Detection method of nitrobenzene and extraction head

Abstract

The present application discloses a method for detecting nitrobenzene, comprising the following steps: preparing a Poly-PY-DA-IL-CMK-3 composite extraction head; wherein, IL is 1-butyl-3-methylimidazolium hexafluorophosphate; subjecting the nitrobenzene to headspace extraction with the composite extraction head; constructing a gas chromatography-mass spectrometry (GC-MS), and detecting nitrobenzene with the extraction head. The beneficial effect is that the Poly-PY-DA-IL-CMK-3 composite extraction head has better extraction efficiency and mechanical stability for nitrobenzene. Applying the method of the present application to the detection of nitrobenzene in actual samples has good sensitivity and practicability.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical technology, and particularly relates to a method for detecting nitrobenzene and an extraction head. Background Art

[0002] Nitrobenzene is a widely used chemical raw material, commonly used in solvents, the manufacture of aniline, dyes, etc. Due to the stable structure of nitrobenzene, it is relatively difficult to degrade. Therefore, the detection of nitrobenzene in water bodies is of great significance. At present, the detection methods of nitrobenzene mainly include high performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (HPLC-MS) and gas chromatography-mass spectrometry (GC-MS), fluorescence spectrometry, electrochemical biosensor detection, spectroscopic analysis technology, etc. However, the sample pretreatment in almost all of the above methods is complex, time-consuming and costly. Therefore, the sample pretreatment technology has always been one of the important contents in the field of analytical chemistry. Summary of the Invention

[0003] In view of the above existing problems, the present invention provides a method for detecting nitrobenzene and an extraction head.

[0004] According to one aspect of the present invention, there is provided a method for detecting nitrobenzene, comprising the following steps: preparing a Poly-PY-DA-IL-CMK-3 composite extraction head; wherein, IL is 1-butyl-3-methylimidazolium hexafluorophosphate; subjecting the composite extraction head to headspace extraction of nitrobenzene; constructing gas chromatography-mass spectrometry (GC-MS), and using the extraction head to detect nitrobenzene. The beneficial effect is that the Poly-PY-DA-IL-CMK-3 composite extraction head has better extraction efficiency and mechanical stability for nitrobenzene. Applying the method of the present application to the detection of nitrobenzene in actual samples has good sensitivity and practicability.

[0005] In some embodiments, preparing the composite extraction head comprises the following steps: configuring a mixed solution containing PY and DA as comonomers, and CMK-3 and 1-butyl-3-methylimidazolium hexafluorophosphate as dopants; immersing the electrode system into the mixed solution and performing cyclic voltammetry (CV) scanning to prepare the composite extraction head. The beneficial effect is that the obtained composite extraction head has good conductivity and mechanical stability, and has good sensitivity for the detection of nitrobenzene.

[0006] In some embodiments, the PY is 8.6 μg / mL; and / or the DA is 0.14 mg / mL; and / or the CMK-3 is 0.20 mg / mL; and / or the 1-butyl-3-methylimidazolium hexafluorophosphate is 2.0 μL / mL. The beneficial effect is that the obtained composite extraction head has good conductivity and mechanical stability, and has good sensitivity for the detection of nitrobenzene.

[0007] In some embodiments, the following steps are further included: fixing the extraction head in a self-made injector, and after air-drying, an injection device of Poly-PY-DA-IL-CMK-3 is obtained. The beneficial effect is that impurities on the extraction head are purified, and the detection accuracy and sensitivity are improved.

[0008] In some embodiments, the aging conditions are as follows: inserting the injection device into the vaporization chamber of the gas chromatograph for aging, setting the injection port temperature to 90 °C, and aging for 30 min; then continuously raising the injection port temperature to 230 - 250 °C, and continuously aging for 1.5 h and then setting aside for use. The beneficial effect is that impurities on the extraction head can be purified, and the detection accuracy and sensitivity are improved.

