Preparation method and application of a gas chromatography column based on trifluoromethyl covalent organic framework

Abstract

The invention discloses a preparation method of a trifluoromethyl-functionalized COFs-bonded capillary column, belonging to the technical field of chromatographic separation. Monomers Tp, Tb containing aldehyde groups and TFMB, Pa-CF3 containing trifluoromethyl groups are selected to synthesize trifluoromethyl-functionalized COFs TpTFMB, TbTFMB and TpPa-CF3, and are used to prepare COFs-bonded gas chromatography columns. The prepared chromatographic column has good separation ability for non-isomers such as alkylbenzenes, n-alkanes, mixed alcohols and mixed esters, and can also achieve baseline separation of isomers such as ethylbenzene and xylene, chlorotoluene, dichlorobenzene, propylbenzene, nitrotoluene, etc. At the same time, it has good repeatability, providing a new idea for designing stationary phases for separating isomers.

Description

Technical Field

[0001] The present invention belongs to the technical field of chromatographic separation, in particular to a preparation method and application of a trifluoromethyl-functionalized covalent organic framework-based gas chromatography column. Background Art

[0002] Isomers are a class of compounds with the same molecular formula but different structures. Due to their similar properties, they are challenging to separate. For example, ethylbenzene and xylene are called C8 aromatic compounds, and the separation of xylene is one of the 7 major separations that affect the world as commented by Nature. Xylene is a product of catalytic reforming of crude oil, usually accompanied by ethylbenzene as a by-product and exists in the form of a mixture. o-xylene, m-xylene, p-xylene, and ethylbenzene respectively play important roles in the synthesis of phthalic anhydride, isophthalic acid, polyethylene terephthalate, and styrene. Therefore, the separation of them has important economic significance.

[0003] Gas chromatography has become an effective tool for the separation and analysis of complex samples due to its powerful separation ability. Its separation is mainly based on the difference in the interaction between the stationary phase and the analyte to achieve separation. Therefore, the development of new stationary phases is an important way to improve gas chromatography separation. Covalent organic frameworks (COFs) are a new type of porous crystalline organic polymer, which have a wide range of applications in sensing, catalysis, energy storage, and separation due to their large specific surface area, designable structure, and high stability. Functionalization of COFs can effectively expand their applications or improve their performance. Fluorine element has unique properties due to its small atomic radius and high electronegativity. Trifluoromethyl group has great potential in structural recognition due to its steric effect and strong electron-withdrawing ability. However, the potential of trifluoromethyl-functionalized COFs in the separation field has not been explored. Therefore, the development of a bonded trifluoromethyl-functionalized COF-based gas chromatography column for the separation of isomers is of great significance for solving the problem of difficult isomer separation and expanding the applications of COFs. Summary of the Invention

[0004] Based on the difficult but meaningful separation of isomers, the present invention provides a method for preparing a trifluoromethyl-functionalized COF for a gas chromatography capillary column and its application in separating isomers. Trifluoromethyl has a steric effect and strong electron-withdrawing ability, which is easy to cause dipole interaction in unsaturated compounds and has potential in structural recognition. Ligands with trifluoromethyl functional groups are selected to synthesize COFs TpTFMB, TbTFMB, and TpPa-CF3 with high specific surface area and thermal stability as gas chromatography stationary phases. The prepared bonded capillary column can achieve baseline separation of isomers such as ethylbenzene and xylene, chlorotoluene, dichlorobenzene, propylbenzene, and nitrotoluene; and non-isomers such as alkylbenzenes, n-alkanes, mixed alcohols, and mixed esters, and has good repeatability. In this experiment, trifluoromethyl was successfully introduced into COFs, and the application of trifluoromethyl-functionalized COFs in the field of isomer separation was further studied, providing a new solution for designing stationary phases for isomer separation.

