VOCs gas generating device with stable concentration and evaluation method thereof

Abstract

The invention relates to a VOCs gas generation device with stable concentration. The VOCs gas generation device comprises a sample injection assembly, a gas source assembly, a gasification assembly, a pressure control assembly and a mixer. The sample injection assembly comprises a precise injection pump, a micro-injection needle and a capillary injection pipeline. The gasification assembly comprises a shell, a quartz liner tube, a heater and a quartz capillary column. The VOCs solution is gasified in the quartz liner tube and diluted for the first time. And the VOCs gas is diluted for the second time in the mixer. The pressure control assembly comprises a pressure stabilizing valve and a needle valve. The pressure stabilizing valve is used for adjusting the flow of diluent gas released by the diluent gas source flowing into the quartz liner tube and stabilizing the pressure of the gas flowing into the quartz capillary column. The needle valve is used for adjusting the flow of gas flowing out of the flow dividing opening, and then the flow of gas flowing into the quartz capillary column in the quartz liner tube is adjusted. According to the invention, from three directions of a liquid source, a gas source and a gasification process, the defects of non-uniform gasification, unstable gasification process, easy pulsation and discontinuous liquid gasification of the existing dynamic generator method are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of VOCs gas generating devices, and in particular to a VOCs gas generating device with stable concentration and an evaluation method thereof. Background Art

[0002] VOCs (volatile organic compounds) are important precursors of O3 and secondary organic aerosols. Long-term exposure will have a direct negative impact on human health, accompanied by PM 2.5 With the further deepening of coordinated control with ozone, various VOCs monitoring equipment and purification technologies have emerged in large numbers. The performance evaluation of VOCs monitoring equipment and purification technologies is the basis for subsequent application research. As an important part of performance evaluation, the reliability and accuracy of the gas source directly affect the results of the performance test of the monitoring equipment and purification technology. In the prior art, the commonly used VOCs loading methods include the bubbling method, the diffusion tube / permeation tube method, the volume ratio method and the dynamic generator method.

[0003] Among them, the disadvantages of the bubbling method are poor stability and low total control accuracy. The diffusion tube / permeation tube method has extremely high requirements for temperature control, diffusion rate and weighing mass accuracy. There are many sources of error in the actual operation process, which is easily affected by the environment and the measurement results are very unstable. The multi-component VOCs cylinder standard gas in the concentration range required by the volume ratio method is not easy to obtain, and the stability during long-term use is difficult to guarantee. The dynamic generator method has uneven gasification, especially when low concentration occurs, the gasification process is unstable, and pulsation and intermittent liquid gasification are prone to occur. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a VOCs gas generating device with stable concentration.

[0005] The VOCs gas generating device with stable concentration provided by the present invention adopts the following technical solution:

[0006] A VOCs gas generating device with stable concentration, comprising an injection component, a gasification component, a gas source component, a mixer and a pressure control component; wherein the injection component comprises a precision injection pump, a microinjection needle and a capillary injection line; one end of the capillary injection line is connected to the microinjection needle, and the other end is connected to the gasification component; the precision injection pump is connected to the microinjection needle for driving the microinjection needle to inject the VOCs solution contained in the microinjection needle into the injection line; the gasification component comprises a shell, a quartz liner, a heater, a quartz capillary column and a gasification channel; the gasification channel is arranged inside the shell; the quartz liner is arranged in the gasification channel; the quartz capillary column is located outside the shell; a diversion port is opened on the side wall of the gasification channel; the quartz liner is connected to the capillary injection line, the quartz capillary column and the diversion port so that the VOCs After the solution is vaporized in the quartz liner, it flows to the quartz capillary column and the diversion port respectively; the quartz liner is filled with glass wool; the gas source component includes a dilution gas source; the dilution gas source is connected to the quartz liner; the mixer has a first inlet, a second inlet and a first outlet; the first inlet is connected to the dilution gas source; the second inlet is connected to the quartz capillary column; the first outlet is used to discharge the gas in the mixer; the pressure control component includes a pressure regulating valve and a needle valve; the pressure regulating valve is arranged between the dilution gas source and the shell; the needle valve is arranged downstream of the diversion port; the pressure regulating valve is used to adjust the flow rate of the dilution gas released by the dilution gas source flowing into the quartz liner, and stabilize the pressure of the gas flowing into the quartz capillary column; the needle valve is used to adjust the flow rate of the gas flowing out of the diversion port, and then adjust the flow rate of the gas in the quartz liner flowing into the quartz capillary column.

[0007] Optionally, the pressure control assembly further includes a back pressure valve; the back pressure valve is connected to the mixer and is used to stabilize the pressure of the gas discharged from the mixer and eliminate fluctuations in flow and pressure generated at the mixer outlet.

[0008] Optionally, the gas source assembly further includes a pressure reducing valve; the pressure reducing valve is connected to the dilution gas source and is used to adjust the output pressure of the output gas source.

[0009] Optionally, the pressure control component further includes a mass flow meter; the mass flow meter is disposed between the dilution gas source and the mixer, and is used to control the flow rate of the dilution gas input from the dilution gas source into the mixer.

[0010] Optionally, the injection assembly also includes a contaminant liquid bottle and a three-way liquid inlet valve; the contaminant liquid bottle is used to hold VOCs solution; the two inlets of the three-way liquid inlet valve are respectively connected to the microinjection needle and the contaminant liquid bottle, and the outlet is connected to the capillary injection line; the three-way liquid inlet valve is used to control the microinjection needle to be connected to the capillary injection line to inject the VOCs solution into the quartz liner, or to control the microinjection needle to be connected to the contaminant liquid bottle so that the microinjection needle can absorb the VOCs solution in the contaminant liquid bottle.

[0011] Optionally, it also includes a waste gas treatment component; the waste gas treatment component includes an adsorbent tube; the front end of the adsorbent tube is connected to the outlet of the needle valve and the first outlet, so as to treat unused VOCs gas.

[0012] Optionally, the exhaust gas treatment component further includes a VOCs sensor; the VOCs sensor is disposed at the end of the adsorbent tube to monitor the content of VOCs in the gas discharged from the end of the adsorbent tube.

[0013] Optionally, all parts in contact with VOCs in the VOCs gas generating device with stable concentration are subjected to silanization treatment.