[0009] In some embodiments, the headspace extraction of nitrobenzene by the composite extraction head includes the following steps: adding saturated sodium chloride solution into the extraction container to form a first mixed solution; stirring the first mixed solution and performing constant-temperature water bath; then adding nitrobenzene solution and stirring; inserting the injection device into the extraction bottle and exposing the extraction head to the headspace of the solution, and performing headspace extraction under stirring; retracting the extraction head into the protective sleeve, quickly inserting it into the gas chromatograph vaporization chamber, and after pushing out the extraction head for desorption, then performing GC-MS separation and detection. The beneficial effect is that subsequent detection operations can be more conveniently carried out.

[0010] In some embodiments, the temperature of the constant-temperature water bath is: 60 °C; and / or the stirring is magnetic stirring, the stirring speed is 200 - 400 r / min, and the stirring time is 30 - 50 min. The beneficial effect is that the coating of the extraction head is evenly distributed at this temperature, with good stability, thus having better conductivity and sensitivity for detecting target substances.

[0011] In some embodiments, the extraction time is 30 - 50 min; and / or the extraction temperature is 20 - 70 °C; and / or the desorption time is 3 - 5 min. The beneficial effect is that the coating of the extraction head is evenly distributed at this temperature and time, with good stability, thus having better conductivity and sensitivity for detecting target substances.

[0012] 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 effect is that the coating of the extraction head prepared thereby is evenly distributed, with good stability, thus having better conductivity and sensitivity for detecting target substances.

[0013] According to another aspect of the present application, an extraction head for detecting nitrobenzene, characterized in that the extraction head comprises a composite material of PPY, DA, IL, and CMK-3. The beneficial effects are as follows: The coating of the extraction head is evenly distributed and has good stability, thus having better conductivity and sensitivity for detecting target substances. The beneficial effects are as follows: The coating of the extraction head is evenly distributed and has good stability, thus having better conductivity and sensitivity for detecting target substances. Description of the Drawings

[0014] Figure 1 is the infrared spectrum of different extraction head coatings;

[0015] Figure 2 is the SEM image of Poly-PY-DA-IL-CMK-3 magnified 400 times;

[0016] Figure 3 is the SEM image of Poly-PY-DA-IL-CMK-3 magnified 500 times;

[0017] Figure 4 is the SEM image of Poly-PY-DA-IL-CMK-3 magnified 1000 times;;

[0018] Figure 5 is the SEM image of Poly-PY-DA-IL-CMK-3 magnified 10000 times;;

[0019] Figure 6 is the SEM image of Poly-PY-DA-IL-CMK-3 magnified 20000 times;

[0020] Figure 7 is the SEM image of Poly-PY-DA-IL-CMK-3 magnified 40000 times;

[0021] Figure 8 is the voltammetric behavior diagram of the Poly-PY extraction head;

[0022] Figure 9 is the voltammetric behavior of the Poly-PY-DA extraction head;

[0023] Figure 10 is the voltammetric behavior of the Poly-PY-DA-IL extraction head;

[0024] Figure 11 is the voltammetric behavior of Poly-PY-DA-CMK-3;

[0025] Figure 12 is the voltammetric behavior of the Poly-PY-DA-IL-CMK-3 extraction head;

[0026] Figure 13 is the peak area response of p-nitrobenzene for different extraction heads;

[0027] Figure 14 is the performance graph of the stability of the coating;

[0028] Figure 15 is the influence of ionic liquid concentration on the peak area of the p-nitrobenzene response;

[0029] Figure 16 is the influence of mesoporous carbon concentration on the peak area;

[0030] Figure 17 is the influence of stirring rate on the peak area;

[0031] Figure 18 is the influence of extraction temperature on the peak area;

[0032] Figure 19 is the influence of extraction time on the peak area

[0033] Figure 20 is the influence of salt concentration on the peak area;

[0034] Figure 21 is the influence of the volume of saturated salt solution on the peak area;

[0035] Figure 22 is the influence of desorption time on the peak area;

[0036] Figure 23 is the standard curve graph of p-nitrobenzene;

[0037] Figure 24 is the chromatogram of water sample 1;

[0038] Figure 25 is the chromatogram of water sample 2;

[0039] Figure 26 is the chromatogram of water sample 3;

[0040] Figure 27 is the linear correlation graph of water sample recovery. Specific implementation mode

[0041] The present invention will be further described in detail below with reference to the accompanying drawings, operating conditions, examples, etc.