[0005] The first object of the present invention is to provide a method for preparing a trifluoromethyl covalent organic framework-based gas chromatography column, and the method includes the following steps:

[0006] Step 1, the fused silica capillary column is pretreated before use. Inject 0.5 - 1 mol / L -1 sodium hydroxide into the capillary column for treatment for 1 - 3 h, and treat it with 0.1 - 0.5 mol / L -1 HCl for 1 - 3 h. Then rinse it with deionized water until the effluent is neutral, rinse the capillary column with an organic solvent that is miscible with water and has a low boiling point for 20 - 60 min, blow out the internal liquid with N2, and dry it at 80 - 150 °C for 2 - 5 h;

[0007] Step 2, amino-functionalize the capillary column. Dilute the amino-silane coupling agent with an organic solvent in a volume ratio of 1:1 - 1:2, inject the mixed solution into the capillary column, block both ends of the chromatographic column, keep it at 70 - 120 °C for 6 - 48 h, then rinse the capillary column with a solvent with a low boiling point and miscible with the above organic solvent for 20 - 40 min and dry it in an N2 environment at 100 - 150 °C for 2 - 5 h; The amino-silane coupling agent includes γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropyldimethoxysilane, N-β-aminoethyl-γ-aminopropyltriethoxysilane, and N-β-aminoethyl-γ-aminopropyldiethoxysilane;

[0008] Step 3: Prepare a chromatographic column of trifluoromethyl covalent organic framework. Use the prepared reaction solvent to disperse the amino ligand containing trifluoromethyl evenly under ultrasonic conditions. Similarly, use the prepared reaction solvent to disperse the ligand containing aldehyde group evenly under ultrasonic conditions. Pour the amino ligand into the aldehyde ligand solution under ultrasonic conditions, and add a catalyst. After the mixed solvent is ultrasonically treated for 1 - 3 min, use a syringe to fill the capillary column with it, and block both ends of the capillary column. The uniformly mixed system can nucleate quickly and evenly in the capillary column in a short time, which is beneficial to the uniform growth of the material on the capillary column. Place the capillary column at room temperature - 120 °C for reaction for 12 - 72 h. Within the first 10 h of the reaction, turn the capillary column every 30 min to assist its uniform growth on the inner wall of the capillary. After the reaction is completed, rinse the capillary column with an organic solvent with a low boiling point and miscible with the reaction solvent and dry it at 80 - 120 °C for 2 - 5 h in an N2 environment. The amino ligand containing trifluoromethyl includes 2,5 - diamino - trifluorotoluene (Pa - CF3), 2,2’ - bis(trifluoromethyl) - 4,4’ - diamino - biphenyl (TFMB), and 3,3' - bis(trifluoromethyl) - 4,4' - diamino - biphenyl. The ligand containing aldehyde group includes 2,4,6 - trimethylbenzene - 1,3,5 - tricarbaldehyde (Tp) or 1,3,5 - trimethylbenzene - tricarbaldehyde (Tb).

[0009] Step 4: The prepared chromatographic column needs to be aged on a gas chromatograph before use. The aging procedure is as follows: Heat from room temperature - 60 °C at a heating rate of 3 - 10 °C min -1 to 190 - 300 °C. The final temperature after heating should be 50 °C lower than the thermal stability measurement temperature of the material, and maintain it for 2 - 12 h under this condition, with a flow rate of 0.5 - 3 mL min -1 .

[0010] In one embodiment, the water - miscible and low - boiling organic solvent in Step 1 includes ethanol, methanol, tetrahydrofuran, or acetone;

[0011] The organic solvent for diluting the amino - silane coupling agent in Step 2 includes methanol, ethanol, isopropanol, or N,N - dimethylformamide;

[0012] The low - boiling solvent miscible with the above - mentioned organic solvent in Step 2 includes methanol, ethanol, isopropanol, tetrahydrofuran, and dichloromethane;

[0013] The low - boiling organic solvent for rinsing the capillary column in Step 3 and miscible with the reaction solvent includes ethanol, methanol, tetrahydrofuran, or acetone.

[0014] In one embodiment, the inner diameter of the fused - silica capillary column in Step 1 includes any one of 0.25 mm, 0.32 mm, and 0.53 mm;

[0015] The column length of the fused silica capillary column in step 1 includes any one of 10 m, 15 m or 30 m.

[0016] In one embodiment, the reaction solvent in step 3 is a mixed solution of o-dichlorobenzene and n-butanol, a mixed solution of mesitylene and 1,4-dioxane, a mixed solution of acetonitrile and ethanol, acetonitrile, or a mixed solution of o-dichlorobenzene and N,N-dimethylacetamide.

[0017] In one embodiment, the catalyst in step 3 is an acetic acid aqueous solution of 3 mol / L -1 , 6 mol / L -1 or 9 mol / L -1 .

