A rapid calibration device and calibration method for the sampling rate of a tube axial passive sampler for VOCs in ambient air

Abstract

The present invention provides a rapid calibration device and calibration method for the sampling rate of a tube axial passive sampler for VOCs in ambient air. The calibration device includes an air bag, a passive sampling tube, a temperature and humidity meter, and an active sampler. The passive sampling tube and the temperature and humidity meter are placed inside the air bag to passively sample the gas inside the air bag while monitoring the temperature and humidity of the sampling. The active sampler is located outside the air bag and is connected to the air bag for actively collecting the gas inside the air bag. The calibration device of the present invention is designed according to the actual needs of the current determination of the passive sampling rate of VOCs in ambient air, and has the advantages of being portable, simple to operate, and low in price.

Description

Technical Field

[0001] The invention belongs to the technical field of air monitoring instruments, and particularly relates to a rapid calibration device and a calibration method for the sampling rate of a VOCs tube axial passive sampler in ambient air. Background Art

[0002] Volatile organic compounds (VOCs) are numerous and complex in composition, and the detection and analysis methods are cumbersome. Active sampling with adsorption tubes has the advantages of convenient sampling, high sensitivity, low detection limit, etc., and is the standard test method for VOCs sampling specified in the national standards of our country. The disadvantage of this sampling method is that it requires power support, is not suitable for long-term sampling, cannot meet the requirements of dynamic sample collection, is difficult to give effective exposure information, and at the same time has high requirements for personnel operation skills, and non-professional operation may bring large human errors. Compared with active samplers, passive sampling methods do not require sampling pumps and power, and the sampling work is more convenient and feasible, and also reduces the cost required for sampling. And the passive sampling method provides the time-weighted average concentration (TWA) of pollutants, which more truly and accurately reflects the concentration information and exposure level of VOCs in the environment. However, it has been found that the performance of passive samplers for detecting VOCs is still not stable enough, manifested as large fluctuations in the detection uncertainty of passive samplers. The main factor affecting the uncertainty of VOCs concentration is the passive sampling rate. Experiments by Plaisance et al. (Plaisance H, Leonardis T, Gerboles M. Assessment of uncertainty of benzene measurements by Radiello diffusive sampler. Atmospheric Environment, 2008, 42: 2555-2568) have confirmed that the change in the passive sampling rate contributes more than 80% of the uncertainty. Therefore, in order to improve the accuracy and stability of detecting the concentration of VOCs in indoor and outdoor environments using passive samplers, it is necessary to calibrate the passive sampling rate before each detection of the VOCs concentration in ambient air.

[0003] At present, among the domestic patents on passive sampling of organic substances in the air, most are directed at passive sampling methods and sampling devices for organic pollutants. For example, Patent CN101852691A discloses a passive adsorption sampling device for detecting the concentration of volatile pollutants in indoor air. The device includes a cylindrical adsorbent, a base, an outer cover, and a rubber gasket. By placing the cylindrical adsorbent on the base, the outer cover is sleeved outside the cylindrical adsorbent and sealed with the base through the rubber gasket. After sampling, the sample concentration is directly analyzed using a gas chromatograph or gas chromatography-mass spectrometry instrument with an automatic thermal desorption (ATD) function. This device is simple and reliable and can achieve the function of collecting multiple polluted gases with one adsorption tube. Patent CN 205808778U discloses a passive sampler with a cylindrical sampler housing. It is internally provided with an adsorption resin filler for sampling, and an opening is provided at the lower part. Air mainly enters in a diffusion manner through the opening to contact the adsorption resin filler. The sampling efficiency of this passive sampler is not easily affected by wind speed and turbulence. However, there has been no patent application for a method for calibrating the adsorption rate of a passive sampler for volatile organic compounds in the air so far.

[0004] Therefore, it is very necessary to develop a rapid calibration device and calibration method for the sampling rate of a VOCs tubular axial passive sampler in ambient air. Summary of the Invention

[0005] Aiming at the defect that the detection of VOCs concentration by the existing passive sampler is unstable, the present invention aims to provide a rapid calibration device and calibration method for the sampling rate of a VOCs tubular axial passive sampler in ambient air. The calibration device of the present invention is designed according to the actual needs of measuring the passive sampling rate of VOCs in ambient air at present, and has the advantages of being portable, simple to operate, and low in price. The passive sampling rates of various volatile organic compounds obtained after calibration can be applied to the monitoring of VOCs in indoor and outdoor ambient air.

[0006] To achieve the above object, in the first aspect of the present invention, a rapid calibration device for the sampling rate of a VOCs tubular axial passive sampler in ambient air is provided, adopting the following technical solution:

[0007] A rapid calibration device for the sampling rate of a VOCs tubular axial passive sampler in ambient air includes an air bag, a passive sampling tube, a temperature and humidity meter, and an active sampler. The passive sampling tube and the temperature and humidity meter are placed in the air bag to passively sample the gas in the air bag while monitoring the temperature and humidity of the sampling. The active sampler is located outside the air bag and is connected to the air bag for actively collecting the gas in the air bag.