[0042] I. Instrument and reagent description

[0043] 1. Main instruments and models

[0044] Table 1 - Experimental instruments and models

[0045]

[0046] 2. Reagents

[0047] Table 2 Experimental Reagents

[0048]

[0049] II. GC Operating Conditions

[0050] Using the chromatographic column DB-1701 as the separation column, the column oven temperature is 80 °C; the inlet temperature is 230 °C, with splitless injection mode; the pressure is 65.2 kPa; the total flow rate is 40.0 mL / min; the column flow rate is 1.00 mL / min; the linear velocity is 36.8 cm / sec; the purge flow rate is set to 3.0 mL / min; the column oven temperature programming is set as follows: hold at 50 °C for 3 min, then increase the temperature to 110 °C at a rate of 10 °C / min, and then increase the temperature to 120 °C at a rate of 2 °C / min and hold for 5 min. The total duration of the whole program is 19 min. The ion source temperature is 200 °C; the interface temperature is 250 °C; the solvent delay is 3 min. The qualitative and quantitative ions of nitrobenzene are shown in Table 3

[0051] Table 3 is the characteristic selection ion table of nitrobenzene

[0052]

[0053] III. Examples

[0054] Example 1: Preparation of Composite SEPM Head

[0055] Assemble a three-electrode electrochemical working system with a platinum wire as the counter electrode, a saturated calomel electrode as the reference electrode, and a stainless steel wire as the working electrode. Immerse the three electrodes in a deionized water mixed electrolyte containing 8.6 μg / mL pyrrole (PY), 0.14 mg / mL dopamine (DA), 0.20 mg / mL ordered mesoporous carbon (CMK-3), and 2.0 μL / mL ionic liquid (IL). In the cyclic voltammetry range of 0 - 1.5 V, scan 100 cycles at a speed of 0.05 mV / s; then, take out the prepared SPME head of Poly-PY-DA-IL-CMK-3, rinse it with ethanol and deionized water to remove the impurities on its surface, and dry it for later use. Then, bond the extraction head to the handle of the self-made injector in this experiment with a mixed resin of epoxy resin and polyamide resin in a ratio of 1:1, and dry it. Next, use the injector obtained after curing the resin to perform headspace extraction of nitrobenzene. Then, insert the SPME head into the GC injection port through the injection handle. At the injection port temperature of 250 °C, age the extraction head at a programmed gradient temperature. First, age it at 90 °C for 30 min, and then gradually increase the temperature to 250 °C and age it for 90 min, and then take it out for later use

[0056] In addition, the preparation methods and conditions of the following extraction heads, namely a. pyrrole (PY); b. pyrrole + dopamine (PY-DA); c. pyrrole + dopamine + ionic liquid (PY-DA-IL); d. pyrrole + dopamine + mesoporous carbon (PY-DA-CKM-3), are the same as above.

[0057] Example 2: Headspace extraction

[0058] Add 5 mL of prepared saturated sodium chloride solution into a 20 mL extraction bottle, and add a magnetic stir bar. Add the nitrobenzene standard solution, then seal it airtight with raw tape, plug in a rubber stopper, and seal it with an aluminum cap. Then, place this extraction bottle in a constant temperature water bath at 50 °C. Under magnetic stirring at 500 r / min, insert the self-made injector containing the extraction head in this example into the headspace extraction bottle, and push the extraction head out of the protective sleeve and expose it above the extraction bottle for headspace extraction for 40 min. After completion, retract the extraction head into the protective sleeve, insert it into the injection port of the gas chromatography vaporization chamber that is ready for standby in the shortest time, and push out the extraction head in the handle protective sleeve. After fully desorbing for 3 min, pull out the injector containing the extraction head, and start the GC-MS to automatically perform separation and detection.

[0059] Example 3: Infrared characterization of the extraction head

[0060] Figure 1 are the infrared spectra of different extraction head coatings.

