An online precise calibration device and calibration method for gaseous trace acid and alkali species

Abstract

The present invention belongs to the technical field of environmental monitoring, and specifically discloses an online precise calibration device and calibration method for trace acid and alkali species in gaseous state. The present invention realizes online calibration of acid and alkali species with low concentration, high precision and high stability based on the principle of acid-base titration through the coordinated work of a permeation tube, a series of acid / alkali absorption bottles and a numerical control center. The permeation tube can stably release trace acidic or alkaline gases of constant concentration for a long time; an absorption solution and a pH meter of a specific concentration are placed in the series absorption bottle, and the concentration of the acidic or alkaline gas in the airflow is determined according to the absorption time of the solution and the change law of the indication of the pH meter; the numerical control center monitors and adjusts various parameters in real time by controlling various electronic units and sensors to ensure stable operation of the system. The device of the present invention can be used in conjunction with a chemical ionization mass spectrometer to realize real-time online precise calibration of trace acid and alkali species in gaseous state. At the same time, the device has the advantages of high precision and automation, which improves the accuracy and convenience of calibration.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental monitoring, and in particular relates to an online precise calibration device and a calibration method for gaseous trace acid and alkali species. Background Art

[0002] Gaseous trace acids and bases in the atmosphere, such as sulfuric acid (H 2 SO 4 ), nitric acid (HNO 3 ), ammonia (NH 3 ) and organic amines, etc., play a vital role in the generation of new particles. The generation of new particles is one of the important sources of fine particulate matter in the atmosphere, contributing about 50% of the world's cloud condensation nuclei, and has a profound impact on human health, air quality and climate change. Accurate monitoring and quantitative analysis of gaseous trace acid and base species in the atmosphere are of great significance for understanding the mechanism of new particle generation and formulating effective strategies for controlling atmospheric secondary particle pollution.

[0003] At present, chemical ionization mass spectrometry has been widely used to determine trace acid and base substances such as sulfuric acid, nitric acid, ammonia and organic amines in the atmosphere. The basic principle of measurement is that the substance to be measured undergoes a molecular-ion reaction with the reagent ion, and the product ions that can be detected by the mass spectrometer are generated by soft ionization. The calibration of trace acid and base substances in the atmosphere can be carried out by using a stable sample of known concentration or a sample generated in situ to calibrate the chemical ionization mass spectrometer. The calibration method using a gaseous standard sample of known concentration is highly accurate, but requires a stable and reliable standard gas source; and the viscosity of the acid and base species is relatively large, and there will be a large wall loss in the standard gas cylinder, resulting in a large change in the standard gas concentration, resulting in an inability to accurately calibrate the mass spectrometer. The calibration of substances generated in situ, such as sulfuric acid, is as follows: 1) ultraviolet radiation with a wavelength of 184.9 nm frees water molecules to form OH free radicals; 2) an excess of sulfur dioxide is introduced; 3) in the presence of water, the OH free radicals oxidize sulfur dioxide to sulfuric acid molecules. However, in this method, when the water vapor concentration is low, part of the SO 3 The sulfuric acid is detected before it is converted into sulfuric acid, resulting in a low sulfuric acid detection signal. In addition, this method is usually an offline calibration method, and it is impossible to achieve online automatic calibration of the mass spectrometer. Therefore, it is difficult to achieve real-time and accurate calibration of gaseous trace acid and alkali species in the atmosphere based on current calibration methods.

[0004] The precise calibration of gaseous trace acid and base species in the atmosphere requires a continuous gas phase source. The permeation device can provide a continuous source of the required substances, and the permeation tube can be made by acidic and alkaline substances. The permeation rate of the permeation tube is determined by capturing the absorption liquid, and the concentration of the calibration substance is quantitatively determined by monitoring the pH value of the absorption liquid during the acid-base titration process. The online calibration of acid and base substances in the atmosphere requires the mass spectrometer to set an automatic calibration function to maintain the accuracy of the measurement, but the automatic calibration is currently difficult to achieve or requires frequent manual intervention. In summary, there is still a lack of a technical method that can accurately quantify and calibrate the gaseous trace acid and base species in the atmosphere in real time online. In order to remedy this defect, the present invention develops an online precise calibration device for gaseous trace acid and base species based on the acid-base titration principle combined with a chemical ionization mass spectrometer, in order to achieve online precise calibration of gaseous trace acid and base species in the atmosphere. Summary of the invention

[0005] In view of the shortcomings of the existing online precise calibration methods for gaseous trace acid and base species in the atmosphere, one of the objectives of the present invention is to provide an online precise calibration device for gaseous trace acid and base species based on the acid-base titration principle and coupled with a chemical ionization mass spectrometer.

