A quantitative analysis method of tobacco medium polarity vocs

Abstract

The application discloses a quantitative analysis method of tobacco medium-polarity VOCs, which comprises the following steps: S1, inert gas is used to purge tobacco, and meanwhile, the tobacco is heated and sampled, so that the medium-polarity VOCs in the tobacco are collected; and S2, the medium-polarity VOCs in the tobacco are enriched by using MWCNTs-COOH / rGO, then, the medium-polarity VOCs are subjected to thermal desorption, and then, the medium-polarity VOCs are subjected to secondary enrichment and secondary analysis by using a cold trap, and finally, the medium-polarity VOCs are subjected to quantitative analysis by using GC-MS. When the MWCNTs-COOH / rGO is used as the adsorption medium of the thermal desorption of the purge and trap method, the flow rate, time and secondary enrichment temperature of the inert gas purging during the enrichment of the medium-polarity VOCs in the tobacco are simultaneously controlled, so that the quantitative analysis method of the medium-polarity VOCs in the tobacco is established. The enrichment effect of the medium-polarity VOCs in the tobacco is improved, and the accuracy of the quantitative analysis of the medium-polarity VOCs in the tobacco is also improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tobacco volatile organic compound analysis and detection, and particularly relates to a quantitative analysis method of medium-polarity VOCs in tobacco. BACKGROUND

[0002] Medium-polarity VOCs (volatile organic compounds) in tobacco are mainly esters, alcohols and ketones, which are extremely important components of tobacco volatile organic compounds and are also the key to improving the quality of tobacco smoke.

[0003] There are many quantitative analysis methods of volatile organic compounds. For example, a quantitative analysis method combining purge and trap (P&T) and gas chromatography-mass spectrometry (GC-MS) uses inert gas to purge the surface of the sample, and captures trace volatile organic compounds through a thermal desorption tube filled with solid enrichment medium, and then uses gas chromatography-mass spectrometry (GC-MS) to quantitatively analyze the captured volatile organic compounds. When this method is used to quantitatively analyze medium-polarity VOCs in tobacco, if multi-walled carbon nanotubes (MWCNTs) are selected as the enrichment medium filled in the thermal desorption tube of the purge and trap method, it is difficult to accurately quantitatively analyze the volatile organic compounds in tobacco, not to mention accurately quantitatively analyzing the medium-polarity VOCs in tobacco.

[0004] Therefore, it is of great significance to develop a method that can accurately quantitatively analyze medium-polarity VOCs in tobacco. SUMMARY

[0005] The purpose of the present application is to solve the problem of inaccurate quantitative analysis of medium-polarity VOCs in tobacco, and to provide a quantitative analysis method of medium-polarity VOCs in tobacco. MWCNTs-COOH / rGO synthesized by carboxylation of multi-walled carbon nanotubes (MWCNTs-COOH) and reduced graphene oxide (rGO) is used as the adsorption medium for thermal desorption of the purge and trap method, and GC-MS analysis is performed by matching the specific conditions of the purge and trap method (such as the flow rate, time of inert gas purge for enrichment of medium-polarity VOCs in tobacco, and secondary enrichment temperature, etc.), to achieve accurate quantitative analysis of medium-polarity VOCs in tobacco.

[0006] In order to achieve the above purpose, the technical solution adopted by the present application is:

[0007] A quantitative analysis method of medium-polarity VOCs in tobacco, comprising the following steps:

[0008] S1. Purge the tobacco with inert gas while heating and sampling to collect medium-polarity VOCs in tobacco;

[0009] S2. enriching the medium-polar VOCs in tobacco with MWCNTs-COOH / rGO, then performing thermal desorption, and then performing secondary enrichment and secondary analysis with a cold trap, and finally performing quantitative analysis with GC-MS;

[0010] In step S2, inert gas is used for purging when the MWCNTs-COOH / rGO enriches the medium-polar VOCs in tobacco, the flow rate of the inert gas purging is 0.3-0.9 L / min, and the time of the inert gas purging is 4-12 min.

[0011] In step S2, the temperature of the secondary enrichment is -30 to -90℃, the MWCNTs-COOH / rGO is prepared from carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and reduced graphene oxide (rGO), and the mass ratio of the carboxylated multi-walled carbon nanotubes and the reduced graphene oxide is 1:(0.2-10).

[0012] According to the principle of "like dissolves like", by adjusting the polarity of the enrichment medium to match the polarity of the medium-polar VOCs in tobacco, the enrichment capacity of the medium-polar VOCs in tobacco can be improved. Compared with the multi-walled carbon nanotubes (MWCNTs) alone, the MWCNTs-COOH / rGO synthesized from carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and reduced graphene oxide (rGO) has a more similar polarity to the medium-polar VOCs in tobacco, which is more conducive to enriching the medium-polar VOCs in tobacco. When the MWCNTs-COOH / rGO is used as the adsorption medium for thermal desorption in the purging and trapping method, by simultaneously adjusting the flow rate, time, and secondary enrichment temperature of the inert gas purging when enriching the medium-polar VOCs in tobacco, a quantitative analysis method for the medium-polar VOCs in tobacco is established, which not only improves the enrichment effect of the medium-polar VOCs in tobacco, but also improves the accuracy of the quantitative analysis of the medium-polar VOCs in tobacco.

[0013] Preferably, the medium-polar VOCs in tobacco include one or more of ethyl butyrate, hexanal, 2-methoxy pyrazine, nonanal, 2-ethylhexanol, methyl benzoate, acetophenone, 5-methyl furfural, ethyl phenyl acetate, methyl cyclopentenolone, 2-acetyl pyrrole, coumarin, or methyl heptenone.

[0014] Preferably, the thermal desorption temperature in step S2 is 200-325℃.

[0015] Preferably, the thermal desorption time in step S2 is 2-10 min.

[0016] Preferably, the secondary analysis temperature of the cold trap in step S2 is 200-320℃.

