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, and belongs to the technical field of water quality detection.The specific method comprises the steps that a to-be-detected water sample is subjected to precipitation centrifugal separation treatment, supernate is taken for purge and trap-gas chromatography detection, an adsorbent used in purge and trap is a modified carbon nanotube, and the modified carbon nanotube is an organic solvent. In the preparation of the modified carbon nano tube, firstly, 4-methoxy-3-butene-2-ketone and 2-ethyleneoxy tetrahydropyran are subjected to a polymerization reaction, and then the product reacts with the carbon nano tube to obtain the modified carbon nano tube. The method for detecting the benzene series in the water based on the purge and trap-gas chromatography provided by the invention has high precision and high accuracy, and can be widely applied to detection of the benzene series in a water sample.

Description

Technical Field

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

[0002] As a class of organic pollutants with significant toxicity and environmental harmfulness, benzene series compounds not only pose a serious threat to human health, but also cause persistent pollution to the ecological environment. In view of their harmfulness, benzene series compounds have been listed as core control indicators in multiple environmental standards. Currently, the detection of benzene series compounds in water mainly relies on gas chromatography and gas chromatography - mass spectrometry, combined with pretreatment techniques such as purge and trap or headspace. Among them, the purge and trap - gas chromatography method has been widely used in grass - roots laboratories such as environmental monitoring stations at all levels due to its advantages of simple operation, high sensitivity, and relatively low equipment cost.

[0003] However, when actually applying the current industry standard "Water Quality - Determination of Volatile Organic Compounds - Purge and Trap / Gas Chromatography Method" (HJ 686 - 2014) for the detection of benzene series compounds, it is found that if the standard intermediate solution and working solution are prepared strictly in accordance with this standard method, obvious methanol peak tailing phenomenon will occur, and this interference will seriously affect the accurate quantification of benzene. The existence of this problem may lead to deviation of the detection results, and further affect the accurate assessment of the pollution status of benzene series compounds in environmental water quality, which brings technical troubles to the actual detection work. Therefore, it is urgent to establish an improved purge and trap - gas chromatography detection method to ensure the accuracy and reliability of detection data. Summary of the Invention

[0004] The purpose 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 solution adopted by the present invention to achieve the above - mentioned purpose is as follows: A method for detecting benzene series compounds in water based on purge and trap - gas chromatography, including subjecting the water sample to be tested to precipitation and centrifugal separation treatment, 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.

[0006] The present invention prepares the standard intermediate solution and working solution of benzene series compounds in methanol by gradually diluting with pure water, reduces the introduction amount of methanol, separates methanol from benzene, and improves the determination accuracy of benzene; and by optimizing the experimental conditions of purge and trap - gas chromatography, reduces the method detection limit, which is more conducive to the determination of low - concentration benzene series compound samples.

[0007] Preferably, the adsorbent is carbon nanotubes and / or modified carbon nanotubes.

[0008] More preferably, in the preparation of the modified carbon nanotubes, 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran are first subjected to a polymerization reaction under the action of azobisisobutyronitrile, and then high-temperature treatment and carbonization treatment are carried out with carbon nanotubes, potassium chloride and phenolic resin to obtain the modified carbon nanotubes. In the present invention, 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran are first used for polymerization reaction, and then the carbon nanotubes are modified, which may significantly increase the number of its adsorption active sites in the carbon nanotubes, enhance its adsorption and enrichment ability for benzene series compounds, effectively reduce the detection limit and relative standard deviation of the method, and at the same time significantly improve the average recovery rate of benzene series compounds.

[0009] Even more preferably, the mass ratio of azobisisobutyronitrile to 4-methoxy-3-buten-2-one is 1:1-5.

[0010] Even more preferably, the mass ratio of azobisisobutyronitrile to 2-vinyloxy tetrahydropyran is 1:3-5.

[0011] Even more preferably, the mass ratio of azobisisobutyronitrile to carbon nanotubes is 1:5-20.

[0012] Even more preferably, the mass ratio of carbon nanotubes to potassium chloride is 1:1-5.

[0013] Even more preferably, the mass ratio of carbon nanotubes to phenolic resin is 1:1-2.

[0014] Even more preferably, the temperature of the high-temperature treatment is 140-160 °C.

[0015] Even more preferably, the time of the high-temperature treatment is 8-12 h.