[0006] In order to achieve the above object, the specific technical solution adopted by the present invention is as follows:

[0007] An online precise calibration device for gaseous trace acid and alkali species based on the acid-base titration principle and coupled with a chemical ionization mass spectrometer, comprising: a gas circuit 1, a gas circuit 2, a gas circuit 3 and a numerical control center;

[0008] The gas circuit one is used to measure the stable concentration of the acidic or alkaline gas generated by the permeation tube; the gas circuit one includes: a carrier gas, and a first mass flow controller, a first solenoid valve, a permeation tube assembly, a second solenoid valve, a first three-way joint, a first absorption bottle, and a second absorption bottle connected in series in sequence; wherein the carrier gas is zero air or high-purity nitrogen, the permeation tube assembly includes a permeation tube and a temperature control device, the first absorption bottle and the second absorption bottle have a built-in pH meter, and a thermostat is wrapped outside; the numerical control center is connected to the first mass flow controller, the first solenoid valve, the permeation tube assembly, the second solenoid valve, the pH meter of the first absorption bottle and the second absorption bottle, and the external thermostat through a signal transmission line;

[0009] The gas circuit 2 is used to dilute the acidic or alkaline gas volatilized by the permeation tube, and by adjusting the dilution ratio, different concentrations of acidic or alkaline gas are obtained; the gas circuit 2 includes: diluent gas, a second mass flow controller, a second three-way connector, a fourth solenoid valve, a fifth solenoid valve, a detection instrument, and an activated carbon filter connected to the other circuit of the fifth solenoid valve in series; wherein the diluent gas is zero air or high-purity nitrogen, and the detection instrument is a chemical ionization mass spectrometer; the numerical control center is connected to the second mass flow controller, the fourth solenoid valve and the fifth solenoid valve through a signal transmission control line;

[0010] The gas circuit three is used to detect the concentration of acidic or alkaline gas substances in the ambient air; the gas circuit three includes: an external ambient air sampling inlet, a third solenoid valve, a fourth solenoid valve, a fifth solenoid valve, a detection instrument connected in series in sequence, and an activated carbon filter connected to the other side of the fifth solenoid valve; the CNC center is connected to the third solenoid valve, the fourth solenoid valve, and the fifth solenoid valve through a signal transmission control line.

[0011] In the above calibration device:

[0012] The permeation tube assembly, wherein the permeation tube is used to stably release constant concentration acid and alkali gas for a long time, serving as a stable and reliable standard gas source; at the same time, the temperature control device thereof adjusts the permeation temperature of the permeation tube to ensure the generation of acid and alkali gas with appropriate concentration;

[0013] The first absorption bottle is used to absorb acidic or alkaline substances in the airflow; a pH meter is built in to record the change of the pH value of the solution in real time; and a constant temperature device is wrapped outside to prevent the temperature change from affecting the pH value of the solution;

[0014] The second absorption bottle is used to ensure that the acidic or alkaline substances in the air flow are completely absorbed; at the same time, a built-in pH meter records the change of the pH value of the solution in real time; and a constant temperature device is wrapped outside to prevent the temperature change from affecting the pH value of the solution;

[0015] The numerical control center is used to control the flow rate of two mass flow controllers; adjust the temperature control device to control the permeation temperature of the permeation tube; adjust the temperature of the thermostatic device outside the absorption bottle; record the pH meter reading and the corresponding absorption time in the absorption bottle in real time; control the gas path switching of the first solenoid valve, the second solenoid valve, the fourth solenoid valve and the fifth solenoid valve; and control the switching time of the third solenoid valve;

[0016] The first solenoid valve is used to control the carrier gas to directly enter the absorption bottle through the first three-way joint or to flow through the permeation tube and then enter the absorption bottle; when calibrating trace acidic species in the atmosphere, the carrier gas directly enters the gas path of the absorption bottle through the first three-way joint to detect the background carbon dioxide concentration in the carrier gas;

[0017] The second solenoid valve is used to control the carrier gas and the acidic or alkaline gas volatilized from the permeation tube to flow to the absorption bottle or to the second gas path;

[0018] The third solenoid valve is used to open or close the ambient air sampling inlet;

[0019] The fourth solenoid valve is used to open the mixed air inlet of gas circuit 1 and gas circuit 2, and close the ambient air inlet through the third solenoid valve; or close the mixed air inlet of gas circuit 1 and gas circuit 2, and open the ambient air inlet through the third solenoid valve;

[0020] The fifth solenoid valve is used to control the carrier gas, the acidic or alkaline gas volatilized from the permeation tube and the diluent gas to flow directly to the detection instrument or to flow to the detection instrument after passing through the activated carbon filter; that is, it is used to switch the actual value or background value in the measurement gas path;

[0021] The detection instrument is used to measure the concentration of the standard acidic or alkaline gas released by the permeation tube and the concentration of the substance in the actual atmosphere.

[0022] Further, the permeation tube assembly comprises:

[0023] The permeation tube is a polytetrafluoroethylene (Teflon) tube, sealed at both ends with Teflon rods, and filled with a calibration substance solution (acidic or alkaline solution of a specific concentration);

[0024] The stainless steel tube has a porous tube section at the front end and a hollow tube section at the rear end; the porous tube section has a plurality of parallel through-holes connected to the hollow tube section, which are used to disperse the heated airflow so that the airflow is heated evenly; the hollow tube section is used to accommodate the permeation tube so that the airflow with even heating passes through the permeation tube;

[0025] An X-shaped bracket is placed inside the hollow tube section to support the permeation tube and keep the permeation tube located at the center of the stainless steel tube to ensure uniform heating;

[0026] The temperature control housing is wrapped around the outside of the stainless steel tube and serves as a temperature control device for the permeation tube, and is used to adjust the permeation temperature of the carrier gas and the permeation tube (ie, to adjust the permeation rate of the acid and base species).

