A method for simultaneous determination of multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples

Abstract

This invention discloses a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons (PAHs) in environmental water samples, comprising the following steps: Step 1, preparing a cobalt / nickel bimetallic organic framework composite molybdenum sulfide (CNMMS) coating material; Step 2, preparing solid-phase microextraction (SPE) fibers; Step 3, performing immersion SPE; and Step 4, determining multiple PAHs in the sample using gas chromatography-mass spectrometry (GC-MS). This invention prepares a CNMMS coating material, which is then coated onto a stainless steel wire substrate to form a coating. This coating serves as the extraction head for SPE to extract PAHs from environmental water samples. By combining this method with GC-MS, it can simultaneously detect PAHs in environmental water samples with different properties, exhibiting a low detection limit, a wide linear range, good stability in determining multiple PAHs in environmental water samples, and excellent accuracy.

Description

Technical Field

[0001] This invention relates to the field of water quality monitoring technology, and more particularly to a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons (HPAs) in environmental water samples. A method for determining halogenated PPAs based on CNMMS coating materials and its application. Background Technology

[0002] Halogenated polycyclic aromatic hydrocarbons (PAHs) are structurally similar to hybrids of chloro / bromodioxins and PAHs, and their formation process is also similar to that of dioxins and PAHs. Studies have shown that thousands of halogenated PAH homologues exist in the environment, but only a few dozen have been detected to date. Halogenated PAHs can persist stably in the environment, exhibiting carcinogenic, teratogenic, and mutagenic properties comparable to or even higher than their parent PAHs, posing a potential threat to the ecological environment and human health, and are a new class of high-risk toxic organic pollutants. It has been confirmed that halogenated PAHs can be generated during tap water disinfection and pipeline transportation. Furthermore, halogenated PAHs have also been detected in surface water and sewage, mainly due to urbanization processes such as electronic waste recycling, chlorination industries, and vehicle exhaust, which generate halogenated PAHs and further release them into water bodies through sewage discharge, surface runoff, and groundwater infiltration. Therefore, there is an urgent need to develop simple, economical, and efficient analytical methods to determine halogenated PAHs in different types of water bodies.

[0003] Due to the extremely low concentration of halogenated polycyclic aromatic hydrocarbons (HPAHs) in aqueous environments, the complex environmental media, and significant matrix interference, extremely high demands are placed on analytical methods. Pretreatment techniques are fundamental to analytical methods. Currently, most pretreatment studies of HPAHs in aqueous phases are based on liquid-liquid extraction and solid-phase extraction (SPME). Some samples requiring purification require further removal of impurities in the matrix, such as lipids and pigments, using silica gel columns, activated carbon columns, or gel permeation chromatography. However, these methods have drawbacks, such as the use of large amounts of organic solvents affecting operator health, long pretreatment times, and low extraction efficiency. Solid-phase microextraction (SPME) effectively solves these problems. SPME is a pretreatment technique that integrates sample collection, extraction, concentration, and injection. Compared to other methods, it allows direct sample contact, eliminating the need for cumbersome pretreatment work, reducing analyst exposure to toxic reagents, and is environmentally friendly, more efficient, and more environmentally friendly. Given the limited variety and high cost of commercially available SPME fibers, developing fibers with high extraction performance, good selectivity, and stable durability is currently a hot topic in SPME research. Currently, gas chromatography-tandem mass spectrometry (GC-MS) is the most commonly used method for the chemical analysis of halogenated polycyclic aromatic hydrocarbons (HPAHs) in water. However, since the occurrence level of HPAHs in the aquatic environment is very low, this places high demands on the detection limit of the instrument. Summary of the Invention

[0004] Purpose of the invention: To address the drawback of high instrument detection limits for the detection of halogenated polycyclic aromatic hydrocarbons (HPAHs), this invention provides a method for simultaneously determining multiple HPAHs in environmental water samples.