[0018] In one embodiment, the reaction time in step 3 is 12 h to 72 h; the reaction temperature is from room temperature to 120 °C.

[0019] In one embodiment, the amino ligand containing trifluoromethyl is 2,5-diaminobenzotrifluoride; the ligand containing aldehyde group is 2,4,6-triformylphloroglucinol.

[0020] The second object of the present invention is to provide a bonded trifluoromethyl-functionalized covalent organic framework-based gas chromatography column.

[0021] The third object of the present invention is to provide an application of a bonded trifluoromethyl-functionalized covalent organic framework-based gas chromatography column for gas chromatography separation of position isomers, carbon chain isomers or cis-trans isomers.

[0022] In one embodiment, the position isomers include ethylbenzene, xylene, chlorotoluene, dichlorobenzene or nitrotoluene; the carbon chain isomers include propylbenzene; the cis-trans isomers include 1,3-dichloropropene.

[0023] Beneficial effects

[0024] The present invention introduces trifluoromethyl into COFs for preparing a gas chromatography capillary column bonded with trifluoromethyl-functionalized COFs and applying it to the separation of isomers. The material of the prepared chromatographic column grows uniformly on the inner wall and has high thermal stability at the same time. It can achieve baseline separation of isomers such as ethylbenzene and xylene, chlorotoluene, dichlorobenzene, propylbenzene and nitrotoluene; and non-isomers such as alkylbenzene, n-alkane, mixed alcohol and mixed ester. It also has good repeatability. The column efficiency of ethylbenzene and xylene on the prepared TpTFMB-bonded chromatographic column is 24,852 - 33,255 plates / m; the column efficiency of chlorotoluene is 37,112 - 39,920 plates / m; the column efficiency of nitrotoluene is 13,241 - 18,109 plates / m. The column efficiency of dichlorobenzene on the prepared TbTFMB-bonded chromatographic column is 14,412 - 18,498 plates / m, the column efficiency of nitrotoluene is 10,735 - 13,774 plates / m; the column efficiency of propylbenzene is 6,015 - 10,125 plates / m; which proves that the prepared trifluoromethyl-functionalized COFs is a highly selective gas chromatography separation material. Description of the Drawings

[0025] Figure 1 Synthesis and preparation diagram of COF TpTFMB

[0026] Figure 2 (a) XRD diagram and (b) thermogravimetric analysis diagram of TpTFMB

[0027] Figure 3 Scanning electron microscope image of the cross-section of the TpTFMB-bonded capillary column

[0028] Figure 4 Chromatogram of the separation of isomers by the TpTFMB-bonded capillary column prepared in Example 1, where (a) ethylbenzene, xylene isomers, (b) chlorotoluene isomers and (c) nitrotoluene isomers

[0029] Figure 5 Synthesis and preparation diagram of COF TbTFMB

[0030] Figure 6 (a) XRD diagram and (b) thermogravimetric analysis diagram of TbTFMB

[0031] Figure 7 Scanning electron microscope image of the cross-section of the TbTFMB-bonded capillary column

[0032] Figure 8 Chromatogram of the separation of isomers by the TbTFMB-bonded capillary column prepared in Example 2, where (a) dichlorobenzene isomers, (b) propylbenzene isomers and (c) nitrotoluene isomers

[0033] Figure 9Chromatogram of ethylbenzene and xylene separated by the statically bonded TpTFMB-1 capillary column prepared in Comparative Example 3

[0034] Figure 10 Chromatograms of (a) dichlorobenzene and (b) nitrotoluene separated by the TbTFMB-1 capillary chromatographic column prepared in Comparative Example 4

[0035] Figure 11 Synthesis preparation diagram of COF TpPa-CF3

[0036] Figure 12 (a) XRD diagram and (b) thermogravimetric analysis diagram of TpPa-CF3

[0037] Figure 13 Scanning electron microscope image of the cross-section of the capillary column bonded with TpPa-CF3

[0038] Figure 14 Chromatogram of n-alkanes separated by the TpTFMB-bonded capillary column prepared in Example 1

[0039] Figure 15 Chromatogram of alkylbenzenes separated by the TpTFMB-bonded capillary column prepared in Example 1

[0040] Figure 16 Chromatogram of mixed esters separated by the TpTFMB-bonded capillary column prepared in Example 1