[0016] Preferably, a method for detecting benzene series compounds in water based on purge and trap-gas chromatography is as follows: The water sample to be tested is subjected to precipitation centrifugation separation, and the supernatant is taken for the detection of benzene series by a purge and trap instrument and a gas chromatograph. The adsorbent in the purge and trap is carbon nanotubes or modified carbon nanotubes. The parameter settings of the purge and trap are as follows: the purge temperature is 20 - 30 °C, the purge time is 5 - 15 min, the dry purge time is 3 - 5 min, the baking temperature is 220 - 260 °C, the baking time is 5 - 10 min, the desorption time is 1 - 2 min, the desorption temperature is 180 - 220 °C, the purge gas is nitrogen, and the purge flow rate is 30 - 50 mL / min. The parameter settings of the gas chromatograph are as follows: the inlet temperature is 180 - 220 °C, the detector temperature is 250 - 300 °C, the carrier gas flow rate is 1 - 3 mL / min, and the temperature programming is to maintain at 40 - 50 °C for 5 - 10 min initially, then increase the temperature at a rate of 5 - 10 °C / min to 90 - 110 °C and maintain for 1 - 2 min, and then increase the temperature at a rate of 5 - 10 °C / min to 150 - 200 °C.

[0017] More preferably, the preparation of the modified carbon nanotubes is specifically as follows. Under a nitrogen atmosphere, the alkenyl unit is dissolved in dimethyl carbonate, azobisisobutyronitrile is added, and the reaction is carried out at 60 - 80 °C for 8 - 24 h. After the reaction, methyl tert-butyl ether is slowly added dropwise for precipitation, and the solid is retained by centrifugation separation. Carbon nanotubes, potassium chloride, and phenolic resin are added, and vacuum drying is carried out for 12 - 24 h. Treatment is carried out at 140 - 160 °C for 8 - 12 h, and then the temperature is increased to 800 - 1000 °C at a rate of 2 - 5 °C / min and maintained for 1 - 2 h. After the treatment, it is naturally cooled to room temperature and ground to obtain the modified carbon nanotubes.

[0018] Even more preferably, the alkenyl unit includes at least one of 4-methoxy-3-buten-2-one, 2-vinyloxytetrahydropyran, and 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate. The present invention further uses 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate to optimize the surface adsorption sites of carbon nanotubes and optimize the interaction between the adsorbent and the analyte, thereby effectively reducing the detection limit and relative standard deviation of the method, and at the same time significantly improving the average recovery rate of benzene series.

[0019] Even more preferably, the mass ratio of azobisisobutyronitrile to 4-methoxy-3-buten-2-one is 1:1 - 5.

[0020] Even more preferably, the mass ratio of azobisisobutyronitrile to 2-vinyloxytetrahydropyran is 1:3 - 5.

[0021] Even more preferably, the mass ratio of azobisisobutyronitrile to 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate is 1:0.5 - 2.

[0022] More preferably, the dosage ratio of azobisisobutyronitrile to dimethyl carbonate is 1 g: 200 - 300 mL.

[0023] More preferably, the volume ratio of dimethyl carbonate to methyl tert-butyl ether is 1: 1 - 5.

[0024] More preferably, the mass ratio of azobisisobutyronitrile to carbon nanotubes is 1: 5 - 20.

[0025] More preferably, the mass ratio of carbon nanotubes to potassium chloride is 1: 1 - 5.

[0026] More preferably, the mass ratio of carbon nanotubes to phenolic resin is 1: 1 - 2.

[0027] Since the present invention uses 4-methoxy-3-buten-2-one, 2-vinyloxy tetrahydropyran and 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate for polymerization reaction, then modifies carbon nanotubes, and uses the obtained modified carbon nanotubes as adsorbents for purge and trap of benzene series compounds, thus having the following beneficial effects: in the method for detecting benzene series compounds in water by purge and trap-gas chromatography, by preparing the standard intermediate solution and the working solution of benzene series compounds by gradually diluting the standard solution of benzene series compounds in methanol with pure water, the introduction amount of methanol is reduced, methanol and benzene are separated, and the determination accuracy of benzene is improved; and 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 benzene series compound samples. The 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 compounds in water based on purge and trap-gas chromatography with a low relative standard deviation and a high average recovery rate, providing a reliable technical means for the analysis of benzene series compounds in environmental water samples. Description of the Drawings

[0028] Figure 1 It is the ion chromatogram of the benzene standard sample. Detailed Embodiments

[0029] The following further describes the present invention in detail in combination with specific embodiments. The provided embodiments are only for clarifying the present invention, rather than limiting the scope of the present invention. The following provided embodiments can be used as a guide for those of ordinary skill in the art to make further improvements, and do not limit the present invention in any way.

[0030] The experimental methods in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, etc. used in the following embodiments can all be obtained from commercial channels unless otherwise specified.