[0027] Furthermore, the inner diameter of the permeation tube is 1 / 4 inch and the length is 5-10 cm; the inner diameter of the entire stainless steel tube is 1 / 2 inch and the total length is 25 cm, the length of the porous tube section is 10 cm, and the length of the hollow tube section is 15 cm.

[0028] Furthermore, a strongly acidic or alkaline solution, a pH meter probe, and a glass tube for bubbling that penetrates into the bottom of the absorption bottle are placed in the first absorption bottle. If the calibration substance is acidic, a strongly alkaline solution is placed in the bottle, and vice versa. The bubbling glass tube penetrates below the liquid surface to disperse the gas in the solution in the form of bubbles, increasing the gas-liquid contact area to ensure that the solution fully absorbs the gas; as the solution gradually absorbs the acidic or alkaline gas, the pH value of the solution changes after a neutralization reaction, and the concentration of the standard acidic or alkaline substance absorbed by the solution is calculated in combination with the solution absorption time. In addition, the thermostat wrapped on the outside of the absorption bottle is a temperature control shell, which effectively avoids the influence of ambient temperature changes on the pH of the absorption liquid.

[0029] Furthermore, the second absorption bottle is configured in the same manner as the first absorption bottle, the purpose of which is to ensure that the acidic or alkaline gas in the airflow is completely absorbed; and the tail of the second absorption bottle is connected to an activated carbon tube, and the tail gas flow is discharged into the air after passing through the activated carbon tube.

[0030] Furthermore, the numerical control center is provided with an electronic control unit and a sensor; the electronic control unit is used to set and adjust the flow rate of the carrier gas entering the permeation tube and the flow rate of the dilution gas in the second gas circuit; control the temperature of the temperature control shell outside the stainless steel tube; adjust the temperature of the constant temperature device outside the absorption bottle; control the gas circuit switching of the first solenoid valve, the second solenoid valve, the fourth solenoid valve and the fifth solenoid valve; control the switching time of the third solenoid valve; record the reading and absorption time of the pH meter in the first absorption bottle and the second absorption bottle, and the sensor is used to monitor and record the above parameters in real time; ensure the stability and safety of the system operation.

[0031] Furthermore, the outsides of the pipelines of different gas paths are wrapped with thermal insulation materials to reduce the wall loss of the material to be calibrated in the gas path.

[0032] The second object of the present invention is to provide a method for online calibration of gaseous trace acid and base species using the above device, comprising the following steps:

[0033] Step 1: Make a permeation tube for the required calibration substance, fill the standard solution sample into the polytetrafluoroethylene tube, and seal it with a Teflon rod; put the permeation tube into the stainless steel tube and support it with an X-shaped bracket, wrap the stainless steel tube with a temperature control shell, connect the stainless steel tube to the gas path 1, and adjust the permeation temperature of the permeation tube according to the required standard substance concentration to complete the installation of the permeation tube assembly;

[0034] Step 2: The carrier gas enters the permeation tube assembly through the first mass flow controller, and the carrier gas flow rate is set to 40-100 mL / min. The carrier gas carrying the calibration substance enters the absorption bottle through the second solenoid valve; if the calibration substance is an acidic species, the carrier gas needs to flow directly into the absorption bottle from the first solenoid valve and the first three-way connector to detect the concentration of background carbon dioxide in the carrier gas and eliminate the influence of carbon dioxide on the pH value of the solution in the absorption bottle;

[0035] Step 3: Place a strong acid or strong alkaline solution, a pH meter probe and a glass tube for bubbling that penetrates into the bottom of the absorption bottle in the first absorption bottle and the second absorption bottle, and wrap a constant temperature device on the outside; the strong acid or strong alkaline solution in the first absorption bottle absorbs most of the alkali or acid substances required for calibration in the gas path; ensure that the calibration substances in the gas path are completely absorbed in the second absorption bottle, and connect an activated carbon tube to the tail of the second absorption bottle, and the tail gas flow is released into the air after passing through the activated carbon tube; the pH value of the solution in the first absorption bottle and the second absorption bottle changes with the absorption time and is recorded in the CNC center;

[0036] Step 4: After the first absorption bottle and the second absorption bottle absorb for 12h-72h, the pH value of the solution changes linearly with the absorption time. At this time, the permeation tube releases a constant concentration of the calibration substance, and the concentration is calculated by the pH value of the solution and the absorption time;

[0037] Step 5: The CNC center adjusts the gas path conversion of the second solenoid valve from gas path 1 to gas path 2; the CNC center adjusts the flow rate of the second mass flow controller, and sets the gradient flow rate of the dilution gas at intervals of 5 to 15 minutes, that is, different dilution ratios of the calibration substance with a constant concentration to dilute the substance to be calibrated;