[0008] In the above-mentioned rapid calibration device for the sampling rate of the tubular axial passive sampler for VOCs in ambient air, as a preferred embodiment, the gas bag is provided with a valve and a sealing strip adapted thereto. The valve is connected to the active sampler for enabling the connection between the gas bag and the active sampler, and the sealing strip is used to open and seal the gas bag. Preferably, the volume of the gas bag is 10-100L. Preferably, the operating temperature range of the gas bag is -20°C to +110°C. Preferably, the material of the gas bag is polyvinyl fluoride (PVF), the material of the valve is polytetrafluoroethylene (Teflon), and the sealing strip is an SNS sealing strip.

[0009] In the present invention, the gas bag made of polyvinyl fluoride (PVF) film has low adsorption and good gas barrier properties. It has the advantages of being light, easy to operate, and inexpensive, and the gas bag can be replaced at will, thus achieving zero cross-contamination and greatly shortening the equilibration time. The valve made of polytetrafluoroethylene is connected to the active sampler. Opening the valve can connect the gas bag with the active sampler, so that the active sampler can collect the gas in the gas bag to achieve active sampling. Closing the valve seals the gas bag without affecting passive sampling. The SNS sealing strip is used to open and seal the gas bag, so that the passive sampling tube and the temperature and humidity meter can be put into or taken out of the gas bag before or after use. The calibration device of the present invention is designed according to the actual needs of measuring the passive sampling rate of VOCs in ambient air at present. It has the advantages of being light, easy to operate, and inexpensive. The passive sampling rates of various volatile organic compounds obtained after calibration can be directly used for monitoring VOCs in indoor and outdoor ambient air. Since the device is light and simple, the passive sampling rate can be calibrated at any time according to changes in the external environment or absorbent, etc., so as to ensure the accuracy of the detection results under different conditions.

[0010] In the above-mentioned rapid calibration device for the sampling rate of the tubular axial passive sampler for VOCs in ambient air, as a preferred embodiment, the passive sampling tube is filled with an adsorbent. One end of the passive sampling tube is provided with a sealing cap for sealing, and the other end is in an open state. Preferably, the adsorbent is granular. Preferably, the particle size of the adsorbent is 20-80 mesh (such as 40 mesh, 60 mesh, 80 mesh), and the mass of the adsorbent is 0.1-0.3g (such as 0.15g, 0.2g, 0.25g). Preferably, the adsorbent is one or more of Tenax TA, Carbopack B, Carbopack C, Carbopack X, and Tenax GR. Preferably, the diameter of the passive sampling tube is 1 / 4 inch and the length is 3.5 inches. The material of the passive sampling tube is stainless steel or glass. Preferably, the material of the sealing cap is brass. Preferably, the number of passive sampling tubes is 3-7 (such as 4, 5, 6).

[0011] In the present invention, Tenax TA refers to 2,6-diphenylfuran porous polymer resin; Carbopack B, Carbopack C, and Carbopack X refer to three graphitized carbon black adsorbents; Tenax GR is Tenax TA containing a certain amount of graphitized carbon black. The two are not simply mixed together, but are obtained by coprecipitation of graphitized carbon black and Tenax polymer. The passive sampling tube in the present invention is compatible with a thermal desorption instrument, that is, it can be directly installed at the corresponding position of the thermal desorption instrument for cleaning, aging, or gas thermal desorption.

[0012] In the above rapid calibration device for the sampling rate of a tubular axial passive sampler for VOCs in ambient air, as a preferred embodiment, the temperature and humidity meter is an instrument with electronic display of temperature value and humidity value at the same time. The temperature measurement range of the temperature and humidity meter is -50°C to +70°C, and the measurement accuracy is ±1°C. The humidity measurement range of the temperature and humidity meter is 10%RH to 99%RH, and the measurement accuracy is ±5%RH.

[0013] In the above rapid calibration device for the sampling rate of a tubular axial passive sampler for VOCs in ambient air, as a preferred embodiment, the active sampler includes an active sampling tube and a sampling pump. The sampling pump is connected to the gas bag through the active sampling tube; preferably, the inside of the active sampling tube is filled with an adsorbent, one end is connected to the sampling pump, and the other end is connected to the gas bag; preferably, the adsorbent is granular, and the type of adsorbent in the active sampling tube is the same as that in the passive sampling tube; preferably, the particle size of the adsorbent is 20 - 80 mesh (such as 40 mesh, 60 mesh, 80 mesh), and the mass of the adsorbent is 0.1 - 0.3 g (such as 0.15 g, 0.2 g, 0.25 g); preferably, the adsorbent is one or more of Tenax TA, Carbopack B, Carbopack C, Carbopack X, Tenax GR; preferably, the diameter of the active sampling tube is 1 / 4 inch and the length is 3.5 inches, and the material of the active sampling tube is stainless steel or glass.

[0014] The sampling pump in the present invention is a low-flow constant-speed sampling pump. The active sampling tube in the present invention can be the same as the passive sampling tube. After the active sampling tube is used, it can be detached and both ends are sealed with a sealing cap. The material of the sealing cap is preferably brass. After passive sampling, one end of the passive sampling tube in the open state is sealed with a sealing cap.

[0015] The second aspect of the present invention provides a rapid calibration method for the sampling rate of a tubular axial passive sampler for VOCs in ambient air. Sampling is carried out using the above calibration device, including the following steps:

[0016] (1) Use a thermal desorption instrument to clean and age the passive sampling tube and the active sampling tube. After the aging is completed, immediately seal both ends with a sealing cap and wrap both ends with tinfoil, and store them at 0 - 4°C.

