Method for improving the sensitivity of online detection of ammonia in ammonia-containing gas

Abstract

The application provides a method for improving the sensitivity of ammonia online detection in ammonia-containing gas. The method replaces the dry compensation gas in the reaction zone with high-humidity gas, so that the water concentration in the reaction zone is much higher than the concentration of reagent molecules, i.e. acetone, to generate hydrated ammonia ions, thereby increasing the reactivity of reagent ions and sample ammonia gas molecules. Under the action of drift gas, the migration zone is kept dry and high-concentration acetone, so that the generated hydrated ammonia ions are converted into Ac2NH4 + again during the migration in the migration zone. The product ions are highly stable during the migration in the migration tube. In the whole process of the application, water molecules participate in the reaction, which improves the sensitivity of ammonia detection to a certain extent. The finally generated product ions remain unchanged, and a single ammonia product peak is presented on the ion mobility spectrum. Meanwhile, the introduced humidification gas keeps the reaction zone at saturated humidity, and the humidity change of the sample gas does not affect the detection, thereby eliminating the influence of different sample humidity on the detection accuracy. The method is simple to operate and is suitable for the detection of trace ammonia in ammonia-containing gas.

Description

Technical Field

[0001] This invention belongs to the field of analytical chemistry instruments, specifically relating to a method for online detection sensitivity of ammonia in ammonia-containing gas. Based on reagent molecule doping technology, it achieves high-sensitivity detection of low concentrations of ammonia under different humidity levels. Background Technology

[0002] Ammonia is an essential component of human metabolism, participating in multiple physiological processes. It is closely associated with diseases such as kidney failure, cirrhosis or hepatitis, hepatic encephalopathy, Helicobacter pylori infection, and halitosis. It is also a potential biomarker in exercise physiology and drug metabolism research. Simultaneously, ammonia exhibits neurotoxicity, making rapid bedside monitoring crucial for the identification and early warning of critical illnesses. Since the partial pressure of ammonia in the alveoli and arteries is almost equal, changes in the concentration of ammonia in exhaled breath can indicate corresponding pathophysiological alterations.

[0003] In recent years, there have been many studies on online detection of exhaled ammonia. In 2011, ZH Endre et al. used SIFT-MS to continuously monitor exhaled ammonia in hemodialysis patients, showing that exhaled ammonia can effectively assess the efficacy of dialysis. In 2016, Bayrakli et al. used spectral detection to detect exhaled ammonia in healthy individuals and patients with Helicobacter pylori, demonstrating the potential advantages of exhaled ammonia detection in the non-invasive diagnosis of Helicobacter pylori. In 2020, Chen Mingren et al. used a semiconductor sensor to detect respiratory ammonia in 121 patients with chronic kidney disease, and the results showed a good correlation between exhaled ammonia and blood urea nitrogen levels, serum creatinine levels, and glomerular filtration rate. In 2021, Jinya Ishida et al. used a chemical sensor to detect exhaled ammonia in patients with chronic liver disease, confirming the relationship between exhaled ammonia and liver dysfunction, and verifying the feasibility of using exhaled ammonia in the diagnosis of chronic liver disease.

[0004] Exhaled ammonia testing can be conducted using both offline and online methods. Offline methods typically involve collecting exhaled air using a gas bag. However, ammonia readily adsorbs onto the inner surface of the sampling bag, and the high humidity of exhaled air further facilitates the dissolution of ammonia, significantly impacting the accuracy of the test results. Online testing, on the other hand, eliminates the differences caused by the material of the offline sampling bag and sample storage.

[0005] Among current detection methods, spectrometers and mass spectrometers are bulky, costly, and complex to operate. Their sensors suffer from poor accuracy, slow response, instability, and require repeated calibration. Human exhaled ammonia concentrations are low, humidity is high, and background is complex, placing extremely high demands on exhaled ammonia sampling and detection. To date, there is no stable and accurate detection technology or real-time analytical method.