[0031] Example 1: Method for detecting benzene series in water based on purge and trap-gas chromatography, including, Performing precipitation centrifugation separation on the water sample to be tested, taking the supernatant, and detecting benzene series using a purge and trap instrument and a gas chromatograph. The adsorbent used in purge and trap is carbon nanotubes. The parameter settings for purge and trap are: purge temperature is 30 °C, purge time is 10 min, dry purge time is 4 min, baking temperature is 240 °C, baking time is 8 min, desorption time is 2 min, desorption temperature is 200 °C, purge gas is nitrogen, and purge flow rate is 40 mL / min. The parameter settings for gas chromatography are: injection port temperature is 200 °C, detector temperature is 280 °C, carrier gas flow rate is 2.5 mL / min, and the temperature programming is to hold at 40 °C for 5 min initially, then increase the temperature to 100 °C at a rate of 5 °C / min and hold for 2 min, and then increase the temperature to 200 °C at a rate of 5 °C / min.

[0032] Example 2: Preparation of modified carbon nanotubes, including, Under a nitrogen atmosphere, dissolve 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran in dimethyl carbonate, add azobisisobutyronitrile and react at 65 °C for 12 h. After the reaction, slowly add methyl tert-butyl ether for precipitation, centrifuge and separate to retain the solid, add carbon nanotubes, potassium chloride, and phenolic resin, vacuum dry for 24 h, treat at 150 °C for 8 h, then increase the temperature to 900 °C at a rate of 2 °C / min and hold for 2 h. After the treatment, naturally cool to room temperature and grind to obtain modified carbon nanotubes. The mass ratio of azobisisobutyronitrile to 4-methoxy-3-buten-2-one is 1:5; the mass ratio of azobisisobutyronitrile to 2-vinyloxy tetrahydropyran is 1:5; the dosage ratio of azobisisobutyronitrile to dimethyl carbonate is 1 g:250 mL; the volume ratio of dimethyl carbonate to methyl tert-butyl ether is 1:2; the mass ratio of azobisisobutyronitrile to carbon nanotubes is 1:10; the mass ratio of carbon nanotubes to potassium chloride is 1:2; the phenolic resin is purchased from Shanghai Macklin Biochemical Co., Ltd., and the mass ratio of carbon nanotubes to phenolic resin is 1:1.

[0033] The method for detecting benzene series in water based on purge and trap-gas chromatography, compared with Example 1, except that the adsorbent is replaced with the modified carbon nanotubes prepared in this example, other conditions are the same as in Example 1.

[0034] Example 3: Preparation of modified carbon nanotubes, compared with Example 2, except that the mass ratio of azobisisobutyronitrile to 4-methoxy-3-buten-2-one is changed to 1:1, other conditions are the same as in Example 2.

[0035] The method for detecting benzene series compounds in water based on purge and trap-gas chromatography, compared with Example 1, except that the adsorbent is replaced with the modified carbon nanotubes prepared in this example, other conditions are the same as those in Example 1.

[0036] Example 4: The preparation of modified carbon nanotubes, compared with Example 2, except that the mass ratio of azobisisobutyronitrile to 2-vinyloxy tetrahydropyran is changed to 1:3, other conditions are the same as those in Example 2.

[0037] The method for detecting benzene series compounds in water based on purge and trap-gas chromatography, compared with Example 1, except that the adsorbent is replaced with the modified carbon nanotubes prepared in this example, other conditions are the same as those in Example 1.

[0038] Example 5: The preparation of modified carbon nanotubes includes, Under a nitrogen atmosphere, 4-methoxy-3-buten-2-one, 2-vinyloxy tetrahydropyran and 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate are dissolved in dimethyl carbonate, azobisisobutyronitrile is added and the reaction is carried out at 65 °C for 12 h. After the reaction, methyl tert-butyl ether is slowly added dropwise for precipitation, and the solid is retained by centrifugation. Carbon nanotubes, potassium chloride and phenolic resin are added, and vacuum drying is carried out for 24 h. Treatment is carried out at 150 °C for 8 h, and then the temperature is raised to 900 °C at a rate of 2 °C / min and maintained for 2 h. After the treatment, it is naturally cooled to room temperature and ground to obtain modified carbon nanotubes. The mass ratio of azobisisobutyronitrile to 4-methoxy-3-buten-2-one is 1:5; the mass ratio of azobisisobutyronitrile to 2-vinyloxy tetrahydropyran is 1:5; the mass ratio of azobisisobutyronitrile to 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate is 1:2; the dosage ratio of azobisisobutyronitrile to dimethyl carbonate is 1 g:250 mL; the volume ratio of dimethyl carbonate to methyl tert-butyl ether is 1:2; the volume ratio of dimethyl carbonate to acetone is 1:2; the mass ratio of azobisisobutyronitrile to carbon nanotubes is 1:10; the mass ratio of carbon nanotubes to potassium chloride is 1:2; the phenolic resin is purchased from Shanghai Macklin Biochemical Co., Ltd., and the mass ratio of carbon nanotubes to phenolic resin is 1:1.

