Detection methods and extraction heads for benzene series compounds

Abstract

This application discloses a method and extraction head for the detection of benzene series compounds. A PAM / CNMs composite extraction head is prepared, and benzene series compounds are extracted from the headspace using this composite extraction head. The benzene series compounds are BTEX, PMA, and DPA. Gas chromatography-mass spectrometry (GC-MS) is constructed, and the benzene series compounds are detected using the extraction head. The advantages are that the PAM / CNMs composite extraction head has better extraction efficiency and mechanical stability for benzene series compounds. Applying the method of this application to the detection of benzene series compounds in actual samples demonstrates good sensitivity and practicality.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and in particular to a method for detecting benzene series compounds and an extraction head. Background Technology

[0002] Organic pollutants are characterized by low water solubility and high lipid solubility, easily accumulating in adipose tissue and amplifying along the food chain. They pose significant health risks, even exhibiting carcinogenic, teratogenic, and mutagenic effects, damaging or inhibiting the nervous and immune systems, disrupting or interfering with the endocrine system, affecting human reproductive function, interfering with hormones, causing growth disorders and genetic defects, and constituting a major threat to human survival, reproduction, and sustainable ecological development, seriously impacting population health. Therefore, the detection of organic pollution in water bodies is particularly important. However, current traditional water sample detection methods involve complex sample pretreatment processes, cumbersome operations, organic reagent contamination, and high costs. Solid-phase microextraction (SPE) offers numerous advantages, such as simple sample pretreatment, fewer organic reagents required, ease of operation, and versatility in detecting a wide range of pollutants, leading to its application and attention in the analytical testing field.

[0003] Therefore, the detection of benzene series compounds in water, namely xylene (BTEX), p-methylaniline (PMA), and diphenylamine (DPA), is of great significance. Currently, existing detection methods mainly include high-performance liquid chromatography (HPLC), high-performance liquid chromatography-mass spectrometry (HPLC-MS), gas chromatography-mass spectrometry (GC-MS), fluorescence spectroscopy, electrochemical biosensors, and spectroscopic analysis techniques. However, almost all of these methods involve complex sample pretreatment, are time-consuming, and costly, and their sensitivity and stability need improvement. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a method for detecting benzene compounds and an extraction head.

[0005] According to one aspect of the present invention, a PAM / CNMs composite extraction head is provided for headspace extraction of benzene series compounds, wherein the benzene series compounds are BTEX, PMA, and DPA; gas chromatography-mass spectrometry (GC-MS) is constructed, and the benzene series compounds are detected using the extraction head. The advantages are that the PAM / CNMs composite extraction head exhibits better extraction efficiency and mechanical stability for benzene series compounds. Applying the method of this application to the detection of benzene series compounds in actual samples demonstrates good sensitivity and practicality.

[0006] In some embodiments, the preparation of the composite extraction head includes the following steps: preparing a mixed solution containing AM as the polymer monomer and CNMs as the dopant; immersing the electrode system in the mixed solution and performing CV scanning to prepare the composite extraction head. The beneficial effects are that the resulting composite extraction head exhibits good conductivity and mechanical stability, and has good sensitivity for the detection of benzene compounds.

[0007] In some embodiments, the CNMs are N-MWCNTs; and / or the N-MWCNTs are 0.02 mg / mL; and / or the AM is 0.05 mol / L. The beneficial effects are that the resulting composite extraction head has good conductivity and mechanical stability, and exhibits good sensitivity for the detection of benzene compounds.

[0008] In some embodiments, the method further includes the following step: fixing the extraction head into a self-made sample injector, drying it, and thus obtaining a sample injection device for PAM / N-MWCNTs. The beneficial effect is that it purifies impurities on the extraction head, improving detection accuracy and sensitivity.

[0009] In some embodiments, the aging conditions are as follows: the injection device is inserted into the vaporization chamber of the gas chromatograph for aging, the injection port temperature is set to 90°C, and aging is carried out for 30 minutes; then the injection port temperature is continuously raised to 230-250°C, and aging continues for 1.5 hours before being set aside for later use. Its beneficial effects are: it can purify impurities on the extraction head, improving detection accuracy and sensitivity.