[0006] This invention provides an online detection method for exhaled ammonia that improves sensitivity. Based on photoionization ion mobility spectrometry, it develops a highly selective and sensitive method for exhaled ammonia detection. This method is non-invasive, simple, rapid, efficient, low-cost, and repeatable. It provides an effective screening and detection method for the early detection and diagnosis of patients with organ dysfunction, and provides timely diagnostic evidence and prognostic assessment for critical illnesses. Summary of the Invention

[0007] This invention relates to a method for online detection of ammonia in ammonia-containing gases using ion mobility spectrometry. The technical problem to be solved is to achieve highly specific and sensitive online detection of low concentrations of ammonia in complex matrices, unaffected by sample ammonia humidity, and to provide a simple, rapid, efficient, low-cost, and repeatable ammonia detection method.

[0008] The ammonia detection method is based on photoionization source ion mobility spectrometry detection technology. It uses a non-radioactive vacuum ultraviolet lamp ionization source (1) and a TPG ion gate (2) to divide the entire migration tube into two regions: an ionization reaction region (4) and an ion migration region (5). The reaction region (4) is provided with an outlet (9), a sample gas inlet (10), and a compensation gas inlet (11). The migration region (5) is provided with a drift gas inlet (7) on the outer side near the Faraday disk (3). The carrier gas continuously generates acetone reagent molecules with a constant volume concentration through the reagent molecule generating device (8) as a dopant, which enter the migration region (5) and the reaction region (4) together with the drift gas. The drift gas and the carrier gas are one or more of air, helium, nitrogen, and argon.

[0009] The acetone reagent molecules are continuously volatilized by a carrier gas through the reagent molecule generating device (8) to obtain a constant volume concentration, and enter the migration zone and reaction zone together with the drift gas.

[0010] Acetone molecules, under the action of a photoionization source, generate reactant ions Ac₂H₂O. + Driven by the electric field within the ionization region, the sample gas carrying ammonia molecules migrates towards the ion gate; the sample gas enters the reaction region through the sample gas inlet, and the reaction reagent ions Ac₂H₂O migrate towards the ion gate. + It undergoes a highly selective molecular substitution reaction with ammonia molecules (NH3) to generate the product ion Ac2NH4 corresponding to NH3. + ;

[0011] By replacing the dry compensating gas with a high-humidity gas, the high-concentration water in the reaction zone is converted into a high-concentration (H2O) under the action of a photoionization source. n H + It reacts more readily with NH3 to form hydrated ammonium ions, which then react with high concentrations of acetone molecules in a dry migration region via a periodically opening ion gate, transforming into Ac2NH4. +Driven by the electric field in the migration region, the ions reach the Faraday disk and form a single product ion peak in the spectrum corresponding to the ion migration time, thus achieving highly sensitive detection of ammonia molecules.

[0012] The sample gas injection rate is 50-200 ml / min, the drift gas injection rate is 200-700 ml / min, the humidification compensation gas flow rate is 50-100 ml / min, and the humidity is 85-100% RH.

[0013] This invention provides an ion mobility spectrometry method to improve the sensitivity of online detection of ammonia in ammonia-containing gases. While improving the sensitivity of ammonia detection, it eliminates the influence of different sample humidity, so that ammonia-containing samples do not require pretreatment. The method is simple to operate and has high specificity and sensitivity, achieving efficient detection of low concentrations of ammonia in ammonia-containing gases.

