A method, apparatus and use for the preparation of a standard gas

Abstract

The application provides a preparation method of standard gas, a device and use thereof, in particular, an online preparation method of gaseous nitrous acid standard gas, a device and use thereof. The preparation method and the device can realize online generation of unstable and moisture-absorbing standard gas, and provide a real-time, accurate, stable and reliable gas source calibration method for online monitoring of high-activity key parameters of ambient air, and can be applied to calibration of various point-type monitoring atmospheres, such as point-type monitoring of atmospheric HONO.

Description

Technical Field

[0001] This invention relates to a method, apparatus, and application for preparing a standard gas, particularly an online method, apparatus, and application for preparing gaseous nitrous acid standard gas, belonging to the field of environmental monitoring technology, especially the field of atmospheric measurement technology. Background Technology

[0002] Standard gases are measuring gases with uniform concentration, good stability, and accurate values. Common standard gases, categorized by application, include: gas alarm standard gases, power energy standard gases, petrochemical standard gases, environmental monitoring standard gases, medical and health standard gases, and instrumentation standard gases. In recent years, standard gases have also been widely used in environmental monitoring, measurement of toxic organic compounds, automotive emission testing, natural gas BTU measurement, liquefied petroleum gas calibration standards, and supercritical fluid processes.

[0003] However, the preparation of standard gases for highly reactive and hygroscopic unstable gases faces numerous challenges. For example, gaseous nitrous acid (HONO) is an important trace nitrogen species in the atmosphere. High concentrations of HONO can contribute 30%–90% of OH radicals (·OH) through photolysis during the day. These OH radicals can initiate a series of chain reactions, ultimately leading to the formation of ozone and secondary organic aerosols. Therefore, HONO has become a hot topic in atmospheric chemistry research, and its concentration detection methods in the atmosphere have attracted researchers' attention. Existing methods for measuring gaseous nitrous acid include spectroscopic and wet chemical methods, but due to the extremely high reactivity, hygroscopicity, and instability of HONO, it is still difficult to prepare stable, reliable, and storable standard gases, resulting in a lack of effective means for calibrating online monitoring instruments. Some researchers have used the bubbling method to react a mixed solution of sulfuric acid and nitrite with a carrier gas to generate HONO, but the concentration of gaseous HONO produced by this method is unstable and has a high impurity content. Although some reports describe continuously passing a low-concentration mixture of sulfuric acid and nitrite into a flow reactor and aerating it to reduce impurities, precise control of the resulting HONO concentration remains difficult. Furthermore, while some researchers have used solid nitrite and acidic gas to prepare HONO via a gas-solid reaction, these methods suffer from drawbacks such as difficulty in controlling experimental conditions and poor reproducibility.

[0004] Given that existing methods and devices for preparing HONO standard gas have drawbacks such as excessive solution and carrier gas flow rates, high maintenance costs, and large waste volumes, and also have numerous problems in terms of the effectiveness of concentration control and gas stability, there is an urgent need to propose an improved method and device for preparing gaseous nitrous acid standard gas. Summary of the Invention

[0005] To address the problems of the prior art, the present invention provides a method for preparing a standard gas, the method comprising the following steps: (1) Under the purging of carrier gas, the reactants are reacted in the microfluidic chip to obtain the reaction products; (2) The reaction products of step (1) are separated into gas and liquid by a gas-liquid separation unit; (3) Mix the gas obtained in step (2) with the dilution gas to obtain the diluted standard gas.

[0006] According to an embodiment of the present invention, the preparation method further includes the following steps: (4) The standard gas prepared in step (3) is delivered to a gas monitoring and / or detection device for calibration or correction of the instrument.

[0007] According to an embodiment of the present invention, the preparation method further includes the following steps: (5) After diluting the liquid obtained in step (2), the solution was sent to an ion chromatograph to measure the NO2 content in the tail end solution after the reaction. - Concentration, and by inferring the NO2 concentration during HONO generation based on the measurement results. - The reaction efficiency.

[0008] According to an embodiment of the present invention, the temperature of the microfluidic chip in step (1) is different from the temperature of the gas-liquid separation unit in step (2).

[0009] According to an embodiment of the present invention, the temperature of the gas-liquid separation unit in step (2) is different from the delivery temperature of the standard gas to the gas monitoring and / or detection device in step (4).

[0010] According to an embodiment of the present invention, the temperature difference between the microfluidic chip in step (1) and the gas-liquid separation unit in step (2) is >10°C. The temperature difference is preferably ≥20°C, more preferably 20~22°C, such as 21°C.

[0011] According to an embodiment of the present invention, in step (4), the temperature difference between the temperature at which the standard gas is delivered to the gas monitoring and / or detection device and the temperature difference between the gas and liquid separation unit and the temperature at which the gas is delivered is >10°C. The temperature difference is preferably ≥20°C, more preferably 20~22°C, such as 21°C.

[0012] According to an embodiment of the present invention, the temperature of the microfluidic chip in step (1) is the same as or different from the delivery temperature of the standard gas to the gas monitoring and / or detection device in step (4), and is independently selected from a temperature above 25°C, preferably 29~31°C, more preferably 30±0.1°C.

[0013] According to an embodiment of the present invention, the temperature of the gas-liquid separation unit is below 15°C, preferably 8~10°C, and more preferably 9±0.1°C.

[0014] According to an embodiment of the present invention, the carrier gas and / or dilution gas source is nitrogen, preferably high-purity nitrogen, and more preferably nitrogen with a purity greater than 99.999%.

[0015] According to an embodiment of the present invention, the total flow rate of the carrier gas and the dilution gas is 3.5~4.5L / min, preferably 3.8~4.2L / min, and more preferably 4.0L / min.

[0016] According to an embodiment of the present invention, the flow rate ratio of the carrier to the dilution gas can be (2.5~10):1, for example (2.6~8):1, such as (2.8~7):1, and examples can be 1.05:2.95, 0.5:3.5.

[0017] According to an embodiment of the present invention, the flow rate of the carrier gas can be less than 2 L / min, for example, 0.5 to 1.8 L / min, preferably 0.5 to 1.05 L / min.

[0018] According to an embodiment of the present invention, the flow rate of the dilution gas can be higher than 2.5 L / min, preferably 2.95~3.5 L / min.