[0014] Based on the above concept, the present invention also provides a method for evaluating a VOCs gas generating device with a stable concentration, which is used to evaluate the above VOCs gas generating device with a stable concentration. The method comprises: S1, verification of generated gas concentration:

[0015] Obtain standard gas; the standard gas is VOCs gas with known concentration; prepare VOCs gas according to the concentration of the standard gas through the VOCs gas generating device with stable concentration and collect the test gas;

[0016] The concentrations of the standard gas and the test gas are measured respectively by using a pre-concentration / gas chromatography-mass spectrometer, and the measurements are repeated n times, where n≥6, and the average of the measured values ​​is calculated. The actual concentration value of the gas generated by the VOCs gas generating device with a stable concentration is calculated using the following formula:

[0017]

[0018] Where: A is the actual concentration of the test gas, nmol·mol -1 ρ S is the nominal concentration value of the standard gas, nmol·mol -1 ; is the average value of the test gas measurement results, nmol·mol -1; is the average value of the concentration measurement results of the standard gas, nmol·mol -1 ;

[0019] S2. Stability test of the VOCs gas generating device with stable concentration:

[0020] After the stable concentration VOCs gas generator runs stably, it is set to generate VOCs gas of a specified concentration, and the gas is collected once every time t, t≥0.5h, and a total of n groups are collected, n≥2; the collected VOCs gas is measured by pre-concentration / gas chromatography-mass spectrometry, and each group is measured m times, m≥2, and the average value of the m measurement results is taken as the measurement value of the group, and the stability of the stable concentration VOCs gas generator is calculated by the following formula:

[0021]

[0022] Wherein: S is the stability of the gas generated by the VOCs gas generating device with stable concentration, %; is the maximum value of gas concentration among groups, nmol·mol -1 ; is the minimum value of gas concentration among groups, nmol·mol -1 ; is the average value of gas concentration among groups, nmol·mol -1 ; C is the range coefficient;

[0023] S3. Uncertainty assessment:

[0024] According to the formula in step S1 and the law of uncertainty propagation, the calculation formula for the synthetic standard uncertainty is obtained:

[0025] u r 2 =c1 2 u1 2 +c2 2 u2 2 +c3 2 u3 2 =u1 2 +u2 2 +u3 2 ;

[0026] Wherein, u1 is the uncertainty of the standard gas; u2 is the uncertainty of the pre-concentration / gas chromatography-mass spectrometer; u3 is the relative standard uncertainty introduced by the VOCs gas generating device with stable concentration; c1, c2, c3 are sensitivity coefficients, and

[0027] Among them, u1 is calculated by the following formula:

[0028]

[0029] Where U s is the expanded uncertainty of the standard gas; k is the coverage factor;

[0030] u2 is calculated by the following formula:

[0031]

[0032] In the formula, y si is the i-th measured value of the standard gas, nmol·mol -1 ; is the average value of n measurements, nmol·mol -1 ; n is the number of measurements; m is the number of repeated measurements;

[0033] u3 is calculated by the following formula:

[0034]

[0035] Wherein, S is the stability of the gas generated by the VOCs gas generating device with stable concentration; m is the number of repeated measurements;

[0036] u r Calculated by the following formula:

[0037] U r = k × u r ;

[0038] In the formula, u r is the combined standard uncertainty; k is the confidence factor.

[0039] As described above, the VOCs gas generating device with stable concentration of the present invention has at least the following beneficial effects:

[0040] The present invention uses a precision injection pump to inject VOCs solution, which can accurately control the advancement speed of the microinjection needle, and the capillary injection pipeline uses a capillary column micropore to feed the liquid, which can ensure the continuity and stability of the liquid feeding process, effectively solve the problems of instability, pulsation and intermittent gasification of the gasification process, and ensure the stability of the liquid source of the VOCs solution. The flow rate and pressure of the dilution gas flowing out of the dilution gas source are controlled by a pressure reducing valve, a pressure regulating valve, a needle valve, and a mass flow meter to ensure the stability of the dilution gas source. The gasification of the VOCs solution occurs in a quartz liner filled with glass wool, and the gasification is uniform, which ensures the stability of the gasification process. Furthermore, the shortcomings of the existing dynamic generator method, such as uneven gasification, unstable gasification process, easy pulsation and intermittent liquid gasification, are solved from the three directions of liquid source, gas source, and gasification process. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the structure of a VOCs gas generating device with a stable concentration.

[0042] Figure 2 is a schematic diagram of the gasification component structure.

[0043] Figure numerals: 1. precision injection pump; 2. microinjection needle; 3. capillary injection line; 4. pollutant liquid bottle; 41. three-way liquid inlet valve; 5. outer shell; 51. quartz liner; 52. heater; 53. quartz capillary column; 54. vaporization channel; 6. diversion port; 7. mixer; 8. pressure regulating valve; 9. pressure reducing valve; 10. needle valve; 11. back pressure valve; 12. mass flow meter; 13. dilution gas source; 14. adsorbent tube; 15. VOCs sensor. DETAILED DESCRIPTION

[0044] The following is an explanation of the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the features in the following embodiments and the embodiments can be combined with each other without conflict. It should also be understood that the terms used in the embodiments of the present invention are intended to describe specific embodiments, rather than to limit the scope of protection of the present invention. The test methods for which specific conditions are not specified in the following examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturers.

[0045] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of their relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0046] Please refer to Figure 1 , 2The present invention discloses a VOCs gas generating device with stable concentration, which includes: a sampling component, a gasification component, a gas source component, a mixer 7 and a pressure control component.

[0047] The injection assembly includes a precision injection pump 1, a microinjection needle 2 and a capillary injection line 3. One end of the capillary injection line 3 is connected to the microinjection needle 2, and the other end is connected to the gasification assembly. The precision injection pump 1 is connected to the microinjection needle 2, and is used to drive the microinjection needle 2 to inject the VOCs solution contained in the microinjection needle 2 into the injection line.

[0048] Specifically, the precision injection pump 1 has a microinjection needle 2 and a capillary injection line 3. One end of the microinjection needle 2 is located in the precision injection pump 1, and the other end is connected to the capillary injection line 3. The precision injection pump 1 pushes the microinjection needle 2 to move, pump out the VOCs solution, and inject it into the quartz liner 51 through the capillary injection line 3. The precision injection pump 1 can accurately control the advancement speed of the injection needle to ensure that the VOCs solution can be accurately, evenly and continuously output.

