A method for detecting benzene series in water based on purge and trap-gas chromatography

Abstract

The invention discloses a method for detecting benzene series in water based on purge and trap gas chromatography, which belongs to the field of water quality detection technology. The specific method includes subjecting a water sample to be tested to sedimentation centrifugation treatment, taking the supernatant for purge and trap gas chromatography detection, and using modified carbon nanotubes as the adsorbent used in the purge and trap. In the preparation of the modified carbon nanotubes, 4-methoxy-3-butene-2-one and 2-ethyleneoxytetrahydropyran are first polymerized, and then reacted with carbon nanotubes to obtain modified carbon nanotubes. The method for detecting benzene series in water based on purge and trap gas chromatography provided by the present invention has high precision and high accuracy and can be widely used in the detection of benzene series in water samples.

Description

Technical Field

[0001] The present invention relates to the technical field of water quality detection, and in particular to a method for detecting benzene series compounds in water based on a purge and trap-gas chromatography method. Background Art

[0002] Benzene series, a class of organic pollutants with significant toxicity and environmental hazards, not only pose a serious threat to human health but also cause persistent pollution to the ecological environment. Due to their hazardous nature, benzene series have been included in the core control indicators of multiple environmental standards. Currently, the detection of benzene series in water primarily relies on gas chromatography and gas chromatography-mass spectrometry, combined with pretreatment techniques such as purge and trap or headspace analysis. Purge and trap gas chromatography, due to its ease of operation, high sensitivity, and relatively low equipment cost, is widely used in grassroots laboratories such as environmental monitoring stations at all levels.

[0003] However, when applying the current industry standard, "Purge and Trap / Gas Chromatography Method for the Determination of Volatile Organic Compounds in Water" (HJ 686-2014), for the detection of BTEX, it has been found that if standard intermediate solutions and working solutions are prepared strictly according to this standard method, significant methanol peak tailing will occur. This interference seriously affects the accurate quantification of benzene. This problem can lead to biased test results, further affecting the accurate assessment of BTEX contamination in environmental water quality, and poses technical challenges in actual detection. Therefore, there is an urgent need to develop an improved purge and trap-gas chromatography detection method to ensure the accuracy and reliability of test data. Summary of the Invention

[0004] The object of the present invention is to provide a method for detecting benzene series compounds in water based on purge and trap-gas chromatography, so as to improve the precision and accuracy of detecting benzene series compounds in water.

[0005] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are:

[0006] A method for detecting benzene series in water based on purge and trap-gas chromatography comprises: subjecting a water sample to sedimentation and centrifugation, and taking the supernatant for purge and trap-gas chromatography detection; the adsorbent used in the purge and trap is carbon nanotubes; the purge flow rate of the purge and trap is 30-50 mL / min, and the purge time is 5-15 min.

[0007] The present invention uses pure water to gradually dilute a BTEX standard solution in methanol to prepare a BTEX standard intermediate solution and a working solution, thereby reducing the amount of methanol introduced, separating methanol from benzene, and improving the accuracy of benzene determination. In addition, by optimizing the experimental conditions of purge and trap-gas chromatography, the method detection limit is reduced, which is more conducive to the determination of low-concentration BTEX samples.

[0008] Preferably, the adsorbent is carbon nanotubes and / or modified carbon nanotubes.

[0009] More preferably, in the preparation of the modified carbon nanotubes, 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran are first polymerized in the presence of azobisisobutyronitrile, and then subjected to high-temperature treatment and carbonization with carbon nanotubes, potassium chloride, and phenolic resin to obtain the modified carbon nanotubes. The present invention first polymerizes 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran before modifying the carbon nanotubes. This may significantly increase the number of adsorption active sites in the carbon nanotubes, thereby enhancing their ability to adsorb and enrich benzene series compounds, effectively reducing the detection limit and relative standard deviation of the method, while significantly improving the average recovery rate of benzene series compounds.

[0010] More preferably, the mass ratio of azobisisobutyronitrile to 4-methoxy-3-butene-2-one is 1:1-5.

[0011] More preferably, the mass ratio of azobisisobutyronitrile to 2-vinyloxytetrahydropyran is 1:3-5.