[0017] (2) First, prepare a standard stock solution of VOCs (multiple volatile organic compounds), and then inject a certain volume of the VOCs standard stock solution into a gas collection bag containing 80% synthetic air or high-purity nitrogen with the maximum volume. Place it at 20 - 25°C for 1 - 2 h or at 60°C for 0.5 h, and mix well to obtain a VOCs standard mixed gas.

[0018] (3) First, separate the active sampler from the gas bag. Then, inject 80% synthetic air or high-purity nitrogen with the maximum volume into the gas bag by opening the valve. Then, inject a certain volume of the above VOCs standard mixed gas into the gas bag. After inflation, close the valve and connect the active sampler to the gas bag to start passive sampling. During the passive sampling process, use the active sampler to conduct active sampling at regular intervals, and record the temperature and relative humidity inside the gas bag at the same time. After the passive sampling is completed, immediately seal both ends with a sealing cap and wrap both ends with tinfoil, and store them at 0 - 4°C.

[0019] (4) Use a thermal desorption / gas chromatography - mass spectrometry instrument to analyze the mass of VOCs in the passive sampling tube and the active sampling tube in step (3).

[0020] (5) Calculate the sampling rate of the passive sampler using formula I:

[0021] R = Mp,i / (Ca,i × t × 60 × 10 -6 ) Formula I

[0022] where R is the sampling rate of the passive sampling tube for the i-th VOC, mL / min;

[0023] Mp,i is the mass of the i-th VOC sampled by the passive sampling tube, ng;

[0024] Ca,i is the concentration of the i-th VOC sampled by the active sampler, ng / m 3 ;

[0025] t is the time of passive sampling, h.

[0026] In the present invention, an active sampling method is used as a reference method to conduct a calibration experiment on the adsorption rate of passive sampling. The mass of VOCs in the active sampling tube is obtained by an instrument. By setting the active sampling time and active sampling rate, the active sampling volume can be obtained, and then the concentration Ca,i of the i-th VOC sampled by the active sampler can be obtained. Since the gas concentration in the gas bag is constant, the concentration Ca,i of the i-th VOC sampled by the active sampler is the same as the concentration of the i-th VOC sampled by the passive sampling tube. The mass of VOCs in the passive sampling tube is measured by the instrument, and the passive sampling time t and the concentration of the i-th VOC sampled by the passive sampling tube are known. Then, the sampling rate of the passive sampler is calculated by formula I.

[0027] The main purpose of using synthetic air or high-purity nitrogen in steps (2) and (3) of the present invention is to dilute the VOC standard gas mixture. The synthetic air is composed of 21% oxygen by volume and 79% nitrogen by volume, and the purity of the high-purity nitrogen is ≥99.99%.

[0028] In the above-mentioned rapid calibration method for the sampling rate of the tubular axial passive sampler for VOCs in ambient air, as a preferred embodiment, in step (1), the conditions for cleaning and aging are as follows: the aging temperature is 300°C - 400°C (such as 320°C, 350°C, 380°C), the aging flow rate is 30 - 50 mL / min (such as 35 mL / min, 40 mL / min, 45 mL / min), and the aging time is 15 - 60 min (such as 20 min, 30 min, 40 min, 50 min).

[0029] In the above-mentioned rapid calibration method for the sampling rate of the tubular axial passive sampler for VOCs in ambient air, as a preferred embodiment, step (3) can be replaced by: first, separate the active sampler from the gas bag, then directly inject the ambient air to be measured into the gas bag by opening the valve. After inflation, close the valve and connect the active sampler to the gas bag to start passive sampling. During the passive sampling process, use the active sampler to conduct active sampling at regular intervals, and record the temperature and relative humidity in the gas bag at the same time. After the passive sampling is completed, immediately seal both ends with a sealing cap and wrap both ends with tin foil, and store it at 0 - 4°C.

[0030] The present invention can also conduct a calibration test by directly opening the valve to inject the ambient air to be measured into the gas bag. Taking passive sampling for 24 hours as an example, after filling the ambient air to be measured, the concentration of VOCs in the gas bag needs to meet the requirements that benzene series and alkanes (C6 - C10) ≥ 1 μg / m 3 , and other pollutants ≥ 5 μg / m 3Calibration using the ambient air to be measured is more accurate. Calibration using the above-mentioned standard mixed gas can be carried out in the laboratory without carrying the device to the environment to be measured. When calibrating using the above-mentioned VOCs standard mixed gas, it is also necessary to ensure that the concentration of VOCs in the gas bag after filling the VOCs standard mixed gas meets the requirements: benzene series and alkanes (C6-C10) ≥ 1 μg / m 3 , other pollutants ≥ 5 μg / m 3 .

[0031] In the above rapid calibration method for the sampling rate of the VOCs tubular axial passive sampler in ambient air, as a preferred embodiment, in the step (2), the volume of the gas collection bag is 1 L, and the volume of the VOCs standard stock solution injected is 20 - 30 μL (such as 22 μL, 25 μL, 28 μL); preferably, the material of the gas collection bag is Teflon; preferably, the VOCs standard stock solution is one or more of benzene, n-heptane, toluene, ethylbenzene, m-xylene, p-xylene, n-nonane, o-xylene, n-decane, n-undecane, n-dodecane, naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol.