[0049] In a preferred embodiment of the present invention, the minimum linear velocity of the microinjection needle 2 is 3 μm / min, and when >30% of the full stroke, the control error is ≤±0.4%. The distance of each microstep is 0.05 μm, and the injection volume of each microstep is 0.01 nL (using a 10 μL microinjection needle 2). A Luer connector is provided at one end of the microinjection needle 2 connected to the capillary injection line 3. The microinjection needle 2 can be airtightly connected to the capillary injection line 3 through the Luer connector. The capillary injection line 3 uses a quartz capillary column 53 or a stainless steel capillary column micropore to inlet liquid, thereby ensuring the continuity and stability of the liquid inlet process.

[0050] In some other embodiments of the present invention, the microinjection needle 2 may have other specifications, such as 25 μL or 100 μL.

[0051] By using a precision injection pump 1 to inject the VOCs solution, the advancement speed of the microinjection needle 2 can be accurately controlled, and the capillary injection line 3 uses a capillary column micropore to inlet liquid, which can ensure the continuity and stability of the liquid inlet process and effectively solve the problems of unstable and pulsating gasification process and intermittent liquid gasification.

[0052] In a preferred embodiment of the present invention, the injection assembly further includes a pollutant liquid bottle 4 and a three-way liquid inlet valve 41. The pollutant liquid bottle 4 is used to contain a VOCs solution. The two inlets of the three-way liquid inlet valve 41 are respectively connected to the microinjection needle 2 and the pollutant liquid bottle 4, and the outlet is connected to the capillary injection line 3. The three-way liquid inlet valve 41 is used to control the microinjection needle 2 to be connected to the capillary injection line 3 to inject the VOCs solution into the quartz liner 51, or to control the microinjection needle 2 to be connected to the pollutant liquid bottle 4 so that the microinjection needle 2 can absorb the VOCs solution in the pollutant liquid bottle 4.

[0053] When the microinjection needle 2 injects the VOCs solution into the quartz liner 51, the microinjection needle 2 is connected to the capillary injection line 3. When the VOCs solution in the microinjection needle 2 is used up, the three-way liquid inlet valve 41 is switched to connect the microinjection needle 2 with the pollutant liquid bottle 4, so that the microinjection needle 2 absorbs the VOCs solution in the pollutant liquid bottle 4 under the drive of the precision injection pump 1. After the absorption is completed, the three-way liquid inlet valve 41 is switched to connect the microinjection needle 2 with the capillary injection line 3 again, and the VOCs solution can be continuously injected into the quartz liner 51. The computer program controls the precision injection pump 1, the microinjection needle 2 and the liquid inlet three-way valve, so that when the VOCs solution in the microinjection needle 2 is insufficient, the VOCs solution in the pollutant liquid bottle 4 is automatically absorbed to replenish it, thereby greatly extending the continuous working time of the VOCs gas generating device with stable concentration of the present invention.

[0054] Furthermore, one or more VOCs solutions can be stored in the pollutant liquid bottle 4. The microinjection needle 2 can absorb different types of VOCs solutions to meet the requirements of different VOCs gas generation processes without having to replace the microinjection needle 2, which helps to improve the working efficiency of the VOCs gas generation device with stable concentration of the present invention.

[0055] Please continue to refer to Figure 1 , the gas source assembly includes a dilution gas source 13. The dilution gas source 13 is connected to the quartz liner 51. The dilution gas source 13 can be a gas cylinder, or other suitable devices for storing dilution gas. The dilution gas can be nitrogen, or other suitable gases. In a preferred embodiment of the present invention, the dilution gas source 13 is a steel cylinder, and the dilution gas is nitrogen. In addition, the pressure and flow rate of the released gas are controlled by a pressure reducing valve 9 at the outlet of the steel cylinder.

[0056] The gasification component includes a shell 5, a quartz liner 51, a heater 52, a quartz capillary column 53 and a gasification channel 54. The gasification channel 54 is arranged inside the shell 5. The quartz liner 51 is arranged in the gasification channel. The quartz capillary column 53 is located outside the shell 5. A diversion port 6 is provided on the side wall of the gasification channel 54. The quartz liner 51 is connected to the capillary injection line 3, the quartz capillary column 53 and the diversion port 6, so that the VOCs solution flows to the quartz capillary column 53 and the diversion port 6 respectively after being gasified in the quartz liner 51. The quartz liner 51 is filled with glass wool.

[0057] For details, please refer to Figure 1 , 2The outer shell 5 of the gasification component is in the shape of a rectangular parallelepiped and is made of aluminum alloy or 316L stainless steel. The gasification channel 54 is cylindrical and made of stainless steel. Its function is to ensure the sealing of the quartz liner 51, and at the same time facilitate the discharge of the gas in the quartz liner 51, or the introduction of external gas and liquid into the quartz liner 51. The quartz liner 51 is a hollow structure, and a chamber for gasification of the VOCs solution is formed therein. A heater 52 mounting hole is opened on the side wall of the outer shell 5, and the heater 52 extends into the outer shell 5 through the mounting hole. The heater 52 can be cylindrical (such as Figure 2 As shown), it can also be spiral-shaped and coiled on the inner wall of the shell 5 to heat the shell 5, thereby heating the VOCs solution in the quartz liner 51 to ensure the gasification speed of the VOCs solution.

[0058] After the liquid inlet assembly injects the VOCs solution into the quartz liner 51, the VOCs solution is heated and vaporized, and is diluted for the first time after mixing with the dilution gas from the gas source assembly. The VOCs gas after the first dilution is divided into two paths, the first path is discharged from the diversion port 6, and the second path flows into the quartz capillary column 53 and flows to the mixer 7.

[0059] The inner surface area of ​​the quartz liner 51 is limited. In order to increase the vaporization surface area of ​​the heated VOCs solution, glass wool is filled inside the quartz liner 51. Glass wool can increase the vaporization surface area of ​​the VOCs solution and promote the vaporization of the VOCs solution. Under stable pressure, as the liquid continues to flow into the quartz liner 51, the VOCs gas will be output stably and quantitatively, effectively reducing the uneven vaporization.