[0012] More preferably, the mass ratio of azobisisobutyronitrile to carbon nanotubes is 1:5-20.

[0013] More preferably, the mass ratio of carbon nanotubes to potassium chloride is 1:1-5.

[0014] More preferably, the mass ratio of the carbon nanotubes to the phenolic resin is 1:1-2.

[0015] More preferably, the temperature of the high temperature treatment is 140-160°C.

[0016] More preferably, the high temperature treatment time is 8-12 hours.

[0017] Preferably, a method for detecting benzene series in water based on purge and trap-gas chromatography is specifically,

[0018] The water sample to be tested was subjected to sedimentation and centrifugation, and the supernatant was collected and tested for benzene series using a purge and trap instrument and gas chromatograph. The adsorbent in the purge and trap instrument was carbon nanotubes or modified carbon nanotubes. The purge and trap parameters were set as follows: purge temperature of 20-30°C, purge time of 5-15 minutes, dry sweep time of 3-5 minutes, baking temperature of 220-260°C, baking time of 5-10 minutes, desorption time of 1-2 minutes, desorption temperature of 180-220°C, stripping gas of nitrogen, and purge flow rate of 30-50 mL / min. The gas chromatography parameters were set as follows: injection port temperature of 180-220°C, detector temperature of 250-300°C, carrier gas flow rate of 1-3 mL / min, and the heating program was initially 40-50°C for 5-10 min, then heated to 90-110°C at 5-10°C / min for 1-2 min, and then heated to 150-200°C at 5-10°C / min.

[0019] More preferably, the preparation of modified carbon nanotubes is specifically as follows:

[0020] Under a nitrogen atmosphere, the alkenyl unit is dissolved in dimethyl carbonate, azobisisobutyronitrile is added and the mixture is reacted at 60-80°C for 8-24 hours. After the reaction, methyl tert-butyl ether is slowly added dropwise for precipitation, the solid is retained by centrifugation, carbon nanotubes, potassium chloride and phenolic resin are added, vacuum dried for 12-24 hours, treated at 140-160°C for 8-12 hours, then heated to 800-1000°C at a rate of 2-5°C / min and maintained for 1-2 hours. After the treatment, the mixture is naturally cooled to room temperature and ground to obtain modified carbon nanotubes.

[0021] More preferably, the alkenyl unit comprises at least one of 4-methoxy-3-butene-2-one, 2-vinyloxytetrahydropyran, and 2-(2-methoxyethoxy)ethyl 2-methyl-2-acrylate. The present invention further utilizes 2-(2-methoxyethoxy)ethyl 2-methyl-2-acrylate to optimize adsorption sites on the carbon nanotube surface and the interaction between the adsorbent and the analyte, thereby effectively reducing the detection limit and relative standard deviation of the method while significantly improving the average recovery rate of benzene series.

[0022] More preferably, the mass ratio of azobisisobutyronitrile to 4-methoxy-3-butene-2-one is 1:1-5.

[0023] More preferably, the mass ratio of azobisisobutyronitrile to 2-vinyloxytetrahydropyran is 1:3-5.

[0024] More preferably, the mass ratio of azobisisobutyronitrile to 2-(2-methoxyethoxy)ethyl 2-methylpropenoate is 1:0.5-2.

[0025] More preferably, the usage ratio of azobisisobutyronitrile and dimethyl carbonate is 1 g:200-300 mL.

[0026] More preferably, the volume ratio of dimethyl carbonate to methyl tert-butyl ether is 1:1-5.

[0027] More preferably, the mass ratio of azobisisobutyronitrile to carbon nanotubes is 1:5-20.

[0028] More preferably, the mass ratio of carbon nanotubes to potassium chloride is 1:1-5.

[0029] More preferably, the mass ratio of the carbon nanotubes to the phenolic resin is 1:1-2.