[0014] This invention replaces the drying compensation gas in the reaction zone with a high-humidity gas, where the water concentration in the reaction zone is much higher than the acetone concentration of the reagent molecules, generating hydrated ammonium ions and thus increasing the reactivity between the reagent ions and the ammonia molecules in the sample. Under the action of the bleaching gas, the migration zone maintains dry conditions and a high acetone concentration, causing the generated hydrated ammonium ions to be converted back into Ac₂NH₄ during their migration within the migration zone. + The product ions are highly stable during migration in the migration tube. Water molecules participate in the reaction throughout the entire process, which improves the sensitivity of ammonia detection to some extent. The final product ions remain unchanged, exhibiting a single ammonia product peak on the ion migration spectrum. Simultaneously, the introduced humidifying gas maintains the reaction zone at saturated humidity, and changes in sample gas humidity do not affect the detection, thus eliminating the influence of different sample humidity levels on detection accuracy. This method is simple to operate and suitable for the detection of trace ammonia in exhaled breath. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the ion mobility spectrometry detection method used in this invention.

[0016] Figure 2 The ion migration spectrum of 100 ppb ammonia detection in this invention is shown when the compensating gas is a dry gas (0% RH).

[0017] Figure 3 The ion migration spectrum of 100 ppb ammonia detection in this invention is shown when the compensating gas is a high humidity gas (95% RH).

[0018] Figure 4 This invention relates to the response of 100 ppb ammonia in samples with different humidity levels. Detailed Implementation

[0019] Example 1

[0020] A schematic diagram of the ion mobility spectrometer is shown below. Figure 1 As shown, the system includes a vacuum ultraviolet lamp ionization source 1, an ion gate 2, a Faraday disk 3, an ionization reaction zone 4, an ion migration zone 5, an amplifier 6, a drift gas inlet 7, a reagent molecule generator 8, an outlet 9, a sample inlet 10, and a compensation gas inlet 11. Acetone reagent molecules are generated by the reagent molecule generator 8 (a sealed container with an inlet and an outlet, containing acetone or an open container containing acetone) and enter the migration zone along with the drift gas. The carrier gas flow rate is set to 100 ml / min, generating acetone reagent molecules with a volume concentration of approximately 1300 ppm. The drift gas flow rate is set to 300 ml / min, the compensation gas flow rate is set to 150 ml / min, and a vacuum pump connected to the outlet is used to draw gas at a flow rate of 600 ml / min, creating a negative pressure within the migration chamber. Sample gas is automatically drawn in at a rate of 50 ml / min from the sample inlet. In this embodiment, dry purified air is used for the carrier gas, drift gas, and compensation gas. Finally, the gas is extracted by a pump through the outlet near the ionization source in the reaction zone.

[0021] When the compensating gas is dry and purified gas (0% RH), the real-time ion mobility spectrum signal intensity spectrum obtained by detecting 100 ppb dry ammonia is as follows. Figure 2 As shown, the two signal peaks in the spectrum represent the acetone reagent ion peak (RIP) and the ammonia product ion peak, respectively, with the ammonia product ion peak intensity being 140 mV. Figure 3 The image shows the corresponding signal intensity spectrum obtained by ion mobility spectrometry for detecting 100 ppb dry ammonia when the compensating gas is replaced with a high humidity gas (95% RH), where the peak intensity of the ammonia product ion is 305 mV. The method increases the signal intensity of the ammonia product ion by approximately two times for the same concentration, demonstrating that the present invention can improve the detection sensitivity of ammonia.

[0022] Example 2

[0023] A dilution gas, diluted with 5 ppm ammonia standard gas, was passed through a humidifier placed in a water bath to obtain ammonia samples with a concentration of 100 ppb at relative humidities of 0%, 20%, 40%, 65%, and 85%. Using the detection method described in Example 1, the drying compensation gas was replaced with a high-humidity (95% RH) gas, and ion migration response spectra of the ammonia samples at these different humidities were obtained. The peak intensity of the ammonia product ion with a migration time of 4.92 ms was continuously tracked in the spectra, with at least 100 points continuously detected at each humidity level, and the average value was taken. Figure 4The changes in response signal intensity of 100 ppb ammonia samples with different humidity levels are shown below. It can be seen that as the sample humidity increases, the average peak intensity of ammonia ions at the same concentration (100 ppb) with different humidity levels, and the mean signal intensity of ammonia product ions at different humidity levels, are 305 mV, 326 mV, 325 mV, 310 mV, and 306 mV, respectively, with a relative standard deviation of 3.28%. This demonstrates the advantage of the method provided by this invention being unaffected by the humidity of the ammonia sample, while also improving the spectral response signal intensity of ammonia at the same concentration.