[0060] The mixer 7 has a first inlet, a second inlet and a first outlet. The first inlet is connected to the dilution gas source 13. The second inlet is connected to the quartz capillary column 53. The first outlet is used to discharge the gas in the mixer 7. The VOCs gas diluted for the first time in the gasification component enters the mixer 7 through the quartz capillary column 53 and the second inlet. At the same time, the dilution gas released by the dilution gas source 13 enters the mixer 7 through the first inlet. The VOCs gas is diluted for the second time in the mixer 7, and its concentration is further reduced. The mixer 7 can adopt various components with two inlets and one outlet. Preferably, the mixer 7 adopts a three-way valve in this embodiment.

[0061] A certain concentration of VOCs gas can be generated by dilution of the gasification component and the dilution gas, but the volume of the gasification component is limited, which limits the minimum concentration of VOCs gas that can be obtained through the gasification component. VOCs gas with a lower concentration cannot be obtained by the gasification component alone. By setting the mixer 7, the VOCs gas generating device with a stable concentration of the present invention can stably obtain VOCs gas with a lower concentration.

[0062] The pressure control assembly includes a pressure regulating valve 8, a needle valve 10, a back pressure valve 11 and a mass flow meter 12. The pressure regulating valve 8 is arranged between the dilution gas source 13 and the housing 5. The needle valve 10 is arranged downstream of the diversion port 6. The pressure regulating valve 8 is used to adjust the flow rate of the dilution gas released by the dilution gas source 13 flowing into the quartz liner 51, and stabilize the pressure of the gas flowing into the quartz capillary column 53. The needle valve 10 is used to adjust the flow rate of the gas flowing out of the diversion port 6, and then adjust the flow rate of the gas in the quartz liner 51 flowing into the quartz capillary column 53.

[0063] Specifically, the amount of VOCs gas vaporized per unit time in the quartz liner 51 is constant, so the gas flow rate flowing into the quartz capillary column 53 mainly depends on the flow rate of the dilution gas flowing into the quartz liner 51 and the flow rate of the gas flowing to the diversion port 6. Therefore, the flow rate of the dilution gas flowing into the quartz liner 51 is controlled by the pressure regulating valve 8, and the flow rate of the gas flowing to the diversion port 6 is controlled by the needle valve 10, thereby realizing the control of the gas flow rate in the quartz capillary column 53.

[0064] Since the inner diameter of the quartz capillary column 53 is extremely thin, the flow resistance in the quartz capillary column 53 can be controlled by controlling the length of the quartz capillary column 53. Furthermore, by adjusting the length of the quartz capillary column 53, in conjunction with the pressure regulating valve 8 and the needle valve 10, the flow rate of the gas in the quartz capillary column 53 can be stably controlled.

[0065] One of the reasons why the pressure regulating valve 8 is provided between the dilution gas source 13 and the housing 5 instead of the mass flow meter is that the mass flow meter controls the flow rate according to the temperature change of its inlet and outlet. Since different gases have different specific heat capacities, the mass flow meter needs to be calibrated with different correction coefficients when controlling the flow rate of different gases, which is inconvenient to use, especially when the gas passing through it contains multiple components, the calibration is more inconvenient and the measurement will also be biased.

[0066] Another reason is that the pressure regulating valve 8 cooperates with the needle valve 10 to control the flow of gas in the quartz capillary column 53. The needle valve 10 is a flow regulating valve. In the mechanical flow control system, the working mechanism of the flow regulating valve requires the pressure before its inlet to be stable in order to ensure the constant flow control at the outlet. Therefore, the pressure regulating valve 8 helps to improve the stability of the flow control of the needle valve 10.

[0067] More specifically, the pressure regulating valve 8 is arranged on the pipeline connecting the dilution gas source 13 and the quartz liner 51. The pressure regulating valve 8 can adjust the flow rate of the dilution gas by controlling the opening of the opening and closing member of the valve body, and keep the pressure after the valve stable. In a preferred embodiment of the present invention, the pressure regulating valve 8 is made of stainless steel, the maximum output pressure is 550Kpa, and the output flow rate is 0-1000mL / min.

[0068] The needle valve 10 can ensure that when the gas flow rate or pressure input into the quartz liner 51 changes, the gas diluted for the first time in the quartz liner 51 can still stably flow into the mixer 7 through the quartz capillary column 53. In a preferred embodiment of the present invention, the needle valve 1010 is made of stainless steel, with a maximum input pressure of 750Kpa and an output flow rate of 0-1000mL / min.

[0069] The back pressure valve 11 is connected to the mixer 7, and is used to stabilize the pressure of the gas discharged from the quartz liner 51, and eliminate the fluctuations in flow and pressure generated at the outlet of the mixer 7. The provision of the back pressure valve 11 is conducive to the subsequent collection and utilization of the VOCs gas generated in the device. The back pressure valve 11 can be made of stainless steel. The back pressure valve 11 has two switchable outlets, and the VOCs gas with a concentration that meets the requirements is discharged from one of the outlets for collection and utilization, and the VOCs gas with a concentration that does not meet the requirements is discharged from the other outlet.

[0070] The mass flow meter 12 is disposed between the dilution gas source 13 and the mixer 7, and its function is to accurately control the flow rate of the dilution gas flowing to the mixer 7 according to the gas distribution requirements of the VOCs gas. In a preferred embodiment of the present invention, the flow range of the mass flow meter 12 is 0-10L / min.

[0071] Through the pressure control component, the dilution gas source 13 can stably dilute the VOCs gas to reach the required concentration, and can also stably output the VOCs gas generated in the device to facilitate subsequent collection and utilization.

[0072] When VOCs gas begins to occur but is not stable, the concentration of VOCs gas does not meet the requirements and cannot be collected and utilized, but it cannot be directly discharged into the atmosphere, otherwise it will cause harm to the human body and the environment.

[0073] Therefore, the VOCs gas generating device with stable concentration of the present invention further includes an exhaust gas treatment component. The exhaust gas treatment component includes an adsorbent tube 14 and a VOCs sensor 15. The front end of the adsorbent tube 14 is connected to the back pressure valve 11 and the needle valve 10, and is used to adsorb VOCs in the exhaust gas during the VOCs gas generation process.