[0038] Step 6: The mixed airflow of the dilution gas, the carrier gas and the calibration substance released by the permeation tube enters the detection instrument through the fourth solenoid valve and the fifth solenoid valve; the CNC center adjusts the fourth solenoid valve to close the ambient air inlet through the third solenoid valve; the CNC center adjusts the gas path switching time of the fifth solenoid valve to 5-15 min. After 15 min, the mixed airflow passes through the activated carbon filter and then enters the detection instrument to obtain the background concentration of the mixed airflow; by analyzing the measurement results of the detection instrument, at least one group of background values ​​plus 3-5 groups of signal values ​​of the calibration substance at different dilution ratios are obtained, the relationship between the concentration of the calibration substance and the signal value of the detection instrument is established, and the calibration curve is drawn;

[0039] Step 7: After obtaining the calibration curve, the CNC center controls to open the third solenoid valve; the fourth solenoid valve closes gas path 1 and gas path 2, and opens gas path 3; the fifth solenoid valve is controlled to close the activated carbon filter channel; then the ambient air directly enters the detection instrument through the three solenoid valves; by analyzing the measurement signal of the detection instrument and combining the calibration curve, the concentration of gaseous trace acid and alkali species in the atmosphere is obtained, thereby realizing the online accuracy calibration of gaseous trace acid and alkali species in the atmosphere;

[0040] Among them, the flow rates of the carrier gas and the dilution gas, the temperature of the stainless steel tube outside the permeation tube, the constant temperature device of the absorption bottle, the first solenoid valve, the second solenoid valve, the third solenoid valve, the fourth solenoid valve, the fifth solenoid valve, the pH meter reading and the solution absorption time are all controlled and recorded by the CNC center.

[0041] The present invention has the following beneficial effects:

[0042] The present invention provides an online precise calibration device for gaseous trace acid and base species based on the acid-base titration principle and combined with a chemical ionization mass spectrometer, which has the advantages of high precision and automation. Through the coordinated work of a permeation tube, a series absorption bottle and a numerical control center, the online calibration of trace acid and base species in the atmosphere with high precision and high stability can be achieved based on the acid-base titration principle. A stable and continuous calibration material gas is provided through a permeation tube; the concentration of the calibration material is determined according to the absorption time of the solution in the absorption bottle and the indication of the pH meter; the calibration material of a constant concentration is diluted using different dilution ratios, and a detection instrument (chemical ionization mass spectrometer) is used for signal detection; the numerical control center adjusts and monitors various parameters in real time. The device can be used in conjunction with measuring instruments such as a mass spectrometer to achieve real-time online precise calibration of gaseous trace acid and base species. The accuracy and convenience of calibration are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The schematic diagram is a working principle diagram of an online precise calibration device for gaseous trace acid and base species based on the acid-base titration principle coupled with chemical ionization mass spectrometry.

[0044] Figure 2 The schematic diagram of the structure of the permeation tube assembly. In the figure, the left is the left view, the middle is the main view, and the right is the right view; the blue part is hollow.

[0045] Figure 3 It is a schematic diagram of the specific structure of the X-type bracket.

[0046] Figure 4 This is a schematic diagram of the results of calibrating dimethylamine based on the principle of hydrochloric acid titration.

[0047] In the figure: 1, numerical control center, 2, first mass flow controller, 3, first solenoid valve, 4, permeation tube assembly, 5, second solenoid valve, 6, first three-way connector, 7, first absorption bottle, 8, second absorption bottle, 9, second mass flow controller, 10, second three-way connector, 11, third solenoid valve, 12, fourth solenoid valve, 13, fifth solenoid valve, 14, activated carbon filter, 15, detection instrument;

[0048] 4-1, permeation tube, 4-2, stainless steel tube, 4-3, X-shaped bracket, 4-4, temperature control shell; 4-2a, porous tube section, 4-2b, hollow tube section. DETAILED DESCRIPTION

[0049] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0050] Embodiment: An online precise calibration device for gaseous trace acid and base species based on the acid-base titration principle and coupled with chemical ionization mass spectrometry, such as Figure 1 As shown, it includes gas circuit 1, gas circuit 2, gas circuit 3 and CNC center 1;

[0051] The gas circuit 1 is used to measure the stable concentration of the acidic or alkaline gas generated by the permeation tube 4-1; the gas circuit 1 includes: a carrier gas, and a first mass flow controller 2, a first solenoid valve 3, a permeation tube assembly 4, a second solenoid valve 5, a first three-way joint 6, a first absorption bottle 7, and a second absorption bottle 8 connected in series in sequence; wherein the first solenoid valve 3 is also directly connected to the first three-way joint 6, the carrier gas is zero air or high-purity nitrogen, the permeation tube assembly 4 includes a permeation tube 4-1 and a temperature control device, the first absorption bottle 7 and the second absorption bottle 8 have built-in pH meters, and are wrapped with a constant temperature device on the outside; the numerical control center 1 is connected to the pH meters and external constant temperature devices of the first mass flow controller 2, the first solenoid valve 3, the permeation tube assembly 4, the second solenoid valve 5, the first absorption bottle 7 and the second absorption bottle 8 through a signal transmission line;