[0019] According to embodiments of the present invention, the reaction reagents are those reactants known in the art that can be used in chemical reactions to generate the desired chemical components of the target standard gas online. For example, when the target standard gas is gaseous nitrous acid, the reaction reagents can be nitrites and acids.

[0020] According to an embodiment of the present invention, the nitrite may be sodium nitrite.

[0021] According to an embodiment of the present invention, the acid may be a sulfuric acid solution, such as an aqueous sulfuric acid solution.

[0022] According to an embodiment of the present invention, the flow ratio of the sulfuric acid solution to the nitrite solution can be greater than 1:1, for example (1~20):1, such as (1~15):1, and examples can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1.

[0023] According to an embodiment of the present invention, the concentration of the nitrite solution can be adjusted according to actual needs, for example, it can be 10 μg / L or more, such as 50~5000 μg / L, preferably 80~2000 μg / L, such as 100~1500 μg / L.

[0024] According to an embodiment of the present invention, the flow rate of the nitrite solution can be 0.005~0.1 mL / min, for example 0.005 mL / min, 0.025 mL / min, 0.05 mL / min, 0.075 mL / min or 0.1 mL / min.

[0025] According to an embodiment of the present invention, the flow rate of the sulfuric acid solution can be 0.05~0.10 mL / min.

[0026] According to an embodiment of the present invention, the sulfuric acid solution is a dilute sulfuric acid solution with a weight percentage concentration of about 1 to 2 wt / ‰ and / or a pH value of 1 to 2.

[0027] The present invention also provides a standard gas preparation apparatus, the apparatus comprising a flow control module, a quantitative reaction control module, and a solution delivery module; The flow control module includes a carrier gas source flow control unit and a dilution gas source flow control unit. The carrier gas source flow control unit includes a gas flow meter and a gas transmission pipeline. The dilution gas source flow control unit includes a gas flow meter and a gas transmission pipeline. The gas transmission pipeline inlet of the carrier gas source flow control unit and the gas transmission pipeline inlet of the dilution gas source flow control unit are respectively connected to the gas source. The quantitative reaction control module includes a microfluidic chip and a gas-liquid separation unit, with the outlet of the microfluidic chip connected to the inlet of the gas-liquid separation unit; The solution delivery module includes at least two reagent storage units, an injection pump with at least two channels, a liquid delivery line, and a liquid mixing line. The inlet of the injection pump with at least two channels is connected to the at least two reagent storage units through the liquid delivery line, and the outlet of the injection pump with at least two channels is connected to the inlet of the liquid mixing line through the liquid delivery line. The gas transmission pipeline outlet of the carrier gas source flow control unit in the flow control module and the liquid mixing pipeline outlet of the solution delivery module are connected to the microfluidic chip in the quantitative reaction control module via a three-way unit. The gas outlet of the gas-liquid separation unit and the gas transmission pipeline outlet of the dilution gas source flow control unit in the flow control module are connected to the output pipeline of the standard gas via a three-way unit. According to an embodiment of the present invention, the standard gas is a standard gas of a gas with extremely high reactivity and / or high hygroscopicity, such as a standard gas of gaseous nitrous acid.

[0028] According to an embodiment of the present invention, the quantitative reaction control module further includes a temperature control unit, such as a temperature control chamber.

[0029] According to an embodiment of the present invention, the thermostatic unit includes a temperature control unit (such as a heating element and / or a cooling element) and a temperature sensor.

[0030] Preferably, the constant temperature unit is used to control the temperature of the microfluidic chip and the gas-liquid separation unit, and more preferably to control the temperature with high precision (e.g., the error range does not exceed ±0.1℃).

[0031] According to an embodiment of the present invention, the microfluidic chip and the gas-liquid separation unit are at different temperatures. Preferably, different temperature control units are used to control the microfluidic chip and the gas-liquid separation unit at different temperatures.

[0032] According to an embodiment of the present invention, the temperature difference between the temperature of the microfluidic chip and the temperature of the gas-liquid separation unit is >10°C. Preferably, the temperature difference is ≥20°C, more preferably 20~22°C, such as 21°C.

[0033] According to an embodiment of the present invention, the temperature of the microfluidic chip is higher than 25°C, preferably 29~31°C, and more preferably 30±0.1°C.

[0034] According to an embodiment of the present invention, the temperature of the gas-liquid separation unit is below 15°C, preferably 8~10°C, and more preferably 9±0.1°C.

[0035] According to embodiments of the present invention, the standard gas preparation apparatus may further include a waste gas and / or waste liquid discharge unit. The discharge unit may include, for example, a waste gas and / or waste liquid discharge outlet and its discharge pipeline. Those skilled in the art will understand that, if appropriate, the waste gas or waste liquid discharge units generated in the various components of the preparation apparatus may be provided individually or in combination.

[0036] According to an embodiment of the present invention, the standard gas preparation apparatus further includes a liquid dilution unit of the gas-liquid separation unit and an ion chromatograph, wherein the liquid dilution unit of the gas-liquid separation unit is connected to the ion chromatograph to measure NO2 in the liquid of the gas-liquid separation unit. - Concentration, and by inferring the NO2 concentration during HONO generation based on the measurement results. - The reaction efficiency.

[0037] According to an embodiment of the present invention, the flow control module includes a gas source storage unit, a flow control branch I, and a flow control branch II. Flow control branch I includes a first gas flow meter, and flow control branch II includes a second gas flow meter and a first mixing tee connected in sequence. The gas source storage unit is divided into two paths, one connected to the first gas flow meter in flow control branch I and the other connected to the second gas flow meter in flow control branch II. The first gas flow meter in flow control branch I is connected to the gas inlet of the microfluidic chip via a gas pipeline. The inlet of the third mixing tee in flow control branch II is connected to flow control branch II, and the two outlets of the first mixing tee in flow control branch II are respectively connected to the gas outlet of the gas-liquid separation device and the detection unit in the quantitative reaction control unit. The flow control module is used to control the liquid flow rate of different reaction reagents (such as sodium nitrite solution and sulfuric acid solution), ensuring the stable transfer of HONO from the liquid phase to the gas phase and preventing droplets from condensing at the outlet of the gas-liquid separation bottle and being carried into the gas generation pipeline by the gas flow, causing contamination.

[0038] According to an embodiment of the present invention, the quantitative reaction control module includes a second mixing tee, a microfluidic chip, and a gas-liquid separation unit (such as a gas-liquid separation bottle).