[0017] Preferably, the mass of the MWCNTs-COOH / rGO in step S2 is 0.01-0.05 g.

[0018] Preferably, the preparation method of the MWCNTs-COOH / rGO in step S2 is as follows: heating carboxylated multi-walled carbon nanotubes (MWCNTs-COOH), reduced graphene oxide (rGO), iron powder and hydrochloric acid in water, removing excess iron powder after the reaction, and obtaining MWCNTs-COOH / rGO.

[0019] Further preferably, the preparation method of the MWCNTs-COOH / rGO in step S2 is as follows: adding carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and reduced graphene oxide (rGO) into water, ultrasonicating, adding iron powder, stirring and slowly adding hydrochloric acid, stirring, heating and standing, adding concentrated hydrochloric acid to remove excess iron powder, suction filtering, washing with water and anhydrous ethanol alternately, and drying to obtain MWCNTs-COOH / rGO.

[0020] Further preferably, the hydrochloric acid is HCl with a mass fraction of 36%.

[0021] Preferably, the specific operation of step S2 is as follows:

[0022] (1) loading MWCNTs-COOH / rGO into a thermal desorption tube, filling dead glass wool at both ends of the thermal desorption tube, and aging to obtain a MWCNTs-COOH / rGO thermal desorption tube for standby use;

[0023] (2) sequentially connecting a gas sampling bag containing tobacco medium-polarity VOCs, the MWCNTs-COOH / rGO thermal desorption tube and a sampling pump, purging with inert gas at a flow rate of 0.3-0.9 L / min for 4-12 min to enrich tobacco medium-polarity VOCs, then inserting into a thermal desorption chamber for thermal desorption, and then using a cold trap at a temperature of -30 to -90℃ for secondary enrichment, followed by secondary analysis, and finally using GC-MS for quantitative analysis.

[0024] Preferably, the inert gas is nitrogen.

[0025] Preferably, the device structure used for sampling in step S1 is as follows: an inert gas source 1, a first gas guide pipe 2, a sample bottle 3, a vacuum valve 11, a second gas guide pipe 4, a diaphragm pump 5 and a gas sampling bag 6 are sequentially connected, and a water bath heating tank 7 and a magnetic stirrer 10 are further included; the sample bottle 3 is located in the water bath heating tank 7; the magnetic stirrer 10 includes a stirring rod 1001 and a base 1002 of the magnetic stirrer, the water bath heating tank 7 is located on the base 1002 of the magnetic stirrer, and the stirring rod 1001 is located in the inner cavity of the sample bottle 3.

[0026] The inventor found in multiple experiments that, compared with the existing purge and trap method sampling device, the quantitative analysis method of the present application can better improve the accuracy of quantitative analysis of medium polarity VOCs in tobacco after being used with the device (tobacco medium polarity VOCs purge and trap method sampling device) described in step S1.

[0027] Preferably, the specific operation of step S1 is:

[0028] (1) The tobacco is crushed, freeze-dried, placed in a sample bottle, and sealed for use;

[0029] (2) The tobacco in the sample bottle is purged with inert gas while stirring and heating, and the gas stream containing medium polarity VOCs in tobacco is collected in a gas sampling bag into which a medium polarity VOCs internal standard has been injected in advance, and is left to stand and shake evenly.

[0030] Further preferably, the medium polarity VOCs internal standard is cinnamaldehyde.

[0031] Further preferably, the ratio of the volume of the sample bottle to the maximum value of the mass of the tobacco is (30mL:1g)~(50mL:1g).

[0032] More preferably, the ratio of the volume of the sample bottle to the maximum value of the mass of the tobacco is 50mL:1g.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] When MWCNTs-COOH / rGO is used as the adsorption medium for purge and trap thermal desorption, by simultaneously regulating the flow rate, time of inert gas purging during enrichment of medium polarity VOCs in tobacco, and secondary enrichment temperature, a quantitative analysis method for medium polarity VOCs in tobacco is established, which not only improves the enrichment effect of medium polarity VOCs in tobacco, but also improves the accuracy of quantitative analysis of medium polarity VOCs in tobacco. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a structure diagram of a tobacco medium polarity VOCs enrichment device, in which: 6-Tedlar gas sampling bag, 8-MWCNTs-COOH / rGO thermal desorption tube, 9-sampling pump.

[0036] Figure 2The structure diagram of the sampling device for the purge and trap method of tobacco medium polarity VOCs is shown in the figure: 1-inert gas source, 2-first gas guide pipe, 3-sample bottle, 4-second gas guide pipe, 5-septum pump, 6-Tedlar gas sampling bag, 7-water bath heating tank, 10-magnetic stirrer, 1001-stirring rod, 1002-base of the magnetic stirrer, 11-vacuum valve.

[0037] Figure 3 The SEM graph of MWCNTs-COOH / rGO.

[0038] Figure 4 The thermogravimetric curve graph of MWCNTs-COOH / rGO.

[0039] Figure 5 The peak area statistical graph of tobacco medium polarity VOCs of Examples 1-4.

[0040] Figure 6 The peak area statistical graph of tobacco medium polarity VOCs of Examples 1, 5-7 and Comparative Example 1.

[0041] Figure 7 The peak area statistical graph of tobacco medium polarity VOCs of Examples 1, 8-11 and Comparative Example 2.

[0042] Figure 8 The peak area statistical graph of tobacco medium polarity VOCs of Examples 1, 12-14 and Comparative Example 3.

[0043] Figure 9 The peak area statistical graph of tobacco medium polarity VOCs of Examples 1 and 15-19.

[0044] Figure 10 The peak area statistical graph of tobacco medium polarity VOCs of Examples 1 and 20-23.

[0045] Figure 11 The peak area statistical graph of tobacco medium polarity VOCs of Examples 1 and 24-27.

[0046] Figure 12 The peak area statistical graph of tobacco medium polarity VOCs of Examples 1 and 28-31.