[0041] Figure 17 Chromatogram of mixed alcohols separated by the TpTFMB-bonded capillary column prepared in Example 1 Detailed implementation method

[0042] Example 1:

[0043] Preparation of a trifluoromethyl-functionalized covalent organic framework-based gas chromatography column: The TpTFMB-bonded capillary column achieved good separation effects for a series of isomers, and the specific steps are as follows:

[0044] (1) A fused silica capillary (15 m long × 0.32 mm inner diameter) was treated with 1 mol L -1 sodium hydroxide for 2 h, treated with 0.1 mol L -1 HCl for 2 h, then rinsed with deionized water until pH = 7, rinsed with ethanol for 30 min, and the internal liquid was further blown out with N2 and dried at 120 °C.

[0045] (2) Amination of the capillary column: Inject a mixed solution of methanol / 3-aminopropyltrimethoxysilane (1:1, v / v) into the capillary column, block both ends of the chromatographic column, maintain at 70 °C for 24 h, then rinse the capillary column with ethanol for 30 min and dry it at 120 °C under N2 atmosphere.

[0046] (3) Weigh 5.3 mg of Tp and 12 mg of TFMB into 0.75 mL of acetonitrile solution respectively, ultrasonically disperse and mix them evenly, inject them into the capillary column with a syringe and react at 120 °C for 5 h. Turn the capillary column every 30 min, then rinse with ethanol and dry with N2. Further inject a mixed solution of o-dichlorobenzene / n-butanol / 6 mol L -1 (5:5:2, v / v / v) and react for 72 h. Then, thoroughly clean the unbonded materials in the chromatographic column with EtOH and dry it with N2 at 120 °C.

[0047] (4) The prepared chromatographic column needs to be aged on a gas chromatograph before use. The aging program is as follows: Heat from 35 °C at a heating rate of 3 °C min -1 to 190 °C and maintain for 120 min under this condition, with a flow rate of 1 mL min -1 .

[0048] The synthesis preparation diagram of COF TpTFMB is as Figure 1 shown.

[0049] The XRD pattern and thermogravimetric analysis diagram of TpTFMB are as Figure 2 shown. The appearance of the characteristic diffraction peak at 3.4° proves that the aldehyde monomer and amino monomer form a crystalline structure through Schiff base reaction, self-repair and error correction. Thermogravimetric analysis is used to investigate the thermal stability of the prepared material. The results prove that under N2 atmosphere, the TpTFMB material remains stable at 400 °C and can be used as a gas chromatographic stationary phase.

[0050] The scanning electron microscope image of the cross-section of the capillary column bonded with TpTFMB is as Figure 3 shown. The growth of the COF material can be clearly observed on the inner wall of the capillary, proving the successful preparation of the capillary column bonded with TpTFMB.

[0051] Example 2:

[0052] Preparation of a trifluoromethyl covalent organic framework-based gas chromatographic column: The capillary column bonded with TbTFMB achieved good separation effects for a series of isomers, and the specific steps are as follows:

[0053] (1) Fused silica capillary (15 m long × 0.32 mm inner diameter), use 1 mol L -1Treated with sodium hydroxide for 2 h, 0.1 mol / L -1 Treated with HCl of 0.1 mol / L for 2 h, then rinsed with deionized water until the effluent was neutral, rinsed the capillary column with ethanol for 30 min, and further blew out the internal liquid with N2 and dried at 120 °C.

[0054] (2) Amination of the capillary column: Inject the mixed solution of methanol / 3-aminopropyltrimethoxysilane (1:1, v / v) into the capillary column, block both ends of the chromatographic column, keep it at 70 °C for 24 h, then rinse the capillary column with methanol for 30 min and dry it at 120 °C under N2 environment.

[0055] (3) Weigh 5.4 mg of Tb and 18 mg of TFMB respectively, add 0.5 mL of the mixed solution of ACN / EtOH (7:3, v / v) to each, mix under ultrasonic conditions and add 300 μL of 6 mol / L -1 acetic acid solution. The mixed solution was kept under ultrasonic for 1 min and injected into the capillary column with a syringe. React at room temperature for 3 d under the condition of sealing both ends of the capillary column. In the first 10 h of the reaction, turn the capillary column every 30 min to assist the uniform growth on the inner wall. After the reaction is completed, wash with EtOH and age the capillary column before use.