[0010] In some embodiments, the headspace extraction of benzene compounds using the composite extraction head includes the following steps: adding a saturated sodium chloride solution to the extraction container to form a first mixture; stirring the first mixture and maintaining a constant temperature water bath; adding a benzene compound solution and stirring; inserting the injection device into the extraction bottle and exposing the extraction head to the headspace of the solution, performing headspace extraction while stirring; retracting the extraction head into the protective sleeve, quickly inserting it into the gas chromatography vaporization chamber, and then pushing the extraction head out for desorption before performing GC-MS separation and detection. The advantage is that this makes subsequent detection operations more convenient.

[0011] In some embodiments, the temperature of the constant-temperature water bath is 50°C; and / or the stirring is magnetic stirring at a speed of 500 r / min. The beneficial effects are that the coating of the extraction head is uniformly distributed and has good stability at this temperature, thus exhibiting better conductivity and sensitivity for detecting the target substance.

[0012] In some embodiments, the extraction time is 50 min; and / or the extraction temperature is 50°C; and / or the saturated sodium chloride concentration is 0.35 g / mL; and / or the volume of saturated sodium chloride is 8.00 mL; and / or the elution time is 3–5 min. The beneficial effects are that the coating of the extraction head at this temperature and time is uniformly distributed and has good stability, thus exhibiting better conductivity and sensitivity for detecting the target substance.

[0013] In some embodiments, the cyclic voltammetry range of the CV scan is 0–1.5 V; the scan rate is 0.05 mV / s; and the number of scans is 100 cycles. The beneficial effects are: the extraction head thus produced has a uniform coating distribution and good stability, thereby exhibiting better conductivity and sensitivity for detecting the target substance.

[0014] According to another aspect of this application, an extraction head for detecting benzene series compounds is characterized in that the extraction head comprises a composite material of PAM and CNMs. Its advantages are: the coating of the extraction head is uniformly distributed and has good stability, thereby exhibiting better conductivity and sensitivity for detecting target substances. Attached Figure Description

[0015] Figure 1 Extraction effect diagrams for different types of SPME coatings;

[0016] Figure 2 Extraction effect diagrams for different types of SPME coatings;

[0017] Figure 3 Extraction effect diagrams for different types of SPME coatings;

[0018] Figure 4 Extraction effect diagrams for different types of SPME coatings;

[0019] Figure 5 Extraction effect diagrams for different types of SPME coatings;

[0020] Figure 6 CV diagram of PAM / N-MWCNTs coating;

[0021] Figure 7 SEM image of PAM / N-MWCNTs coating;

[0022] Figure 8 SEM image of PAM / N-MWCNTs coating;

[0023] Figure 9 The effect of extraction time on the peak area of ​​the target analyte;

[0024] Figure 10 The effect of extraction temperature on the peak area of ​​the target analyte;

[0025] Figure 11 The effect of saline concentration on the peak area of ​​the target analyte;

[0026] Figure 12 The effect of saline volume on the peak area of ​​the target analyte response;

[0027] Figure 13 The effect of stirring rate on the peak area of ​​the target analyte response;

[0028] Figure 14 Standard operating curves for xylene, p-methylaniline, and diphenylamine;

[0029] Figure 15 This is the chromatogram of the actual sample. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings, operating conditions, and embodiments.

[0031] I. Instrument and Reagent Instructions

[0032] 1. Main instruments and models

[0033] Table 1 - Experimental Instruments and Models

[0034] Main instruments and models: Gas chromatograph-mass spectrometer (Shimadzu GC-MS-QP2010), gas chromatograph (Shimadzu GC-2010), electrochemical workstation (CHI600E), ultrasonic cleaner (KQ5200E), thermostatic magnetic stirrer (S10-3), scanning electron microscope (SEM), and injector (self-made in the laboratory).