[0032] In the above rapid calibration method for the sampling rate of the VOCs tubular axial passive sampler in ambient air, as a preferred embodiment, in the step (3), the volume of the VOCs standard mixed gas injected into the gas bag is 1 - 5 ml; preferably, the passive sampling time is 8 h - 24 h (such as 10 h, 12 h, 15 h, 18 h, 20 h); preferably, the passive sampling time is 8 h; more preferably, the passive sampling time is 24 h; preferably, the active sampling time interval is 1 - 4 h, the active sampling rate is 10 - 100 mL / min (such as 30 mL / min, 50 mL / min, 70 mL / min, 90 mL / min), and the active sampling time for each time is 1 - 10 min (such as 2 min, 5 min, 7 min).

[0033] In the above rapid calibration method for the sampling rate of the tube axial passive sampler for VOCs in ambient air, as a preferred embodiment, in the step (4), the thermal desorption conditions are as follows: the dehumidification time of the sample tube is 2 min; the valve temperature is 225 °C; the transfer line temperature is 230 °C; the primary desorption temperature is 260 °C; the primary desorption time is 5 min; the cold trap temperature is -30 °C - 290 °C (heating rate 40 °C / s); the secondary desorption time is 2 min; the chromatographic conditions are as follows: an HP-VOC chromatographic column (60 m × 0.20 mm × 1.12 μm) is used; the carrier gas is high-purity He, the column flow rate is 1 mL / min, and the split ratio is 10:1; the initial column oven temperature is 45 °C, held for 2 min, heated to 120 °C at 8 °C / min and held for 5 min, then heated to 200 °C at 8 °C / min and held for 8 min, then heated to 250 °C at 10 °C / min and held for 8 min, then heated to 280 °C at 20 °C / min and held for 2 min; the mass spectrometry conditions are as follows: an electron impact ion source (EI), the electronization energy is 70 eV, the ion source temperature is 230 °C; the quadrupole temperature is 150 °C; the transfer line temperature is 280 °C; the scanning mode is full scan, and the scanning mass range is 50 - 450 amu.

[0034] Compared with the prior art, the present invention has the following remarkable effects:

[0035] (1) The present invention uses an air bag as the environmental chamber, which does not require complex pipeline connections, standard gas sources, and temperature and humidity control devices, making the production and operation simpler and the price lower.

[0036] (2) The rapid calibration device for the sampling rate of the passive sampler of the present invention has a simple assembly, is flexible, and can be used for on-site calibration tests in various indoor and outdoor environments and enclosed spaces. At the same time, the air bag used as the environmental chamber can be replaced at will, thus achieving zero cross-contamination and greatly shortening the equilibration time.

[0037] (3) The present invention preferably performs passive sampling tests for 8 h and 24 h. The results show that the passive sampling rate obtained by the rapid calibration device and calibration method of the present invention is suitable for the monitoring of VOCs in indoor and outdoor ambient air, and with the extension of the sampling time, the test results are more stable, having good application prospects. Description of the Drawings

[0038] Figure 1 is a schematic structural diagram of the rapid calibration device for the sampling rate of the tube axial passive sampler for VOCs in ambient air of the present invention;

[0039] Reference numerals in the drawings: 1, air bag; 11, valve; 2, passive sampling tube; 3, thermometer and hygrometer; 4, active sampler; 41, active sampling tube; 42, sampling pump. Detailed Embodiments

[0040] In order to make the technical solutions and advantages of the present invention clearer and more understandable, the following further details the exemplary embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than an exhaustive list of all embodiments, and without conflict, the embodiments in this description and the features in the embodiments can be combined with each other.

[0041] The present invention discloses a rapid calibration device for the sampling rate of a VOCs tube axial passive sampler in ambient air. As Figure 1 shown, the calibration device includes an air bag 1, a passive sampling tube 2, a temperature and humidity meter 3, and an active sampler 4. The passive sampling tube 2 and the temperature and humidity meter 3 are placed inside the air bag 1 to passively sample the gas inside the air bag 1 at a certain temperature and humidity; the active sampler 4 is located outside the air bag 1 and connected to the air bag 1 for actively collecting the gas inside the air bag 1; a valve 11 and a sealing strip adapted to the air bag 1 are provided on the air bag 1. Gas can be injected into or extracted from the air bag 1 by opening the valve 11, and the air bag 1 is sealed by pressing the sealing strip; the inside of the passive sampling tube 2 is filled with an adsorbent. One end of the passive sampling tube 2 is provided with a sealing cover for sealing, and the other end is in an open state; the adsorbent is granular, the particle size of the adsorbent is 20 - 80 mesh, and the mass is 0.1 - 0.3 g; the active sampler 4 includes an active sampling tube 41 and a sampling pump 42. The active sampling tube 41 is set to be the same as the passive sampling tube 2. The inside of the active sampling tube 41 is filled with an adsorbent, one end is communicated with the sampling pump 42, and the other end is communicated with the air bag 1. The adsorbent is granular, the particle size of the adsorbent is 20 - 80 mesh, and the mass of the adsorbent is 0.1 - 0.3 g; the sampling pump 42 is connected to the valve 11 on the air bag 1 through the active sampling tube 41, so that under the pressure of the sampling pump 42, gas can be extracted from the air bag 1 and then collected by the active sampling tube 41;

[0042] Specifically, the volume of the air bag 1 is 10 - 100 L; the material of the air bag 1 is polyvinyl fluoride (PVF), the material of the valve 11 is polytetrafluoroethylene (Teflon), and the sealing strip is an SNS sealing strip.