[0039] The method for detecting benzene series compounds in water based on purge and trap-gas chromatography, compared with Example 1, except that the adsorbent is replaced with the modified carbon nanotubes prepared in this example, other conditions are the same as those in Example 1.

[0040] Example 6: The preparation of modified carbon nanotubes, compared with Example 5, except that the mass ratio of azobisisobutyronitrile to 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate is changed to 1:0.5, other conditions are the same as those in Example 5.

[0041] The method for detecting benzene series compounds in water based on purge and trap - gas chromatography. Compared with Example 1, except that the adsorbent is replaced with the modified carbon nanotubes prepared in this example, other conditions are the same as those in Example 1.

[0042] Comparative Example 1: The preparation of modified carbon nanotubes. Compared with Example 2, except that 2 - ethenyloxytetrahydropyran is not added, other conditions are the same as those in Example 2.

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

[0044] Comparative Example 2: The preparation of modified carbon nanotubes. Compared with Example 2, except that 4 - methoxy - 3 - buten - 2 - one is not added, other conditions are the same as those in Example 2.

[0045] The method for detecting benzene series compounds in water based on purge and trap - gas chromatography. Compared with Example 1, except that the adsorbent is replaced with the modified carbon nanotubes prepared in this example, other conditions are the same as those in Example 1.

[0046] Comparative Example 3: The preparation of modified carbon nanotubes. Compared with Example 5, except that 4 - methoxy - 3 - buten - 2 - one and 2 - ethenyloxytetrahydropyran are not added, other conditions are the same as those in Example 5.

[0047] The method for detecting benzene series compounds in water based on purge and trap - gas chromatography. Compared with Example 1, except that the adsorbent is replaced with the modified carbon nanotubes prepared in this example, other conditions are the same as those in Example 1.

[0048] Experimental Example: 1. Standard curve and detection limit Take 100 μL of benzene standard solution with a concentration of 1000 μg / mL and mix it with 800 μL of methanol to prepare a benzene standard intermediate solution. Then, take 0, 5 μL, 10 μL, 30 μL, 50 μL, and 100 μL of the benzene standard intermediate solution into 100 mL volumetric flasks respectively, add pure water for volume fixation to obtain a series of benzene standard working solutions. Test according to the method for detecting benzene series compounds in water based on purge and trap - gas chromatography in Example 1. Inject samples in ascending order of the concentration of the benzene standard working solutions, and determine the concentration by the external standard method to draw a standard curve.

[0049] Figure 1 It is the ion 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, indicating that the method established in the present invention can detect benzene and meet the quantitative requirements.

[0050] 2. Precision Dilute the benzene standard solution with a concentration of 1000 μg / mL to a final concentration of 200 μg / mL with pure water, and detect benzene according to the methods of Examples 1-6 and Comparative Examples 1-3. Each group of experiments is set with 10 replicates. Calculate the measured concentration of benzene based on the standard curve and evaluate its relative standard deviation. Table 1 shows the relative standard deviation (%).

[0051] Table 1 Relative standard deviation (%)

[0052] As can be seen from Table 1, the relative standard deviation of Examples 2-4 of the present invention is lower than that of Example 1 because in the method for detecting benzene series in water based on purge and trap-gas chromatography, carbon nanotubes were used as the adsorbent for purge and trap in Example 1, while modified carbon nanotubes were used as the adsorbent for purge and trap in Examples 2-4. This indicates that when the modified carbon nanotubes prepared in the present invention are used as the adsorbent for purge and trap, it helps to improve the precision of detecting benzene series. The relative standard deviation of Example 2 is lower than that of Examples 3-4 because the usage amounts of 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran are different in the preparation of modified carbon nanotubes; the relative standard deviation of Example 2 is lower than that of Comparative Examples 1-2 because in the preparation of modified carbon nanotubes, Example 2 synergistically uses 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran to modify carbon nanotubes, Comparative Example 1 only uses 4-methoxy-3-buten-2-one alone, and Comparative Example 2 only uses 2-vinyloxy tetrahydropyran alone. This shows that compared with the individual use of 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran, the synergistic use of 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran to modify carbon nanotubes and using the obtained modified carbon nanotubes for detecting benzene series in water based on purge and trap-gas chromatography helps to improve the detection precision.