[0039] According to an embodiment of the present invention, the microfluidic chip includes a capillary main board, an air inlet, a liquid inlet, and a temperature control board, wherein the capillary main board includes a capillary, an air inlet, and a liquid inlet.

[0040] According to an embodiment of the present invention, during use, high-purity nitrogen gas and liquid enter the capillary tube sequentially, and the gas and liquid fully contact and mix in the capillary tube.

[0041] According to an embodiment of the present invention, the microfluidic chip is preferably made of quartz material, and more preferably a sheet-like chip made of quartz material. Preferably, the thickness of the microfluidic chip is less than 10 mm, more preferably less than 5 mm, for example 1 mm, 2 mm, 3 mm, 4 mm or 5 mm.

[0042] According to an embodiment of the present invention, the surface of the microfluidic chip includes a wavy groove, and the two ends of the wavy groove are provided with gas-liquid inlets and outlets.

[0043] As an example, the microfluidic chip has an internal cross-sectional area of ​​0.64 mm. 2 Its external dimensions can be 5.5 cm x 5.5 cm.

[0044] Preferably, the outer wall of the microfluidic chip is covered with a light-shielding material to eliminate interference from temperature fluctuations, bubbles, photolysis of nitrous acid molecules, etc.

[0045] According to an embodiment of the present invention, the upper end of the gas-liquid separation unit is the gas and liquid inlet, and the lower end is the gas-liquid separation chamber.

[0046] According to an embodiment of the present invention, the solution delivery module includes at least two reagent storage units. Preferably, the solution delivery module includes at least one nitrite solution (such as an aqueous solution of sodium nitrite) storage unit and one acidic solution (such as an aqueous solution of an acid) storage unit. For example, the nitrite may be sodium nitrite. As another example, the acid may be sulfuric acid.

[0047] According to an embodiment of the present invention, the solution delivery module may include an injection pump having two or more channels, preferably a micro-injection pump. As an example, the solution delivery module may include a four-channel micro-electric injection pump.

[0048] According to an embodiment of the present invention, the solution delivery module may further include a waste liquid pump. Preferably, the waste liquid pump may be selected from, for example, a peristaltic pump.

[0049] According to an embodiment of the present invention, the solution delivery module can be used to precisely deliver reaction reagents (such as sodium nitrite solution and sulfuric acid solution) and discharge waste liquid. For example, the solution delivery module includes a reaction reagent bottle, a solenoid valve, a four-channel micro-electric injection pump, and a waste liquid pump. For example, the first, second, and third injection pumps of the four-channel micro-electric injection pump connect the reaction reagent (such as sodium nitrite solution) in the first reagent bottle to the first solenoid three-way valve; the fourth injection pump connects the reaction reagent (such as sulfuric acid solution) in the second reagent bottle to the second solenoid three-way valve; the pure water in the third reagent bottle is connected to both the first and second solenoid three-way valves; the sixth solenoid three-way valve is connected to the inlet of the microfluidic chip through a liquid pipeline; and the waste liquid pump is connected to the liquid outlet of the gas-liquid separation bottle in the quantitative reaction control unit.

[0050] According to an embodiment of the present invention, in the solution delivery module, under the action of a four-channel micro-electric syringe pump, 1 / 16” PTFE tubing is used to deliver reaction reagents (such as sulfuric acid solution and nitrite solution) to the microfluidic chip at a certain flow rate. Preferably, the flow control range of the four-channel micro-electric syringe pump is 0.01 mL / min to 0.1 mL / min.

[0051] According to an embodiment of the present invention, the standard gas preparation apparatus further includes a control and data acquisition circuit. For example, the control and data acquisition circuit includes a main circuit board with an output port. The main circuit board controls the temperature and the solution delivery module, and acquires and outputs temperature information and detection signals. The temperature information and / or detection signal data can be output from the output port on the main circuit board. As an example, the output port is a USB port.

[0052] According to an embodiment of the present invention, the standard gas preparation apparatus further includes a display device, such as a display screen. For example, the control and data acquisition circuit is connected to the display device, so that temperature, flow rate, detection signal, and HONO concentration are displayed on the display screen.

[0053] According to an embodiment of the present invention, the carrier gas and / or dilution gas source is nitrogen, preferably high-purity nitrogen, and more preferably nitrogen with a purity greater than 99.999%.

[0054] According to an embodiment of the present invention, the output pipeline of the standard gas is connected to a gas monitoring and / or detection device, such as a HONO online monitoring instrument, for calibration or correction of the instrument.

[0055] According to an embodiment of the present invention, the temperature of the standard gas output pipeline is higher than 25°C, preferably 29~31°C, and more preferably 30±0.1°C. For this purpose, the standard gas output pipeline can be additionally equipped with a temperature control unit, such as a temperature control chamber. Alternatively, if it is desired to control the standard gas output pipeline and the microfluidic chip at the same temperature, the standard gas output pipeline and the microfluidic chip can share a common temperature control unit.

[0056] According to an embodiment of the present invention, the HONO online monitoring instrument can be a point-type environmental monitoring instrument, such as a long-path HONO online monitoring instrument, an online ion chromatograph, a cavity-enhanced HONO absorption spectrometer, etc.

[0057] According to an embodiment of the present invention, the standard gas preparation apparatus is used in the standard gas preparation method described in the context of this specification. For this purpose and to reduce space, when using the standard gas preparation apparatus to prepare standard gases, it may have the parameters or characteristics such as reaction reagents, flow rates, and temperatures mentioned in the context of this specification.

[0058] The present invention also provides the above-mentioned microfluidic chip.

[0059] According to an embodiment of the present invention, the microfluidic chip includes a capillary main board, an air inlet, a liquid inlet, and a temperature control board, wherein the capillary main board includes a capillary, an air inlet, and a liquid inlet; Preferably, the microfluidic chip is a sheet-like chip made of quartz material; Preferably, the thickness of the microfluidic chip is less than 10 mm, and more preferably less than 5 mm; Preferably, the surface of the microfluidic chip includes a wavy groove, and the two ends of the wavy groove are provided with gas-liquid inlets and outlets; More preferably, the outer wall of the microfluidic chip is covered with a light-shielding material.