[0043] Specifically, the diameter of the passive sampling tube 2 is 1 / 4 inch, the length is 3.5 inches, and the material is stainless steel or glass; the adsorbent inside the passive sampling tube 2 is one or several of Tenax TA, Carbopack B, Carbopack C, Carbopack X, Tenax GR; the material of the sealing cover on the passive sampling tube 2 is brass. The passive sampling tube 2 is compatible with a thermal desorption instrument, that is, it can be directly installed in the corresponding position of the thermal desorption instrument for cleaning, aging, or gas thermal desorption. The passive sampling tube 2 is set to be 3 - 7. After passive sampling, the open end of the passive sampling tube 2 is sealed with a sealing cover.

[0044] Specifically, the thermometer-hygrometer 3 is an electronic display instrument for simultaneously displaying temperature and humidity values. The temperature measurement range of the thermometer-hygrometer 3 is -50°C to +70°C, and the measurement accuracy is ±1°C. The humidity measurement range of the thermometer-hygrometer 3 is 10%RH to 99%RH, and the measurement accuracy is ±5%RH.

[0045] Specifically, the diameter of the active sampling tube 41 is 1 / 4 inch, the length is 3.5 inches, and the material is stainless steel or glass; the adsorbent in the active sampling tube 41 is one or several of Tenax TA, Carbopack B, Carbopack C, Carbopack X, Tenax GR; after use, the active sampling tube 41 can be detached and both ends are sealed with a sealing cap. The material of the sealing cap is preferably brass. The active sampling tube 41 can be compatible with the thermal desorption instrument, that is, it can be directly installed at the corresponding position of the thermal desorption instrument for cleaning and aging or gas thermal desorption. The sampling pump 42 is a low-flow constant-flow sampling pump 42.

[0046] The present invention also provides a rapid calibration method for the sampling rate of a VOCs tubular axial passive sampler in ambient air. Sampling is carried out using the above calibration device, and the method includes the following steps:

[0047] (1) Use a thermal desorption instrument to clean and age the passive sampling tube 2 and the active sampling tube 41. The aging conditions are: the aging temperature is 300°C to 400°C, the aging flow rate is 30 - 50 mL / min, and the aging time is 15 - 60 min. After aging, immediately seal both ends with a sealing cap and wrap both ends with tinfoil, and store at 0 - 4°C;

[0048] (2) First, prepare a VOCs (multiple volatile organic substances) standard stock solution, and then inject 20 - 30 μL of the VOCs standard stock solution into a 1L Teflon gas collection bag containing up to 80% synthetic air (or high-purity nitrogen). Place it at 20 - 25°C for 1 - 2 h or at 60°C for 0.5 h, and mix well to obtain a VOCs standard mixed gas. The VOCs standard stock solution is one or more of benzene, n-heptane, toluene, ethylbenzene, m,p-xylene, n-nonane, o-xylene, n-decane, n-undecane, n-dodecane, naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol;

[0049] (3) First, separate the active sampler 4 from the gas bag 1. Then, inject 80% of the maximum volume of synthetic air or high-purity nitrogen into the gas bag 1 by opening the valve 11. Next, inject a certain volume of the above VOCs standard mixed gas into the gas bag 1 or directly open the valve 11 to inject a certain volume of the ambient air to be measured into the gas bag 1. Close the valve 11 and connect the active sampler 4 to the gas bag 1 to start passive sampling. During the passive sampling process, perform active sampling using the active sampler 4 at regular intervals, and record the temperature and relative humidity inside the gas bag simultaneously. After the passive sampling is completed, immediately seal both ends with a sealing cap and wrap both ends with tin foil, and store it at 0 - 4°C. The time interval for active sampling is 1 - 4 h, the active sampling rate is 10 - 100 mL / min, and the time for each active sampling is 1 - 10 min;

[0050] (4) Use a thermal desorption / gas chromatography - mass spectrometry instrument to analyze the mass of VOCs in the passive sampling tube 2 and the mass of VOCs in the active sampling tube 41 in step (3); among them, the thermal desorption conditions are: the sample tube dehumidification time is 2 min; the valve temperature is 225°C; the transfer line temperature is 230°C; the primary desorption temperature is 260°C; the primary desorption time is 5 min; the cold trap temperature is -30°C - 290°C (heating rate 40°C / s); the secondary desorption time is 2 min; the chromatographic conditions are: use an HP - VOC chromatographic column (60 m × 0.20 mm × 1.12 μm); the carrier gas is high-purity He, the column flow rate is 1 mL / min, and the split ratio is 10:1; the initial column oven temperature is 45°C, hold for 2 min, increase to 120°C at 8°C / min and hold for 5 min, then increase to 200°C at 8°C / min and hold for 8 min, then increase to 250°C at 10°C / min and hold for 8 min, then increase to 280°C at 20°C / min and hold for 2 min; the mass spectrometry conditions are: electron impact ionization source (EI), electronization energy 70 ev, ion source temperature 230°C; quadrupole temperature 150°C; transfer line temperature 280°C; the scanning mode is full scan, and the scanning mass range is 50 - 450 amu;

[0051] (5) Calculate the sampling rate of the passive sampler using formula I: R = Mp,i / (Ca,i × t × 60 × 10 -6 )(Formula I) where, R is the sampling rate of the passive sampling tube for the i-th VOC, mL / min; Mp,i is the mass of the i-th VOC obtained by sampling with the passive sampling tube, ng; Ca,i is the concentration of the i-th VOC obtained by sampling with the active sampler, ng / m 3 ; t is the time of passive sampling, h.