[0074] The waste gas in the VOCs gas generation process includes: VOCs gas that is diluted for the first time in the quartz liner 51 and discharged from the diversion port 6 and the needle valve 10 in order to adjust the gas flow in the quartz capillary column 53; and also includes VOCs gas that is diluted for the second time in the mixer 7 but the concentration does not meet the requirements.

[0075] The adsorbents used in the adsorbent tube 14 include one or more of activated carbon, silica gel, molecular sieve and the like. The VOCs sensor 15 is disposed at the end of the adsorbent tube 14 to monitor the effect of the adsorbent tube 14 on adsorbing VOCs. When VOCs detects that the effect of the adsorbent tube 14 on adsorbing VOCs has deteriorated, it indicates that the adsorbent in the adsorbent tube 14 has reached adsorption saturation, thereby reminding the staff to replace the adsorbent in time.

[0076] More specifically, the components in contact with VOCs in the VOCs gas generator with stable concentration of the present invention are all subjected to silanization treatment, such as the valve body of the mixer 7, the pressure regulating valve 8, the back pressure valve 11, and the needle valve 10. The silanization treatment can form a silane film with a mesh structure on the surface of the component, thereby enhancing the wear resistance and corrosion resistance of the component.

[0077] The implementation principle of the VOCs gas generating device with stable concentration of the present invention is as follows: the VOCs solution is injected into the quartz liner 51 by pushing the microinjection needle 2 at a certain speed through the precision injection pump 1, and the liquid entering the quartz liner 51 is quickly vaporized and mixed with the dilution gas output by the dilution gas source 13 to complete the first dilution. After that, the gas in the quartz liner 51 is divided into two paths, one path is discharged, and the other path enters the shunt pipe and enters the mixer 7 at the same time as the dilution gas output by the dilution gas source 13 to complete the second dilution. The gas in the mixer 7 is stably output at a constant pressure and flow rate through the back pressure valve 11, and the excess gas and the gas directly discharged from the quartz liner 51 enter the adsorbent tube 14 for adsorption recovery, and at the same time, the VOCs sensor 15 is used to monitor whether the adsorbent has reached adsorption saturation.

[0078] It should be noted here that when the required VOCs gas concentration is high and the corresponding concentration can be reached after the first dilution in the quartz liner 51, it is not necessary to use the mixer 7 for the second dilution, and the gas diluted once in the quartz liner 51 can be directly taken out from the needle valve 10 for use. Therefore, the VOCs gas generating device with stable concentration of the present invention can switch between high concentration and low concentration according to the required VOCs gas concentration, thereby increasing the range of VOCs gas concentration that can be generated, and thus helping to enrich the application scenarios of the device.

[0079] The following takes VOCs gas as gaseous toluene as an example to explain the implementation principle of the present invention in detail:

[0080] The amount of toluene liquid is calculated according to the desired concentration of gaseous toluene. When using a microinjection needle 2 with a certain inner diameter, the delivery amount of toluene liquid is controlled by adjusting the propulsion speed of the precision injection pump 1. In practical applications, the delivery amount is related to the inner diameter of the microinjection needle 2 and the propulsion speed of the precision injection pump 1. The delivery amount of the injection pump is calculated according to the desired concentration of the target substance. By replacing injection needles of different specifications and adjusting the propulsion speed of the injection pump, the target concentration can be achieved. If the desired toluene concentration is 10nmol·mol -1 When using the microinjection needle 2 with a diameter of 25 μL and an inner diameter of 0.73 mm, the delivery volume of the precision injection pump 1 is 0.047 μL / min and the propulsion speed is 112.8 μm / min.

[0081] The heating temperature of the heater 52 is set. After the temperature is set, the heater 52 starts to heat the shell 5 of the vaporization device and enters the preheating process. The heater 52 has a temperature control module. The temperature control module controls the start and stop of the heater 52 through the temperature feedback from the temperature sensor to maintain the set heating temperature. The heating temperature must ensure that the inner wall temperature of the quartz liner 51 in the vaporization chamber is higher than the boiling point of toluene. If it is used to generate other single VOCs or composite VOCs such as benzene and xylene, according to the boiling point of the target component, generally a temperature setting 30-50°C higher than the high boiling point of the target component is selected to ensure the vaporization of the target component.

[0082] After the preheating is completed, the precision injection pump 1 is started, and the microinjection needle 2 is pushed by the precision injection pump 1 at a speed of 112.8 μm / min to inject the VOCs liquid into the quartz liner 51. The liquid entering the quartz liner 51 is quickly vaporized and mixed with the dilution gas with a flow rate of 1000 mL / min output through the pressure reducing valve 9 and the pressure stabilizing valve 8 to complete the first dilution. After that, it is divided into two paths, one path is discharged through the needle valve 10 at a flow rate of 999 mL / min, and enters the adsorbent tube 14 for adsorption and recovery, and the other path is diverted into the quartz capillary column 53 at a flow rate of 1 mL / min, and enters the mixer 7 at the same time as the dilution gas with a flow rate of 1000 mL / min controlled by the mass flowmeter 12 to complete the second dilution. After that, the gas passes through the back pressure valve 11 and is stably output at a constant pressure and flow rate, and the excess gas enters the adsorbent tube 14 for adsorption and recovery.

[0083] During the generation process, the concentration of toluene can be controlled by adjusting the first dilution flow rate and the second dilution flow rate. The concentration of gaseous toluene is calculated by the following formula:

[0084]

[0085] Where: C i is the calculated concentration of the target compound toluene, nmol·mol -1; D is the inner diameter of the injection needle, mm; V is the injection speed, mm·min -1 ρ i is the liquid density of the target compound, mg·μL -1 ; Q1 first dilution flow rate, mL·min -1 ; Q2 is the output flow rate after the first dilution, mL·min -1 ; Q3 is the second dilution gas flow rate, mL·min -1 ;M i is the molar mass of the target compound toluene, g·mol -1 ; 22.4 is the molar volume of an ideal gas, L·mol -1 .

[0086] It should be noted that the generation of gas components of different concentrations can also be achieved by adjusting the concentration of the liquid component in the pollutant liquid bottle 4 to control the generation concentration of the gaseous target component. This can also be achieved by adjusting the output flow of the pressure regulating valve 8, the needle valve 10 or the output flow of the mass flow meter 12.