[0030] The present invention utilizes 4-methoxy-3-butene-2-one, 2-vinyloxytetrahydropyran, and 2-(2-methoxyethoxy)ethyl 2-methylpropenoate for polymerization, then modifies carbon nanotubes, and uses the resulting modified carbon nanotubes as an adsorbent for purging and trapping benzene series. The invention has the following beneficial effects: in a method for detecting benzene series in water using purge and trap-gas chromatography, a standard benzene series solution in methanol is prepared by gradually diluting the standard solution with pure water to prepare a standard intermediate solution and a working solution, thereby reducing the amount of methanol introduced, separating methanol from benzene, and improving the accuracy of benzene determination. Furthermore, by optimizing the experimental conditions of the purge and trap-gas chromatography, the detection limit of the method is reduced, making it more conducive to the determination of low-concentration benzene series samples. Experimental results show that the relative standard deviation of the detection method of the present invention is 0.99-1.87%, and the average recovery rate is 89.7-108.3%. Therefore, the present invention provides a method for detecting benzene series in water based on purge and trap-gas chromatography with low relative standard deviation and high average recovery rate, which provides a reliable technical means for the analysis of benzene series in environmental water samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the ion current chromatogram of the benzene standard sample. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.

[0033] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are commercially available unless otherwise specified.

[0034] Example 1:

[0035] The method for detecting benzene series in water based on purge and trap-gas chromatography includes:

[0036] The water sample to be tested was subjected to sedimentation and centrifugation, and the supernatant was collected and analyzed for benzene series using a purge-and-trap instrument and gas chromatography. The adsorbent used in the purge-and-trap was carbon nanotubes. The purge-and-trap parameters were set as follows: purge temperature of 30°C, purge time of 10 minutes, dry sweep time of 4 minutes, baking temperature of 240°C, baking time of 8 minutes, desorption time of 2 minutes, desorption temperature of 200°C, stripping gas of nitrogen, and purge flow rate of 40 mL / min. The gas chromatography parameters were set as follows: inlet temperature of 200°C, detector temperature of 280°C, carrier gas flow rate of 2.5 mL / min, and a temperature ramp of 40°C for 5 minutes, followed by a temperature ramp of 5°C / min to 100°C, hold for 2 minutes, and then a temperature ramp of 5°C / min to 200°C.

[0037] Example 2:

[0038] Preparation of modified carbon nanotubes, comprising:

[0039] Under a nitrogen atmosphere, 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran were dissolved in dimethyl carbonate, azobisisobutyronitrile was added and the mixture was reacted at 65°C for 12 hours. After the reaction, methyl tert-butyl ether was slowly added dropwise for precipitation. The solid was retained by centrifugation, carbon nanotubes, potassium chloride and phenolic resin were added, and the mixture was vacuum dried for 24 hours. The mixture was treated at 150°C for 8 hours, then heated to 900°C at a rate of 2°C / min and maintained for 2 hours. After the treatment, the mixture was naturally cooled to room temperature and ground to obtain modified carbon nanotubes. The mass ratio of azobisisobutyronitrile and 4-methoxy-3-butene-2-one is 1:5; the mass ratio of azobisisobutyronitrile and 2-vinyloxytetrahydropyran is 1:5; the usage ratio of azobisisobutyronitrile and dimethyl carbonate is 1 g:250 mL; the volume ratio of dimethyl carbonate and methyl tert-butyl ether is 1:2; the mass ratio of azobisisobutyronitrile and carbon nanotubes is 1:10; the mass ratio of carbon nanotubes and potassium chloride is 1:2; phenolic resin was purchased from Shanghai MacLean Biochemical Technology Co., Ltd., and the mass ratio of carbon nanotubes and phenolic resin is 1:1.

[0040] The method for detecting benzene series in water based on purge and trap-gas chromatography is the same as that in Example 1 except that the adsorbent is replaced by the modified carbon nanotubes prepared in this example. Other conditions are the same as those in Example 1.

[0041] Example 3:

[0042] The preparation of modified carbon nanotubes was performed under the same conditions as in Example 2 except that the mass ratio of azobisisobutyronitrile to 4-methoxy-3-butene-2-one was changed to 1:1.

[0043] The method for detecting benzene series in water based on purge and trap-gas chromatography is the same as that in Example 1 except that the adsorbent is replaced by the modified carbon nanotubes prepared in this example. Other conditions are the same as those in Example 1.