[0056] (4) The prepared chromatographic column needs to be aged on a gas chromatograph before use. The aging program is as follows: Heat from 35 °C at a heating rate of 3 °C / min -1 to 190 °C and keep it at this condition for 120 min, with a flow rate of 1 mL / min -1 .

[0057] The synthesis preparation diagram of COF TbTFMB is as shown in Figure 5 the figure.

[0058] The XRD pattern and thermogravimetric analysis diagram of TbTFMB are as shown in Figure 6 the figure. A characteristic diffraction peak appears at a small angle of 3.3° in the XRD pattern, proving the successful preparation of the material. At the same time, the thermal stability of the material was investigated by thermogravimetric analysis. The results show that the prepared TbTFMB material can stably exist at 500 °C, meeting the requirements as a gas-phase stationary phase.

[0059] The scanning electron microscopy image of the cross-section of the capillary column bonded with TbTFMB is as shown in Figure 7 the figure. A layer of spherical morphology material growth can be clearly observed on the inner wall of the capillary, proving the successful preparation of the capillary column bonded with TbTFMB.

[0060] Comparative Example 3

[0061] Preparation of TpTFMB-1 bonded capillary: It is basically the same as the preparation method in Example 1, except that after injecting the material into the capillary with a syringe, the reaction is carried out directly under static conditions.

[0062] Comparative Example 4

[0063] Preparation of TbTFMB-1 bonded capillary: It is basically the same as the preparation method in Example 2, except that the reaction solvent used is mesitylene / ethanol (1:1, v / v).

[0064] Example 5

[0065] Preparation of a trifluoromethyl-functionalized covalent organic framework-based gas chromatography column: The capillary column bonded with COF TpPa-CF3 achieved good separation effects for a series of isomers, and the specific steps are as follows:

[0066] It is basically the same as the preparation method in Example 1, except that 5.3 mg of Tp and 6.6 mg of Pa-CF3 are weighed, the reaction solution is mesitylene / 1,4-dioxane (1:1, v / v), and 100 μL of 6 mol L -1 acetic acid solution is added as a catalyst. After the reaction is completed, the capillary column is rinsed with EtOH and dried with N2 and aged.

[0067] The synthesis preparation diagram of COF TpPa-CF3 is as Figure 11 shown.

[0068] The XRD diagram and thermogravimetric analysis diagram of TpPa-CF3 are as Figure 12 shown. The appearance of the characteristic diffraction peak at 4.5° proves the successful preparation of the material. Thermogravimetric analysis proves that the material can maintain the structural stability at 400 °C and has the potential to become a gas chromatography stationary phase.

[0069] The scanning electron microscope diagram of the cross-section of the capillary column bonded with TpPa-CF3 is as Figure 13 shown. There is a uniform and dense layer of material covering inside the capillary column, which proves the successful preparation of the capillary column bonded with TpPa-CF3.

[0070] Example 6

[0071] The TpTFMB bonded capillary column (15 m × 0.32 mm) prepared in Example 1 was used to separate ethylbenzene and xylene, and isomers of chlorotoluene and nitrotoluene. The experiment was carried out in a constant temperature mode for separation, with N2 as the carrier gas, and split injection was used, and the split ratio was 80:1; as Figure 4 shown, the TpTFMB bonded chromatographic column can be at 170 °C (1 mL min -1 ), 220 °C (1 mL min -1), 260 °C (2 mL min -1 ) Baseline separations of ethylbenzene and xylene, chlorotoluene and nitrotoluene isomers were achieved respectively under the conditions, and the column efficiencies were 33255 plates / m (ethylbenzene), 30488 plates / m (m-xylene), 31722 plates / m (p-xylene), 24852 plates / m (o-xylene); 37112 plates / m (o-chlorotoluene), 39234 plates / m (m-chlorotoluene), 39920 plates / m (p-chlorotoluene); 13241 plates / m (o-nitrotoluene), 16333 plates / m (m-nitrotoluene), 18109 plates / m (p-nitrotoluene).