[0047] Figure 13 The peak area statistical graph of tobacco medium polarity VOCs of Examples 1 and Comparative Examples 4-5.

[0048] Figure 14Chromatograms of medium polarity VOCs in tobacco for Example 32 and its spiked experiment, wherein a is the chromatogram of medium polarity VOCs in tobacco of Example 32, b is the chromatogram of medium polarity VOCs in tobacco of Example 32 spiked experiment, and the spiked amount of the spiked experiment is: 1 200.0 ng / g ethyl butyrate, 2 200.0 ng / g hexanal, 3 200.0 ng / g 2-methoxypyrazine, 4 200.0 ng / g nonanal, 5 100.0 ng / g 2-ethylhexanol, 6 120.0 ng / g methyl benzoate, 7 80.0 ng / g acetophenone, 8 760.0 ng / g 5-methylfurfural, 9 200.0 ng / g ethyl phenylacetate, 10 320.0 ng / g methylcyclopentenolone, 11 200.0 ng / g 2-acetylpyrrole, 12 80.0 ng / g coumarin, and IS 1000.0 ng / g cinnamaldehyde. DETAILED DESCRIPTION

[0049] The present application is further illustrated by the following examples. These examples are intended to be illustrative only and are not intended to limit the scope of the present application. Unless otherwise indicated, the experimental procedures in the following example were carried out under conventional conditions or under conditions recommended by the manufacturer; the materials and reagents used were commercially available unless otherwise specified. Any non-essential changes and substitutions made by those skilled in the art based on the present application are within the scope of the present application.

[0050] In the detailed description of the application section:

[0051] Each example and comparative example was repeated at least 3 times;

[0052] The internal standard of medium polarity VOCs was cinnamaldehyde;

[0053] The tobacco was provided by Guangdong Tobacco Industry Co., Ltd.;

[0054] The inert gas was high-purity nitrogen;

[0055] The Tedlar gas sampling bag had a capacity of 20 L;

[0056] The conditions for GC-MS quantitative analysis were as follows:

[0057] Chromatographic column: DB-WAXetr (30 m x 0.25 mm x 0.25 μm, AGILENT Technologies, Palo Alto, CA, USA); carrier gas: high purity helium (purity > 99.999%); temperature program: 50 °C for 0.5 min, 20 °C / min to 95 °C for 3 min, 4 °C / min to 110 °C, 15 °C / min to 230 °C; transfer line temperature: 250 °C; ionization energy: 70 eV; ion source temperature: 250 °C; solvent delay time 3 min, analyzed in SIM mode.

[0058] Example 1

[0059] The present example provides a quantitative analysis method for tobacco medium polarity VOCs, comprising the following steps:

[0060] S1. Prepare a tobacco medium polarity VOCs standard solution with dichloromethane as the solvent, use a microsyringe to inject 40 μL of the tobacco medium polarity VOCs standard solution into a Tedlar gas sampling bag pre-injected with 40 μL of 1.0 x 10 2 ng / L of a medium polarity VOCs internal standard, and fill with N2. Equilibrate the volatilization at room temperature for 15 min, shake the Tedlar gas sampling bag to evenly distribute the gas inside the bag, and obtain a Tedlar gas sampling bag containing tobacco medium polarity VOCs standard gas;

[0061] S2. Specifically as follows:

[0062] (1) Load 0.03 g of MWCNTs-COOH / rGO into a thermal desorption tube, and fill the thermal desorption tube with deactivated glass wool at both ends. Heat and age at 250 °C for 6 h in the thermal desorption device, and pass 60 mL / min of inert gas during the entire aging process, thereby obtaining a MWCNTs-COOH / rGO thermal desorption tube, ready for use;

[0063] (2) Figure 1 The structure of the tobacco medium polarity VOCs enrichment device is shown in FIG. 1, which comprises a Tedlar gas sampling bag 6, a MWCNTs-COOH / rGO thermal desorption tube 8, and a sampling pump 9 connected in sequence.

[0064] As Figure 1As shown, Tedlar gas sampling bag, MWCNTs-COOH / rGO thermal desorption tube and sampling pump connected in turn were filled with tobacco medium polarity VOCs standard gas, and the tobacco medium polarity VOCs were enriched by blowing inert gas at a flow rate of 0.7 mL / min for 10 min, then inserted into the thermal desorption chamber, and then thermal desorption was carried out at an inert gas blowing flow rate of 30 mL / min and 300°C for 6 min, and then the cold trap was used for secondary enrichment at -70°C and secondary analysis at 290°C, and finally GC-MS quantitative analysis was carried out;

[0065] wherein:

[0066] The preparation method of the MWCNTs-COOH / rGO is as follows: 0.05 g of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and 0.05 g of reduced graphene oxide (rGO) are added to 100 mL of water, ultrasonic treatment is performed for 1 h to form a brown suspension, 3.0 g of iron powder is added, stirring is performed and 10 mL of 36% HCl is slowly added, stirring is performed at 200 rpm for 30 min, heating is performed at 50°C for 390 min, 200 rpm stirring is performed after adding concentrated hydrochloric acid for 5 min, the excess iron powder is removed after standing for 20 min of reaction, suction filtration is performed, and the product is washed with water and anhydrous ethanol alternately for 3 times, and vacuum drying is performed at 60°C for 12 h to obtain the MWCNTs-COOH / rGO, Figure 3 FIG. 3 is a SEM image of the MWCNTs-COOH / rGO, Figure 4 FIG. 4 is a thermogravimetric curve of the MWCNTs-COOH / rGO.

[0067] The tobacco medium polarity VOCs standard solution includes ethyl butyrate, hexanal, 2-methoxypyrazine, nonanal, 2-ethylhexanol, methyl benzoate, acetophenone, 5-methyl furfuryl alcohol, ethyl phenylacetate, methyl cyclopentenolone, 2-acetyl pyrrole and coumarin, each having a concentration of 50 mg / L;

[0068] In the tobacco medium polarity VOCs standard gas, ethyl butyrate, hexanal, 2-methoxypyrazine, nonanal, 2-ethylhexanol, methyl benzoate, acetophenone, 5-methyl furfuryl alcohol, ethyl phenylacetate, methyl cyclopentenolone, 2-acetyl pyrrole and coumarin each have a concentration of 1.0 x 10 2 ng / L.