[0035] Carbon nanomaterials (CNMs) were purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd. (Nanjing, China). The CNMs used were: multi-walled carbon nanotubes (MWCNTs), ultra-high purity carboxylated single-walled carbon nanotubes (CSWCNTs), nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs), nitrogen-doped mesoporous carbon (N-CMK-3), and nitrogen-doped graphene (N-G). Ionic liquids (ILs) were purchased from Beijing Bailingwei Technology Co., Ltd. The ILs used were: 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([APMIm][NTf2]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIm][BF4]), and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]). Tetrabutylammonium perchlorate (99%), 6-aminoindole (AM) (purchased from Beijing Bailingwei Technology Co., Ltd.), acetonitrile (AR, Aladdin Shanghai Co., Ltd.), sodium chloride (AR, Tianjin Fuyu Fine Chemical Co., Ltd.), methanol (premium chromatographic grade, Changtai Xingye Co., Ltd.), Watson's water, dimethylbenzene (BTEX) (Beijing Chemical Plant), p-methylaniline (PMA) (Beijing Chemical Plant), diphenylamine (DPA) (Shanghai Jinshan Tingxin Chemical Reagent Factory). All other reagents not mentioned in this experiment were of analytical grade.

[0036] II. GC Operation Conditions

[0037] GC conditions: An RTX-5MS column (membrane thickness: 0.25 μm, length: 30 m, inner diameter: 0.25 mm) was used for the separation of this sample. The column oven temperature was 60 °C, the inlet temperature was 250 °C, the injection mode was splitless injection, the pressure was 73.0 kPa, the total flow rate was 44.0 mL / min, the column flow rate was 1.21 mL / min, the linear velocity was 40.1 cm / sec, and the purge flow rate was 3.0 mL / min.

[0038] The column oven temperature program setting is as follows: hold at 60℃ for 1 min, increase the temperature to 140℃ at 15℃ / min, and increase the temperature to 180℃ at 25℃ / min and hold for 5 min; the total program time is 12.93 min.

[0039] MS conditions: Ion source temperature 230℃; interface temperature 200℃.

[0040] III. Preparation of Different Types of SPME Coatings in Examples

[0041] Example 1: Preparation of stainless steel wire

[0042] After measuring a 1.5cm stainless steel wire with a ruler, smooth it with an iron ruler. Before using the smooth stainless steel wire, sonicate it for 5 minutes with nitric acid:water = 1:1 (HNO3:H2O = 1:1), then rinse it twice with deionized water, and then wash it twice with anhydrous ethanol. Let it air dry naturally.

[0043] Example 2: Polymerization of SPME coating

[0044] SPME coatings were prepared on an electrochemical workstation (CHI600E) using a single-cell three-electrode configuration. Electrochemical deposition was achieved via cyclic voltammetry (the three electrodes were: a 1.5 cm stainless steel wire as the working electrode, a platinum wire as the auxiliary electrode, and Ag / AgCl as the reference electrode; CV parameters were: InitE (V): 0.4, High E (V): 1.95, Scan Rate (V / s): 0.05, Sweep Segments: 100, Sensitivity (A / V): 1 × 10⁻⁶. － 3) Immerse the assembled three-electrode system in the prepared solution. Under the set CV parameters, start the electrochemical workstation (CHI600E) to complete the polymerization of the SPME coating. The concentration of AM solution is 0.05 mol / L, the concentration of tetrabutylammonium perchlorate is 0.08 mol / L, the concentration of CNMs is 0.02 mg / mL, the concentration of ILs is 10.0 μL / mL, and the solvent is acetonitrile.

[0045] Example 3: Fabrication of the sample injector and aging of the SPME coating

[0046] After the SPME coating has polymerized, remove the coating and allow it to air dry. Then, use epoxy resin and a curing agent to attach the extraction head to the solid-phase microextraction handle. After the epoxy resin has cured, insert the extraction head into the vaporization chamber of a gas chromatograph for aging at a temperature of 250°C for 2 hours.

[0047] Example 4 Solution preparation

[0048] 1. Preparation of standard solutions

[0049] Accurately weigh or transfer BTEX, PMA, and DPA into a beaker, dissolve them in an appropriate amount of methanol, transfer the solution to a 10.00 mL volumetric flask, dilute to volume with methanol, and obtain a 1.00 mg / mL standard solution.

[0050] 2. Preparation of working solution

[0051] Store the aforementioned standard solutions in a refrigerator (4°C). During the experiment, accurately transfer appropriate amounts of the three substances, dissolve them in methanol, and dilute to a 10.00 mL volumetric flask to obtain a 50.00 μg / mL mixture. Other concentrations of the mixture can be prepared by diluting the 50.00 μg / mL mixture. Transfer 7.00 mL of saturated saline solution to a 15.00 mL extraction flask, add 1.00 mL of the mixture of different concentrations, and obtain the working solution.