[0052] The gas circuit 2 is used to dilute the acidic or alkaline gas volatilized by the permeation tube 4-1, and obtains acidic or alkaline gas of different concentrations by adjusting the dilution ratio; the gas circuit 2 includes: diluent gas, a second mass flow controller 9, a second three-way connector 10, a fourth solenoid valve 12, a fifth solenoid valve 13, a detection instrument 15, and an activated carbon filter 14 connected to the other side of the fifth solenoid valve 13 in series; wherein the diluent gas is zero air or high-purity nitrogen, and the detection instrument 15 is a chemical ionization mass spectrometer; the CNC center 1 is connected to the second mass flow controller 9, the fourth solenoid valve 12 and the fifth solenoid valve 13 through a signal transmission control line;

[0053] The gas circuit three is used to detect the concentration of acidic or alkaline gas substances in the ambient air; the gas circuit three includes: an external ambient air sampling inlet, a third solenoid valve 11, a fourth solenoid valve 12, a fifth solenoid valve 13, a detection instrument 15 connected in series in sequence, and an activated carbon filter 14 connected to the other side of the fifth solenoid valve 13; the CNC center 1 is connected to the third solenoid valve 11, the fourth solenoid valve 12, and the fifth solenoid valve 13 through a signal transmission control line.

[0054] More specifically, Figure 2As shown, the permeation tube assembly 4 includes a permeation tube 4-1, a stainless steel tube 4-2, an X-shaped bracket 4-3 and a temperature control housing 4-4. The permeation tube 4-1 is a polytetrafluoroethylene tube with an inner diameter of 1 / 4 inch and a length of 5 to 10 cm, and is filled with a calibration substance solution. The inner diameter of the entire section of the stainless steel tube 4-2 is 1 / 2 inch and the total length is 25 cm; the front end is a porous tube section 4-2a with a length of 10 cm, and the rear end is a hollow tube section 4-2b with a length of 15 cm; the porous tube section 4-2a has a plurality of parallel through-holes connected to the hollow tube section 4-2b, which are used to disperse the heated airflow so that the airflow is evenly heated, and the hollow tube section 4-2b is used to accommodate the permeation tube 4-1 so that the airflow with uniform heating passes through the permeation tube. The X-shaped bracket 4-3 is placed inside the hollow tube section 4-2b to support the permeation tube 4-1 and keep the permeation tube 4-1 at the center of the stainless steel tube 4-2 to ensure uniform heating. Specifically, the structure of the X-shaped bracket 4-3 in this embodiment is as follows: Figure 3 As shown, it includes a circular hole channel for the permeation tube 4-1 to be placed in the middle position and three X-shaped support units arranged at intervals and welded to the outer wall of the circular hole channel. The outer end of the X-shaped support unit abuts against the inner wall of the stainless steel tube 4-2. The X-shaped support 4-3 can ensure the balance and stability of the placement of the permeation tube. The temperature control housing 4-4 ​​is wrapped around the outside of the stainless steel tube 4-2 as a temperature control device. The structural design of the permeation tube assembly 4 allows the permeation tube 4-1 to stably release a constant concentration of calibration material gas for a long time, thereby improving the accuracy of material calibration.

[0055] The first absorption bottle 7 is filled with a strongly acidic or alkaline solution, a pH meter probe, and a glass tube for bubbling that goes deep into the bottom of the absorption bottle. If the calibration substance is acidic, a strongly alkaline solution is placed in the bottle, and vice versa. The bubbling glass tube goes deep below the liquid surface to disperse the gas in the solution in the form of bubbles, increasing the gas-liquid contact area to ensure that the solution fully absorbs the gas; as the solution gradually absorbs the acidic or alkaline gas, the pH value of the solution changes after a neutralization reaction, and the concentration of the standard acidic or alkaline substance absorbed by the solution is calculated in combination with the solution absorption time. In addition, the thermostat wrapped around the outside of the absorption bottle in this embodiment is also a temperature control shell, which effectively avoids the influence of ambient temperature changes on the pH of the absorption liquid.

[0056] The second absorption bottle 8 is configured the same as the first absorption bottle 7, and its purpose is to ensure that the acidic or alkaline gas in the airflow is completely absorbed; and the tail of the second absorption bottle 8 is connected to an activated carbon tube, and the tail gas flow is discharged into the air after passing through the activated carbon tube.

[0057] The numerical control center 1 is provided with an electronic control unit for setting and adjusting the parameters of the connected devices and a sensor for recording each parameter. Specifically, the electronic control unit is used to set and adjust the flow rate of the carrier gas entering the permeation tube 4-1 and the flow rate of the dilution gas in the second gas path; control the temperature of the temperature control shell 4-4 outside the stainless steel tube 4-2; adjust the temperature of the thermostatic device outside the absorption bottle; control the gas path switching of the first solenoid valve 3, the second solenoid valve 5, the fourth solenoid valve 12 and the fifth solenoid valve 13; control the switching time of the third solenoid valve 11; record the reading and absorption time of the pH meter in the first absorption bottle 7 and the second absorption bottle 8, and the sensor is used to monitor and record the above parameters in real time; ensure the stability and safety of the system operation.

[0058] In addition, the outside of the pipes of different gas paths are wrapped with thermal insulation materials to reduce the wall loss of the material to be calibrated in the gas path.