[0005] Technical solution: To solve the above problems, this invention employs a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples, comprising the following steps:

[0006] Step 1: Preparation of cobalt / nickel bimetallic organic framework composite molybdenum sulfide coating material; 2,5-dihydroxyterephthalic acid, cobalt nitrate hexahydrate, and nickel nitrate hexahydrate are weighed and dissolved in a mixture of N,N-dimethylformamide, anhydrous ethanol, and deionized water to prepare a bimetallic organic framework; molybdenum sulfide is added, with the addition ratio of molybdenum sulfide being 10%-50% of the mass of the synthesized bimetallic organic framework; the mixture is transferred to a reaction vessel and placed in an oven for crystallization; the crystallized product is cooled to room temperature, centrifuged, and washed, and then impregnated with methanol to displace N,N-dimethylformamide; after impregnation, it is placed in an oven for drying to obtain the cobalt / nickel bimetallic organic framework composite molybdenum sulfide coating material;

[0007] Step 2: Preparation of solid-phase microextraction fibers; Stainless steel wire was used as the substrate for preparing cobalt / nickel bimetallic organic framework composite molybdenum sulfide fibers. One end of the stainless steel wire was etched with hydrofluoric acid solution. The stainless steel wire was cleaned and dried. Silicone glue was placed in a centrifuge tube, diluted with n-hexane, and sonicated until homogeneous. The diluted silicone glue solution was coated onto the etched stainless steel wire. The stainless steel wire was inserted into the cobalt / nickel bimetallic organic framework composite molybdenum sulfide coating material and rotated repeatedly to obtain coated fibers with a thickness of 40-50 μm and a coating length of 1.0-1.5 cm. Finally, the coated fibers were dried at room temperature. The prepared coated fibers were assembled into a syringe and aged to obtain solid-phase microextraction fibers.

[0008] Step 3: Immersion solid-phase microextraction; Adjust the pH range of the sample solution to 6-8, immerse the solid-phase microextraction fiber in the sample solution, stir and extract, and after extraction, retract the solid-phase microextraction fiber into the syringe and thermally desorb at the gas phase inlet.

[0009] Step 4: Determine the presence of various halogenated polycyclic aromatic hydrocarbons in the sample using gas chromatography-mass spectrometry. Further, in step 1, weigh 0.1485 g of 2,5-dihydroxyterephthalic acid, 0.1803-0.5049 g of cobalt nitrate hexahydrate, and 0.1800-0.5400 g of nickel nitrate hexahydrate, respectively.

[0010] Furthermore, in step 1, the volume ratio of the mixture of N,N-dimethylformamide, anhydrous ethanol, and deionized water is 1:1:1.

[0011] Furthermore, in step 1, the crystallization temperature is 100-120℃ and the crystallization time is 18-24h.

[0012] Furthermore, in step 2, before etching the stainless steel wire, the stainless steel wire is first ultrasonically cleaned with methanol and then with ultrapure water for 10-15 minutes, and then dried in a 60℃ oven.

[0013] Furthermore, in step 2, take 0.4-0.6g of silicone gel into a centrifuge tube, add 2.0-3.0mL of n-hexane to dilute it, and then sonicate until homogeneous.

[0014] Furthermore, in step 2, the specific operation of aging is as follows: place the syringe containing the coated fiber into the gas phase injection port, and age it for 20-30 minutes at 150℃, 200℃, 260℃ and 280℃ respectively.

[0015] Furthermore, in step 3, the specific operation of extraction is as follows: add 0.50-0.75g of sodium chloride, stir at a constant speed of 500-800rpm at an extraction temperature of 50-60℃, and the extraction time is 25-35min.

[0016] Furthermore, in step 3, the thermal desorption temperature is 260-280℃, and the desorption time is 2-5 min.

[0017] Furthermore, in step 4, the gas chromatography-mass spectrometry (GC-MS) analytical method uses a 30m × 0.25mm × 0.25μm DB-5MS column, with high-purity helium (≥99.999%) as the carrier gas, a flow rate of 1mL / min, and splitless injection. The column temperature program is as follows: initial temperature 60-70℃, held for 1-2 min, then increased to 280-300℃ at 6-15℃ / min, held for 3-7 min. The injection port temperature is 260-280℃, the electron accelerating voltage is 70eV, the ion source is an electron impact ionization source at 230-280℃, and the transfer line temperature is 260-280℃.