[0052] To further understand the content of the invention, the invention will be described in detail in combination with the embodiments.

[0053] Example 1

[0054] A rapid calibration device for the sampling rate of a tube axial passive sampler for VOCs in ambient air in this embodiment. The calibration device includes an air bag 1, a passive sampling tube 2, a temperature and humidity meter 3, and an active sampler 4. In this embodiment, the air bag 1 is a 20L PVF air bag (Tedlar), and the air bag 1 is equipped with a high-temperature resistant SNS sealing strip and a valve 11 made of polytetrafluoroethylene (Teflon). The diameter of the passive sampling tube 2 is 1 / 4 inch, the length is 3.5 inches, and the material is stainless steel. The inside of the passive sampling tube 2 is filled with 0.2g of granular Tenax TA adsorbent (Marks, UK), and the particle size of the adsorbent is 20-60 mesh. Four passive sampling tubes 2 are provided; the active sampler 4 includes an active sampling tube 41 and a low-flow constant flow sampling pump 42. The diameter of the active sampling tube 41 is 1 / 4 inch, the length is 3.5 inches, and the material is stainless steel. The inside of the active sampling tube 41 is filled with 0.2g of granular Tenax TA adsorbent (Marks, UK), and the particle size of the adsorbent is 20-60 mesh; when the calibration device is used, the passive sampling tube 2 and the temperature and humidity meter 3 are placed in the air bag 1. One end of the active sampling tube 41 is connected to the valve 11 of the air bag 1, and the other end is connected to the low-flow constant flow sampling pump 42.

[0055] A rapid calibration method for the sampling rate of a tube axial passive sampler for VOCs in ambient air in this embodiment is as follows:

[0056] (1) Use a thermal desorption instrument to clean and age the passive sampling tube 2 and the active sampling tube 41. The aging conditions are: the aging temperature is 350°C, the aging flow rate is 40 mL / min, and the aging time is 30 min. After aging, immediately seal both ends with a sealing cap and wrap both ends with tin foil, and store them in a refrigerator at 0-4°C.

[0057] (2) Use an electronic balance with a precision of one hundred-thousandth to weigh a certain mass of each substance and mix them to prepare a VOCs standard stock solution (details are shown in Table 1). The VOCs standard stock solution is a mixture of 15 substances including benzene, n-heptane, toluene, ethylbenzene, m,p-xylene, n-nonane, o-xylene, n-decane, n-undecane, n-dodecane, naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, 2,6-di-tert-butylphenol, and 2,6-di-tert-butyl-p-cresol; then, 793 mL of high-purity nitrogen is filled into a 1L Teflon gas collection bag, and 25 μL of the above VOCs standard stock solution is injected, and it is placed at 25°C for 2 h and mixed evenly to obtain a VOCs standard mixed gas.

[0058] (3) First, separate the active sampler 4 from the gas bag 1. Then, inject 15.8 L of high-purity nitrogen into the 20 L gas bag 1 by opening the valve 11. Next, inject 1 mL of the above VOCs standard mixture gas into the gas bag 1. Close the valve 11 and connect the active sampler 4 to the gas bag 1 to start passive sampling. Use the active sampler 4 to actively collect gas from the gas bag 1 through the valve 11 once every 2 h. The active sampling flow rate is 50 mL / min each time, and the active sampling time is 2 min. Calibrate the active sampling flow rate with a soap film meter before and after active sampling to ensure that the flow error during active sampling is less than 2%. At the same time, record the temperature and relative humidity inside the gas bag 1. The passive sampling time is 8 h. After the passive sampling is completed, immediately cover the sealing caps of the passive sampling tube 2 and the active sampling tube 41 and seal both ends with tin foil. Place it in a refrigerator and store it at 0 - 4 °C, and analyze it within 1 day.

[0059] (4) Use a thermal desorption / gas chromatography-mass spectrometry instrument to analyze the mass of VOCs in the passive sampling tube 2 and the mass of VOCs in the active sampling tube 41 in step (3). Among them, the thermal desorption conditions are: the sample tube dehumidification time is 2 min; the valve temperature is 225 °C; the transfer line temperature is 230 °C; the primary desorption temperature is 260 °C; the primary desorption time is 5 min; the cold trap temperature is -30 °C to 290 °C (heating rate 40 °C / s); the secondary desorption time is 2 min; the chromatographic conditions are: using an HP-VOC chromatographic column (60 m × 0.20 mm × 1.12 μm); the carrier gas is high-purity He, the column flow rate is 1 mL / min, and the split ratio is 10:1; the initial column oven temperature is 45 °C, hold for 2 min, rise to 120 °C at 8 °C / min and hold for 5 min, rise to 200 °C at 8 °C / min and hold for 8 min, rise to 250 °C at 10 °C / min, hold for 8 min, rise to 280 °C at 20 °C / min, and hold for 2 min; the mass spectrometry conditions are: electron impact ionization source (EI), electronization energy 70 ev, ion source temperature 230 °C; quadrupole temperature 150 °C; transfer line temperature 280 °C; the scanning mode is full scan. Qualify the 15 mixed standards using the retention time of GC and the mass spectrometry database. The scanning mass range is 50 - 450 amu, and external standard method is used for quantification.