[0069] Examples 2-4

[0070] Examples 2-4 provide different quantitative analysis methods for tobacco medium polarity VOCs, and the difference from Example 1 is only that the mass ratio of carboxylated multi-walled carbon nanotubes and reduced graphene oxide is different in the preparation of MWCNTs-COOH / rGO in step S2, and the rest is consistent with Example 1, as shown in Table 1:

[0071] Mass ratio of carboxylated multi-walled carbon nanotubes and reduced graphene oxide in step S2 of Table 1 Examples 1-4

[0072]

[0073] Examples 5-7 and Comparative Example 1

[0074] Examples 5-7 and Comparative Example 1 provide a different quantitative analysis method for tobacco medium polarity VOCs than Example 1, differing only in that the flow rate of inert gas purge while enriching for tobacco medium polarity VOCs in step S2 is different, with the rest being consistent with Example 1, as shown in Table 2:

[0075] Table 2 Flow rate of inert gas purge while enriching for tobacco medium polarity VOCs in step S2 of Examples 1, 5-7 and Comparative Example 1

[0076] Flow rate of inert gas purge (L / min) Example 1 0.7 Example 5 0.5 Example 6 0.3 Example 7 0.9 Comparative Example 1 0.1

[0077] Examples 8-11 and Comparative Example 2

[0078] Examples 8-11 and Comparative Example 2 provide a different quantitative analysis method for tobacco medium polarity VOCs than Example 1, differing only in that the time of inert gas purge while enriching for tobacco medium polarity VOCs in step S2 is different, with the rest being consistent with Example 1, as shown in Table 3:

[0079] Table 3 Time of inert gas purge while enriching for tobacco medium polarity VOCs in step S2 of Examples 1, 8-11 and Comparative Example 2

[0080] Time of inert gas purge (min) Example 1 10 Example 8 6 Example 9 8 Example 10 4 Example 11 12 Comparative Example 2 2

[0081] Examples 12-14 and Comparative Example 3

[0082] Examples 12-14 and Comparative Example 3 provide a different quantitative analysis method for tobacco medium polarity VOCs than Example 1, differing only in that the temperature of secondary enrichment in step S2 is different, with the rest being consistent with Example 1, as shown in Table 4:

[0083] Table 4 Temperature of secondary enrichment in step S2 of Examples 1, 12-14 and Comparative Example 3

[0084]

[0085]

[0086] Examples 15-19

[0087] Examples 15-19 provide different quantitative analysis methods of tobacco medium polarity VOCs, which are identical to Example 1 except that the thermal desorption temperature in step S2 is different, and the specific embodiments are shown in Table 5:

[0088] Table 5 Thermal desorption temperature in step S2 of Examples 1 and 15-19

[0089] Temperature of thermal desorption (°C) Example 1 300 Example 15 225 Example 16 250 Example 17 275 Example 18 200 Example 19 325

[0090] Examples 20-23

[0091] Examples 20-23 provide different quantitative analysis methods of tobacco medium polarity VOCs, which are identical to Example 1 except that the thermal desorption time in step S2 is different, and the specific embodiments are shown in Table 6:

[0092] Table 6 Thermal desorption time in step S2 of Examples 1 and 20-23

[0093] Time of thermal desorption (min) Example 1 6 Example 20 4 Example 21 2 Example 22 8 Example 23 10

[0094] Examples 24-27

[0095] Examples 24-27 provide different quantitative analysis methods of tobacco medium polarity VOCs, which are identical to Example 1 except that the secondary analysis temperature of the cold trap in step S2 is different, and the specific embodiments are shown in Table 7:

[0096] Table 7 Secondary analysis temperature of the cold trap in step S2 of Examples 1 and 24-27

[0097] Temperature of secondary resolution (°C) Example 1 290 Example 24 230 Example 25 260 Example 26 200 Example 27 320

[0098] Examples 28-31

[0099] Examples 28-31 provide different quantitative analysis methods of tobacco medium polarity VOCs, which are identical to Example 1 except that the mass of MWCNTs-COOH / rGO in step S2 is different, and the specific embodiments are shown in Table 8:

[0100] Table 8 Mass of MWCNTs-COOH / rGO in step S2 of Examples 1 and 28-31

[0101] Mass of MWCNTs-COOH / rGO (g) Example 1 0.03 Example 28 0.01 Example 29 0.02 Example 30 0.04 Example 31 0.05

[0102] Example 32

[0103] The present example provides a quantitative analysis method of tobacco medium polarity VOCs, comprising the following steps:

[0104] S1. Specifically as follows:

[0105] (1) Pulverize the tobacco (i.e. tobacco shreds) through a 20-mesh sieve, freeze-dry for 12 hours, thaw to room temperature, take 5g and put it into a 250mL sample bottle, and plug a small amount of deactivated glass wool at the outlet end of the sample bottle's airflow, and quickly seal the device for later use.

[0106] (2) Figure 2 This is a schematic diagram of a sampling device for the purge and trap method of medium polar VOCs in tobacco. It includes an inert gas source 1, a first gas delivery tube 2, a sample bottle 3, a vacuum valve 11, a second gas delivery tube 4, a diaphragm pump 5, and a gas sampling bag 6 connected in sequence. It also includes a water bath heating tank 7 and a magnetic stirrer 10. The sample bottle 3 is located inside the water bath heating tank 7. The magnetic stirrer 10 includes a stir bar 1001 and a base 1002. The water bath heating tank 7 is located on the base 1002 of the magnetic stirrer, and the stir bar 1001 is located inside the cavity of the sample bottle 3.