[0018] Beneficial effects: Compared with the prior art, the present invention prepares a CNMMS coating material and coats it on the surface of a stainless steel wire substrate to form a coating. This coating is used as an extraction head for solid-phase microextraction to extract halogenated polycyclic aromatic hydrocarbons in environmental water samples. By combining it with gas chromatography-mass spectrometry, halogenated polycyclic aromatic hydrocarbons in environmental water samples with different properties can be detected simultaneously. The method has a low detection limit, a wide linear range, and good stability in determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples. At the same time, the method has excellent accuracy. Attached Figure Description

[0019] Figure 1Scanning electron microscope (SEM) images of coating materials with different composite ratios in Examples 1-5: (a) 0.0115 g-10%; (b) 0.023 g-20%; (c) 0.0345 g-30%; (d) 0.0460 g-40%; (e) 0.0575 g-50%; and (f) CNMMS solid-phase microextraction fibers prepared.

[0020] Figure 2 Infrared spectra of coatings with different CNM and MoS2 composite ratios in Examples 1-5;

[0021] Figure 3 The graph shows a comparison of the extraction capabilities of materials prepared with different CNM and MoS2 composite ratios in Examples 1-5 for 11 kinds of halogenated polycyclic aromatic hydrocarbons in water.

[0022] Figure 4 Chromatograms of 11 halogenated polycyclic aromatic hydrocarbons and chromatograms of different types of environmental water samples;

[0023] Figure 5 For example, different Co 2+ and Ni 2+ Comparison of extraction capabilities of bimetallic organic frameworks with different composite ratios;

[0024] Figure 6 X-ray diffraction (XRD) patterns of CNM, MoS2 and CNMMS coated materials;

[0025] Figure 7 A comparison of the extraction capabilities of CNM, MoS2 and CNMMS solid-phase microextraction fibers for 11 halogenated polycyclic aromatic hydrocarbons in water;

[0026] Figure 8 Thermogravimetric analysis curves of MoS2, CNM and CNMMS coating materials;

[0027] Figure 9 The XRD patterns of MoS2, CNM, and CNMMS coatings are shown in comparison between un-soaked and 7-day-soaked materials.

[0028] Figure 10 The contact angle characterization results are for MoS2, CNM, and CNMMS coating materials;

[0029] Figure 11 A comparison chart showing the extraction capabilities of two extraction methods for 11 halogenated polycyclic aromatic hydrocarbons in water;

[0030] Figure 12 Example 1: Comparison of the ability of CNMMS self-made fiber and commercial fiber to extract 11 halogenated polycyclic aromatic hydrocarbons. Detailed Implementation

[0031] Example 1

[0032] This embodiment describes a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in an environmental water sample, comprising the following steps:

[0033] Step 1: Preparation of cobalt / nickel bimetallic organic framework composite molybdenum sulfide coating material. Weigh 0.1485 g of 2,5-dihydroxyterephthalic acid, 0.3606 g of cobalt nitrate hexahydrate, and 0.3600 g of nickel nitrate hexahydrate, and dissolve them in 60 mL of a mixture of N,N-dimethylformamide, anhydrous ethanol, and deionized water (volume ratio 1:1:1). Sonicate the solution for a period of time until the reactants are completely dissolved to prepare the bimetallic organic framework. Then add molybdenum sulfide at a ratio of 30% of the synthesized bimetallic organic framework mass. Based on multiple bimetallic organic framework synthesis experiments, the dried bimetallic organic framework was found to be stable at approximately 0.115 g. Therefore, 0.0345 g of MoS2 was added, i.e., an addition of 30% by mass. The mixture was transferred to a stainless steel reactor lined with polytetrafluoroethylene and placed in an oven at 100°C (temperature can be selected from 100-120°C) for crystallization for 24 hours (crystallization time can be selected from 18-24 hours). After natural cooling to room temperature, the product was collected in centrifuge tubes and centrifuged. It was then washed three times with N,N-dimethylformamide to remove unreacted reactants. After that, it was impregnated with methanol for 24 hours to displace N,N-dimethylformamide. After impregnation, it was dried in an oven to obtain a cobalt / nickel bimetallic organic framework composite molybdenum sulfide (CNMMS) coating material.