[0061] In the figure, a. pyrrole (PY); b. pyrrole + dopamine (PY-DA); c. pyrrole + dopamine + ionic liquid (PY-DA-IL); d. pyrrole + dopamine + mesoporous carbon (PY-DA-CKM-3); e. pyrrole + dopamine + ionic liquid + mesoporous carbon (PY-DA-IL-CMK-3); it can be clearly seen in the spectrum that there is an N-H bond at 1350 - 000 cm -1 and an olefin C=C bond at 1675 - 1640 cm -1 which are composed of the pyrrole structure, and there is an amino group at 3500 - 3100 cm -1 and at 3500 - 3200 cm -1The presence of intermolecular O-H bonds proves the existence of the dopamine structure, indicating that dopamine can be adsorbed onto the extraction head. The infrared spectra of b and e show obvious offset changes in the figure, especially the peak position change of e.PY-DA-IL-CMK-3. This is mainly due to the interaction between the two meta-hydroxy groups in the DA structure and another hydroxyl group or amino group. The other infrared spectra have relatively large similarities because they have little impact on the functional groups of the adsorbed substances. However, this does not mean that the doped substances are meaningless. They also play a role in improving the microscopic configuration of the coating surface. The infrared spectrum of the coating polymerized after doping IL and CMK-3 shows an obvious shift to shorter wavelengths. This is because the re-doping of pyrrole and dopamine with IL and OMC equalizes the electron cloud density, thereby reducing the stretching vibration frequency and causing a significant shift of the absorption peak of the proton donor to lower wavenumbers. Further, it can be concluded that the extraction coating, which is a polymerized monomer of pyrrole and dopamine, can have a certain impact, indicating that the two substances interact with each other.

[0062] Characterization of the Microscopic Morphology of the Extraction Head in Example 4

[0063] The experiment also characterized the microscopic morphology of the prepared Poly-PY-DA-IL-CMK-3 extraction head using SEM. From its Figure 2 and Figure 3 it can be seen that this type of extraction can adhere well to the stainless steel wire and has a porous structure. To further characterize its microscopic structure, from Figure 4 (magnification 20,000 times), Figure 5 (magnification 40,000 times), it is clearly seen that it has a unique cauliflower-like structure and a porous three-dimensional structure. Such a structure provides innate advantages for molecular adsorption or loading of other nanomaterials. From Figure 6 and Figure 7 more microscopic structural characterizations can be seen. When 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid (IL) and ordered mesoporous carbon (CMK-3) are added to the electrolyte, they can significantly fill the surface and gaps of the co-monomer, so that the structure of the extraction head becomes compact and ordered.

[0064] CV of the Electrochemical Polymerization Preparation of the Poly-PY-DA-IL-CMK-3 Extraction Head in Example 5

[0065] Record the CV diagram of the electrochemical preparation of the Poly-PY+DA+IL+CMK-3 extraction head. As Figure 8 shown, at a potential of 0.8 V, an obvious oxidation peak of PY appears. And from Figure 9It can be seen that only when the comonomer polymerizes, the oxidation peak is not obvious and there is still not much change as the number of cycles increases. Since DA has better solubility than PY, it adsorbs onto the steel wire first, and PY adsorbs later. Under neutral conditions, DA has weak electron transfer and poor conductivity. As Figure 10 and Figure 11 shown, the response current in the CV diagrams doped with IL or CMK-3 separately increases significantly. In comparison, CMK-3 has a better effect than IL. One reason is due to the structural advantages of the mesoporous carbon material, and the other reason is that the selected ionic liquid has low solubility and cannot be well integrated into the electrolyte. As Figure 12 shown, the diagram becomes significantly better after both are added. At the same time, the oxidation peak potential of DA is approximately 0.4V. At a potential of 0.4V, an obvious oxidation peak appears. As the voltage increases to 0.8V, an over-oxidation peak appears. With the increase in the number of polymerization cycles and the growth of the polymerization time, the peak current gradually increases and becomes more uniform and dense, highlighting the advantages of doping and significantly indicating that the polymerized coating has good conductivity after being doped with IL and CMK-3.