[0107] based on Figure 2 The assembled tobacco moderately polar VOCs purge and trap sampling device is shown. Using a diaphragm pump, tobacco in the sample vial is purged with inert gas at a flow rate of 5 L / min for 6 min, while simultaneously magnetically stirred and heated to 30°C. The gas stream containing moderately polar tobacco VOCs is collected in a container pre-injected with 40 μL of 1.0 × 10⁻⁶ mol / L gas. 2 Place the Tedlar gas sampling bag containing ng / L of medium polar VOCs internal standard, let stand for 15 minutes, and then shake the Tedlar gas sampling bag to make the gas distribution inside the bag uniform.

[0108] S2. Specifically as follows:

[0109] (1) 0.03g MWCNTs-COOH / rGO is loaded into the thermal desorption tube and deactivated glass wool is filled at both ends of the thermal desorption tube. The tube is heated and aged at 250℃ for 6h in the thermal desorption device. During the entire aging process, an inert gas of 60mL / min is passed through to obtain the MWCNTs-COOH / rGO thermal desorption tube for later use.

[0110] (2) Figure 1 As shown, a Tedlar gas sampling bag containing moderately polar VOCs from tobacco, a MWCNTs-COOH / rGO thermal desorption tube, and a sampling pump were connected sequentially. The moderately polar VOCs from tobacco were enriched by purging with inert gas at a flow rate of 0.7 mL / min for 10 min. Then, the thermal desorption chamber was inserted, and thermal desorption was performed for 6 min at an inert gas purging flow rate of 30 mL / min and 300 °C. The VOCs were then enriched again in a cold trap at -70 °C, followed by a second desorption at 290 °C. Finally, GC-MS quantitative analysis was performed.

[0111] in:

[0112] The preparation method of the MWCNTs-COOH / rGO is as follows: 0.05 g of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and 0.05 g of reduced graphene oxide (rGO) are added to 100 mL of water, ultrasonic treatment is performed for 1 h to form a brown suspension, 3.0 g of iron powder is added, stirring is performed and 10 mL of 36% HCl by mass fraction is slowly added, stirring is performed at 200 rpm for 30 min, heating is performed at 50°C for 390 min, 200 rpm stirring is performed after 5 min of addition of concentrated hydrochloric acid, 20 min of standing is performed to remove excess iron powder, suction filtration is performed, and the product is washed with water and anhydrous ethanol alternately for 3 times, and vacuum drying is performed at 60°C for 12 h, thereby obtaining the MWCNTs-COOH / rGO.

[0113] Example 33

[0114] The present example provides a quantitative analysis method for tobacco medium polarity VOCs, and two batches of a series of tobacco medium polarity VOCs standard gases with concentrations in the range of 2.0-1.5 x 10 3 ng / L are used for experiments, respectively, to measure the linear range and detection limit of different tobacco medium polarity VOCs (ethyl butyrate, hexanal, 2-methoxypyrazine, nonanal, 2-ethylhexanol, methyl benzoate, acetophenone, 5-methyl furfural, ethyl phenylacetate, methyl cyclopentenolone, 2-acetyl pyrrole and coumarin) in the quantitative analysis method of the present application, and 3 experiments (n=3) are repeatedly performed for each batch of a series of tobacco medium polarity VOCs standard gases, including the following steps:

[0115] S1. A series of different concentrations of tobacco medium polarity VOCs standard solutions are prepared with dichloromethane as a solvent, 40 μL of the tobacco medium polarity VOCs standard solution is removed by a microsyringe and injected into a Tedlar gas sampling bag in which 40 μL of 1.0 x 10 2 ng / L of a medium polarity VOCs internal standard has been injected in advance, and N2 is filled, and the volatile is balanced at room temperature for 15 min, the Tedlar gas sampling bag is shaken to make the gas in the bag evenly distributed, thereby obtaining a series of Tedlar gas sampling bags containing tobacco medium polarity VOCs standard gases with concentrations in the range of 2.0-1.5 x 10 3 ng / L;

[0116] S2. Specifically as follows:

[0117] (1) 0.03 g of MWCNTs-COOH / rGO is loaded into a thermal desorption tube, and deactivated glass wool is filled into both ends of the thermal desorption tube, and the thermal desorption tube is heated and aged at 250°C for 6 h in the thermal desorption device, and 60 mL / min of inert gas is passed through during the whole aging process, thereby obtaining the MWCNTs-COOH / rGO thermal desorption tube, which is ready for use;

[0118] (2) As shown in FIG. 2, Tedlar gas sampling bag, MWCNTs-COOH / rGO thermal desorption tube and sampling pump were connected in sequence, and the tobacco medium polarity VOCs standard gas was introduced into the Tedlar gas sampling bag. The tobacco medium polarity VOCs were enriched by blowing inert gas at a flow rate of 0.7 mL / min for 10 min, and then inserted into the thermal desorption chamber. The thermal desorption was performed at an inert gas blowing flow rate of 30 mL / min and 300°C for 6 min. The cold trap was used for secondary enrichment at -70°C and secondary analysis at 290°C, and finally the GC-MS quantitative analysis was performed. Figure 1

[0119] In the formula, R represents a C1-C6 alkyl group, and n represents an integer of 1-3.

[0120] The preparation method of the MWCNTs-COOH / rGO is as follows: 0.05 g of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and 0.05 g of reduced graphene oxide (rGO) are added to 100 mL of water, ultrasonic treatment is performed for 1 h to form a brown suspension, 3.0 g of iron powder is added, stirring is performed and 10 mL of 36% HCl is slowly added, stirring is performed at 200 rpm for 30 min, heating is performed at 50°C for 390 min, 200 rpm stirring is performed after 5 min of adding concentrated hydrochloric acid, 20 min of standing is performed to remove excess iron powder, suction filtration is performed, and the product is washed with water and anhydrous ethanol for 3 times, and vacuum drying is performed at 60°C for 12 h to obtain the MWCNTs-COOH / rGO.