[0053] 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-(2-methoxyethoxy)ethyl 2-methylacrylate 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 usage amount of 2-(2-methoxyethoxy)ethyl 2-methylacrylate 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-(2-methoxyethoxy)ethyl 2-methylacrylate to modify the carbon nanotubes, without using 4-methoxy-3-buten-2-one and 2-ethenyloxytetrahydropyran. This shows that the present invention further uses 2-(2-methoxyethoxy)ethyl 2-methylacrylate to modify the carbon nanotubes and uses the obtained modified carbon nanotubes for detecting benzene series in water based on purge and trap-gas chromatography, which helps to further improve the detection accuracy.

[0054] 3. Accuracy Dilute the benzene standard solution with a concentration of 1000 μg / mL to a final concentration of 200 μg / mL with pure water to obtain a standard working solution of benzene, and its concentration is denoted as C0. Refer to the methods of Examples 1-6 and Comparative Examples 1-3 to detect benzene in surface water, and conduct a standard addition recovery experiment. Denote the benzene concentration in surface water as C1 and the detected concentration of the standard working solution as C2. The average recovery rate (%) = (C2 - C1) / C0 × 100%. Table 2 shows the average recovery rate (%).

[0055] Table 2 Average recovery rate (%)

[0056] As can be seen from Table 2, the average recovery rates of Examples 2-4 of the present invention are higher than those of Example 1. This is because in the method for detecting benzene series compounds in water based on purge and trap-gas chromatography, carbon nanotubes were used as the adsorbent for purge and trap in Example 1, while modified carbon nanotubes were used as the adsorbent for purge and trap in Examples 2-4. This shows that when the modified carbon nanotubes prepared by the present invention are used as the adsorbent for purge and trap, it helps to improve the accuracy of detecting benzene series compounds. The average recovery rate of Example 2 is higher than those of Examples 3-4 because the usage amounts of 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran are different in the preparation of the modified carbon nanotubes; the average recovery rate of Example 2 is higher than those of Comparative Examples 1-2 because in the preparation of the modified carbon nanotubes, Example 2 synergistically uses 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran to modify the carbon nanotubes, Comparative Example 1 only uses 4-methoxy-3-buten-2-one alone, and Comparative Example 2 only uses 2-vinyloxy tetrahydropyran alone. This shows that compared with using 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran alone, synergistically using 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran to modify the carbon nanotubes and using the obtained modified carbon nanotubes for detecting benzene series compounds in water based on purge and trap-gas chromatography helps to improve the detection accuracy.

[0057] The average recovery rates of Examples 5-6 of the present invention are higher than those of Example 2 because in the preparation of the modified carbon nanotubes, Examples 5-6 further use 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate to modify the carbon nanotubes; the average recovery rate of Example 5 is higher than that of Example 6 because the usage amount of 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate is different in the preparation of the modified carbon nanotubes; 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-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate to modify the carbon nanotubes without using 4-methoxy-3-buten-2-one and 2-vinyloxy tetrahydropyran. This shows that further using 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate to modify the carbon nanotubes of the present invention and using the obtained modified carbon nanotubes for detecting benzene series compounds in water based on purge and trap-gas chromatography helps to further improve the detection accuracy.

[0058] The conventional operations in the operation steps of the present invention are well-known to those skilled in the art and will not be elaborated here.

[0059] The above-described examples have elaborated on the technical solutions of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any changes and variations made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting benzene series compounds in water based on purge and trap - gas chromatography, comprising subjecting a water sample to be measured to precipitation centrifugation separation treatment, and taking the supernatant for purge and trap - gas chromatography detection; the adsorbent used in the purge and trap is carbon nanotubes and / or modified carbon nanotubes; in the preparation of the modified carbon nanotubes, first, under the action of azobisisobutyronitrile, 4 - methoxy - 3 - buten - 2 - one and 2 - vinyloxy tetrahydropyran are subjected to a polymerization reaction, and then high - temperature treatment and carbonization treatment are carried out with carbon nanotubes, potassium chloride and phenolic resin to obtain 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 series in water based on purge and trap-gas chromatography according to claim 1, wherein The mass ratio of azobisisobutyronitrile to 4 - methoxy - 3 - buten - 2 - one is 1:1 - 5.

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

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

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

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

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

8. The method for detecting benzene series compounds in water based on purge and trap-gas chromatography according to claim 1, characterized in that, The time of the high - temperature treatment is 8 - 12 h.

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

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

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