[0044] Example 4:

[0045] The preparation of modified carbon nanotubes was performed under the same conditions as in Example 2 except that the mass ratio of azobisisobutyronitrile to 2-ethyleneoxytetrahydropyran was changed to 1:3.

[0046] The method for detecting benzene series in water based on purge and trap-gas chromatography is the same as that in Example 1 except that the adsorbent is replaced by the modified carbon nanotubes prepared in this example. Other conditions are the same as those in Example 1.

[0047] Example 5:

[0048] Preparation of modified carbon nanotubes, comprising:

[0049] Under a nitrogen atmosphere, 4-methoxy-3-butene-2-one, 2-vinyloxytetrahydropyran and 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester were dissolved in dimethyl carbonate, azobisisobutyronitrile was added and the mixture was reacted at 65°C for 12 hours. After the reaction, methyl tert-butyl ether was slowly added dropwise for precipitation. The solid was retained by centrifugation, carbon nanotubes, potassium chloride and phenolic resin were added, and the mixture was vacuum dried for 24 hours. The mixture was treated at 150°C for 8 hours, then heated to 900°C at a rate of 2°C / min and maintained for 2 hours. After the treatment, the mixture was naturally cooled to room temperature and ground to obtain modified carbon nanotubes. The mass ratio of azobisisobutyronitrile and 4-methoxy-3-butene-2-one is 1:5; the mass ratio of azobisisobutyronitrile and 2-vinyloxytetrahydropyran is 1:5; the mass ratio of azobisisobutyronitrile and 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester is 1:2; the amount ratio of azobisisobutyronitrile and dimethyl carbonate is 1 g:250 mL; the volume ratio of dimethyl carbonate and methyl tert-butyl ether is 1:2; the volume ratio of dimethyl carbonate and acetone is 1:2; the mass ratio of azobisisobutyronitrile and carbon nanotubes is 1:10; the mass ratio of carbon nanotubes and potassium chloride is 1:2; phenolic resin was purchased from Shanghai MacLean Biochemical Technology Co., Ltd., and the mass ratio of carbon nanotubes and phenolic resin is 1:1.

[0050] The method for detecting benzene series in water based on purge and trap-gas chromatography is the same as that in Example 1 except that the adsorbent is replaced by the modified carbon nanotubes prepared in this example. Other conditions are the same as those in Example 1.

[0051] Example 6:

[0052] The preparation of modified carbon nanotubes was performed under the same conditions as in Example 5 except that the mass ratio of azobisisobutyronitrile to 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester was changed to 1:0.5.

[0053] The method for detecting benzene series in water based on purge and trap-gas chromatography is the same as that in Example 1 except that the adsorbent is replaced by the modified carbon nanotubes prepared in this example. Other conditions are the same as those in Example 1.

[0054] Comparative Example 1:

[0055] The preparation of modified carbon nanotubes was performed under the same conditions as in Example 2 except that 2-ethyleneoxytetrahydropyran was not added.

[0056] The method for detecting benzene series in water based on purge and trap-gas chromatography is the same as that in Example 1 except that the adsorbent is replaced by the modified carbon nanotubes prepared in this example. Other conditions are the same as those in Example 1.

[0057] Comparative Example 2:

[0058] The preparation of modified carbon nanotubes was carried out under the same conditions as in Example 2 except that 4-methoxy-3-butene-2-one was not added.

[0059] The method for detecting benzene series in water based on purge and trap-gas chromatography is the same as that in Example 1 except that the adsorbent is replaced by the modified carbon nanotubes prepared in this example. Other conditions are the same as those in Example 1.

[0060] Comparative Example 3:

[0061] The preparation of modified carbon nanotubes was similar to that of Example 5 except that 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran were added. Other conditions were the same as those of Example 5.

[0062] The method for detecting benzene series in water based on purge and trap-gas chromatography is the same as that in Example 1 except that the adsorbent is replaced by the modified carbon nanotubes prepared in this example. Other conditions are the same as those in Example 1.