[0052] Example 5 HS-SPME Operation Procedure

[0053] Transfer 7.00 mL of saturated sodium chloride solution to a 15.00 mL extraction flask, place a magnetic stir bar inside, add 1.00 mL of a 50.00 μg / mL mixed solution of BTEX, PMA, and DPA, seal the flask with raw rubber tape, plug it with a rubber stopper, and then seal it with an aluminum cap. Maintain the temperature of the S10-3 chamber at 50℃ and the stirring speed at 500 rpm. Fix the extraction flask containing the solution in the S10-3 chamber, insert the syringe into the extraction flask, and push out the extraction head to expose it to the extraction flask. Perform headspace extraction for 30 min. After completion, pull the extraction head back into the protective sleeve and directly insert it into the GC-MS injection port for analysis and detection.

[0054] GC-MS, combining the efficient separation method of gas chromatography with the precise detection method of mass spectrometry, can perform qualitative and quantitative analysis of samples. This application uses an Rtx-5MS column as the separation column and an electron impact ionization (EI) source as the mass separator for the MS. The retention times and qualitative and quantitative analysis of fragment ions for BTEX, PMA, and DPA were obtained, as shown in Table 1.

[0055] Table 1 Characteristic Selected Ions for BTEX, PMA, and DPA

[0056]

[0057] Example 6 Performance Characterization

[0058] 1. Extraction performance of different types of SPME coatings

[0059] ILs and CNTs are widely used in the preparation of SPME coatings to improve their performance and lifespan. Therefore, this experiment doped the polymer monomer with three ILs ([APMIm][NTf2], [HMIm][BF4], [BMIm][PF6]) and five CNMs (MWCNTs, HPCSWCNTs, N-MWCNTs, N-G, N-CMK-3). A total of 24 SPME coatings were prepared, and the extraction capabilities of different types of SPME coatings for BTEX, PMA, and DPA were investigated. The extraction results are shown in the figure. Figure 1 - Figure 5 As shown:

[0060] (1) Extraction of PAM / ILs coating

[0061] SPME coatings containing ILs were prepared using AM as the polymer monomer. Figure 1 It can be seen that, compared with the blank coating without ILs, the PAM / ILs coating showed a significant decrease in the extraction efficiency of PMA; the PAM / ILs coating showed poor extraction efficiency of BTEX; and the PAM / ILs coating showed excellent extraction efficiency of DPA. These results indicate that the PAM / ILs coating exhibits excellent selectivity for DPA.

[0062] (2) Extraction of PAM / CNMs coating

[0063] SPME coatings containing CNMs were prepared using AM as the polymerizable monomer. Figure 2 It can be seen that, compared with the blank coating, the adsorption behavior of different analytes on the PAM / CNMs coating is not regular, indicating that the adsorption of different analytes on the PAM / CNMs coating is a competitive process. Secondly, due to the abundance of defect sites and oxygen-containing carboxyl groups in HPCNTs, PAM / HPCSWCNTs exhibits superior selectivity for DPA compared to other PAM / CNMs coatings. Finally, due to the increased solubility and enhanced conductivity of N-doped functionalized MWCNTs in solvents, as well as the defect-filled tube walls and numerous and extensive interlayer pores of MWCNTs, N-MWCNTs exhibit more uniform adsorption of BTEX, PMA, and DPA compared to other coatings.

[0064] (3) Extraction of PAM / [APMIm][NTf2] / CNMs coating

[0065] like Figure 3 It can be seen that SPME coatings containing the same IL-[APMIm][NTf2] but different CNMs exhibit varying extraction effects on BTEX, PMA, and DPA. Compared to the PAM / [APMIm][NTf2] coating, coatings doped with CNTs show different extraction capabilities for the analytes. However, the figure shows that the PAM / [APMIm][NTf2] / N-G coating exhibits good analytical performance for the analytes, which is mainly attributed to the π-π interaction between [APMIm][NTf2] and N-G.

[0066] (4) Extraction of PAM / [HMIm][BF4] / CNMs coating

[0067] like Figure 4It can be seen that SPME coatings containing the same IL-[HMIm][BF4] but different CNMs have varying extraction effects on BTEX, PMA, and DPA. The results indicate that CNMs have poor dispersibility in solutions containing [HMIm][BF4], and compared to PAM / [HMIm][BF4] coatings, coatings doped with CNTs did not improve the extraction efficiency of the analytes.

