PTR-tof method and system for atmospheric organic detection

Abstract

This invention belongs to the field of PTR-TOF atmospheric organic matter detection technology. This invention provides a PTR-TOF atmospheric organic matter detection method, comprising the following steps: introducing b mL / min of pyrrole and a 1 a L / min of the gas to be tested, and obtaining a detection signal value X. 吡测 and X 测 ; Calculate the detection compensation coefficient K 测 =X 吡测 / X 吡背 Based on the detection compensation coefficient K 测 Calculate X 测补 ==X 测 / K 测 Based on the standard curve and X 测补 The C of the gas to be tested was obtained. 测 The method of this invention can greatly improve the stability of the instrument and ensure the accuracy of substance concentration monitoring.

Description

Technical Field

[0001] This invention belongs to the field of PTR-TOF atmospheric organic matter detection technology. Background Technology

[0002] The proton transfer ion source used in PTR-TOF is a soft ionization method, utilizing H3O + Or other reagent ions ionize organic molecules into ions, and ions of different mass numbers are detected after passing through the flight chamber at different velocities. PTR-TOF primarily uses a direct sample introduction method for atmospheric organic monitoring, introducing gas into the device through tubes, valves, and pumps, and then analyzing the results. The general analytical procedure involves calibrating the device by introducing background gas and standard gas after initial setup, writing the calibrated parameters into the program, and then performing formal monitoring. During this process, external tubes, valves, and the instrument itself can adsorb or release organic matter, causing changes in background and standard concentrations. A common practice is to repeat the calibration process by introducing background gas and standard gas again after the instrument has been running for a period of time (usually one day or more). This method, by shortening the calibration interval, can reduce the impact of instrument signal changes to some extent, but many problems still exist in practical applications. This method has two main drawbacks. First, it requires a significant amount of time for instrument calibration, which affects the collection of normal atmospheric monitoring data and reduces the amount of data collected, making it impossible to fully reflect the changing patterns of pollutant concentrations in the atmosphere. Second, the calibration cycle is relatively long, and the data during this period will still be affected by changes in instrument signals, with the impact increasing as the interval lengthens.

[0003] Current methods for analyzing atmospheric organic pollutants calibrate the instrument's qualitative and quantitative parameters by introducing background and standard gases separately. These calibration methods aim to minimize the impact of instrument or system variations on the data by shortening the calibration cycle. However, this method requires a considerable amount of time for calibration. After introducing the background or standard gases, multiple samples need to be collected continuously over a period of time until the signal intensity stabilizes before a suitable data file can be selected. This makes it impossible to shorten the calibration cycle too much, as this would be counterproductive and result in poor continuity of the collected atmospheric monitoring data. Even with a longer calibration cycle, the significant time spent on instrument calibration disrupts normal atmospheric monitoring data collection, reducing the amount of data collected and failing to comprehensively reflect the changing patterns of pollutants in the atmosphere. Furthermore, during normal monitoring periods, the effects of instrument / system variations continue to impact data quality, and this impact increases with the length of the calibration cycle, leading to decreased stability and accuracy. Summary of the Invention

[0004] In view of this, the present invention provides a PTR-TOF method for detecting atmospheric organic matter, comprising the following steps: introducing b mL / min of pyrrole and a mL / min of the gas to be tested, and obtaining a detection signal value X. 吡测 and X 测 ; Calculate the detection compensation coefficient K 测 =X 吡测 / X 吡背 Based on the detection compensation coefficient K 测 Calculate X 测补 =X 测 / K 测 Based on the standard curve and X 测补 The C of the gas to be tested was obtained. 测 .

[0005] In a specific embodiment of the present invention, the method for obtaining the standard curve includes the following steps: introducing b mL / min of pyrrole and a mL / min of background gas as the detection signal value of 0 ppb, and measuring X. 吡背 and X 背 Different concentrations of C were introduced respectively. 标 Using a standard gas at a mL / min and pyrrole at a mL / min, the detection signal value X of the analyte was obtained. 标 and X 吡标 ; Calculate the standard compensation coefficient K 标 =X 吡标 / X 吡背 Based on the standard compensation coefficient K 标 Calculate X 标补 =X 标 / K 标 According to X 标补 Plot a standard curve using the corresponding concentration data.

[0006] In a specific embodiment of the present invention, b is 1.