[0063] Experimental example:

[0064] 1. Standard curve and detection limit

[0065] Get 100 μ L concentration and be 1000 μ g / mL benzene standard solution and 800 μ L methanol mixed preparation and obtain benzene standard intermediate solution, then take 0,5 μ L, 10 μ L, 30 μ L, 50 μ L and 100 μ L benzene standard intermediate solution in 100mL volumetric flask respectively, add pure water and carry out constant volume, obtain the benzene standard use liquid of series concentration.Test according to the method based on benzene series in purge and trap-gas chromatography detection water in embodiment 1, use the concentration of liquid from low to high sample introduction according to benzene standard, measure concentration with external standard method, draw standard curve.

[0066] Figure 1 This is the ion current chromatogram of the benzene standard sample. The linear regression equation of benzene is y=0.6086x+1.3×10 -3 , the correlation coefficient was 0.998, and the detection limit was 0.5 μg / L, which showed that the method established in the present invention could detect benzene and meet the quantitative requirements.

[0067] 2. Accuracy

[0068] A 1000 μg / mL benzene standard solution was diluted with pure water to a final concentration of 200 μg / mL. Benzene was detected using the same methods as in Examples 1-6 and Comparative Examples 1-3, with 10 replicates per experiment. The measured benzene concentration was calculated based on the standard curve, and the relative standard deviation (RSD) was evaluated. Table 1 shows the RSD (%).

[0069] Table 1 Relative standard deviation (%)

[0070]

[0071] As shown in Table 1, the relative standard deviations of Examples 2-4 of the present invention are lower than those of Example 1. This is because, in the method for detecting BTEX in water using purge and trap-gas chromatography, Example 1 uses carbon nanotubes as the purge and trap adsorbent, while Examples 2-4 use modified carbon nanotubes. This demonstrates that the modified carbon nanotubes prepared by the present invention, when used as the purge and trap adsorbent, can improve the accuracy of BTEX detection. The relative standard deviation of Example 2 is lower than that of Examples 3-4 because different amounts of 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran are used in the preparation of the modified carbon nanotubes. The relative standard deviation of Example 2 is lower than that of Comparative Examples 1-2 because, in the preparation of the modified carbon nanotubes, Example 2 uses 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran in combination to modify the carbon nanotubes, while Comparative Example 1 uses only 4-methoxy-3-butene-2-one, and Comparative Example 2 uses only 2-vinyloxytetrahydropyran. This indicates that, compared with using 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran alone, using 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran in combination to modify carbon nanotubes helps improve detection accuracy when the resulting modified carbon nanotubes are used for the detection of benzene series in water using purge and trap gas chromatography.

[0072] The relative standard deviation of Examples 5-6 of the present invention is lower than that of Example 2 because, in the preparation of the modified carbon nanotubes, Examples 5-6 further use 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester to modify the carbon nanotubes; the relative standard deviation of Example 5 is lower than that of Example 6 because, in the preparation of the modified carbon nanotubes, the amount of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester used is different; the relative standard deviation of Example 5 is lower than that of Comparative Example 3 because, in the preparation of the modified carbon nanotubes, Comparative Example 3 only uses 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester to modify the carbon nanotubes, without using 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran. This shows that the present invention further uses 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester to modify carbon nanotubes, and the obtained modified carbon nanotubes are used to detect benzene series in water based on purge and trap-gas chromatography, which helps to further improve the detection accuracy.

[0073] 3. Accuracy

[0074] A 1000 μg / mL benzene standard solution was diluted with pure water to a final concentration of 200 μg / mL to obtain a standard working solution of benzene, whose concentration was recorded as C0. Benzene in surface water was detected using the methods of Examples 1-6 and Comparative Examples 1-3. A spiked recovery experiment was conducted using the standard addition method. The benzene concentration in surface water was recorded as C1, and the detected concentration of the standard working solution was recorded as C2. The average recovery (%) was calculated as (C2 - C1) / C0 × 100%. Table 2 shows the average recovery (%).