[0087] The VOCs gas generating device with stable concentration of the present invention is suitable for the generation of toluene and other volatile organic pollutants such as benzene, ethylbenzene, xylene, n-hexane, ethyl acetate, etc. When it is used to generate other volatile organic compounds other than toluene, it can be adjusted accordingly according to the properties of the organic compounds to be generated by referring to the above-mentioned implementation principles.

[0088] Compared with the prior art, the VOCs gas generating device with stable concentration of the present invention has the following advantages:

[0089] The present invention uses a precision injection pump 1 to inject VOCs solution, which can accurately control the propulsion speed of the microinjection needle 2, and the capillary injection line 3 uses a capillary column micropore to feed the liquid, which can ensure the continuity and stability of the liquid feeding process, effectively solve the problems of instability, pulsation and intermittent gasification of the gasification process, and ensure the stability of the VOCs solution source. The flow rate and pressure of the dilution gas flowing out of the dilution gas source 13 are controlled by a pressure reducing valve 9, a pressure regulating valve 8, a needle valve 10, and a mass flowmeter 12, ensuring the stability of the dilution gas source. The gasification of the VOCs solution occurs in a quartz liner 51 filled with glass wool, and the gasification is uniform, ensuring the stability of the gasification process. Furthermore, the shortcomings of the existing dynamic generator method, such as uneven gasification, unstable gasification process, easy pulsation and intermittent liquid gasification, are solved from the three directions of liquid source, gas source, and gasification process.

[0090] In addition, the present invention also discloses a method for evaluating a VOCs gas generating device with a stable concentration, the method being used to evaluate the VOCs gas generating device with a stable concentration, comprising:

[0091] S1. Verification of gas concentration:

[0092] Obtain standard gas. Standard gas is VOCs gas with known concentration. Use a VOCs gas generator with stable concentration to prepare VOCs gas according to the concentration of standard gas and collect the test gas.

[0093] The concentrations of the standard gas and the test gas are measured by pre-concentration / gas chromatography-mass spectrometry, respectively. The measurements are repeated n times (n≥6), and the average value of the measured values ​​is calculated. The actual concentration value of the gas generated by the VOCs gas generating device with stable concentration is calculated by the following formula:

[0094]

[0095] Where: A is the actual concentration of the test gas, nmol·mol -1 ρ S is the nominal value of the concentration of the standard gas, nmol·mol -1 . is the average value of the test gas measurement results, nmol·mol -1 . is the average value of the concentration measurement results of the standard gas, nmol·mol -1 .

[0096] Specifically, the standard gas can be obtained by purchasing national primary or secondary gas standard materials with known concentrations to ensure the accuracy of their concentrations. The prepared VOCs gas can be collected by gas sampling bags or Summa cans.

[0097] S2. Stability test of VOCs gas generating device with stable concentration:

[0098] After the VOCs gas generator with stable concentration runs stably, it is set to generate VOCs gas of specified concentration, and collects it once every time t (t≥0.5h), and collects n groups (n≥2) in total. The collected VOCs gas is measured by pre-concentration / gas chromatography-mass spectrometry, and each group is measured m times (m≥2). The average value of the m measurement results is taken as the measurement value of the group. The stability of the VOCs gas generator with stable concentration is calculated by the following formula:

[0099]

[0100] Where: S is the stability of the gas generated by the VOCs gas generating device with stable concentration, %; is the maximum value of gas concentration among groups, nmol·mol -1 ; is the minimum value of gas concentration among groups, nmol·mol -1 ; is the average value of gas concentration among groups, nmol·mol -1 ; C is the range coefficient;

[0101] S3. Uncertainty assessment:

[0102] According to the formula in step S1 and the law of uncertainty propagation, the calculation formula for the synthetic standard uncertainty is obtained:

[0103] u r 2 =c1 2 u1 2 +c2 2 u2 2 +c3 2 u3 2 =u1 2 +u2 2 +u3 2 ;

[0104] The formula is based on JJF1059.1-2012 (Evaluation and Expression of Uncertainty in Measurement), where u1 is the uncertainty of the standard gas; u2 is the uncertainty of the pre-concentration / gas chromatography-mass spectrometer; u3 is the relative standard uncertainty introduced by the VOCs gas generation device with stable concentration; c1, c2, c3 are sensitivity coefficients, and

[0105] Among them, u1 is calculated by the following formula:

[0106]

[0107] Where U s is the expanded uncertainty of the standard gas; k is the coverage factor;

[0108] u2 is calculated by the following formula:

[0109]

[0110] In the formula, y si is the measured value of the standard gas for the i-th time, nmol·mol -1 ; is the average value of n measurements, nmol·mol -1 ; n is the number of measurements; m is the number of repeated measurements;

[0111] u3 is calculated by the following formula:

[0112]

[0113] Where S is the stability of the gas generated by the VOCs gas generating device with stable concentration; m is the number of repeated measurements;

[0114] u r Calculated by the following formula:

[0115] U r = k × u r ;

[0116] In the formula, u r is the combined standard uncertainty; k is the confidence factor.

[0117] In the evaluation method of a VOCs gas generating device with a stable concentration of the present invention, the accuracy of the concentration of the gas generated by the device is evaluated through step S1, the stability of the gas generated by the device is evaluated through step S2, and the uncertainty of the gas generated by the device is evaluated through step S3, thereby achieving a comprehensive evaluation of the performance of the VOCs gas generating device with a stable concentration.

[0118] It should be noted that steps S1 and S2 are independent of each other and do not interfere with each other, so the order of implementing steps S1 and S2 can be interchanged.

[0119] Below, the performance of the VOCs gas generator with stable concentration is evaluated by taking the toluene generated by the VOCs gas generator with stable concentration as an example:

[0120] First, step S1 is performed to purchase 5 μmol·mol -1 Toluene gas standard material GBW(E)081675 (U=2.6%, k=2) in nitrogen was diluted to 5 μmol·mol -1 Gas standard substances were diluted to 10 nmol·mol -1 (The gas dynamic dilution device meets the requirement of 20-1000 times accurate dilution). The VOCs gas generating device with stable concentration of the present invention is used to generate toluene gas of corresponding concentration, and the gas is collected by gas sampling bag / Suma tank. The gas standard substance and the gas generated by the device are measured by pre-concentration / gas chromatography-mass spectrometer respectively, and the measurement is repeated 6 times, and the average value of the measured values ​​is taken. and The results are shown in Tables 1 and 2.