[0121] In any one of the tobacco medium polarity VOCs standard gases, the concentrations of ethyl butyrate, hexanal, 2-methoxypyrazine, nonanal, 2-ethylhexanol, methyl benzoate, acetophenone, 5-methyl furfural, ethyl phenylacetate, methyl cyclopentenolone, 2-acetyl pyrrole and coumarin are the same, and are in the range of 2.0-1.5×10 3 ng / L.

[0122] Example 34

[0123] The difference between the quantitative analysis method of the tobacco medium polarity VOCs of the present embodiment and that of Example 1 is only that the tobacco medium polarity VOCs standard solution and the tobacco medium polarity VOCs standard gas are different, and the rest is the same as that of Example 1, and the specific process is as follows:

[0124] The tobacco medium polarity VOCs standard solution of the present embodiment includes ethyl butyrate, hexanal, methyl heptenone, 2-methoxypyrazine, nonanal, methyl benzoate, acetophenone, ethyl phenylacetate, 2-acetyl pyrrole and coumarin, all with a concentration of 50 mg / L.

[0125] In the tobacco medium polarity VOCs standard gas of the present embodiment, ethyl butyrate, hexanal, methyl heptenone, 2-methoxypyrazine, nonanal, methyl benzoate, acetophenone, ethyl phenylacetate, 2-acetyl pyrrole and coumarin are included, all with a concentration of 1.0×10 2 ​ethyl butanoate, hexanal, methyl heptenone, 2-methoxy pyrazine, nonanal, methyl benzoate, acetophenone, ethyl phenyl acetate, 2-acetyl pyrrole, and coumarin.

[0126] Comparative Example 4

[0127] Comparative Example 4 provides a quantitative analysis method of tobacco medium polarity VOCs, which is identical to Example 34 except that MWCNTs-NH2 / rGO is used instead of MWCNTs-COOH / rGO, and the preparation method of the MWCNTs-NH2 / rGO is as follows: 0.05 g of amino-functionalized multi-walled carbon nanotubes (MWCNTs-NH2) and 0.05 g of reduced graphene oxide (rGO) are added to 100 mL of water, ultrasonic treatment is performed for 1 h to form a brown suspension, 3.0 g of iron powder is added, stirring is performed and 10 mL of 36% by mass HCl is slowly added, stirring is performed at 200 rpm for 30 min, heating is performed at 50°C and the mixture is left to stand for 390 min, 200 rpm stirring is performed for 5 min after the addition of concentrated hydrochloric acid, the mixture is left to stand for 20 min to remove excess iron powder, suction filtration is performed, and the mixture is washed with water and anhydrous ethanol alternately for 3 times, vacuum drying is performed at 60°C for 12 h, and MWCNTs-NH2 / rGO is obtained.

[0128] Comparative Example 5

[0129] Comparative Example 5 provides a quantitative analysis method of tobacco medium polarity VOCs, which is identical to Example 34 except that MWCNTs / rGO is used instead of MWCNTs-COOH / rGO, and the preparation method of the MWCNTs / rGO is as follows: 0.05 g of multi-walled carbon nanotubes (MWCNTs) and 0.05 g of reduced graphene oxide (rGO) are added to 100 mL of water, ultrasonic treatment is performed for 1 h to form a brown suspension, 3.0 g of iron powder is added, stirring is performed and 10 mL of 36% by mass HCl is slowly added, stirring is performed at 200 rpm for 30 min, heating is performed at 50°C and the mixture is left to stand for 390 min, 200 rpm stirring is performed for 5 min after the addition of concentrated hydrochloric acid, the mixture is left to stand for 20 min to remove excess iron powder, suction filtration is performed, and the mixture is washed with water and anhydrous ethanol alternately for 3 times, vacuum drying is performed at 60°C for 12 h, and MWCNTs / rGO is obtained.

[0130] Sample Characterization

[0131] Figure 3 SEM image of MWCNTs-COOH / rGO. From the Figure 3It can be seen that the MWCNTs-COOH / rGO has a loose layered structure, and the carboxylated multi-walled carbon nanotubes are uniformly doped therein. The thin two-dimensional MWCNTs-COOH / rGO layer is bent and folded to form a thermodynamically stable porous three-dimensional particle, which is beneficial to increase the specific surface area of the MWCNTs-COOH / rGO and improve the enrichment capacity of the MWCNTs-COOH / rGO for the tobacco medium-polarity VOCs.

[0132] Figure 4 The figure is a thermogravimetric curve of the MWCNTs-COOH / rGO. It can be seen that the weight loss rate of the MWCNTs-COOH / rGO is less than 9% within 800°C, and the thermal stability is strong, which is sufficient to adapt to the thermal desorption working environment 200-325°C of the adsorption medium of the present application. Figure 4

[0133] Performance test

[0134] 1. Experimental results of the quantitative analysis method for the tobacco medium-polarity VOCs of each example and comparative example

[0135] Figure 5 The figure is a peak area statistical diagram of the tobacco medium-polarity VOCs of Examples 1-4. It can be seen that by adjusting the mass ratio of the carboxylated multi-walled carbon nanotubes and the reduced graphene oxide, the polarity of the MWCNTs-COOH / rGO can be controlled, so that the polarity of the MWCNTs-COOH / rGO is more similar to the polarity of the tobacco medium-polarity VOCs, which is more conducive to the enrichment of the tobacco medium-polarity VOCs, thereby improving the accuracy of the quantitative analysis of the tobacco medium-polarity VOCs. When the mass ratio of the carboxylated multi-walled carbon nanotubes and the reduced graphene oxide is 1:1, the enrichment effect of the MWCNTs-COOH / rGO on the tobacco medium-polarity VOCs is the best. Figure 5

