim 8, characterized in that: The long optical path absorption cell is LWCC, the optical path is 100 cm, the sample volume is 125 μL, and the light signal is enhanced by total internal reflection.

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