[0007] In a specific embodiment of the present invention, a is 99.

[0008] In a specific embodiment of the present invention, the background gas is nitrogen.

[0009] The method of this invention can greatly improve the stability of the instrument and ensure the accuracy of substance concentration monitoring. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of a system for detecting VOCs components in atmospheric samples using PTR-TOF. Detailed Implementation

[0011] Example

[0012] PTR-TOF: Proton transfer reaction time-of-flight mass spectrometry.

[0013] This patent designs an atmospheric organic matter analysis method and system based on internal standards and PTR-TOF, which improves the accuracy of the instrument in qualitative and quantitative analysis of atmospheric organic matter, as well as the instrument's operational stability.

[0014] The atmospheric organic matter analysis system based on internal standard and PTR-TOF includes PTR-TOF, a first three-way valve, a flow controller, a first gas inlet, a second three-way valve, a sampling pump, and a second gas inlet;

[0015] The first three-way valve is connected to the PTR-TOF, the flow controller, and the second three-way valve through gas pipelines; the flow controller is connected to the first three-way valve and the first gas inlet through gas pipelines; the second three-way valve is connected to the first three-way valve, the second gas inlet, and the sampling pump through gas pipelines.

[0016] The PTR-TOF can monitor VOCs in ambient air in real time and can quickly monitor atmospheric samples. Its time resolution can be as fast as the second level, and it generally uses a time resolution of about 1 minute.

[0017] This method involves adding internal standards to the sample (including background gas and ambient air) in real time, monitoring and compensating for changes in mass spectrometry peaks over time in the data file, and eliminating the influence of the instrument itself. Additionally, background gas monitoring can be performed every hour or less to provide the latest background subtraction data. This method effectively reduces the frequency of calibration using standard gases, improves the acquisition rate of atmospheric monitoring data, and also enhances the instrument's operational stability and data accuracy.

[0018] Let m, n, and o represent the signal values ​​of pyrrole in background gas, standard gas, and ambient air, respectively. By adjusting n and o based on m, we can obtain that when the instrument is still measuring the background gas, the theoretical signal intensity of the instrument needs to be multiplied by the coefficients m / n and m / o. In other words, the spectral signal values ​​of other samples measured (represented by x) can be adjusted and compensated by the pyrrole signal value of the background gas (the compensation coefficient is m / x).

[0019] In this method, due to the high temporal resolution of PTR-TOF, the sampling frequency of the background gas can be accelerated so that it is updated to m` without significant change. The compensation coefficient of the subsequently collected sample (standard gas or ambient air) becomes m` / x (x represents n` of the standard gas and o` of the ambient air).

[0020] In this method, a substance with a fixed concentration (such as pyrrole) is continuously introduced into the system as an internal standard. This substance can be stably detected by the instrument and does not interfere with (or interferes very little or deterministically with) the VOCs to be measured in the ambient air or water clusters generated by reagent ions. The spectral peak signal value of this substance in each acquired spectrum characterizes the state and changes in instrument performance, and compensates for the spectral signal value at that moment to eliminate signal fluctuations caused by changes in the concentration of this non-analyte substance. Based on high time resolution monitoring equipment such as PTR-TOF, by monitoring the internal standard signal value of the background gas at high frequency and compensating for subsequent monitoring data in real time, the stability of the instrument can be greatly improved, and the accuracy of substance concentration monitoring can be guaranteed.

[0021] Because internal standards are used for compensation in real time, calibration is performed to a certain extent, thus partially replacing the use of external standards (standard gases). This method effectively reduces the frequency of calibration using standard gases, improving the acquisition rate and effectiveness of atmospheric monitoring data.

[0022] Example implementation: The injection flow rate of PTR-TOF is 100 mL / min, and the internal standard is pyrrole standard gas with a concentration of 1 ppm and a flow rate of 1 mL / min, which is controlled by a flow controller; therefore, the concentration of pyrrole standard gas entering PTR-TOF is 10 ppb.

[0023] When establishing a standard curve by using the detection signal value of the analyte and its concentration, the detection signal value is detected by PTR-TOF after being thoroughly mixed with pyrrole standard gas. Therefore, 1 mL of pyrrole standard gas will not affect the establishment of the standard curve.