Claims

1. A method for improving the sensitivity of online detection of ammonia in ammonia-containing gas, characterized in that: The ion mobility spectrometer used includes a photoionization source and an ion mobility tube with an internal ion gate. The ion gate divides the entire ion mobility tube cavity into two regions: a reaction region (4) and a migration region (5). The photoionization source is located on the side of the reaction region (4) away from the ion gate. An outlet (9) is provided on the wall of the reaction region (4) near the photoionization source. A compensation gas port (11) is provided on the wall of the reaction region (4) near the ion gate. A sample gas inlet (10) is provided on the wall of the reaction region (4) between the outlet (9) and the compensation gas port (11). A drift gas inlet (7) is provided on the wall of the migration region (5) near the Faraday disk (3). The sample gas to be tested enters the reaction zone through the sample gas inlet (10); The compensating gas enters the reaction zone through the compensating gas port (11); the compensating gas is clean air at 20-30℃ and 85-100% relative humidity; The carrier gas carries acetone reagent molecules through the reagent molecule generating device (8) and enters the migration zone (5) together with the bleaching gas; the carrier gas volatilizes through the acetone reagent molecule generating device to generate acetone reagent molecules with a volume concentration of 1000-2000ppm and enters the migration zone together with the bleaching gas. Finally, the gas exits through the outlet near the ionization source in the reaction zone.

2. The method according to claim 1, characterized in that: The reagent molecule generating device (8) is a sealed container with an inlet and an outlet. The sealed container contains acetone or an open container containing acetone. The inlet is connected to the carrier gas source through a pipeline, and the outlet is connected to the drift gas through a pipeline. The carrier gas volatilizes through the reagent molecule generating device (8) to continuously generate reagent molecules with a constant volume concentration, which act as dopants and enter the migration region (5) together with the drift gas.

3. The method according to claim 1, characterized in that: The ion mobility spectrometer uses a non-radioactive vacuum ultraviolet lamp ionization source (1) and a TPG ion gate (2); Finally, the gas is extracted by a pump through the outlet near the ionization source in the reaction zone.

4. The method according to claim 1, characterized in that: The sample gas flow rate is 50-200 ml / min. Dry clean air is used as both the carrier gas and the bleaching gas. The carrier gas flow rate is 50-300 ml / min, the bleaching gas injection flow rate is 200-700 ml / min, and the compensation gas flow rate is 100-200 ml / min.

5. The method according to claim 1, characterized in that: Ammonia-containing gas enters the ionization region through the injection port; acetone molecules, under the action of a photoionization source, generate reactant ions Ac₂H₂. + Ammonia-containing gas carrying ammonia molecules enters the reaction zone through the injection port, and the reaction reagent ions Ac₂H₂O + It undergoes a highly selective molecular substitution reaction with ammonia molecules to produce the product ion Ac₂NH₄ corresponding to NH₃. + ; The high-humidity gas at the compensating gas inlet, under the action of the photoionization source, generates a high concentration of hydrated hydrogen ions, which more readily react with NH3 to form hydrated ammonia ions. Through the periodically opening ion gate, this ion cluster reacts with a high concentration of acetone molecules in the dry migration region, transforming into Ac2NH4. + Driven by the electric field in the migration region, the ions reach the Faraday disk, forming a single ammonia product ion peak in the spectrum corresponding to the ion migration time, thus achieving highly sensitive detection of ammonia molecules.

6. The method according to claim 1, characterized in that: Ammonia-containing gas is the exhaled breath of humans or animals.

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