[0066] Example 6 Comparison of the responses of different extraction heads to nitrobenzene

[0067] The example is mainly to verify the detection of the peak area of the same target analyte nitrobenzene by different extraction heads. From Figure 13It can be seen that the peak area of the target analyte of the extraction head of PY-DA monomer is the largest, but it is not much different from the peak area of the extraction head of PY-DA-IL-CMK-3; the peak area of the target analyte detected by the extraction head prepared by adding IL under polymerization conditions is significantly smaller than that of the extraction head of only the monomer. For the extraction head prepared by doping and depositing IL liquid in the electrolyte, the reason for such a result is that IL has a certain impact on the microstructure formed by the polymerization of PY-DA monomer during the electrodeposition process. Also, because IL liquid is doped with pyrrole monomer and co-deposited on the stainless steel wire, filling the voids formed by polypyrrole and dopamine monomer, and then occupying the specific surface area of the extraction head on the basis of poly PY-DA, thus having a reverse effect and reducing its adsorption capacity. Then, observing the peak area of the target analyte detected by the extraction head prepared by adding only CMK-3 to PY-DA monomer in the electrolyte is even smaller than the peak areas of the previous two, and the single addition effect is also not good. However, the effect of doping IL and CMK-3 in PY-DA is not much different from that of only the monomer, but macroscopically, its tightness and the uniformity of the coating layer have obvious effects. When doing repeated experiments, its reproducibility performance is better and a better effect is achieved. CMK-3 is an ordered porous carbon material with characteristics such as high specific surface area, large pore volume, regular pore channels, and narrow pore size distribution. The regular structural arrangement and rich microporous structure of the ordered porous carbon material show great advantages, so it has an ultra-large specific surface area that cannot be compared with other materials. Because of this advantage, although the extraction head prepared only with the monomer has a good absorption peak, the coating is rough, not smooth, and the coating layer is easy to fall off. Making the extraction head prepared by doping an appropriate amount of CMK-3 and IL liquid is more effective and more valuable compared with the extraction head prepared only by doping CMK-3 or IL liquid with the co-monomer.

[0068] Example 7 Investigation of Coating Stability

[0069] The stability of the coatings of the two relatively best extraction heads prepared in the experiment was investigated, and the response of the peak area of the target analyte nitrobenzene under the same concentration and conditions was studied as the number of experiments increased. From Figure 14It can be seen that PY-DA-IL-CMK-3 has better stability. When 2 uL / mL of IL and 0.01 mg / mL of CMK-3 are appropriately added, although the peak area response of the monomer PY-DA to nitrobenzene is better at the beginning, the experimental results of multiple uses show that the stability is not good, and there is a phenomenon of coating peeling off during the experiment. Therefore, the extraction head doped with an appropriate concentration of IL and CMK-3 is selected as the best. At the same time, compared with the commercial quartz fiber, the mechanical strength of the extraction fiber made of stainless steel wire is significantly enhanced, and there will be no phenomenon of easy breakage like the quartz fiber. Since the new coating is a pure inorganic carbon material, compared with the commercial organic polymer coating, it has a smaller swelling effect during the direct extraction process of the solution, and the service life can be extended. Many literatures also confirm that the thermal stability of the coating made of stainless steel wire is significantly better than that of the commercial coating, and it is more suitable for the extraction and analysis of high-boiling-point samples.

[0070] Condition Optimization of Example 8

[0071] 1. Influence of Concentration

[0072] Considering the influence of the IL concentration on the peak area of the nitrobenzene response. As Figure 15 shown, when the concentration of IL in the electrolyte is 0 - 10 μL / mL, the response decreases with the increase of the concentration; however, when the concentration exceeds 10 μL / mL, the response becomes smaller, and the whole process shows a downward trend. The reason for this may be that when too much IL exists on the extraction head, it will affect the spatial porosity of the coating. Too much IL fills into the voids between polypyrrole and dopamine, resulting in the occupation of the original space. At the same time, too much IL is adsorbed, resulting in a significant reduction in the effective adsorption specific surface area of the polypyrrole and dopamine coating. Therefore, the area for adsorbing the target analyte during the extraction process decreases, ultimately affecting the size of the response peak area.