[0060] The present invention also provides a method for preparing a standard gas (such as nitrous acid standard gas), the method comprising preparing a standard gas (such as nitrous acid standard gas) using the above-mentioned standard gas preparation apparatus.

[0061] For example, the method for preparing the standard gas may include the following steps, such as using the standard gas preparation apparatus described above: (A) The reaction reagents (such as sodium nitrite solution and excess sulfuric acid solution) in different reaction reagent storage units are mixed by an injection pump with at least two channels in the solution delivery module; (B) Under the purging of the carrier gas generated by the carrier gas source flow control unit in the flow control module, the mixed reaction reagents are introduced into the microfluidic chip for reaction; (C) The reaction products of the microfluidic chip are passed through the outlet of the microfluidic chip and enter the inlet of the gas-liquid separation unit for gas-liquid separation to obtain gas (such as gaseous HONO). (D) The gas obtained in step (C) (such as gaseous HONO) is mixed with the dilution gas generated by the dilution gas source flow control unit in the flow control module to obtain a diluted standard gas, such as HONO standard gas.

[0062] Preferably, the liquid obtained in step (C) is discharged from the liquid outlet of the gas-liquid separation bottle under the action of a peristaltic pump. The liquid can be collected and detected by ion chromatography to measure the NO2 content in the solution at the tail end of the reaction. - Concentration, and by inferring the NO2 concentration during HONO generation based on the measurement results. - The reaction efficiency.

[0063] According to an exemplary embodiment of the present invention, the preparation method includes the following steps: (a) The nitrite solution and excess sulfuric acid solution are mixed at a certain flow rate using a four-channel micro-electric syringe pump; (b) Under the purging of nitrogen carrier gas controlled by the first gas flow controller in the flow control branch I, the solution mixed in step (a) is passed through a microfluidic chip with high-precision temperature control, and the solution forms a liquid film on the tube wall by relying on the surface tension of the liquid. (c) In the microfluidic chip, the gas-liquid interface increases dramatically. The HONO generated by the mixing of the two solutions rapidly diffuses and mixes with the nitrogen gas. The generated HONO gas flows out from the gas outlet of the gas-liquid separation bottle, and the separated liquid is discharged from the liquid outlet of the gas-liquid separation bottle by the action of a peristaltic pump. The liquid can be collected and detected by ion chromatography to measure the NO2 in the solution at the tail end of the reaction. - Concentration, and by inferring the NO2 concentration during HONO generation based on the measurement results. -The reaction efficiency; (d) The nitrogen dilution gas is mixed again with the generated HONO gas through the second gas flow controller and the second mixing tee in the flow control branch II, and diluted to prepare HONO standard gases with different concentration gradients, thus completing the online preparation of specific gaseous HONO. (e) The prepared gaseous HONO is supplied for use through the gas pipeline and one end of the third mixing tee, while excess gaseous HONO is discharged through the bypass.

[0064] According to an embodiment of the present invention, the step of inferring NO2 from the measurement results during the HONO generation process... - Methods to improve reaction efficiency include: specifically, using the same flow rate, simultaneously outputting the sodium hydroxide aqueous solution and the solution (tail liquid) discharged from the liquid outlet of the gas-liquid separator to the same volumetric flask. The sodium hydroxide solution and tail liquid are mixed to neutralize the tail liquid in the reaction process, thereby terminating the reaction. The mixed solution is then diluted four times, and the NO2 content is measured using ion chromatography. - Concentration. Measured NO2 - Concentration inversely correlates with NO2 during HONO generation - The reaction efficiency is calculated using the formula (1). The obtained reaction efficiency (η) is compared with the HONO production efficiency calculated by the nitrous acid detector, i.e., NO2. - The utilization rates (ηcal) are compared to verify whether they match.

[0065] (1) In the formula, η: NO2 - Reaction efficiency; NO2 in tail liquid - concentration; NO2 - Initial concentration.

[0066] According to an embodiment of the present invention, the concentration of the sodium hydroxide aqueous solution can be 200 mg / L-500 mg / L, such as 250 mg / L.

[0067] The present invention also provides the use of the apparatus and / or method for preparing the standard gas for calibrating a monitoring device for gaseous substances, such as gaseous nitrous acid (HONO), for example, a point-based monitoring device for calibrating gaseous nitrous acid.

[0068] The present invention also provides a monitoring system comprising the standard gas preparation apparatus described above.

[0069] Preferably, the monitoring system is an environmental gas monitoring system, such as an atmospheric monitoring system.

[0070] According to an embodiment of the present invention, the monitoring system further includes an online HONO monitoring instrument, such as a long-path HONO online monitoring instrument, an online ion chromatograph, a cavity-enhanced HONO absorption spectrometer, etc.

[0071] The present invention also provides a gas monitoring and / or detection method, which includes preparing a standard gas using the preparation method described above, and using the standard gas for monitoring and / or detection of environmental gases, such as atmospheric monitoring and / or detection.

[0072] Beneficial effects This invention provides a method, apparatus, and application for preparing a standard gas, particularly an online method, apparatus, and application for preparing gaseous nitrous acid standard gas. The method and apparatus enable the online generation of unstable, hygroscopic standard gas, providing a real-time, accurate, stable, and reliable gas source calibration method for online monitoring of highly reactive key parameters in ambient air. It can be applied to calibrating various point-based atmospheric monitoring systems, such as the HONO (Homo nitrous oxide) monitoring system.

[0073] Surprisingly, the method and apparatus of this invention require neither bulky, lengthy glass spiral tubes nor high carrier gas flow rates to rapidly obtain the desired gaseous HONO concentration gradients, minimizing the impact of humidity on quantitative detection results. Furthermore, the two-stage dilution effect of the carrier gas and dilution gas effectively ensures a dry gas path, achieving stable HONO transport from the liquid phase to the gas phase and obtaining more accurate gaseous HONO concentrations. Simultaneously, it significantly reduces daily maintenance costs and data loss due to peristaltic pump aging. Moreover, the technical solution of this invention can significantly reduce solution and gas flow rates, decrease reagent consumption and volatilization, and significantly reduce waste liquid generation.