[0121] Table 1 Repeatability test results of toluene gas standard substances

[0122]

[0123] Table 2 Repeatability measurement results of toluene gas generated by the device

[0124]

[0125] Then calculate the actual concentration value ρ of the gas generated by the VOCs gas generating device with stable concentrationA :

[0126]

[0127] The relative error between the verified value and the designed value of the gas concentration generated by the VOCs gas generating device with stable concentration is calculated using the following formula. The pre-concentration / gas chromatography-mass spectrometer verification results are shown in Table 3.

[0128]

[0129] Where: δ is the relative error of the gas generated by the device; %; ρ A is the verification value of the gas generated by the device, nmol·mol -1 ρ D is the design value of the gas concentration generated by the device, nmol·mol -1 .

[0130] Table 3 Pre-concentration / gas chromatography-mass spectrometry verification results of gas concentration generated by the device nmol·mol -1

[0131]

[0132] Then, step S2 is performed. After the VOCs gas generating device with stable concentration runs stably, the generated concentration is set to 10 nmol·mol -1 Toluene gas, the generated gas was collected once every 1 hour using a gas sampling bag / Suma tank, and a total of 6 groups were collected. Each group was measured 3 times. Under the selected instrument working conditions, the collected gas was measured using a pre-concentration / gas chromatography-mass spectrometry instrument. The average value of the 3 measurement results was taken as the measurement value of the group. The stability of the VOCs gas generating device with stable concentration was calculated according to the following formula. The results are shown in Table 4.

[0133]

[0134] Where: C is 1.69.

[0135] Table 4 Device stability test results

[0136]

[0137] Finally, step S3 is implemented:

[0138] First calculate the relative standard uncertainty introduced by the diluted gas standard substance: the toluene gas standard substance used in the verification, the concentration after dilution by the dynamic diluter is used as the standard gas concentration, the relative standard uncertainty u1 introduced by the diluted gas standard substance is the standard uncertainty component u introduced by the certified gas standard substance rel (C s) and the standard uncertainty component u introduced by the gas dynamic dilution device rel (F) Composition.

[0139] The concentration after dilution was calculated according to the following formula.

[0140]

[0141] Where: C si is the concentration of the gas standard substance after dilution, nmol·mol -1 ; C s is the concentration of gas standard substance, nmol·mol -1 ; F1 is the gas standard substance flow rate in the dynamic gas dilution device, mL / min; F2 is the zero air flow rate in the dynamic gas dilution device, mL / min.

[0142] C s , F1, and F2 are independent of each other, so the formula for the synthetic relative standard uncertainty is obtained according to the uncertainty propagation law:

[0143]

[0144] Where: u c,rel (C si ) is the relative standard uncertainty of the concentration value of the gas standard substance after dilution, %; u rel (C s ) is the relative standard uncertainty of gas standard substance, %; u rel (F1) is the relative standard uncertainty of the gas standard substance flow rate in the dynamic gas dilution device, %; u rel (F2) is the relative standard uncertainty of zero air flow in the dynamic gas dilution device, %.

[0145] Since the expanded relative uncertainty of the gas standard substance is 2.6%, k = 2, the relative standard uncertainty is 1.3%. The relative standard uncertainty of the calibrated flow of the gas flow controller in the dynamic gas dilution device is 1%. Therefore, the relative uncertainty of the synthetic standard can be obtained:

[0146] Then calculate the relative standard uncertainty u2 introduced by repeated measurements of pre-concentration / gas chromatography-mass spectrometry, which is calculated by the following formula:

[0147]

[0148] Where: y si is the measured value of the gas standard substance for the i-th time, nmol·mol -1 ; is the average value of n measurements, nmol·mol-1 ; n is the number of measurements; m is the number of repeated measurements.

[0149] The relative standard uncertainty introduced by repeated measurements of pre-concentration / gas chromatography-mass spectrometry is calculated as:

[0150] u2=RSD=0.36%.

[0151] Then calculate the relative standard uncertainty u introduced by the stability of the VOCs gas generator with stable concentration 3， Calculated by the following formula:

[0152]

[0153] Where: S is the stability of the VOCs gas generating device with stable concentration; m is the number of repeated measurements.

[0154] The relative standard uncertainty introduced by the stability of the VOCs gas generation device with stable concentration was calculated

[0155] Finally, the relative expanded uncertainty U of the concentration of the VOCs gas generating device with stable concentration is calculated. r , calculated by the following formula:

[0156] U r = k × u r ;

[0157] Where: u r is the combined standard uncertainty; k is the confidence factor.

[0158] Each standard uncertainty component is independent and unrelated to each other, and is combined into the relative standard uncertainty and relative expanded uncertainty (taking coverage factor k=2, confidence level P=95%). The results are shown in Table 5.

[0159] Table 5 Uncertainty components and uncertainty evaluation results

[0160]

[0161]

[0162] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A VOCs gas generating device with stable concentration, characterized in that: It includes a sampling component, a gasification component, a gas source component, a mixer (7) and a pressure control component; wherein, The injection assembly comprises a precision injection pump (1), a microinjection needle (2) and a capillary injection line (3); one end of the capillary injection line (3) is connected to the microinjection needle (2), and the other end is connected to the gasification assembly; the precision injection pump (1) is connected to the microinjection needle (2) and is used to drive the microinjection needle (2) to inject the VOCs solution contained in the microinjection needle (2) into the injection line; The gasification component comprises a shell (5), a quartz liner (51), a heater (52), a quartz capillary column (53) and a gasification channel (54); the gasification channel (54) is arranged inside the shell (5); the quartz liner (51) is arranged inside the gasification channel; the quartz capillary column (53) is located outside the shell (5); a diversion port (6) is provided on the side wall of the gasification channel (54); the quartz liner (51) is connected to the capillary injection pipeline (3), the quartz capillary column (53) and the diversion port (6), so that the VOCs solution flows to the quartz capillary column (53) and the diversion port (6) respectively after being gasified in the quartz liner (51); the quartz liner (51) is filled with glass wool; The gas source assembly comprises a dilution gas source (13); the dilution gas source (13) is connected to the quartz liner (51); The mixer (7) has a first inlet, a second inlet and a first outlet; the first inlet is connected to the dilution gas source (13); the second inlet is connected to the quartz capillary column (53); the first outlet is used to discharge the gas in the mixer (7); The pressure control component comprises a pressure regulating valve (8) and a needle valve (10); the pressure regulating valve (8) is arranged between the dilution gas source (13) and the housing (5); the needle valve (10) is arranged downstream of the dilution port (6); the pressure regulating valve (8) is used to adjust the flow rate of the dilution gas released by the dilution gas source (13) flowing into the quartz liner (51), and stabilize the pressure of the gas flowing into the quartz capillary column (53); the needle valve (10) is used to adjust the flow rate of the gas flowing out of the dilution port (6), and further adjust the flow rate of the gas in the quartz liner (51) flowing into the quartz capillary column (53).