[0136] The figure is a peak area statistical diagram of the tobacco medium-polarity VOCs of Examples 1, 5-7 and Comparative Example 1. It can be seen that when the flow rate of the inert gas blowing during the enrichment of the tobacco medium-polarity VOCs in step S2 is within the range of 0.3-0.9 L / min, the peak area of each tobacco medium-polarity VOCs of the quantitative analysis method for the tobacco medium-polarity VOCs is large, which is beneficial to improve the accuracy of the quantitative analysis method for the tobacco medium-polarity VOCs of the present application. When the flow rate of the inert gas blowing during the enrichment of the tobacco medium-polarity VOCs in step S2 is too low (0.1 L / min), the tobacco medium-polarity VOCs cannot be sufficiently collected, which leads to a large loss of the tobacco medium-polarity VOCs, and is not conducive to improving the accuracy of the quantitative analysis method for the tobacco medium-polarity VOCs of the present application. Figure 6 Figure 6

[0137] Figure 7 ​​​The tobacco medium polarity VOCs peak area statistics chart of Example 1, 8-11 and Comparative Example 2. From Figure 7 It can be seen that when the inert gas purging time for enriching the tobacco medium polarity VOCs in step S2 is in the range of 4-12 min, the peak area of various tobacco medium polarity VOCs of the tobacco medium polarity VOCs quantitative analysis method is large, which is beneficial to improve the accuracy of the tobacco medium polarity VOCs quantitative analysis method of the present application; while when the inert gas purging time for enriching the tobacco medium polarity VOCs in step S2 is too low (2 min), the tobacco medium polarity VOCs cannot be sufficiently collected, resulting in too large loss of the tobacco medium polarity VOCs, which is not conducive to improve the accuracy of the tobacco medium polarity VOCs quantitative analysis method of the present application.

[0138] Figure 8 The tobacco medium polarity VOCs peak area statistics chart of Example 1, 12-14 and Comparative Example 3. From Figure 8 It can be seen that when the temperature of the secondary enrichment in step S2 is in the range of -30 to -90℃, the peak area of various tobacco medium polarity VOCs of the tobacco medium polarity VOCs quantitative analysis method is large, which is beneficial to improve the accuracy of the tobacco medium polarity VOCs quantitative analysis method of the present application; while when the temperature of the secondary enrichment in step S2 is too high (-10℃), the tobacco medium polarity VOCs are not easy to be cold focused and enriched on the cold trap, which is not conducive to improve the accuracy of the tobacco medium polarity VOCs quantitative analysis method of the present application.

[0139] Figure 9 The tobacco medium polarity VOCs peak area statistics chart of Example 1 and 15-19. From Figure 9 It can be seen that when the temperature of the thermal desorption in step S2 is in the range of 200-325℃, the peak area of various tobacco medium polarity VOCs of the tobacco medium polarity VOCs quantitative analysis method is large, which is beneficial to improve the accuracy of the tobacco medium polarity VOCs quantitative analysis method of the present application, especially when the thermal desorption temperature is 300℃, the accuracy is the highest.

[0140] Figure 10 The tobacco medium polarity VOCs peak area statistics chart of Example 1 and 20-23. From Figure 10 It can be seen that when the thermal desorption time in step S2 is in the range of 2-10 min, the peak area of various tobacco medium polarity VOCs of the tobacco medium polarity VOCs quantitative analysis method is large, which is beneficial to improve the accuracy of the tobacco medium polarity VOCs quantitative analysis method of the present application, especially when the thermal desorption temperature is 6 min, the accuracy is the highest.

[0141] Figure 11 The tobacco medium polarity VOCs peak area statistics chart of Example 1 and 24-27. From Figure 11It can be seen that when the secondary desorption temperature of the cold trap in step S2 is in the range of 200 to 320°C, the peak areas of various tobacco medium polar VOCs in the quantitative analysis method of tobacco medium polar VOCs are larger, which is beneficial to improving the accuracy of the quantitative analysis method of tobacco medium polar VOCs of the present invention. In particular, the accuracy is highest when the thermal desorption temperature is 290°C.

[0142] Figure 12 This is a statistical chart of the peak areas of moderately polar VOCs in tobacco from Examples 1 and 28-31. From... Figure 12 It can be seen that when the mass of MWCNTs-COOH / rGO in step S2 is in the range of 0.01 to 0.05 mg, the peak areas of various tobacco medium polar VOCs in the quantitative analysis method of tobacco medium polar VOCs are larger, which is beneficial to improving the accuracy of the quantitative analysis method of tobacco medium polar VOCs of the present invention.

[0143] Figure 13 This is a statistical chart of the peak area of ​​moderately polar VOCs in tobacco from Examples 34 and Comparative Examples 4-5. Figure 13 It can be seen that when MWCNTs-COOH / rGO was selected as the adsorption medium for thermal desorption by the purge and trap method in Example 34, the peak area of ​​most of the moderately polar VOCs in tobacco was larger than that of Comparative Example 4 and Comparative Example 5, which selected MWCNTs-NH2 / rGO. This indicates that compared with MWCNTs-NH2 / rGO and MWCNTs / rGO, the polarity of MWCNTs-COOH / rGO is more similar to that of moderately polar VOCs in tobacco, which is more conducive to enriching moderately polar VOCs in tobacco and improving the accuracy of the quantitative analysis method for moderately polar VOCs in tobacco of the present invention.

[0144] 2. Sensitivity and accuracy of quantitative analysis methods for moderately polar VOCs in tobacco

[0145] (1) Sensitivity of quantitative analysis methods for moderately polar VOCs in tobacco

[0146] Example 33: Two batches of a series of concentrations ranging from 2.0 to 1.5 × 10⁻⁶. 3 Experiments were conducted using standard gases of moderately polar VOCs from tobacco within the ng / L range to measure the linear range and detection limit of different moderately polar VOCs from tobacco in the quantitative analysis method of this invention. The experiment was repeated three times (n=3), and the experimental results are shown in the table below:

[0147] Table 9. Quantitative analysis results of Example 33 on moderately polar VOCs in different tobaccos.