[0034] Step 2: Preparation of Solid-Phase Microextraction (SPME) Fibers. Using stainless steel wire as the substrate for SPME fiber preparation, the stainless steel wire was ultrasonically cleaned with methanol and ultrapure water for 10 min each time (cleaning time can be selected as 10-15 min), and then dried in a 60℃ oven for later use. One end of the clean stainless steel wire was etched with 40% hydrofluoric acid solution for 50 min to form a rough surface. The etched stainless steel wire was then cleaned with ultrapure water and dried in air. 0.4 g of silicone adhesive was placed in a 2 mL centrifuge tube, diluted with 2.0 mL of n-hexane, and ultrasonicated until homogeneous (0.4-0.6 g of silicone adhesive and 2.0-3.0 mL of n-hexane can be used). The diluted silicone adhesive solution was coated onto the etched stainless steel wire, which was then inserted into the CNMMS coating material and rotated repeatedly. This process was repeated three times to obtain a coated fiber with a thickness of approximately 50 μm. Finally, the fiber was dried at room temperature for 24 h. Before use, the prepared fibers are assembled into a 5μL microsyringe and aged at 150℃, 200℃, 260℃ and 280℃ for 30 min each at the gas phase injection port (aging time can be selected as 20-30 min) to obtain solid phase microextraction fibers.

[0035] Step 3: Immersion Solid-Phase Microextraction (SPME). The water sample volume is 50 mL, filtered through a 0.45 μm filter membrane, and stored in a brown glass bottle at 4°C, sealed with a sealing film to prevent loss of the target compound due to volatilization. The water sample volume is 15 mL, and the pH of the water sample is adjusted to 7. The SPME fiber is immersed in the sample solution, and 0.75 g of sodium chloride (0.50-0.75 g) is added. The mixture is stirred at a constant speed of 700 rpm (500-800 rpm) at 55°C (or 500-60°C) for 35 min (or 25-35 min). Afterward, the SPME fiber is retracted into a 5 μL microsyringe, removed from the sample bottle, and immediately inserted into the injection port. Thermal desorption is performed at 260°C for 5 min.

[0036] Step 4: Determine the various halogenated polycyclic aromatic hydrocarbons in the sample using gas chromatography-mass spectrometry (GC-MS). GC-MS test conditions: Column: DB-5MS (30m × 0.25mm × 0.25μm); Carrier gas: Helium (purity ≥ 99.999%); Flow rate: 1 mL / min, splitless injection; Column temperature program: 70℃ for 2 min, ramp to 160℃ at 15℃ / min, ramp to 245℃ at 6℃ / min, hold for 2 min, ramp to 280℃ at 6℃ / min, hold for 3 min; Injector temperature: 260℃. Electron accelerating voltage: 70 eV; Ion source: Electron impact ionization source, temperature: 280℃; Transfer line temperature: 280℃; Scan mode: Selected ion scan. Selected ion scan quantifies based on characteristic fragment ions with large molecular weight and high abundance. Specific fragment ion information and retention times are shown in Table 1.

[0037] Table 1. Fragment ion information and retention times of 11 halocyclic polycyclic aromatic hydrocarbons

[0038]

[0039] Example 2

[0040] In this embodiment, a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in an environmental water sample is described. In step 1, 0.0115 g of MoS2 is added, which is 10% of the total amount. The remaining steps are the same as in Example 1.

[0041] Example 3

[0042] In this embodiment, a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in an environmental water sample is described. In step 1, 0.0230 g of MoS2 is added, which is 20% of the total amount. The remaining steps are the same as in Example 1.

[0043] Example 4

[0044] This embodiment describes a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in an environmental water sample. In step 1, 0.0460 g of MoS2 is added, representing an addition percentage of 40%. The remaining steps are the same as in Example 1.

[0045] Example 5

[0046] In this embodiment, a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in an environmental water sample is described. In step 1, 0.0575 g of MoS2 is added, which is 50% of the total amount. The remaining steps are the same as in Example 1.

[0047] Performance Analysis and Comparison of Examples 1-5

[0048] The CNMMS coating materials prepared in Examples 1-5 were characterized by scanning electron microscopy, and the results are as follows: Figure 1 As shown, the morphology of CNMMS materials with MoS2 addition amounts of (a) 0.0115g-10%, (b) 0.023g-20%, (c) 0.0345g-30%, (d) 0.0460g-40%, and (e) 0.0575g-50% were observed. It was found that the lamellar MoS2 was uniformly distributed on the surface of the bimetallic CNM material, and the higher the composite ratio, the more lamellar MoS2 was composited on the CNM spindle. Figure 1 f shows the CNMMS solid-phase microextraction fiber prepared by physical coating method. It can be seen that CNMMS is uniformly attached to the surface of the stainless steel wire substrate, and the coating thickness is about 50 μm.