2. The VOCs gas generating device with stable concentration according to claim 1, characterized in that: The pressure control assembly further comprises a back pressure valve (11); The back pressure valve (11) is in communication with the mixer (7) and is used to stabilize the pressure of the gas discharged from the mixer (7) and eliminate fluctuations in flow and pressure generated at the outlet of the mixer (7).

3. The VOCs gas generating device with stable concentration according to claim 2, characterized in that: The gas source assembly also includes a pressure reducing valve (9); The pressure reducing valve (9) is in communication with the dilution gas source (13) and is used to adjust the output pressure of the output gas source.

4. The VOCs gas generating device with stable concentration according to claim 3 is characterized in that: The pressure control assembly also includes a mass flow meter (12); The mass flow meter (12) is arranged between the dilution gas source (13) and the mixer (7) and is used to control the flow rate of the dilution gas input from the dilution gas source (13) into the mixer (7).

5. The VOCs gas generating device with stable concentration according to claim 1, characterized in that: The sample injection assembly also includes a pollutant liquid bottle (4) and a three-way liquid inlet valve (41); The pollutant liquid bottle (4) is used to contain the VOCs solution; the two inlets of the three-way liquid inlet valve (41) are respectively connected to the microinjection needle (2) and the pollutant liquid bottle (4), and the outlet is connected to the capillary injection line (3); The three-way liquid inlet valve (41) is used to control the microinjection needle (2) to be connected to the capillary injection line (3) so as to inject the VOCs solution into the quartz liner (51), or to control the microinjection needle (2) to be connected to the pollutant liquid bottle (4) so ​​that the microinjection needle (2) can absorb the VOCs solution in the pollutant liquid bottle (4).

6. The VOCs gas generating device with stable concentration according to claim 1, characterized in that: Also included are exhaust gas treatment components; The exhaust gas treatment assembly includes an adsorbent tube (14); The front end of the adsorbent tube (14) is connected to the outlet of the needle valve (10) and the first outlet, and is used to process unused VOCs gas.

7. The VOCs gas generating device with stable concentration according to claim 6, characterized in that: The exhaust gas treatment component also includes a VOCs sensor (15); The VOCs sensor (15) is arranged at the end of the adsorbent tube (14) and is used to monitor the content of VOCs in the gas discharged from the end of the adsorbent tube (14).

8. The VOCs gas generating device with stable concentration according to claim 1, characterized in that: The components in contact with VOCs in the VOCs gas generating device with stable concentration are all subjected to silanization treatment.

9. A method for evaluating a VOCs gas generator with a stable concentration, for evaluating the VOCs gas generator with a stable concentration as claimed in any one of claims 1 to 8, characterized in that: The method comprises: S1. Verification of gas concentration: Obtain standard gas; the standard gas is VOCs gas with known concentration; prepare VOCs gas according to the concentration of the standard gas through the VOCs gas generating device with stable concentration and collect the test gas; The concentrations of the standard gas and the test gas are measured respectively by using a pre-concentration / gas chromatography-mass spectrometer, and the measurements are repeated n times, where n≥6, and the average of the measured values ​​is calculated. The actual concentration value of the gas generated by the VOCs gas generating device with a stable concentration is calculated using the following formula: Where: A is the actual concentration of the test gas, nmol·mol -1 ρ S is the nominal concentration value of the standard gas, nmol·mol -1 ; is the average value of the test gas measurement results, nmol·mol -1 ; is the average value of the concentration measurement results of the standard gas, nmol·mol -1 ; S2. Stability test of the VOCs gas generating device with stable concentration: After the stable concentration VOCs gas generator runs stably, it is set to generate VOCs gas of a specified concentration, and the gas is collected once every time t, t≥0.5h, and a total of n groups are collected, n≥2; the collected VOCs gas is measured by pre-concentration / gas chromatography-mass spectrometry, and each group is measured m times, m≥2, and the average value of the m measurement results is taken as the measurement value of the group, and the stability of the stable concentration VOCs gas generator is calculated by the following formula: Wherein: S is the stability of the gas generated by the VOCs gas generating device with stable concentration, %; is the maximum value of gas concentration among groups, nmol·mol -1 ; is the minimum value of gas concentration among groups, nmol·mol -1 ; is the average value of gas concentration among groups, nmol·mol -1 ; C is the range coefficient; S3. Uncertainty assessment: According to the formula in step S1 and the law of uncertainty propagation, the calculation formula for the synthetic standard uncertainty is obtained: u r 2 =c1 2 u1 2 +c2 2 u2 2 +c3 2 u3 2 =u1 2 +u2 2 +u3 2 ; Wherein, u1 is the uncertainty of the standard gas; u2 is the uncertainty of the pre-concentration / gas chromatography-mass spectrometer; u3 is the relative standard uncertainty introduced by the VOCs gas generating device with stable concentration; c1, c2, c3 are sensitivity coefficients, and Among them, u1 is calculated by the following formula: Where U s is the expanded uncertainty of the standard gas; k is the coverage factor; u2 is calculated by the following formula: In the formula, y si is the i-th measured value of the standard gas, nmol·mol -1 ; is the average value of n measurements, nmol·mol -1 ; n is the number of measurements; m is the number of repeated measurements; u3 is calculated by the following formula: Wherein, S is the stability of the gas generated by the VOCs gas generating device with stable concentration; m is the number of repeated measurements; u r Calculated by the following formula: IN r =k×u r ; In the formula, u r is the combined standard uncertainty; k is the confidence factor.

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