[0074] The inventors also discovered that by setting the temperature of the microfluidic chip to a higher temperature than that of the gas-liquid separation unit, and / or setting the temperature of the delivery pipeline to a higher temperature than that of the gas-liquid separation unit—a "split-type + variable-temperature" approach—the vapor can be made supersaturated and condensed before entering the gas-generating pipeline, thus being discharged with the waste liquid. This avoids the defects of existing technologies, such as excessive water vapor entering the gas-generating pipeline and condensing in the pipeline, causing HONO re-adsorption, and even the possibility of droplets flowing into the detection equipment and interfering with it. Therefore, the solution of this invention also significantly improves the utilization rate of nitrous acid.

[0075] The results of the closed-loop experiment show that the gaseous nitrous acid prepared by the method and apparatus of this invention can reach the ppb level, and the theoretical concentration has a good correlation with the measured concentration (R). 2= 0.999), with a relative standard deviation of 0.7%-1.8% and a standard deviation of 0.009~0.087. The utilization rate of nitrous acid is as high as 77% or more, which fully meets the conditions for calibrating various point-based monitoring equipment for atmospheric HONO. It is of great significance for improving the accuracy of the instrument in measuring HONO. Attached Figure Description

[0076] Figure 1 This is a schematic diagram of the method and apparatus for preparing standard gas provided in Embodiment 1 of the present invention; Among them, 1—0.5mL syringe pump; 2—2.5mL syringe pump; 3, 4—5mL syringe pump; 5, 6, 7—first to third reagent bottles; 8, 9—first to second gas flow controllers; 10—microfluidic chip; 11—gas-liquid separation bottle; 12, 13, 14, 15, 16, 17—first to sixth three-way solenoid valves; 18, 19, 20—first to second mixing three-way valves; 21—waste liquid pump.

[0077] The arrows in the diagram indicate the flow direction of the liquid or gas.

[0078] Figure 2 This is a schematic diagram of the microfluidic chip structure provided in Embodiment 1 of the present invention.

[0079] Figure 3 This is a schematic diagram of the gas-liquid separation bottle structure provided in Embodiment 1 of the present invention. Detailed Implementation

[0080] The technical solution of the present invention will be described in more detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the technical solution of the present invention, and should not be construed as limiting the scope of protection of this application.

[0081] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0082] It should be understood that the terms "first", "second", "third", "fourth", etc. used in this invention are only used to mark different components and are not intended to imply their relative importance.

[0083] Example 1: Apparatus for preparing standard gases This embodiment provides a standard gas preparation device, the schematic diagram of which is shown below. Figure 1 As shown. The nitrous acid standard gas preparation device includes: a reaction control module, a flow control module, a solution delivery module, a control and data acquisition circuit, and a display screen.

[0084] The flow control module includes a gas source storage unit and flow control branch I and flow control branch II, which are respectively connected to the gas source storage unit through a first mixing tee 20. Flow control branch I includes a first gas flow controller 9 connected to the gas source storage unit through a pipeline, and flow control branch II includes a second gas flow controller 8 connected to the gas source storage unit through a pipeline. The first gas flow controller 9 in flow control branch I is also connected to the gas inlet of the microfluidic chip through a gas pipeline. Flow control branch II is connected to the gas outlet of the gas-liquid separation device in the quantitative reaction control unit through a second mixing tee 18. The quantitative reaction control module includes a third mixing tee 19, a microfluidic chip 10, and a gas-liquid separation bottle 11; in the quantitative reaction module, the microfluidic chip is custom-made from a thin quartz plate, such as... Figure 2 A 0.8*0.8mm wavy groove is engraved on a 3mm quartz sheet. Through holes are opened at both ends of the groove, and nuts are glued to the back as the gas and liquid inlet and outlet. A 0.2mm quartz sheet is then used to bond it, sealing the groove. In this embodiment, the microfluidic chip area is 55*55mm, and the groove length is approximately 600mm. The outer wall of the microfluidic chip is covered with a light-shielding material to eliminate interference from temperature fluctuations, bubbles, and photolysis of nitrous acid molecules. The microfluidic chip includes a capillary main board, an air inlet, a liquid inlet, and a temperature control board. The capillary main board includes a capillary, an air inlet, and a liquid inlet. The microfluidic chip is thin and small in size, and directly uses the temperature control board for constant temperature control. It has a large contact area, uniform heating, a short heat transfer path, and high efficiency, increasing temperature control stability and reducing the energy consumption of the temperature control system. The upper end of the gas-liquid separation bottle 11 is the gas and liquid inlet, and the lower end is the gas-liquid separation chamber. Figure 3 The T-shaped gas-liquid separator bottle is made of glass. The gas-liquid mixture coming out of the microfluidic chip enters the low-temperature gas-liquid separation chamber after colliding with the bottle body at the inlet. After the gas and liquid are fully separated, the gas flows out from the outlet of the gas-liquid separator bottle, and the liquid is drawn out by the peristaltic pump from the waste liquid outlet of the gas-liquid separator bottle.

[0085] The quantitative reaction control module also includes a constant temperature chamber for high-precision temperature control of the microfluidic chip, gas-liquid separation bottle, and standard gas output pipeline. The temperatures of the microfluidic chip and standard gas output pipeline are stabilized at 30±0.1℃, and the temperature of the gas-liquid separation bottle is stabilized at 9±0.1℃. The constant temperature chamber has built-in temperature control elements (such as heaters and coolers) and temperature sensors.

[0086] The solution delivery module includes a first reagent bottle 5, a second reagent bottle 7, first to sixth three-way solenoid valves, a four-channel micro-electric syringe pump 22, and a waste liquid pump 21 (such as a peristaltic pump). The first syringe pump 1, the second syringe pump 2, and the third syringe pump 3 of the four-channel micro-electric syringe pump 22 connect the sodium nitrite solution in the first reagent bottle 5 to the first solenoid three-way valve 12. The fourth syringe pump 4 connects the sulfuric acid solution in the second reagent bottle 7 to the second solenoid three-way valve 13. The pure water in the third reagent bottle 6 is connected to both the first solenoid three-way valve 12 and the second solenoid three-way valve 13. The sixth solenoid three-way valve 17 is connected to the inlet of the microfluidic chip 10 via a liquid pipeline. The waste liquid pump 21 is connected to the liquid outlet of the gas-liquid separation bottle 11 in the quantitative reaction control unit.

[0087] The standard gas preparation apparatus further includes an output pipeline for the standard gas, wherein the output pipeline for the standard gas is connected to a gas monitoring and / or detection device, such as a HONO online monitoring instrument (e.g., a long-path HONO online monitor, an online ion chromatograph, a cavity-enhanced HONO absorption spectrometer, etc.).