[0049] Figure 2 Fourier transform infrared spectra of CNMMS coating materials with different composite ratios. Among them, 1572 cm⁻¹... -1 and 1383cm -1 The absorption peak at 617 cm⁻¹ is attributed to the Co-COO-Co and Ni-COO-Ni groups, corresponding to the asymmetric stretching vibration peak of the carboxyl functional group in the terephthalic acid skeleton. -1 The absorption peak at 697 cm⁻¹ is attributed to the Mo-S bond. When MoS₂ is in air, its surface may be partially oxidized, which is why the absorption peak at 697 cm⁻¹ is observed. -1 The reason for the absorption peak is that, with the increase of the MoS2 addition ratio, the intensity of the characteristic peak corresponding to Mo-S also showed a slight increase.

[0050] The optimal CNM / MoS2 composite ratio was determined by comparing the extraction capabilities of different composite materials for halogenated polycyclic aromatic hydrocarbons. Figure 3It can be seen that the extraction effect of halogenated polycyclic aromatic hydrocarbons is best when the composite ratio is 30%. However, when the proportion of MoS2 is greater than 30%, the excessive MoS2 may affect the role of the metal sites of the bimetallic MOF material to a certain extent, thereby reducing the adsorption effect of the material on halogenated polycyclic aromatic hydrocarbons.

[0051] Under optimal extraction conditions with a composite ratio of 30%, seven mixed standard solutions of different concentrations were prepared by dilution with ultrapure water for extraction, and standard curves were established. Quantification was performed using peak area integration, and the linear equations, linear ranges, correlation coefficients, limits of detection (LODs), and limits of quantitation (LOQs) for each of the 11 halogenated polycyclic aromatic hydrocarbons were calculated. The LODs and LOQs were calculated based on a signal-to-noise ratio of 3 and 10, respectively. The results are shown in Table 2. This method exhibits a wide linear range, from 1 to 1000 ng / L, with relatively low LODs (0.09–0.64 ng / L) and LOQs (0.31–2.13 ng / L). The 11 halogenated polycyclic aromatic hydrocarbons showed good linearity over a wide concentration range, with correlation coefficients R0. 2 The value is greater than 0.994, meeting the requirements for quantitative analysis. The relative standard deviation (RSD) of the same coating (n=5) ranges from 2.3% to 8.2%. The RSD between coatings (n=3) is less than 15%, indicating that the coating preparation method has good reproducibility. The data show that this optimized method can be used for the analysis of trace halogenated polycyclic aromatic hydrocarbons. Furthermore, CNMMS solid-phase microextraction fiber is sensitive and rapid, reducing many complex operations; the extraction process does not require organic solvents, making it a green technology that meets the requirements of modern analytical development. Figure 4 As shown, after optimization, the responses of each substance are higher and the separation is better.

[0052] Table 2. Linear range, correlation coefficient, limit of detection, limit of quantitation, and precision of 11 halogenated polycyclic aromatic hydrocarbons in water samples determined by CNMMS-SPME fiber (n=5)

[0053]

[0054] Example 6

[0055] Keeping the total mass of metal ions in the synthesis solution constant, adjust the Co... 2+ and Ni 2+The mixing ratios were 0%:100% (0.7200 g of nickel nitrate hexahydrate), 25%:75% (0.1803 g of cobalt nitrate hexahydrate and 0.4050 g of nickel nitrate hexahydrate), 50%:50% (0.3606 g of cobalt nitrate hexahydrate and 0.3600 g of nickel nitrate hexahydrate), 75%:25% (0.5409 g of cobalt nitrate hexahydrate and 0.1800 g of nickel nitrate hexahydrate), and 100%:0% (0.7212 g of cobalt nitrate hexahydrate). The effect of different doping ratios of the bimetallic organic framework on the adsorption effect of HPAHs was investigated. Ultimately, it was found that Co... 2+ and Ni 2+ The best results are achieved when the mixing ratio is 1:1. Figure 5 ).