[0068] (5) Extraction of PAM / [BMIm][PF6] / CNMs coating

[0069] like Figure 5 It can be seen that SPME coatings containing the same IL-[BMIm][PF6] but different CNMs have varying extraction effects on BTEX, PMA, and DPA. Compared with the PAM / [BMIm][PF6] coating, the PAM / [BMIm][PF6] / CNMs coating shows some improvement in the extraction effect of the analytes, but it is not significant. This is due to the different synergistic effects of [BMIm][PF6] and different CNMs.

[0070] Example 7: Current-voltage behavior and characterization of PAM / N-MWCNTs coating

[0071] 1. I-V behavior of PAM / N-MWCNTs coating

[0072] By comparing the extraction capabilities of different types of SPME coatings for analytes, PAM / N-MWCNTs, a relatively superior extraction coating, were identified. Figure 6 This is the CV curve of 0.05 mol / L AM and 0.02 mg / mL N-MWCNTs in an acetonitrile solution containing 0.08 mol / L tetrabutylammonium perchlorate. Figure 6 In the first scan, a large cathode peak was observed at 1.0 V, likely formed by amino polymerization. As the scan continued, this peak shifted to the left, eventually forming a small peak at 0.6 V. Three smaller peaks were observed between 1.4 and 2.0 V, which overlapped into a single larger peak as the scan continued. During the experiment, the solution color gradually changed from light brown to brownish-red, indicating that some monomers were oxidized to oligomers, and some oligomers dissolved in the solvent. Simultaneously, the coating thickness increased with each scan, and the cathode peak current decreased with increasing scan count, gradually stabilizing. These phenomena indicate that the PAM / N-MWCNTs coating formed on the working electrode and possesses a certain degree of adsorption.

[0073] 2. Microstructure characterization of PAM / N-MWCNTs coating

[0074] Figure 7 - Figure 8The PAM / N-MWCNTs coating was characterized by SEM. Figure 7 As can be seen from the 500x magnification, N-MWCNTs partially adhere to the coating. However, because N-MWCNTs cannot be completely dispersed in the solvent, their adhesion to the coating surface is uneven. Figure 8 As can be seen from the 20,000x magnification, the PAM / N-MWCNTs coating is loose and porous, and has good adsorption performance.

[0075] Example 8: Optimization of HS-SPME conditions, with the analyte concentration set at 6.250 μg / mL during the optimization process.

[0076] 1. Extraction time

[0077] like Figure 9 The figure shows the relationship between different extraction times and corresponding peak areas between 20 and 60 min. The extraction efficiency of the analytes increases with increasing extraction time. At 50 min, the extraction efficiencies of DPA and PMA reach equilibrium. After 50 min, with increasing time, the BTEX extraction amount increases rapidly, while the extraction amounts of DPA and PMA decrease rapidly. This is likely because DPA and PMA are highly volatile, quickly reaching equilibrium between volatilization and extraction, while BTEX rapidly reaches equilibrium with increasing time, at which point the headspace volume is filled with BTEX, thus reducing the extraction efficiency of DPA and PMA. Too short a time will not achieve the best extraction effect, while too long a time will result in too large a difference in the adsorption amounts of the three analytes. Therefore, the optimal extraction time is 50 min.

[0078] 2. Extraction temperature

[0079] like Figure 10 As shown, in HS-SPME, temperature has a dual effect on the extraction process. Increased temperature increases the diffusion coefficient of the analyte, facilitating its escape from the complex matrix and entry into the headspace phase, thus shortening the equilibrium time. However, absorption and adsorption are exothermic processes; under equilibrium conditions, increased temperature reduces the partition coefficient of the analyte between the coating and the sample, leading to decreased sensitivity. Figure 10 The figure shows the relationship between different temperatures and corresponding peak areas. Between 40 and 50°C, due to the different analytes, some substances have reached extraction equilibrium, while others are in a non-equilibrium state. However, after 50°C, the extraction efficiency decreases for all substances. Considering both extraction speed and sensitivity, the extraction temperature selected for this experiment was 50°C.