[0075] Table 2 Average recovery rate (%)

[0076]

[0077] As shown in Table 2, the average recovery rate of Examples 2-4 of the present invention is higher than that of Example 1. This is because in the method for detecting benzene series in water based on purge and trap-gas chromatography, Example 1 uses carbon nanotubes as an adsorbent for purge and trap, while Examples 2-4 use modified carbon nanotubes as an adsorbent for purge and trap. This shows that the modified carbon nanotubes prepared by the present invention, when used as an adsorbent for purge and trap, help improve the accuracy of benzene series detection. The average recovery rate of Example 2 is higher than that of Examples 3-4 because the amounts of 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran used in the preparation of the modified carbon nanotubes are different; the average recovery rate of Example 2 is higher than that of Comparative Examples 1-2 because in the preparation of the modified carbon nanotubes, Example 2 uses 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran to modify the carbon nanotubes in a coordinated manner, while Comparative Example 1 uses only 4-methoxy-3-butene-2-one alone, and Comparative Example 2 uses only 2-vinyloxytetrahydropyran alone. This shows that compared with using 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran alone, the synergistic use of 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran to modify carbon nanotubes and using the resulting modified carbon nanotubes to detect benzene series in water based on purge and trap-gas chromatography can help improve detection accuracy.

[0078] The average recovery rate of Examples 5-6 of the present invention is higher than that of Example 2 because, in the preparation of the modified carbon nanotubes, Examples 5-6 further use 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester to modify the carbon nanotubes; the average recovery rate of Example 5 is higher than that of Example 6 because, in the preparation of the modified carbon nanotubes, the amount of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester used is different; the average recovery rate of Example 5 is higher than that of Comparative Example 3 because, in the preparation of the modified carbon nanotubes, Comparative Example 3 only uses 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester to modify the carbon nanotubes, without using 4-methoxy-3-butene-2-one and 2-vinyloxytetrahydropyran. This shows that the present invention further uses 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester to modify carbon nanotubes, and the obtained modified carbon nanotubes are used to detect benzene series in water based on purge and trap-gas chromatography, which helps to further improve the detection accuracy.

[0079] The conventional operations in the operating steps of the present invention are well known to those skilled in the art and will not be described in detail here.

[0080] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any changes and modifications made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting benzene in water based on purge and trap-gas chromatography, comprising: subjecting a water sample to sedimentation and centrifugation, and subjecting the supernatant to purge and trap-gas chromatography. The adsorbent used in the purge and trap is modified carbon nanotubes. In preparing the modified carbon nanotubes, 4-methoxy-3-butene-2-one and 2-ethyleneoxytetrahydropyran are first polymerized in the presence of azobisisobutyronitrile, and then subjected to high-temperature treatment and carbonization with carbon nanotubes, potassium chloride, and phenolic resin to obtain the modified carbon nanotubes. The purge flow rate of the purge and trap is 30-50 mL / min, and the purge time is 5-15 min.

2. The method for detecting benzene in water based on purge and trap-gas chromatography according to claim 1, wherein: The mass ratio of the azobisisobutyronitrile to 4-methoxy-3-butene-2-one is 1:1-5.

3. The method for detecting benzene in water based on purge and trap-gas chromatography according to claim 1, wherein: The mass ratio of the azobisisobutyronitrile to 2-ethyleneoxytetrahydropyran is 1:3-5.

4. The method for detecting benzene in water based on purge and trap-gas chromatography according to claim 1, wherein: The mass ratio of the azobisisobutyronitrile to the carbon nanotubes is 1:5-20.

5. The method for detecting benzene in water based on purge and trap-gas chromatography according to claim 1, wherein: The mass ratio of the carbon nanotubes to potassium chloride is 1:1-5.

6. The method for detecting benzene in water based on purge and trap-gas chromatography according to claim 1, wherein: The mass ratio of the carbon nanotubes to the phenolic resin is 1:1-2.

7. The method for detecting benzene in water based on purge and trap-gas chromatography according to claim 1, wherein: The temperature of the high temperature treatment is 140-160°C.

8. The method for detecting benzene in water based on purge and trap-gas chromatography according to claim 1, wherein: The high temperature treatment time is 8-12 hours.

9. The method for detecting benzene in water based on purge and trap-gas chromatography according to claim 1, wherein: The polymerization reaction temperature is 60-80°C.

10. The method for detecting benzene in water based on purge and trap-gas chromatography according to claim 1, characterized in that: The polymerization reaction time is 8-24h.

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