[0073] 2. Influence of CMK-3 Concentration

[0074] Figure 16It shows the response of the peak area of p-nitrobenzene to the concentration of CMK-3 from 0.01 - 0.06 mg / mL. When the concentration of CMK-3 is in the range of 0.00 - 0.02 mg / mL, among which the monomer without adding CMK-3 has the maximum response to the target analyte, the response peak area of the target analyte is the largest when the concentration of nitrogen-doped mesoporous carbon is 0.02 mg / mL. After that, as the concentration of nitrogen-doped mesoporous carbon increases, the response peak area of the target analyte continuously decreases, which should be associated with the solubility of CMK-3 in the electrolyte solution and the effective adsorption of the polymerization coating on the monomer. When the concentration of CMK-3 increases, its effective concentration in the aqueous solution decreases, resulting in that during electropolymerization, too much nitrogen-doped mesoporous carbon cannot be polymerized on the stainless steel wire but remains in the electrolyte solution. Secondly, a fixed amount of pyrrole and dopamine have more space to deposit on the stainless steel wire, correspondingly occupying the space that should have been for nitrogen-doped mesoporous carbon.

[0075] 3. Optimization of stirring rate

[0076] As Figure 17 shown, the influence of the stirring rate on the diffusion of p-nitrobenzene from the liquid phase to the gas phase in the headspace bottle and thus on the response of its peak area was investigated. However, too high a rotation speed is likely to bring too large an error. Therefore, after orthogonal experiments, after the target analyte was extracted and detected at a rotation speed from 300 - 700 r / min. As shown in the figure, the results show that the peak area of the target analyte gradually increases from 300 - 400 r / min, and then starts to decrease and finally the decreasing trend becomes stable. The greater the speed, the more difficult it is to control, which will lead to larger systematic errors and accidental errors in the experiment. Therefore, according to the instrument conditions of this laboratory, 400 rpm is selected as the most appropriate stirring rate.

[0077] 4. Optimization of extraction temperature

[0078] As Figure 18 shown, the change of the peak area of the target analyte was investigated when the extraction temperature varied from 40 - 80 °C. As the temperature increased, the peak area of the target analyte extracted in the experiment became larger and larger, but after reaching a certain value, it started to decline, as Figure 18As shown in the figure, the extraction efficiency is the highest at 50°C. At this time, as the temperature rises, the extraction efficiency of the coating increases. However, when the temperature continues to rise, the extraction effect decreases instead. This should be related to the properties of the extraction head prepared in the experiment, the volatility of the target analyte, and the set temperature. Although the increase in temperature will increase the volatility of the analyte to be measured, it will cause the analyte to be unable to be adsorbed well on the extraction head, but instead circulate and volatilize in the headspace vial. Of course, too high a temperature will also increase the vapor pressure of the gas phase in the headspace vial and promote the adsorption process of the coating. However, since the adsorption of the extraction head is an exothermic process, too high a temperature will cause the distribution coefficient to decrease and the adsorption capacity of the coating to decrease, resulting in a decrease in the sensitivity of the extraction head when detecting the target analyte. This leads to an unsatisfactory detection effect and the inability to measure the desired optimal peak area. Therefore, it is necessary to analyze the optimization conditions of the extraction head prepared in the experiment. Therefore, in this experiment, 50°C is used as the best temperature condition for the headspace extraction experiment.

[0079] 5. Optimization of Extraction Time

[0080] As Figure 19 shown in the figure, in order to explore the extraction heads prepared under different factors, the effect of extraction time on the extraction efficiency was further investigated. From the curve relationship of nitrobenzene, it can be seen that as the extraction time increases, the peak area increases; the peak area of the target analyte is the largest at 40 min. When the extraction time is further increased, the response decreases accordingly. This may be because the adsorption of the extraction head reaches equilibrium at 40 min. After more than 40 min, the adsorbed substances will be desorbed, resulting in a worse effect. Therefore, the extraction time selected in this experiment is 40 min, which has the best effect.

[0081] 6. Optimization of Salt Concentration

[0082] As Figure 20 shown in the figure, the effect of the gradual increase in salt concentration in the range of 0.05 - 0.30 g / mL on the peak area of the target analyte was investigated. From Figure 20 it can be seen that the peak area of nitrobenzene shows an upward trend with the increase in salt concentration and reaches the maximum at 0.30 g / mL, which is the saturated salt solution concentration. This should be because increasing the ionic strength of the solution is beneficial to reducing the solubility of organic substances and promoting their conversion to the gas phase, which is beneficial to the progress of headspace extraction. Therefore, as the salt concentration increases, the extraction efficiency gradually increases. Even when the salt concentration reaches saturation, it still shows an upward trend. Therefore, it is most appropriate to use the saturated salt concentration as the headspace extraction solvent for nitrobenzene.