[0080] 3. Salt concentration

[0081] like Figure 11As shown, salt concentration has two effects on extraction: first, it alters the properties of the phase interface in the solution, thus affecting the partition coefficient; second, it increases the ionic strength of the water sample, reduces the solubility of organic matter in water, and thus acts as salting-out, which is beneficial for the extraction of analytes from the coating. The effect of salt is complex, depending on the polarity of the analyte, the salt concentration, the sample matrix, and the properties of the coating. Figure 11 The figure shows the relationship between different salt concentrations and corresponding peak areas between 0.15 g / mL and 0.45 g / mL. It can be seen from the figure that the effect of salt concentration on my nonpolar compounds BTEX, PMA and DPA is not obvious, but it increases slightly with the increase of salt concentration. According to the figure, the optimal NaCl concentration is 0.35 g / mL.

[0082] 4. Volume of salt water

[0083] The size of the headspace volume directly affects the sensitivity, precision, and equilibration time of the HS-SPME method. A smaller headspace volume results in a higher analyte concentration in the headspace phase, greater extraction yield, and higher analytical sensitivity; the headspace volume also affects the extraction rate. Furthermore, the extraction process is influenced by the partition coefficients of the coating / headspace phase and the headspace phase / solution phase, so there is no clear correlation between headspace volume and its properties. Figure 12 To select the brine volume with the best extraction efficiency for the three analytes, this experiment chose a brine volume of 8.00 mL.

[0084] 5. Stirring speed

[0085] Stirring facilitates the diffusion of analytes from the solution to the gas phase, promotes rapid diffusion equilibrium, and improves extraction efficiency. The effect of stirring rates at five levels (300, 400, 500, 600, and 700) on peak area was investigated. Figure 13 As shown, the results indicate that with the increase of stirring speed, the peak area of ​​DPA gradually increases, while the peak areas of BTEX and PMA gradually decrease. However, the extraction efficiency gradually increases after reaching 600 r / min. This may be because the increased stirring speed may cause the extraction solution to splash onto the extraction head, leading to an increase in the extraction efficiency of the extract. Therefore, 500 r / min is preferred.

[0086] Example 9 Performance Analysis

[0087] 1. Methods and Evaluation

[0088] Under optimized experimental conditions, different concentrations of BTEX, PMA, and DPA were analyzed. Figure 14It can be seen that the peak area of ​​the response increases with increasing concentration. DPA exhibits two different linear concentration ranges: 0.1914–1.562 μg / mL and 1.562–6.250 μg / mL, respectively. The linear concentration ranges for BTEX and PMA are 0.3828–6.250 μg / mL. Simultaneously, three parallel experiments were conducted with one extraction head for the same concentrations of BTEX, PMA, and DPA, with relative standard deviations (RSDs) of 0.78%, 1.6%, and 9.8%, respectively. Comparison of the RSDs of three parallel extraction heads analyzing samples of the same concentration showed values ​​of 5.1%, 12.3%, and 15.2%, respectively, indicating that the extraction coating has good reproducibility.

[0089] Table 2 Analytical parameters of PAM / N-MWCNTs SPME coating on BTEX, PMA, and DPA

[0090]

[0091] Table 3 Comparison of this method with other methods

[0092]

[0093]

[0094] Note: FID-GC (Flame Ionization-Gas Chromatography), FI-HPLC (Fluorescence-High Performance Liquid Chromatography), UV-HPL (Ultraviolet-High Performance Liquid Chromatography), SPE-HPLC (Solid Phase Extraction-High Performance Liquid Chromatography)

[0095] 2. Actual water sample analysis and testing

[0096] Using the methods described above, and under optimized experimental conditions, wastewater from the drainage outlet of the Science College Experimental Building at Honghe University was collected and analyzed to determine the contents of BTEX, PMA, and DPA. The results showed that PMA was detected. Figure 15 To further evaluate the assay method, spiked samples were tested for recovery, with recoveries ranging from 96.40% to 103.5%, indicating that this method can be used for the detection of benzene series compounds (BTEX, PMA, DPA) in water samples (Table 4).