[0088] The standard gas preparation apparatus further includes a control and data acquisition circuit. This control and data acquisition circuit includes a main circuit board with an output port. The main circuit board controls the temperature and the solution delivery module, and acquires and outputs temperature information and detection signals. The temperature information and / or detection signal data can be output from the output port on the main circuit board. The output port is a USB port.

[0089] The standard gas preparation apparatus also includes a display device, such as a display screen. The control and data acquisition circuit is connected to the display device, so that temperature, flow rate, detection signal, and HONO concentration are displayed on the display screen.

[0090] The standard gas preparation apparatus further includes a liquid dilution unit of the gas-liquid separation unit and an ion chromatograph, wherein the liquid dilution unit of the gas-liquid separation unit is connected to the ion chromatograph to measure NO2 in the liquid of the gas-liquid separation unit. - Concentration, and by inferring the NO2 concentration during HONO generation based on the measurement results. - The reaction efficiency.

[0091] Example 2: Preparation method of nitrous acid standard gas The standard gas of nitrous acid was prepared online using the apparatus of Example 1 by the following method: Connect the device from Example 1 to a power source, turn on the instrument, and then perform the following steps: (1) Cleaning the first to fourth syringe pumps: Switch the first solenoid three-way valve 12 to a closed state for the first reagent bottle 5 and an open / closed state for the pure water in the third reagent bottle 6. Switch the second solenoid three-way valve 13 to a closed state for the second reagent bottle 7 and an open / closed state for the pure water in the third reagent bottle 6. Connect all solenoid three-way valves 14, 15, and 16 to the inlet and the waste bottle. Switch the solenoid three-way valve 17 to a state where it is connected to the inlet, open / closed to the waste bottle, and closed to the third mixing three-way valve 19. Make the first to fourth syringe pumps draw water from the entire tube and quickly discharge it. Repeat 3 times.

[0092] (2) System cleaning: Switch the first electromagnetic three-way valve 12 to a closed state for the first reagent bottle 5 and an open / closed state for the pure water in the third reagent bottle 6. Switch the second electromagnetic three-way valve 13 to a closed state for the second reagent bottle 7 and an open / closed state for the pure water in the third reagent bottle 6, so that both the first electromagnetic three-way valve 12 and the second electromagnetic three-way valve 13 are open / closed for the pure water in the third reagent bottle 6. Connect all electromagnetic three-way valves 14, 15 and 16 to the inlet and the waste bottle. Switch the electromagnetic three-way valve 17 to a state that is connected to the inlet, closed to the waste bottle and open / closed to the third mixing three-way valve 19. Use the syringe pump to draw pure water to inject and clean all downstream liquid paths. Open the nitrogen carrier gas with a purity greater than 99.999% in the flow control branch I, and do not introduce the dilution gas in the flow control branch II. The carrier gas flow rate is 0.5 L / min, and the cleaning time is 15-20 min.

[0093] (3) Hydraulic pump rinsing: Switch the first electromagnetic three-way valve 12 to the open / closed state for the first reagent bottle 5 and the closed state for the pure water in the third reagent bottle 6. Switch the second electromagnetic three-way valve 13 to the open / closed state for the second reagent bottle 7 and the closed state for the pure water in the third reagent bottle 6. Connect all electromagnetic three-way valves 14, 15, and 16 to the inlet and the waste bottle. Switch the electromagnetic three-way valve 17 to the state where it is connected to the inlet, open / closed to the waste bottle, and closed to the third mixing three-way valve 19. Draw half a tube of solution with the syringe pump and quickly discharge it. Repeat 3 times.

[0094] (4) Preparation of standard nitrous acid gas of the required concentration: Under the action of the four-channel micro-electric injection pump 22, the sodium nitrite solution in the first reagent bottle 5 (placed in a refrigerator with the temperature controlled at around 15°C) and the 1wt / ‰ dilute sulfuric acid solution in the second reagent bottle 7 are mixed at a certain solution flow rate. Then, high-purity nitrogen gas (purity greater than 99.999%) controlled by the first gas flow controller 9 in the flow control branch I is used as the carrier gas and is blown through the microfluidic chip 10 at a certain flow rate. The solution forms a liquid film on the tube wall of the microfluidic chip 10 by relying on the surface tension of the liquid.

[0095] During use, high-purity nitrogen gas and liquid enter the capillary tube sequentially, allowing for thorough contact and mixing. A constant temperature chamber (with built-in cooling elements and a temperature sensor) is used for high-precision temperature control of the gas-liquid separation bottle, stabilizing the microfluidic system and the separation bottle temperature at 30±0.1℃ and 9±0.1℃, respectively.

[0096] Due to the surge in the gas-liquid interface in the microfluidic chip 10, the HONO generated by the reaction of sodium nitrite solution and dilute sulfuric acid solution diffuses rapidly and mixes with the high-purity nitrogen gas used as a carrier gas. The generated HONO gas flows out from the gas outlet of the gas-liquid separation bottle 11, and the generated waste liquid is transported to the waste liquid bottle from the liquid outlet of the gas-liquid separation bottle 11 by the waste liquid pump 21. High-purity nitrogen gas at a certain flow rate is used as a dilution gas and is mixed again with the generated gaseous HONO through the second gas flow controller 8 in the flow control branch II. Thus, HONO standard gases with different concentration gradients are prepared through dilution, completing the online preparation of specific gaseous HONO.

[0097] The prepared gaseous HONO is supplied for use through a gas delivery pipeline. Excess gaseous HONO is discharged through a bypass of the gas delivery pipeline.

[0098] In the above method, the reaction efficiency of the sodium nitrite solution was verified by a closure experiment using ion chromatography and an online HONO detection device. This invention further measures the NO2 content of the reacted solution. - Concentration measurement: NO2 in the tail solution after the reaction was measured using ion chromatography. - Concentration. Specifically, a 250 mg / L sodium hydroxide aqueous solution and the solution (tail liquid) discharged from the liquid outlet of the gas-liquid separator were simultaneously output to the same volumetric flask using the same flow rate. The sodium hydroxide solution and tail liquid were mixed to neutralize the tail liquid in the reaction process, thereby terminating the reaction. The mixed solution was then diluted four times, and the NO2 content was measured using ion chromatography. - Concentration. Measured NO2 - Concentration inversely correlates with NO2 during HONO generation - The reaction efficiency is calculated using the formula (1). The obtained reaction efficiency (η) is compared with the HONO production efficiency calculated by the nitrous acid detector, i.e., NO2. - The utilization rates (ηcal) are compared to verify whether they match.