[0072] Example 7

[0073] The TbTFMB-bonded capillary column (15 m × 0.32 mm) prepared in Example 2 was used to separate dichlorobenzene, propylbenzene and nitrotoluene isomers. The experiment was carried out in an isothermal mode for separation, using N2 as the carrier gas and split injection with a split ratio of 80:1; as Figure 8 shown, the TbTFMB-bonded chromatographic column can achieve baseline separations of dichlorobenzene, nitrotoluene and propylbenzene isomers respectively at 180 °C (1 mL min -1 ), 250 °C (2 mL min -1 ), 170 °C (1 mL min -1 ), and the column efficiencies were 16457 plates / m (m-dichlorobenzene), 18498 plates / m (p-dichlorobenzene), 14412 plates / m (o-dichlorobenzene), 10735 plates / m (o-nitrotoluene), 12917 plates / m (m-nitrotoluene), 13774 plates / m (p-nitrotoluene), 6015 plates / m (isopropylbenzene), 10125 plates / m (propylbenzene), 7705 plates / m (1,3,5-trimethylbenzene).

[0074] Example 8

[0075] The TpTFMB-1-bonded capillary column (15 m × 0.32 mm) prepared by standing in Comparative Example 3 was used to separate ethylbenzene and xylene isomers. The experiment was carried out in an isothermal mode for separation, using N2 as the carrier gas and split injection with a split ratio of 80:1; as Figure 9 shown, after optimizing the separation conditions (170 °C, 1 mL min -1)The baseline separation of ethylbenzene and xylene cannot be achieved, with the separation degree being 1.379 - 1.763, and the column efficiencies being 18759 plates / m (ethylbenzene), 18635 plates / m (m-xylene), 19414 plates / m (p-xylene), and 14841 plates / m (o-xylene) respectively; both the separation degree and the column efficiency are lower than those of the capillary column prepared in Example 1, proving that at the initial stage of the growth and polymerization of the material inside the capillary, the uniformly mixed solvent and the flipping of the capillary column every 30 minutes to assist the growth of the material result in a uniform growth of the capillary column material, which is beneficial to improving the separation ability of the capillary column.

[0076] Example 9

[0077] The TbTFMB-1 bonded capillary column (15m × 0.32mm) prepared using mesitylene and ethanol as reaction solvents in Comparative Example 4 was used to separate dichlorobenzene and nitro toluene isomers. There was less growth material on the inner wall of the prepared chromatographic column. The experiment was carried out in a constant temperature mode for separation, with N2 as the carrier gas, and split injection was used, with a split ratio of 80:1; as Figure 10 shown, the TbTFMB-1 bonded chromatographic column could not achieve the baseline separation of dichlorobenzene (50°C, 1mL min -1 ) and nitro toluene (60°C, 1mLmin -1 ) isomers after optimizing the separation conditions. Only two incompletely separated chromatographic peaks could be obtained for the ortho, meta, and para isomers of dichlorobenzene, and the separation degree of nitro toluene was 0.642 - 0.906, with a poor separation effect, proving that different solvents have a great influence on the growth of the material on the inner wall of the capillary column, further affecting the separation ability of the chromatographic column.

[0078] Repeatability test of Example 10

[0079] Taking ethylbenzene, xylene isomers, and nitro toluene isomers as representative target substances, the repeatability of the TpTFMB bonded capillary column prepared in Example 1 was tested. The standard deviations of the peak emergence time and peak area within a day (n = 5) and between days (n = 3) were less than 0.77% and 6.49% respectively, proving that the prepared TpTFMB bonded capillary column had good repeatability (Table 1)

[0080] Table 1

[0081]

[0082]

[0083] Example 11

[0084] The TpTFMB bonded capillary column prepared in Example 1 was used to separate the n-alkane mixture (C6 - C13). The separation was carried out in a constant temperature mode, with a flow rate of 1mL min -1, baseline separation of C6-C13 can be achieved at 260 °C ( Figure 14 ); the column efficiencies are 17713 plates / m (C6), 19741 plates / m (C7), 20233 plates / m (C8), 19897 plates / m (C9), 19300 plates / m (C10), 18907 plates / m (C11), 18686 plates / m (C12), and 18794 plates / m (C13) respectively.

[0085] Example 12

[0086] The TpTFMB-bonded capillary column prepared in Example 1 was used to separate benzene homologues, including benzene, toluene, ethylbenzene, propylbenzene, and butylbenzene. The separation was carried out in a programmed temperature mode with a flow rate of 2 mL min -1 , starting from 260 °C and increasing the temperature at a rate of 10 °C min -1 to 270 °C, baseline separation of alkylbenzenes can be achieved ( Figure 15 ); the column efficiencies are 7829 plates / m (benzene), 8769 plates / m (toluene), 9754 plates / m (ethylbenzene), 10624 plates / m (propylbenzene), and 11414 plates / m (butylbenzene) respectively.