[0097] Table 4 Sample Recovery Rate Determination

[0098]

[0099] Based on the above results, it can be seen in this application that:

[0100] A polymer coating with aniline and p-aminobenzoic acid as monomers and CNTs as dopants was prepared in nitric acid solution via a cyclic method, exhibiting good adsorption performance, stability, and sensitivity. This coating was applied to the determination of BTEX, PMA, and DPA in water samples. Under optimized conditions, the analytical method based on PAM / N-MWCNTs was used to detect BTEX, PMA, and DPA in water samples. BTEX and PMA were not detected in the water samples or in spiked samples, but the detection results for DPA were satisfactory. The recoveries of BTEX, PMA, and DPA were between 92.00% and 103.5%, indicating that this method has good practicality for BTEX, PMA, and DPA. Therefore, this coating can also be used to enrich other highly volatile polar compounds.

[0101] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for detecting benzene series compounds, characterized in that, Includes the following steps: Preparation of PAM / CNMs composite extraction head, The composite extraction head is used to extract benzene compounds via headspace extraction; wherein the benzene compounds are BTEX, PMA, and DPA; wherein BTEX is dimethylbenzene, PMA is p-methylaniline, and DPA is diphenylamine; Gas chromatography-mass spectrometry was constructed, and the benzene series compounds were detected using the aforementioned composite extraction head. The preparation of the composite extraction head includes the following steps: A mixed solution was formed by adding AM (monomer), CNMs (dopant), and tetrabutylammonium perchlorate to a solution in acetonitrile; AM is 6-aminoindole. The electrode system is immersed in the mixed solution, and a composite extraction head is prepared by CV scanning; The composite extraction head was fixed in a self-made injector and dried to obtain the injection device for PAM / N-MWCNTs. The CNMs are N-MWCNTs; the N-MWCNTs concentration is 0.02 mg / mL; the AM concentration is 0.05 mol / L; and the tetrabutylammonium perchlorate concentration is 0.08 mol / L. The headspace extraction of benzene compounds using the composite extraction head includes the following steps: A saturated sodium chloride solution is added to the extraction vessel to form the first mixture. The first mixture was stirred and kept in a constant temperature water bath; Add the benzene compound solution and stir. The injection device is inserted into the extraction container and the composite extraction head is exposed to the headspace of the solution. Headspace extraction is performed under stirring. Retract the composite extraction head into the protective sleeve, quickly insert it into the gas chromatography vaporization chamber, and then push the composite extraction head out for analysis before performing GC-MS separation and detection. The cyclic voltammetry range of the CV scan is 0-2V; the scan rate is 0.05mV / s; and the number of scans is 100 cycles.

2. The method for detecting benzene series compounds according to claim 1, characterized in that, Insert the injection device into the vaporization chamber of the gas chromatograph for aging. Set the injection port temperature to 90℃ and age for 30 minutes. Then, continuously raise the injection port temperature to 230-250℃ and continue aging for 2 hours before storing for later use.

3. The method for detecting benzene series compounds according to claim 1, characterized in that, The temperature of the constant temperature water bath is 50℃; And / or the stirring is magnetic stirring at a speed of 500 r / min.

4. The method for detecting benzene series compounds according to claim 1, characterized in that, The extraction time was 50 minutes. and / or the extraction temperature is 50°C; And / or the saturated sodium chloride concentration is 0.35 g / mL; And / or the volume of saturated sodium chloride is 8.00 mL. And / or the parsing time is 3-5 minutes.

5. A composite extraction head for detecting benzene series compounds, characterized in that, The composite extraction head contains a composite material of PAM and CNMs; Among them, the benzene series compounds are BTEX, PMA, and DPA; where BTEX is dimethylbenzene, PMA is p-methylaniline, and DPA is diphenylamine. The composite extraction head is prepared by the following method: A mixed solution was formed by adding AM, a monomer and CNMs, to an acetonitrile solution containing tetrabutylammonium perchlorate; AM is 6-aminoindole. The electrode system was immersed in the mixed solution, and a composite extraction head was prepared by CV scanning; the CNMs were N-MWCNTs; the N-MWCNTs concentration was 0.02 mg / mL; the AM concentration was 0.05 mol / L; and the tetrabutylammonium perchlorate concentration was 0.08 mol / L. The cyclic voltammetry range of the CV scan is 0-2V; the scan rate is 0.05mV / s; and the number of scans is 100 cycles. The benzene series compounds were extracted using the headspace extraction of the composite extraction head; Gas chromatography-mass spectrometry was constructed, and the benzene series compounds were detected using the composite extraction head.

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