[0024] The PTR-TOF atmospheric organic matter detection method includes the following steps:

[0025] 1. Pyrrole at a flow rate of 1 mL / min and nitrogen at a flow rate of 99 mL / min (background gas) were introduced as the detection signal value for 0 ppb, and X was measured. 吡背 and X 背 .

[0026] 2. Pass in different concentrations of C respectively. 标 Using a standard gas at a mL / min and pyrrole at a mL / min, the detection signal value X of the analyte was obtained. 标 and X 吡标 The different concentrations of C 标 The concentrations are 2.5 ppb, 5 ppb, 10 ppb, 20 ppb, and 40 ppb. Preferably, b is 1; preferably, a is 99. And b < <a。

[0027] 3. Calculate the standard compensation coefficient K 标 =X 吡标 / X 吡背 .

[0028] 4. Based on the standard compensation coefficient K 标 Calculate X 标补 =X 标 / K 标 .

[0029] 5. Based on X 标补 A standard curve was plotted using the corresponding concentration data.

[0030] 6. Introduce b ml / min of pyrrole and a ml / min of the gas to be tested, and obtain the detection signal value X. 吡测 and X 测 The b is preferably 1; the a is preferably 99. And b < <a。

[0031] 7. Calculate the detection compensation coefficient K 测 =X 吡测 / X 吡背 .

[0032] 8. Based on the detection compensation coefficient K 测 Calculate X 测补 =X 测 / K 测 .

[0033] 9. Based on the standard curve and X 测补 The C of the gas to be tested was obtained. 测 .

[0034] During normal monitoring, pyrrole (internal standard) gas is continuously introduced at a stable flow rate of b ml / min, and background air, standard gas, or ambient air is introduced at a ml / min as needed to obtain the corresponding mass spectra. And b < <a。

[0035] The injection flow rate of PTR-TOF is 100 mL / min, and the internal standard is pyrrole standard gas with a concentration of 1 ppm and a flow rate of 1 mL / min, which is controlled by a flow controller; therefore, the concentration of pyrrole standard gas entering PTR-TOF is 10 ppb.

[0036] In this embodiment, the corresponding detection signal value is compensated by the corresponding pyrrole signal value, and then a standard curve is plotted by correspondingly mapping the corresponding concentration.

[0037] After establishing the standard curve, a standard gas with a concentration of 10 ppb was continuously introduced for monitoring, and the following data were obtained (using benzene as an example):

[0038]

[0039] As can be seen from the data above, after pyrrole compensation, the accuracy (relative error) and stability (standard deviation) of the instrument are significantly improved.

[0040] In addition, 10 ppb standard gas was continuously monitored at the same time for three consecutive days. After the data stabilized, seven data points were collected and the average value was taken. The results are as follows (taking benzene as an example):

[0041]

[0042] As can be seen from the data above, after pyrrole compensation, the accuracy (relative error) and stability (standard deviation) of the instrument are significantly improved over a long period of operation.

Claims

1. A PTR-TOF method for detecting atmospheric organic matter, characterized in that, Includes the following steps: By introducing b mL / min of pyrrole and a mL / min of the analyte gas, the detection signal value X is obtained. 吡测 and X 测 ; Calculate the detection compensation coefficient K 测 =X 吡测 / X 吡背 ; Based on the detection compensation coefficient K 测 Calculate X 测补 =X 测 / K 测 ; Based on the standard curve and X 测补 The C of the gas to be tested was obtained. 测 ; The method for obtaining the standard curve includes the following steps: Pyrrole at a flow rate of b mL / min and background gas at a flow rate of a mL / min were introduced as the detection signal value of 0 ppb, and X was measured. 吡背 and X 背 ; Different concentrations of C were introduced respectively 标 Using a standard gas at a mL / min and pyrrole at a mL / min, the detection signal value X of the analyte was obtained. 标 and X 吡标 ; Calculate the standard compensation coefficient K 标 =X 吡标 / X 吡背 ; Based on the standard compensation coefficient K 标 Calculate X 标补 =X 标 / K 标 ; According to X 标补 Plot a standard curve using the corresponding concentration data; The b< <a。 2. The PTR-TOF atmospheric organic matter detection method according to claim 1, characterized in that, The value of b is 1.

3. The PTR-TOF atmospheric organic matter detection method according to claim 1, characterized in that, The value of 'a' is 99.

4. The PTR-TOF atmospheric organic matter detection method according to claim 1, characterized in that, The background gas is nitrogen.

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