[0060] (5) Calculate the sampling rate of the passive sampler using formula I: R = Mp,i / (Ca,i × t × 60 × 10 -6 )(Formula I) where, R is the sampling rate of the passive sampling tube for the i-th VOC, mL / min; Mp,i is the mass of the i-th VOC obtained by sampling with the passive sampling tube, ng; Ca,i is the concentration of the i-th VOC obtained by sampling with the active sampler, ng / m 3 ; t is the passive sampling time, h. (The calculation results are shown in Table 1)

[0061] Example 2

[0062] The rapid calibration device and method for the sampling rate of the VOCs tubular axial passive sampler in ambient air in this embodiment are the same as those in Embodiment 1, with the only difference being that the passive sampling time is 24 h. The passive sampling rates of various VOCs are calculated according to Equation I, as shown in Table 1.

[0063] Table 1

[0064]

[0065]

[0066]

[0067] The sampling rate of the passive sampler is the average of the calculation results of 4 passive sampling tubes. During passive sampling, the temperature change range in Embodiment 1 is 26.8 - 29.5 °C, and the humidity change range is 58% - 60%. In Embodiment 2, the temperature change range is 26.3 - 29.5 °C, and the humidity change range is 58% - 62%.

[0068] It can be seen from Table 1 that the 8 h passive adsorption rate range of 15 volatile organic compounds is 0.28 - 0.47 mL / min, and the relative standard deviation range is 1.46% - 12.25%. The 24 h passive adsorption rate range is 0.23 - 0.35 mL / min, and the relative standard deviation range is 1.14% - 8.94%. The calibration method of the present invention has good repeatability. Considering factors such as the instrument detection limit and the stability of pollutants in the gas bag, taking 24 h of passive sampling, the pollutant concentration in the gas bag meets benzene series and alkanes (C6 - C10) ≥ 1 μg / m 3 , and other pollutants ≥ 5 μg / m 3 , and this calibration method can be applied. If the passive sampling time is extended, the applicable concentration will be correspondingly lower.

[0069] Application: Using the passive sampling rate (Embodiment 2) obtained by the rapid calibration device and calibration method of the present invention, the ambient environment of a workplace was monitored and analyzed. Three passive sampling tubes were placed in parallel indoors for 24 h of sampling. At the same time, the active sampling method was used to collect samples once at the beginning and end of sampling. The active sampling rate was 50 mL / min, and each collection was for 10 min. During sampling, the active sampler was about 1.5 meters above the ground, away from pollution sources and air conditioning systems, and interference from personnel activities was avoided. The concentration level results of 15 volatile organic compounds obtained by the two methods are as follows in the table. The results show that there is no significant difference in the measurement results of the passive sampling and active sampling methods, indicating that the passive sampling rate obtained by the rapid calibration device and calibration method of the present invention is suitable for application in the actual on-site environment.

[0070]

[0071]

[0072] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A rapid calibration method for the sampling rate of a tube axial passive sampler for VOCs in ambient air, characterized in that, It is realized by a rapid calibration device for the sampling rate of a tubular axial passive sampler for VOCs in ambient air. The calibration device includes an air bag, a passive sampling tube, a temperature and humidity meter, and an active sampler. The passive sampling tube and the temperature and humidity meter are placed in the air bag to passively sample the gas in the air bag while monitoring the sampling temperature and humidity. The active sampler is located outside the air bag and connected to the air bag for actively collecting the gas in the air bag. The air bag is provided with a valve and a sealing strip adapted thereto. The valve is connected to the active sampler for communicating the air bag with the active sampler, and the sealing strip is used to open and seal the air bag. The inside of the passive sampling tube is filled with an adsorbent. One end of the passive sampling tube is provided with a sealing cap for sealing, and the other end is in an open state. The active sampler includes an active sampling tube and a sampling pump. The sampling pump is communicated with the air bag through the active sampling tube. The inside of the active sampling tube is filled with an adsorbent, one end is communicated with the sampling pump, and the other end is communicated with the air bag. The adsorbent in the active sampling tube is of the same type as the adsorbent in the passive sampling tube. The method includes the following steps: (1) Use a thermal desorption instrument to clean and age the passive sampling tube and the active sampling tube. After the aging is completed, immediately seal both ends with a sealing cap and wrap both ends with tin foil, and store them at 0 - 4 °C. (2) First, prepare a VOCs standard stock solution, and then inject a certain volume of the VOCs standard stock solution into a gas collection bag containing 80% synthetic air or high-purity nitrogen with the maximum volume. Place it at 20 - 25 °C for 1 - 2 h or at 60 °C for 0.5 h, and mix well to obtain a VOCs standard mixed gas. (3) First, separate the active sampler from the air bag, then inject 80% synthetic air or high-purity nitrogen with the maximum volume into the air bag by opening the valve, and then inject a certain volume of the VOCs standard mixed gas into the air bag. After inflation, close the valve and connect the active sampler to the air bag to start passive sampling. During the passive sampling process, use the active sampler to perform active sampling at regular intervals, and record the temperature and relative humidity in the air bag at the same time. After the passive sampling is completed, immediately seal both ends with a sealing cap and wrap both ends with tin foil, and store them at 0 - 4 °C. (4) Use a thermal desorption / gas chromatography-mass spectrometry instrument to analyze the mass of VOCs in the passive sampling tube and the active sampling tube in step (3). (5) Use the active sampling method as a reference method to conduct a calibration experiment on the passive sampling adsorption rate, and calculate the sampling rate of the passive sampler using formula I: R = Mp,i / (Ca,i×t×60×10 -6 ) Formula I Where, R is the sampling rate of the passive sampling tube for the i-th VOCs, mL / min; Mp,i is the mass of the i-th VOCs sampled by the passive sampling tube, ng; Ca,i is the concentration of the i-th VOCs sampled by the active sampler, ng / m 3 ; t is the passive sampling time, h.