[0099] (1) In the formula, η: NO2 - Reaction efficiency; NO2 in tail liquid - concentration; NO2 - Initial concentration; The reaction efficiencies of sodium nitrite solutions at different concentrations are shown in Table 1, and the results of the closed-loop experiment are in high agreement with the HONO concentration. The preparation methods of solution concentration and gas flow rate, as well as the HONO standard gases of different concentrations obtained, are shown in Tables 2 and 3.

[0100] Table 1. Measured HONO concentration and ion chromatography closure experiment results

[0101] Table 2. Flow rate configuration methods for different HONO concentrations

[0102] Note: The theoretical first-level concentration is the concentration of nitrous acid after mixing nitrous acid gas with high-purity nitrogen gas as a carrier gas; The theoretical dilution concentration is the concentration of nitrous acid after dilution with high-purity nitrogen gas, which is used as the dilution gas.

[0103] As shown in Table 2, the configuration methods for different solution concentrations and gas flow rates are as follows: (1) When the actual expected value of HONO concentration is 9.600 ppb, the solution from the third injection pump 3 and the fourth injection pump 4 is pumped to the microfluidic chip 10 at a pump speed of V2, and the corresponding flow rate is 0.100 mL / min. The solution from the first injection pump 1 and the second injection pump 2 is pumped to the waste liquid tube (or discharged back to the solution bottle).

[0104] (2) When the actual expected value of HONO concentration is 4.800 ppb, the solution from the third injection pump 3 and the fourth injection pump 4 is pumped to the microfluidic chip 10 at a pump speed of V1, corresponding to a flow rate of 0.050 mL / min. The solution from the first injection pump 1 and the second injection pump 2 is pumped to the waste pipe (or returned to the solution bottle).

[0105] (3) When the actual expected value of HONO concentration is 2.400 ppb, the solution from the second injection pump 2 and the fourth injection pump 4 is pumped to the microfluidic chip 10 at a pump speed of V1, corresponding to flow rates of 0.025 mL / min and 0.050 mL / min, respectively. The solution from the first injection pump 1 and the third injection pump 3 is pumped to the waste liquid tube (or returned to the solution bottle).

[0106] (4) When the actual expected value of HONO concentration is 0.960 ppb, the solution from the first injection pump 1 and the fourth injection pump 4 is pumped to the microfluidic chip 10 at a pump speed of V2, corresponding to flow rates of 0.010 mL / min and 0.100 mL / min, respectively. The solution from the second injection pump 2 and the third injection pump 3 is pumped to the waste liquid tube (or returned to the solution bottle).

[0107] (5) When the actual expected value of HONO concentration is 0.480 ppb, the solution from the first injection pump 1 and the fourth injection pump 4 is pumped to the microfluidic chip 10 at a pump speed of V1, corresponding to flow rates of 0.005 mL / min and 0.050 mL / min, respectively. The solution from the second injection pump 2 and the third injection pump 3 is pumped to the waste pipe (or returned to the solution bottle).

[0108] (6) Zero point: The electromagnetic three-way valve E switches to pure water, and the solutions of the first injection pump 1 and the fourth injection pump 4 are pumped to the microfluidic chip 10 at a pump speed of V1, corresponding to flow rates of 0.005 mL / min and 0.050 mL / min, respectively. The solutions of the second injection pump 2 and the third injection pump 3 are pumped to the waste liquid pipe (or discharged back to the solution bottle).

[0109] Table 3. Injection pump configurations for different flow rates

[0110] The above experimental results show that the concentration range of gaseous nitrous acid prepared by this invention is 0.4-9.6 ppb. By changing the core parameters such as solution concentration, solution flow rate, and high-purity nitrogen flow rate, the upper and lower limits of the gaseous nitrous acid concentration can be changed. As shown in Table 2, due to the flexibility of the flow rate configuration in this invention, five HONO standard gas concentrations can be generated using only one nitrous acid solution concentration, which is fully applicable to the measurement of HONO in the atmospheric environment. In addition, this invention uses nitrous acid solution concentrations of 100, 500, and 1000 μg / L, and nitrous acid solution flow rates of 0.05 mL / min and 0.1 mL / min, corresponding to carrier gas flow rates of 0.5 L / min and 1.1 L / min, respectively, to conduct HONO concentration gradient experiments. The results of seven experiments show that the theoretical concentration and the measured concentration have a good correlation (R0). 2 = 0.999), with a relative standard deviation of 0.7%-1.8% and a standard deviation of 0.009~0.087 (Table 4). The high-precision isothermal control of the microfluidic system and the low-temperature control of the gas-liquid separation device resulted in good stability and reproducibility of the HONO concentration. The closure performance test results of the atmospheric nitrite standard gas generator conducted in this invention show that the production of HONO is related to NO2... - The consumption is consistent with the requirements, and the utilization rate of nitrous acid is as high as 77% or more, which fully meets the conditions for calibrating various point-based monitoring equipment for atmospheric HONO. This is of great significance for improving the accuracy of the instrument in measuring HONO.

[0111] Table 4 HONO Concentration Gradient Experiment

[0112] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the claims of this application.

Claims

1. A method for preparing a standard gas, characterized in that, The preparation method includes the following steps: (1) Under the purging of carrier gas, the reactants are reacted in the microfluidic chip to obtain the reaction products; (2) The reaction products of step (1) are separated into gas and liquid by a gas-liquid separation unit; (3) Mix the gas obtained in step (2) with the dilution gas to obtain the diluted standard gas; (4) The standard gas prepared in step (3) is delivered to a gas monitoring and / or detection device for calibration or correction of the instrument; (5) After diluting the liquid obtained in step (2), the solution was sent to an ion chromatograph to measure the NO2 content in the tail end solution after the reaction. - Concentration, and by inferring the NO2 concentration during HONO generation based on the measurement results. - The reaction efficiency; In step (1), the temperature of the microfluidic chip is different from the temperature of the gas-liquid separation unit in step (2); The temperature of the gas-liquid separation unit in step (2) is different from the delivery temperature of the standard gas to the gas monitoring and / or detection device in step (4); The temperature difference between the microfluidic chip in step (1) and the gas-liquid separation unit in step (2) is >10℃; In step (4), the temperature difference between the standard gas delivered to the gas monitoring and / or detection device and the temperature of the gas-liquid separation unit is >10℃.