[0059] Taking the workflow of dimethylamine calibration using the above calibration device as an example, the specific operation process of dimethylamine calibration is as follows:

[0060] Step 1: Make a dimethylamine permeation tube. Fill a 60 wt% dimethylamine standard solution sample into a polytetrafluoroethylene tube with an inner diameter of 1 / 4 inch and a length of 5 cm, and seal both ends with Teflon rods; then place the permeation tube 4-1 into a 1 / 2 inch stainless steel tube 4-2, and use an X-shaped bracket 4-3 to support the permeation tube, keeping the permeation tube 4-1 in the center of the 1 / 2 inch stainless steel tube; wrap the stainless steel tube 4-2 with a temperature control shell 4-4 and connect it to gas path 1; and adjust the permeation temperature at 0°C; complete the installation of the permeation tube assembly 4.

[0061] Step 2: Use high-purity nitrogen with a purity of >99.99% as carrier gas, enter the permeation tube assembly 4 through the first mass flow controller 2, set the flow rate to 100 mL / min, and the nitrogen carries the dimethylamine gas volatilized from the permeation tube 4-1 through the second solenoid valve 5 into the series absorption bottle.

[0062] Step 3: Place a hydrochloric acid solution with a pH value of ~4.0 in the series absorption bottle, and add a small amount of potassium chloride (KCl) (~5mM) to the solution to facilitate the pH meter probe to detect the pH of the solution; the two absorption bottles are set up exactly the same, and an activated carbon tube is connected to the tail of the second absorption bottle. The gas flows through the activated carbon tube and is discharged into the air.

[0063] Step 4: The absorption bottle absorbs for 28 hours. The pH value changes linearly with the absorption time. At this time, the permeation tube releases a stable concentration of dimethylamine gas. According to the change of pH value with titration time (such as Figure 4 Left), to obtain the concentration of dimethylamine released by the permeation tube. The specific calculation process is as follows:

[0064] The chemical reaction of dimethylamine titrating hydrochloric acid: (CH3 ) 2 NH+HCl→(CH 3 ) 2 NH 2 + + Cl - ;

[0065] pH = -log [H + ]

[0066] During rt time, [H + ]Total consumption concentration:

[0067]

[0068] The mass of dimethylamine in the solution is:

[0069]

[0070] In the time t, the concentration of dimethylamine gas (in μg / m 3 ):

[0071]

[0072] The concentration of dimethylamine gas in time t (in ppt):

[0073]

[0074] Among them, at the initial moment, the pH of the first absorption bottle 7 and the second absorption bottle 8 are pH 1 and pH 2 At time t (in minutes), the pH values ​​of the first absorption bottle 7 and the second absorption bottle 8 are respectively 3 and pH 4 ; [H + ] total The first absorption bottle 7 and the second absorption bottle 8 have [H + ]Total consumption concentration; V aq is the volume of the solution in the absorption bottle, in L, and the volume of the solution in the first absorption bottle 7 and the second absorption bottle 8 is the same; m[(CH 3 ) 2 NH] is the mass of dimethylamine gas absorbed in the solution, in g; M[(CH 3 ) 2 NH] is the molar mass of dimethylamine, 45.085 g / mol; [(CH 3 ) 2 NH] g is the concentration of dimethylamine in the gas, in μg / m 3 ;v gis the gas flow rate, which is generally set to 0.1 L / min; [(CH 3 ) 2 NH] g ' is the concentration of dimethylamine in the gas, in ppt; 273.15 is the atmospheric temperature under standard conditions, in K; 101.325 is the atmospheric pressure under standard conditions, in KPa; 22.4 is the molar volume of the ideal gas under standard conditions, L / mol; T is the gas temperature, in ℃; P is the atmospheric pressure of the gas, in KPa.

[0075] Step 5: The CNC center 1 controls the second solenoid valve 5, closes the gas line 1, and opens the gas line 2; the CNC center 1 adjusts the flow rate of the second mass flow controller 9, and the dilution gas uses zero air. The flow rates are set to 0 L / min, 20 L / min, 30 L / min, 40 L / min, and 50 L / min, respectively. Each flow rate is maintained for 10 minutes, and the flow rate of the dilution gas is switched in turn every 10 minutes.

[0076] Step 6: The diluent gas with different flow rates is mixed with the dimethylamine and high-purity nitrogen gas flow, and the CNC center 1 controls the opening of the fourth solenoid valve 12 and the fifth solenoid valve 13 to enter the chemical ionization time-of-flight mass spectrometry (CI-TOF-MS) detector; 50 minutes later, the CNC center 1 controls the fifth solenoid valve 13 to open the activated carbon filter 14 channel to detect the background value of the mixed gas flow; by analyzing the measurement results of CI-TOF-MS, at least one group of background values ​​plus four groups of signal values ​​with different dilution ratios are obtained, and the relationship between different dimethylamine concentrations and CI-TOF-MS detection signal values ​​is established, and a calibration curve is drawn, and the r of the calibration curve is 2 >0.99 (e.g. Figure 4 Right), indicating that the calibration effect is good.