[0148]

[0149]

[0150] From Table 9, it can be seen that the quantitative analysis method of the tobacco medium-polarity VOCs of the present application has a linear range of 2.0-1.5 x 10 3 ng / L, and the RSD is 2.1-16.3% when the experiment is repeated for 3 times, indicating that the quantitative analysis method of the present application meets the quantitative analysis of the tobacco medium-polarity VOCs and has high sensitivity.

[0151] (2) Accuracy of the quantitative analysis method of the tobacco medium-polarity VOCs

[0152] The quantitative analysis of the different tobacco medium-polarity VOCs was performed on the tobacco sample of Example 32, and the quantitative analysis method of Example 32 was referenced to perform the standard addition experiment; in the standard addition experiment, the corresponding standard addition solution should be injected into the Tedlar gas sampling bag together with the medium-polarity VOCs internal standard; the experimental results are shown in the following table:

[0153] Table 10 Determination of the content of the tobacco medium-polarity VOCs of Example 32 and the results of the standard addition experiment

[0154]

[0155]

[0156] Note: " / " in the table indicates not detected.

[0157] From Table 10, it can be seen that the content of 12 kinds of tobacco medium-polarity VOCs in the tobacco sample measured by the quantitative analysis method of the tobacco medium-polarity VOCs of the present application is 32.1-1530.0 ng / g; the recovery rate of the standard addition experiment is 72.1-128.7%, and the RSD is 2.4-19.4% when the experiment is repeated for 3 times; it is indicated that the quantitative analysis method of the tobacco medium-polarity VOCs of the present application has high accuracy.

[0158] Figure 14Chromatograms of medium polarity VOCs in tobacco for Example 32 and its spiked experiment, wherein a is the chromatogram of medium polarity VOCs in tobacco of Example 32, b is the chromatogram of medium polarity VOCs in tobacco of Example 32 spiked experiment, and the spiked amounts of spiked experiment are as follows: 1 is 200.0 ng / g ethyl butyrate, 2 is 200.0 ng / g hexanal, 3 is 200.0 ng / g 2-methoxypyrazine, 4 is 200.0 ng / g nonanal, 5 is 100.0 ng / g 2-ethylhexanol, 6 is 120.0 ng / g methyl benzoate, 7 is 80.0 ng / g acetophenone, 8 is 760.0 ng / g 5-methylfurfural, 9 is 200.0 ng / g ethyl phenylacetate, 10 is 320.0 ng / g methyl cyclopentenolone, 11 is 200.0 ng / g 2-acetyl pyrrole, 12 is 80.0 ng / g coumarin, and IS is 1000.0 ng / g cinnamaldehyde.

[0159] Obviously, the above-mentioned embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. All the embodiments are not required to be enumerated. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for the quantitative analysis of tobacco medium polarity VOCs, characterized in that, The method comprises the following steps: S1. Tobacco is purged with inert gas while being heated and sampled to collect medium-polarity VOCs in the tobacco; S2. The medium-polarity VOCs in the tobacco are enriched by MWCNTs-COOH / rGO, and then subjected to thermal desorption, secondary enrichment by a cold trap, secondary analysis by the cold trap, and finally quantitative analysis by GC-MS; In step S2, the MWCNTs-COOH / rGO is purged with inert gas when enriching the medium-polarity VOCs in the tobacco, the flow rate of the inert gas is 0.7-0.9 L / min, and the purging time of the inert gas is 8-10 min; In step S2, the temperature for the secondary enrichment is -70℃, the MWCNTs-COOH / rGO is prepared by reacting carboxylated multi-walled carbon nanotubes and reduced graphene oxide, and the mass ratio of the carboxylated multi-walled carbon nanotubes to the reduced graphene oxide is 1:1; In step S2, the thermal desorption temperature is 250-300℃; In step S2, the thermal desorption time is 4-6 min; In step S2, the secondary analysis temperature of the cold trap is 290℃; In step S2, the mass of the MWCNTs-COOH / rGO is 10-30 mg; In step S1, the device structure used for sampling is as follows, comprising an inert gas source (1), a first gas guide pipe (2), a sample bottle (3), a vacuum valve (11), a second gas guide pipe (4), a diaphragm pump (5), and a gas sampling bag (6) which are sequentially connected, and further comprising a water bath heating tank (7) and a magnetic stirrer (10); the sample bottle (3) is located in the water bath heating tank (7); the magnetic stirrer (10) comprises a stirring rod (1001) and a base (1002) of the magnetic stirrer, the water bath heating tank (7) is located on the base (1002) of the magnetic stirrer, and the stirring rod (1001) is located in the inner cavity of the sample bottle (3).

2. The method of claim 1, wherein, The medium-polarity VOCs in the tobacco include one or more of ethyl butyrate, hexanal, 2-methoxypyrazine, nonanal, 2-ethylhexanol, methyl benzoate, acetophenone, 5-methylfurfural, ethyl phenylacetate, methylcyclopentenolone, 2-acetylpyrrole, coumarin, or methylheptenone.

3. The quantitative analysis method according to claim 1, characterized in that, In step S2, the MWCNTs-COOH / rGO is prepared by heating carboxylated multi-walled carbon nanotubes, reduced graphene oxide, iron powder, and hydrochloric acid in water, and then removing the excess iron powder.

4. The quantitative analysis method according to claim 3, characterized in that, The hydrochloric acid is HCl with a mass fraction of 36%.

5. The method of claim 1, wherein the step of determining the concentration of the target substance is performed by using a calibration curve. The specific operation of step S1 is as follows: (1) The tobacco is crushed, freeze-dried, placed in a sample bottle, and sealed for standby; (2) The tobacco in the sample bottle is purged with inert gas while being stirred and heated, and the gas stream containing the medium-polarity VOCs in the tobacco is collected in a gas sampling bag into which a medium-polarity VOCs internal standard has been injected in advance, and then the gas sampling bag is left to stand and shaken evenly.

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