[0056] Example 7

[0057] Samples of tap water, lake water, domestic sewage, and industrial wastewater were collected. The spiked concentrations (50 ng / L) of 11 halogenated polycyclic aromatic hydrocarbons (PAHs) were detected using a self-made CNMMS (MoS2 added at 30%) solid-phase microextraction fiber. The average recoveries were determined using the standard addition method (Table 3). The recoveries of tap water ranged from 82.1% to 102%, with a relative standard deviation (RSD) of less than 8.7%; the recoveries of lake water ranged from 82.2% to 99.4%, with an RSD of less than 12%; the recoveries of domestic sewage ranged from 84.3% to 102%, with an RSD of less than 14%; and the recoveries of industrial wastewater ranged from 88.2% to 115%, with an RSD of less than 16%. These results indicate that the established CNMMS-SPME-GC-MS method has good accuracy and precision and can be used for the analysis of halogenated PAHs in various real-world water samples. The target compound was not detected in tap water, while only 2-BrFLU was detected in lake water at a concentration of 25.7 ng / L. Higher concentrations were found in domestic sewage and industrial wastewater, with total concentrations of 125 ng / L and 273 ng / L, respectively. 2-BrFLU, 9-BrPHE, and 1-BrPYR were detected in both types of water samples.

[0058] Table 3 shows the spiked recoveries and concentrations of 11 halogenated polycyclic aromatic hydrocarbons in tap water, lake water, domestic sewage, and industrial wastewater determined by this method.

[0059]

[0060] Note: nd indicates not detected.

[0061] Comparative Example 1

[0062] In this comparative example, a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in an environmental water sample is described. In step 1, when preparing the coating material, MoS2 is not added, and a CNM coating material is prepared. The remaining steps are the same as in Example 1.

[0063] Comparative Example 2

[0064] This comparative example describes a method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples. Step 1 is omitted, and step 2 directly uses MoS2 as a coating material to prepare solid-phase microextraction fibers. The remaining steps are the same as in Example 1.

[0065] Structural characterization

[0066] The coating materials of Example 1, Comparative Example 1, and Comparative Example 2 were structurally characterized, and the results are as follows: Figure 6 As shown, the characteristic diffraction peaks of the CNM coating material are near 6.8° and 11.8°, corresponding to the (210) and (300) crystal planes, respectively. The composite material CNMMS (with a MoS2 addition ratio of 30%) also exhibits the above characteristic diffraction peaks, and the intensity is higher after compositing. This indicates that the topological structure of CNM is preserved after compositing, and the addition of MoS2 does not have a significant impact on the crystal structure of CNM. The characteristic diffraction peaks of MoS2 are near 14.4°, 32.8°, 39.6°, 49.8°, and 58.6°, corresponding to the (002), (100), (103), (105), and (110) crystal planes, respectively. This indicates that the synthesized composite material retains the crystallinity and characteristic peaks of MoS2, which confirms that the composite material contains MoS2.

[0067] Depend on Figure 7 It can be seen that the adsorption of halogenated polycyclic aromatic hydrocarbons in water is mainly contributed by CNM, while MoS2 mainly has a certain extraction effect on low-cyclic compounds.

[0068] Thermal stability study of SPME coating

[0069] Because the gas chromatography injection port temperature is high, thermogravimetric analysis (TGA) of the materials is crucial. The TGA curves of the CNMMS-extracted fiber (MoS2 addition ratio 30%) in Example 1, the CNM-extracted fiber in Comparative Example 1, and the MoS2-extracted fiber in Comparative Example 2 are shown below. Figure 8As shown, the sample mass loss mainly consists of three parts as the temperature rises: In the range of room temperature to 250℃, the sample mass decreases slowly with increasing temperature, primarily due to the slow removal of physically adsorbed water; subsequently, in the range of 250–450℃, the sample mass decreases, and the rate of mass loss accelerates compared to the previous stage, indicating the rapid removal of solvent molecules and other adsorbed gas molecules; when the temperature continues to rise to around 450℃, the sample mass decreases slowly again, mainly due to the destruction of the sample framework, at which point CNM is oxidized to amorphous metal oxides. For MoS2, the material exhibits consistently good thermal stability. With the injection port maintained at 260℃, the thermal weight loss rates of MoS2, CNM, and the composite material are 1.5%, 14.3%, and 13.0%, respectively. The introduction of MoS2 material also improves the thermal stability of the composite coating material to some extent. This good thermal stability is beneficial for the thermal desorption of halogenated polycyclic aromatic hydrocarbons adsorbed on the fibers, meeting the requirements for SPME fiber preparation.