2. The preparation method according to claim 1, characterized in that, The temperature of the microfluidic chip in step (1) is the same as or different from the delivery temperature of the standard gas to the gas monitoring and / or detection device in step (4), and is independently selected from temperatures above 25°C. The temperature of the gas-liquid separation unit is below 15°C.

3. The preparation method according to claim 1, characterized in that, The temperature of the microfluidic chip in step (1) is the same as or different from the delivery temperature of the standard gas to the gas monitoring and / or detection device in step (4), and is independently selected from 29~31℃; The temperature of the gas-liquid separation unit is 8~10℃.

4. The preparation method according to claim 1, characterized in that, The carrier gas and / or dilution gas source is nitrogen; The total flow rate of the carrier gas and dilution gas is 3.5~4.5 L / min; The flow rate ratio of the carrier gas to the dilution gas is 2.5 to 10:

1.

5. The preparation method according to claim 1, characterized in that, The total flow rate of the carrier gas and dilution gas is 3.8~4.2 L / min; The flow rate ratio of the carrier gas to the dilution gas is 2.6 to 8:

1.

6. The preparation method according to claim 1, characterized in that, The target standard gas is gaseous nitrous acid, and the reaction reagents are nitrous acid solution and acid; The acid mentioned is a sulfuric acid solution; The flow ratio of the sulfuric acid solution to the nitrite solution is greater than 1:

1.

7. The preparation method according to claim 6, characterized in that, The flow rate ratio of the sulfuric acid solution to the nitrite solution is 1~20:

1.

8. The preparation method according to claim 6, characterized in that, The concentration of the nitrite solution is above 10 μg / L; The flow rate of the nitrite solution is 0.005~0.1 mL / min; The flow rate of the sulfuric acid solution is 0.05~0.10 mL / min.

9. The preparation method according to claim 6, characterized in that, The concentration of the nitrite solution is 50~5000 μg / L.

10. The preparation method according to claim 6, characterized in that, The sulfuric acid solution is a dilute sulfuric acid solution with a weight percentage concentration of 1~2 wt / ‰.

11. The preparation method according to claim 1, characterized in that, The preparation method is a method for preparing nitrous acid standard gas, wherein, In step (1), under the action of an injection pump with at least two channels in the solution delivery module, the sodium nitrite solution and excess sulfuric acid solution in different reaction reagent storage units are mixed; under the purging of the carrier gas generated by the carrier gas source flow control unit in the flow control module, the mixed reaction reagents are introduced into the microfluidic chip for reaction. In step (2), the reaction product of the microfluidic chip is passed through the outlet of the microfluidic chip and enters the inlet of the gas-liquid separation unit for gas-liquid separation to obtain gaseous HONO; In step (3), the gaseous HONO obtained in step (2) is mixed with the dilution gas generated by the dilution gas source flow control unit in the flow control module to obtain the diluted HONO standard gas. In step (5), the liquid obtained from the separation in step (2) is transported to the ion chromatograph through the liquid outlet of the gas-liquid separation bottle by a peristaltic pump, and the NO2 content of the tail solution after the reaction is measured. - Concentration, and by inferring the NO2 concentration during HONO generation based on the measurement results. - The reaction efficiency.

12. The preparation method according to claim 11, characterized in that, In step (1), the nitrite solution and excess sulfuric acid solution are mixed at a certain flow rate under the action of a four-channel micro electric syringe pump; Under the purging of nitrogen carrier gas controlled by the first gas flow controller in flow control branch I, the mixed solution is passed through a microfluidic chip with high-precision temperature control, and the solution forms a liquid film on the tube wall by relying on the surface tension of the liquid. In step (3), the gas-liquid contact interface in the microfluidic chip increases dramatically, and the HONO generated by the mixing of the two solutions diffuses rapidly and mixes with the nitrogen gas. The generated HONO gas flows out from the gas outlet of the gas-liquid separation bottle. In step (5), the separated liquid is transported from the liquid outlet of the gas-liquid separation bottle to the ion chromatograph under the action of a peristaltic pump, and the NO2 content of the tail solution after the reaction is measured. - Concentration, and by inferring the NO2 concentration during HONO generation based on the measurement results. - The reaction efficiency; In step (3), the nitrogen dilution gas is mixed again with the generated HONO gas through the second gas flow controller and the second mixing tee in the flow control branch II, and diluted to prepare HONO standard gases with different concentration gradients, thus completing the online preparation of specific gaseous HONO. In step (4), the prepared gaseous HONO is supplied for use through the gas pipeline and one end of the third mixing tee, while the excess gaseous HONO is discharged through the bypass.

13. The preparation method according to any one of claims 1-12, characterized in that, The method described above involves inferring NO2 from the measurement results during the HONO generation process. - Methods to improve reaction efficiency include: utilizing a solution delivery and mixing structure to simultaneously output sodium hydroxide aqueous solution and the solution discharged from the liquid outlet of a gas-liquid separator to the same volumetric flask at the same flow rate. Sodium hydroxide neutralizes the tail liquid in the reaction process, thereby terminating the reaction. The mixed solution is then diluted four times, and the NO2 content is measured using ion chromatography. - Concentration; measured NO2 - Concentration inversely correlates with NO2 during HONO generation - The reaction efficiency is calculated using the formula (1); the obtained reaction efficiency η is compared with the HONO production efficiency calculated by the nitrous acid detector, i.e., NO2 - Compare the utilization rates ηcal to verify whether the two are consistent; （1） In the formula, η: NO2 - Reaction efficiency; NO2 in tail liquid - concentration; NO2 - Initial concentration.

14. A gas monitoring and / or detection method, characterized in that, The detection method includes preparing a standard gas using the preparation method described in any one of claims 1-13, and using the standard gas for monitoring and / or detection of environmental gases.

15. The gas monitoring and / or detection method according to claim 14, characterized in that, The monitoring and / or detection of ambient gases refers to the monitoring and / or detection of the atmosphere.

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