2. The calibration method according to claim 1, wherein In the step (1), the conditions for the cleaning and aging are: the aging temperature is 300 °C - 400 °C, the aging flow rate is 30 - 50 mL / min, and the aging time is 15 - 60 min.

3. The calibration method according to claim 1, wherein In the step (2), the maximum volume of the gas collection bag is 1 L, and the volume of the VOCs standard stock solution injected is 20 - 30 μL; The material of the gas collection bag is Teflon.

4. The calibration method according to claim 1, wherein The VOCs standard stock solution is one or more of benzene, n-heptane, toluene, ethylbenzene, m,p-xylene, n-nonane, o-xylene, n-decane, n-undecane, n-dodecane, naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol.

5. The calibration method according to claim 1, wherein In the step (3), the volume of the VOCs standard mixed gas injected into the gas bag is 1 - 5 mL.

6. The calibration method according to claim 1, characterized in that, The passive sampling time is 8 h - 24 h.

7. The calibration method according to claim 6, characterized in that, The passive sampling time is 8 h.

8. The calibration method according to claim 6, wherein The passive sampling time is 24 h.

9. The calibration method according to claim 1, wherein The active sampling time interval is 1 - 4 h, the active sampling rate is 10 - 100 mL / min, and the active sampling time for each time is 1 - 10 min.

10. The calibration method according to any one of claims 1-9, characterized in that, In the step (4), the thermal desorption conditions are as follows: the sample tube dehumidification time is 2 min; the valve temperature is 225 °C; the transfer line temperature is 230 °C; the primary desorption temperature is 260 °C; the primary desorption time is 5 min; the cold trap temperature is -30 °C - 290 °C; the secondary desorption time is 2 min; the chromatographic conditions are as follows: using an HP-VOC chromatographic column; the carrier gas is high-purity He, the column flow rate is 1 mL / min, and the split ratio is 10:1; the initial column oven temperature is 45 °C, held for 2 min, then increased to 120 °C at 8 °C / min and held for 5 min, then increased to 200 °C at 8 °C / min and held for 8 min, then increased to 250 °C at 10 °C / min and held for 8 min, then increased to 280 °C at 20 °C / min and held for 2 min; the mass spectrometry conditions are as follows: electron impact ion source, electronization energy 70 eV, ion source temperature 230 °C; quadrupole temperature 150 °C; transfer line temperature 280 °C; the scanning mode is full scan, and the scanning mass range is 50 - 450 amu.

11. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device, the volume of the gas bag is 10 - 100 L.

12. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device, the operating temperature range of the gas bag is -20 °C - +110 °C.

13. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device, the material of the gas bag is polyvinyl fluoride, the material of the valve is polytetrafluoroethylene, and the sealing strip is an SNS sealing strip.

14. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device, the adsorbent is granular.

15. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device, the particle size of the adsorbent is 20 - 80 mesh, and the mass of the adsorbent is 0.1 - 0.3 g.

16. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device, the adsorbent is one or several of Tenax TA, Carbopack B, Carbopack C, Carbopack X, Tenax GR.

17. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device, the diameter of the passive sampling tube is 1 / 4 inch, the length is 3.5 inches, and the material of the passive sampling tube is stainless steel or glass.

18. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device, the material of the sealing cap is brass.

19. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device, the number of passive sampling tubes is 3 - 7.

20. The calibration method according to any one of claims 1-9, characterized in that, In the calibration device described above, the thermometer and hygrometer is an electronic display instrument that simultaneously displays temperature and humidity values. The temperature measurement range of the thermometer and hygrometer is -50°C to +70°C, and the measurement accuracy is ±1°C. The humidity measurement range of the thermometer and hygrometer is 10%RH to 99%RH, and the measurement accuracy is ±5%RH.

21. The calibration method according to any one of claims 1-9, characterized in that In the calibration device described above, the diameter of the active sampling tube is 1 / 4 inch, and the length is 3.5 inches. The material of the active sampling tube is stainless steel or glass.

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