[0070] SPME coating water stability study

[0071] In practical applications, adsorption coating materials come into contact with water molecules. At this time, the unsaturated metal sites in the material are easily occupied by water molecules, and the framework may even collapse, leading to a decrease in adsorption capacity. Therefore, examining the water stability of CNM materials is crucial. Based on this, the water stability of the CNMMS extraction fiber (MoS2 addition ratio of 30%) in Example 1, the CNM extraction fiber in Comparative Example 1, and the MoS2 extraction fiber in Comparative Example 2 was investigated. The samples were immersed in water for 7 days, and their crystal structures were characterized using XRD. The results are as follows: Figure 9 As shown. The characteristic peaks of MoS2 remained even after being placed in water for 7 days, indicating that the crystal structure of the material was not damaged. After immersing CNM in water, the intensity of the XRD diffraction peaks corresponding to its (210) and (300) crystal planes significantly decreased. This is because CNM material contains a large number of unsaturated metal sites within its pores, which are also the optimal adsorption sites for water molecules. Therefore, when water molecules enter the material framework, they preferentially coordinate with the metal sites, while the uncoordinated water molecules will bond with the nearest oxygen atom through hydrogen bonding, thereby changing the coordination state of the metal ions and organic ligands. This leads to a change in the bond length of the chemical bonds formed between the metal center and oxygen atoms in the material, ultimately resulting in a deterioration in the crystallinity of the material. Contact angle characterization showed that the contact angles of MoS2 and CNM were 117.6° and 34.3°, respectively, while after the materials were combined, the contact angle became 61.8°. Figure 10Clearly, the addition of hydrophobic MoS2 reduces the hydrophilicity of the MOF material, and the hydrophobic layer on its surface prevents some water molecules from damaging the MOF structure. The bimetallic MOF after MoS2 composite largely retains its original crystal structure and exhibits good water stability. Halogenated polycyclic aromatic hydrocarbons are hydrophobic compounds, and reducing the hydrophilicity of the material also facilitates the extraction of these compounds.

[0072] Comparative Example 3

[0073] This comparative example illustrates a method for the simultaneous determination of multiple halogenated polycyclic aromatic hydrocarbons (PAHs) in environmental water samples. Step 3 employs headspace extraction, where an extraction fiber is placed in the gas phase above the liquid to extract the compounds in the headspace portion. Figure 11 The diagram shows a comparison of the extraction effects of this comparative example and Example 1. It can be seen that for most halogenated polycyclic aromatic hydrocarbons, immersion extraction is more effective than headspace extraction, especially for compounds with relatively large molecular weights.

[0074] Comparative Example 4

[0075] This comparative example illustrates a method for the simultaneous determination of multiple halogenated polycyclic aromatic hydrocarbons (PAHs) in environmental water samples. Instead of the solid-phase microextraction fiber extraction head prepared in steps 1 / 2, it utilizes commercially available 65 μm polydimethylsiloxane / divinylbenzene (PDMS / DVB) and 100 μm PDMS extraction heads. The extraction capabilities of the three extraction heads for 11 PAHs in the water sample are as follows: Figure 12 As shown in the figure, the results indicate that the self-made CNMMS (MoS2 addition ratio of 30%) solid phase microextraction fiber has a better extraction effect than the commercial SPME.