[0077] Figure 4 The results of a specific application of acid-base titration to realize the calibration of dimethylamine in the atmosphere are shown in Table 1 and Table 2, where Table 1 shows the pH value change data in the experiment, and Table 2 shows the signal value generated by chemical ionization mass spectrometry detection of dimethylamine of different concentrations. In this example, the sensitivity range of chemical ionization mass spectrometry for detecting amine compounds is 5.6~19.4Hz / pptv, and the detection limit is 0.1~0.5pptv. The acid-base titration method has been confirmed by this experiment to have high feasibility and accuracy in field observation. Therefore, the present invention is based on the principle of acid-base titration, and a new type of calibration device used in conjunction with chemical ionization mass spectrometry technology is developed to achieve accurate online calibration of gaseous trace acid and base species.

[0078] Table 1 Changes of pH value of HCl solution with titration time

[0079] Titration time / h pH 0 4.040 2 4.050 4 4.059 6 4.062 8 4.070 10 4.079 12 4.088 14 4.099 16 4.110 18 4.120 20 4.129 22 4.139 24 4.148 26 4.158 28 4.168

[0080] Table 2 Changes of signal values ​​generated by chemical ionization mass spectrometry with dimethylamine concentration

[0081] Dimethylamine concentration / pptv Signal value / Hz 250 1125 272 1220 298 1350 325 1550 360 1800 400 2080 451 2350 520 2600 612 3150

[0082] This specific implementation is only an explanation of the present invention, not a limitation of the present invention. Any changes made by those skilled in the art after reading the specification of the present invention will be protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. An online precise calibration device for gaseous trace acid and alkali species, characterized in that: include: Gas circuit 1, gas circuit 2, gas circuit 3 and numerical control center (1); The gas circuit 1 is used to measure the stable concentration of the acidic or alkaline gas generated by the permeation tube (4-1); the gas circuit 1 comprises: a carrier gas, and a first mass flow controller (2), a first solenoid valve (3), a permeation tube assembly (4), a second solenoid valve (5), a first three-way connector (6), a first absorption bottle (7), and a second absorption bottle (8) which are connected in series in sequence; wherein the first solenoid valve (3) is also directly connected to the first three-way connector (6); the carrier gas is zero air or high-purity nitrogen; the first absorption bottle (7) and the second absorption bottle (8) are equipped with a built-in pH meter and are externally wrapped with a constant temperature device; the permeation tube assembly (4) comprises: The permeation tube (4-1) is a polytetrafluoroethylene tube, sealed at both ends with Teflon rods, and filled with a calibration substance solution; A stainless steel tube (4-2), the front end of which is a porous tube section (4-2a), and the rear end of which is a hollow tube section (4-2b); the porous tube section (4-2a) has a plurality of parallel through-holes connected to the hollow tube section (4-2b), and the hollow tube section (4-2b) is used to accommodate the permeation tube (4-1); An X-shaped bracket (4-3) is placed inside the hollow tube section (4-2b) and is used to support the permeation tube (4-1) and keep the permeation tube (4-1) located at the center of the stainless steel tube (4-2); A temperature control housing (4-4) wrapped around the outside of the stainless steel tube (4-2); The numerical control center (1) is connected to the first mass flow controller (2), the first solenoid valve (3), the permeation tube assembly (4), the second solenoid valve (5), the pH meter of the first absorption bottle (7) and the second absorption bottle (8), and an external thermostat via a signal transmission line; The gas circuit 2 is used to dilute the acidic or alkaline gas volatilized by the permeation tube (4-1), and by adjusting the dilution ratio, different concentrations of acidic or alkaline gas are obtained; the gas circuit 2 comprises: diluent gas, a second mass flow controller (9), a second three-way connector (10), a fourth solenoid valve (12), a fifth solenoid valve (13), a detection instrument (15) connected in series in sequence, and an activated carbon filter (14) connected to the other side of the fifth solenoid valve (13); wherein the diluent gas is zero air or high-purity nitrogen, and the detection instrument (15) is a chemical ionization mass spectrometer; the numerical control center (1) is connected to the second mass flow controller (9), the fourth solenoid valve (12) and the fifth solenoid valve (13) through a signal transmission control line; The gas circuit three is used to detect the concentration of acidic or alkaline gas substances in the ambient air; the gas circuit three comprises: an external ambient air sampling inlet, a third solenoid valve (11), a fourth solenoid valve (12), a fifth solenoid valve (13) connected in series in sequence, a detection instrument (15), and an activated carbon filter (14) connected to the other side of the fifth solenoid valve (13); the numerical control center (1) is connected to the third solenoid valve (11), the fourth solenoid valve (12), and the fifth solenoid valve (13) through a signal transmission control line.

2. The on-line precise calibration device for gaseous trace acid and alkali species according to claim 1, characterized in that: The inner diameter of the permeation tube (4-1) is 1 / 4 inch and the length is 5 to 10 cm; the inner diameter of the entire section of the stainless steel tube (4-2) is 1 / 2 inch and the total length is 25 cm, the length of the porous tube section (4-2a) is 10 cm, and the length of the hollow tube section (4-2b) is 15 cm.

3. The on-line precise calibration device for gaseous trace acid and alkali species according to claim 1, characterized in that: The first absorption bottle (7) contains a strong acidic or alkaline solution, a pH meter probe and a glass tube inserted into the bottom of the absorption bottle for bubbling. The thermostatic device wrapped around the outside of the bottle is a temperature control shell.