[0083] 7. Optimization of the Volume of Saturated Salt Solution

[0084] As Figure 21 shown in the figure, the experiment investigated the effect of the gradual increase in the volume of saturated salt solution in the range of 4 - 8 mL on the peak area of the target analyte nitrobenzene. FromFigure 21 It can be seen that the peak area of nitrobenzene begins to increase with the increase in the volume of the saturated salt solution. After reaching 6 mL, further increasing the volume results in a decreasing trend. Firstly, for the headspace extraction method, the analysis sensitivity is interrelated with the sample volume and the headspace volume. Increasing the sample amount improves the reproducibility and the detected amount. However, when it reaches a certain extent, it reaches the maximum limit. Further increasing the volume occupies the gas phase volume volatilized during the extraction process in a 20 mL extraction bottle, leading to a decrease in the peak area of nitrobenzene. Therefore, the best effect is achieved when 6 mL of the saturated salt concentration volume is taken in this experiment.

[0085] 8. Optimization of the desorption time

[0086] As Figure 22 shown, the influence of gradually increasing the desorption time from 1 - 5 min on the peak area of the target analyte nitrobenzene was investigated. As can be seen from Figure 22 shown, the peak area of nitrobenzene is the largest when the desorption time is 3 min. A major reason is that the boiling point temperature of nitrobenzene itself is around 200 °C and factors such as the set temperature of the GC affect its desorption time. At the same time, choosing an appropriate desorption temperature and sufficient desorption time is beneficial to improving the measurement sensitivity and can also eliminate the memory effect. Therefore, the optimal desorption time for the experiment is 3 min.

[0087] Example 9 Analytical performance

[0088] 1. Method and evaluation

[0089] Under the optimized experimental conditions, nitrobenzene at different concentrations was analyzed respectively. As can be seen from Figure 23 it, its response peak area increases with the increase in concentration, showing a good linear correlation. It can be concluded that this method has good sensitivity and a detection limit (three times the signal-to-noise ratio, 3σ). This indicates that this analytical method has a wide linear range and sensitivity. At the same time, using 1 extraction head to conduct parallel experiments on nitrobenzene at the same concentration 3 times, the relative standard deviation (RSD) is 1.68% respectively. Comparing the analysis of nitrobenzene at the same concentration with 3 parallel-prepared extraction heads, the RSD values are 3.99% respectively, indicating that the experimental precision is relatively high and the reproducibility of the extraction head is good.

[0090] Table 4 - Analytical parameters of the Poly-PY-DA-IL-CMK-3 extraction head for nitrobenzene

[0091]

[0092] 2. Analysis and detection of actual water samples

[0093] To verify the practicability of this treatment method, in the experiment, it was used to extract water samples from the water body in real life for analysis. First, take the lake water from the famous pond in the school. After standing for 1 hour, filter out the solid residues, and use the filtrate as the detection water sample. Then, use this water sample to replace the Watsons deionized water used in the previous experiment, and prepare a saturated sodium chloride solution with the water sample. Then, after the above steps and processes, after instrument detection, there is no target analyte nitrobenzene, indicating that the school lake water is not polluted by nitrobenzene. To further evaluate this determination method, spiked recovery of the sample was carried out. As Figure 24 、 Figure 25 、 Figure 26 shown, 5, 10, and 15 μg / mL of the sample were respectively pipetted into 6.0 mL of the saturated sodium chloride of this water sample for extraction analysis in three parallel experiments; Figure 27 is the linear relationship of the spiked water sample, indicating that at gradient concentrations, the detected peak areas also have a certain positive linear correlation. The recovery rate is between 97.5 - 104.3%, indicating that this method can be used for the detection of actual samples.

[0094] Table 5 Determination of Sample Recovery Rate

[0095]

[0096] In this application, based on the above results, optimized experimental conditions were selected. Using PY-DA as the functional monomer, IL and CMK-3 as dopants, a Poly-PY-DA-IL-CMK-3 extraction head was prepared by CV. Taking nitrobenzene as the analysis object, the performance of the extraction head was investigated, and the experimental conditions affecting SPME: IL concentration, CMK-3 concentration, extraction temperature and time, stirring rate, saturated salt solution volume, desorption time, etc. were optimized, and a method for analyzing nitrobenzene by HS-SPME was established.