Claims

1. A method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples, characterized in that, Includes the following steps: Step 1: Preparation of cobalt / nickel bimetallic organic framework composite molybdenum sulfide coating material; 2,5-dihydroxyterephthalic acid, cobalt nitrate hexahydrate, and nickel nitrate hexahydrate are weighed and dissolved in a mixture of N,N-dimethylformamide, anhydrous ethanol, and deionized water to prepare a bimetallic organic framework; molybdenum sulfide is added, with the addition ratio of molybdenum sulfide being 10%-50% of the mass of the synthesized bimetallic organic framework; the mixture is transferred to a reaction vessel and placed in an oven for crystallization; the crystallized product is cooled to room temperature, centrifuged, and washed, and then impregnated with methanol to displace N,N-dimethylformamide; after impregnation, it is placed in an oven for drying to obtain the cobalt / nickel bimetallic organic framework composite molybdenum sulfide coating material; Step 2: Preparation of solid-phase microextraction fibers; Stainless steel wire was used as the substrate for preparing cobalt / nickel bimetallic organic framework composite molybdenum sulfide fibers. One end of the stainless steel wire was etched with hydrofluoric acid solution. The stainless steel wire was cleaned and dried. Silicone glue was placed in a centrifuge tube, diluted with n-hexane, and sonicated until homogeneous. The diluted silicone glue solution was coated onto the etched stainless steel wire. The stainless steel wire was inserted into the cobalt / nickel bimetallic organic framework composite molybdenum sulfide coating material and rotated repeatedly to obtain coated fibers with a thickness of 40-50 μm and a coating length of 1.0-1.5 cm. Finally, the coated fibers were dried at room temperature. The prepared coated fibers were assembled into a syringe and aged to obtain solid-phase microextraction fibers. Step 3: Immersion solid-phase microextraction; Adjust the pH range of the sample solution to 6-8, immerse the solid phase microextraction fiber in the sample solution, stir and extract, and after extraction, retract the solid phase microextraction fiber into the syringe and thermally desorb at the gas phase inlet. Step 4: Use gas chromatography-mass spectrometry to determine the various halogenated polycyclic aromatic hydrocarbons in the sample.

2. The method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples as described in claim 1, characterized in that, In step 1, 0.1485g of 2,5-dihydroxyterephthalic acid, 0.1803-0.5049g of cobalt nitrate hexahydrate and 0.1800-0.5400g of nickel nitrate hexahydrate are weighed out respectively.

3. The method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples as described in claim 1, characterized in that, In step 1, the volume ratio of the mixture of N,N-dimethylformamide, anhydrous ethanol and deionized water is 1:1:

1.

4. The method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples as described in claim 1, characterized in that, In step 1, the crystallization temperature is 100-120℃ and the crystallization time is 18-24h.

5. The method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples as described in claim 1, characterized in that, In step 2, before etching the stainless steel wire, the stainless steel wire is first ultrasonically cleaned with methanol and then with ultrapure water for 10-15 minutes, and then dried in a 60℃ oven.

6. The method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples as described in claim 1, characterized in that, In step 2, take 0.4-0.6g of silicone gel into a centrifuge tube, add 2.0-3.0mL of n-hexane to dilute it, and then sonicate until homogeneous.

7. The method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples as described in claim 1, characterized in that, In step 2, the specific operation of aging is as follows: place the syringe containing the coated fiber into the gas phase injection port, and age it for 20-30 minutes at 150℃, 200℃, 260℃ and 280℃ respectively.

8. The method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples as described in claim 1, characterized in that, In step 3, the specific operation of extraction is as follows: add 0.50-0.75g of sodium chloride, stir at a constant speed of 500-800rpm at an extraction temperature of 50-60℃, and the extraction time is 25-35min.

9. The method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples as described in claim 1, characterized in that, In step 3, the thermal desorption temperature is 260-280℃, and the desorption time is 2-5 min.

10. The method for simultaneously determining multiple halogenated polycyclic aromatic hydrocarbons in environmental water samples as described in claim 1, characterized in that, In step 4, the gas chromatography-mass spectrometry (GC-MS) analytical method uses a 30m × 0.25mm × 0.25μm DB-5MS column, with high-purity helium (≥99.999%) as the carrier gas, a flow rate of 1mL / min, and splitless injection. The column temperature program is as follows: initial temperature 60-70℃, hold for 1-2 min, increase to 280-300℃ at 6-15℃ / min, hold for 3-7 min; injection port temperature 260-280℃, electron accelerating voltage 70eV, electron impact ionization source at 230-280℃, and transfer line temperature 260-280℃.

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