4. The on-line precise calibration device for gaseous trace acid and alkali species according to claim 3, characterized in that: The second absorption bottle (8) has the same configuration as the first absorption bottle (7), and the tail of the second absorption bottle (8) is connected to an activated carbon tube.

5. The on-line precise calibration device for gaseous trace acid and alkali species according to claim 1, characterized in that: The numerical control center (1) is provided with an electronic control unit for setting and adjusting parameters of connected devices and sensors for recording various parameters.

6. The on-line precise calibration device for gaseous trace acid and alkali species according to claim 1, characterized in that: The outside of the pipes of different gas paths are wrapped with thermal insulation materials.

7. A method for online accurate calibration of gaseous trace acid and alkali species using the calibration device of claim 1, characterized in that: The following steps are involved: Step 1: Prepare a permeation tube (4-1) of the required calibration substance, fill the standard solution sample into a polytetrafluoroethylene tube, and seal it with a Teflon rod; place the permeation tube (4-1) into a stainless steel tube (4-2), and support it with an X-shaped bracket (4-3); wrap the stainless steel tube (4-2) with a temperature control shell (4-4), connect the stainless steel tube (4-2) to gas path 1, and adjust the permeation temperature of the permeation tube according to the required standard substance concentration, and complete the installation of the permeation tube assembly (4); Step 2: The carrier gas enters the permeation tube assembly (4) through the first mass flow controller (2), and the carrier gas flow rate is set to 40-100 mL / min. The carrier gas carries the calibration substance gas through the second solenoid valve (5) and enters the absorption bottle; if the calibration substance is an acidic species, the carrier gas needs to first flow directly into the absorption bottle from the first solenoid valve (3) and the first three-way connector (6) to detect the concentration of background carbon dioxide in the carrier gas and eliminate the influence of carbon dioxide on the pH value of the solution in the absorption bottle; Step 3: A strong acidic or alkaline solution, a pH meter probe and a glass tube for bubbling inserted into the bottom of the absorption bottle are placed in the first absorption bottle (7) and the second absorption bottle (8), and a constant temperature device is wrapped on the outside; the strong acidic or alkaline solution in the first absorption bottle (7) absorbs most of the alkali or acid substances required for calibration in the gas path; the second absorption bottle (8) ensures that the calibration substances in the gas path are completely absorbed, and an activated carbon tube is connected to the tail of the second absorption bottle (8), and the tail gas flow is released into the air after passing through the activated carbon tube; the pH value of the solution in the first absorption bottle (7) and the second absorption bottle (8) changes with the absorption time and is recorded in the numerical control center (1); Step 4: After the first absorption bottle (7) and the second absorption bottle (8) absorb for 12h-72h, the pH value of the solution changes linearly with the absorption time. At this time, the permeation tube (4-1) releases a constant concentration of the calibration substance, and the concentration is calculated by the pH value and absorption time of the solution in the first absorption bottle (7) and the second absorption bottle (8); Step 5: The numerical control center (1) adjusts the gas path conversion of the second solenoid valve (5) from gas path 1 to gas path 2; the numerical control center (1) adjusts the flow rate of the second mass flow controller (9) to set the gradient flow rate of the dilution gas at intervals of 5 to 15 minutes, that is, different dilution ratios of the calibration substance with a constant concentration to dilute the substance to be calibrated; Step 6: The mixed air flow of the diluent gas, the carrier gas and the calibration substance released by the permeation tube enters the detection instrument (15) through the fourth solenoid valve (12) and the fifth solenoid valve (13); the numerical control center (1) adjusts the fourth solenoid valve (12) to close the ambient air inlet through the third solenoid valve (11); the numerical control center (1) adjusts the gas path switching time of the fifth solenoid valve (13) to 5 to 15 minutes. After 15 minutes, the mixed air flow passes through the activated carbon filter (14) and then enters the detection instrument (15) to obtain the background concentration of the mixed air flow; by analyzing the measurement results of the detection instrument (15), at least one group of background values ​​plus 3 to 5 groups of signal values ​​of the calibration substance at different dilution ratios are obtained, the relationship between the concentration of the calibration substance and the signal value of the detection instrument (15) is established, and a calibration curve is drawn; Step 7: After obtaining the calibration curve, the numerical control center (1) controls the opening of the third solenoid valve (11); the fourth solenoid valve (12) closes the gas path 1 and the gas path 2, and opens the gas path 3; the fifth solenoid valve (13) is controlled to close the channel of the activated carbon filter (14); then the ambient air directly enters the detection instrument (15) through the three solenoid valves; by analyzing the measurement signal of the detection instrument (15), combined with the calibration curve, the concentration of the gaseous trace acid and alkali species in the atmosphere is obtained, thereby realizing the online accuracy calibration of the gaseous trace acid and alkali species in the atmosphere; The flow rates of the carrier gas and the diluent gas, the temperature of the stainless steel tube (4-2) outside the permeation tube (4-1), the constant temperature device of the absorption bottle, the first solenoid valve (3), the second solenoid valve (5), the third solenoid valve (11), the fourth solenoid valve (12), the fifth solenoid valve (13), the pH meter reading and the solution absorption time are all controlled and recorded by the numerical control center (1).

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