[0097] Due to the large adsorption capacity and stability of IL and CMK-3, as the scanning rate increases, the membrane structure becomes tighter, the specific surface area of the extraction head increases, the extraction efficiency enhances, the RSD of the extraction head decreases, the reproducibility becomes better, and the stability is stable. Thus, the stability of the coating and the sensitivity of the analysis method are improved, and the analysis of nitrobenzene in water pollution is further broadened. At the same time, it can be seen that the Poly-PY-DA-IL-CMK-3 extraction head can also be used to detect volatile organic pollutants. The extraction head has small and uniform pores, a large specific surface area, good extraction effect, and a long service life, which is conducive to the detection of nitrobenzene in actual water bodies.

[0098] The above are only some embodiments of the present invention. For those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for detecting nitrobenzene, characterized in that It includes the following steps: Prepare a Poly-PY-DA-IL-CMK-3 composite extraction head, where IL is 1-butyl-3-methylimidazolium hexafluorophosphate; Headspace extract nitrobenzene with the composite extraction head; Construct a gas chromatography-mass spectrometry (GC-MS), and use the extraction head to detect nitrobenzene, where preparing the composite extraction head includes the following steps: Configure a mixed solution containing pyrrole PY and dopamine DA as comonomers, ordered mesoporous carbon CMK-3 and 1-butyl-3-methylimidazolium hexafluorophosphate as dopants; Insert the electrode system into the mixed solution and perform CV scanning to prepare the composite extraction head.

2. The method for detecting nitrobenzene according to claim 1, wherein the PY is 8.6 μg / mL; and / or the DA is 0.14 mg / mL; and / or the CMK-3 is 0.20 mg / mL; and / or the 1-butyl-3-methylimidazolium hexafluorophosphate is 2.0 μL / mL.

3. The detection method of nitrobenzene according to claim 1, characterized in that, It further includes the following steps: Fix the extraction head in a self-made injector, and after air-drying, obtain an injection device of Poly-PY-DA-IL-CMK-3.

4. The detection method of nitrobenzene according to claim 3, characterized in that, The aging conditions are: Insert the injection device into the vaporization chamber of the gas chromatography for aging, set the injection port temperature to 90 °C, and age for 30 min; then continuously raise the injection port temperature to 230-250 °C, and continuously age for 1.5 h and then set aside for use.

5. The detection method of nitrobenzene according to claim 3, characterized in that, The headspace extraction of nitrobenzene by the composite extraction head includes the following steps: Add saturated sodium chloride solution to the extraction bottle to form a first mixed solution; Stir the first mixed solution and perform constant temperature water bath; Add nitrobenzene solution and stir; Insert the injection device into the extraction bottle and expose the extraction head to the solution headspace, and perform headspace extraction under stirring; Retract the extraction head into the protective sleeve, quickly insert it into the gas chromatography vaporization chamber, and after pushing out the extraction head for desorption, then perform GC-MS separation and detection.

6. The detection method of nitrobenzene according to claim 5, characterized in that The temperature of the constant temperature water bath is: 50 °C; and / or the stirring is magnetic stirring, the stirring speed is 200-500 r / min, and the stirring time is 30-50 min.

7. The method for detecting nitrobenzene according to claim 5, wherein the extraction time is 30-50 min; and / or the extraction temperature is 20-70 °C; and / or the desorption time is 3-5 min.

8. The detection method of nitrobenzene according to claim 1, characterized in that, The cyclic voltammetry range of the CV scanning is 0-1.5 V; the scanning rate is 0.05 mV / S, and the number of scans is 100 cycles.

9. An extraction head for detecting nitrobenzene, characterized in that, The extraction head is a composite material of PY, DA, IL, and CMK-3; wherein, the preparation method of the extraction head includes the following steps: Configure a mixed solution containing pyrrole PY and dopamine DA as comonomers, ordered mesoporous carbon CMK-3 and 1-butyl-3-methylimidazolium hexafluorophosphate as dopants; Insert the electrode system into the mixed solution and perform CV scanning to prepare the composite extraction head.

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