[0087] Example 13

[0088] The TpTFMB-bonded capillary column prepared in Example 1 was used to separate mixed esters, including ethyl propionate, ethyl butyrate, ethyl valerate, ethyl hexanoate, ethyl heptanoate, ethyl octanoate, and ethyl nonanoate. The separation was carried out in a programmed temperature mode with a flow rate of 2 mL min -1 , starting from 260 °C and increasing the temperature at a rate of 10 °C min -1 to 270 °C, baseline separation of the mixed esters can be achieved ( Figure 16 ); the column efficiencies are 5703 plates / m (ethyl propionate), 6992 plates / m (ethyl butyrate), 8920 plates / m (ethyl valerate), 10845 plates / m (ethyl hexanoate), 12124 plates / m (ethyl heptanoate), 13316 plates / m (ethyl octanoate), and 13325 plates / m (ethyl nonanoate) respectively.

[0089] Example 14

[0090] The TpTFMB-bonded capillary column prepared in Example 1 was used to separate mixed alcohols, including n-propanol, n-butanol, n-pentanol, n-hexanol, and n-heptanol. The separation was carried out in a programmed temperature mode with a flow rate of 1 mL min -1 , holding at 250 °C for 1 min and increasing the temperature at a rate of 30 °C min -1 to 260 °C, baseline separation of the mixed alcohols can be achieved ( Figure 17);The column efficiencies are 19,536 plates / m (n-propanol), 18,660 plates / m (n-butanol), 17,388 plates / m (n-pentanol), 13,258 plates / m (n-hexanol), and 8,290 plates / m (n-heptanol).

Claims

1. A preparation method of a trifluoromethyl covalent organic framework-based gas chromatography column, characterized in that The method includes the following steps: Step 1, the fused silica capillary column is pretreated before use. Inject 0.5 - 1 mol / L -1 sodium hydroxide into the capillary column for treatment for 1 - 3 h, and then treat it with 0.1 - 0.5 mol / L -1 HCl for 1 - 3 h. Then rinse it with deionized water until the effluent is neutral. Rinse the capillary column with an organic solvent that is miscible with water and has a low boiling point for 20 - 60 min. After blowing out the internal liquid with N2, dry it at 80 - 150 °C for 2 - 5 h; Step 2, capillary column amination: Dilute the amino silane coupling agent with an organic solvent, mix in a volume ratio of 1:1 - 1:2, inject the mixed solution into the capillary column, block both ends of the chromatographic column, keep it at 70 - 120 °C for 6 - 48 h, then rinse the capillary column with a solvent that has a low boiling point and is miscible with the above-mentioned organic solvent for 20 - 40 min, and dry it in an N2 environment at 100 - 150 °C for 2 - 5 h; The amino silane coupling agent includes γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropyldimethoxysilane, N-β-aminoethyl-γ-aminopropyltriethoxysilane, and N-β-aminoethyl-γ-aminopropyldiethoxysilane; Step 3, prepare a chromatographic column of trifluoromethyl covalent organic framework: Use the prepared reaction solvent to disperse the amino ligand containing trifluoromethyl evenly under ultrasonic conditions. Similarly, use the prepared reaction solvent to disperse the ligand containing aldehyde group evenly under ultrasonic conditions. Under ultrasonic conditions, pour the amino ligand into the aldehyde ligand solution, add a catalyst, after ultrasonic mixing of the mixed solvent for 1 - 3 min, use a syringe to fill the capillary column with it, and block both ends of the capillary column. The uniformly mixed system can nucleate quickly and evenly in a short time in the capillary column, which is beneficial to the uniform growth of the material on the capillary column; Place the capillary column at room temperature - 120 °C for reaction for 12 - 72 h. Within the first 10 h of the reaction, turn the capillary column every 30 min to assist its uniform growth on the inner wall of the capillary; After the reaction is completed, rinse the capillary column with an organic solvent that has a low boiling point and is miscible with the reaction solvent and dry it in an N2 environment at 80 - 120 °C for 2 - 5 h; The amino ligand containing trifluoromethyl includes 2,5-diaminobenzotrifluoride or 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl or 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl; The ligand containing aldehyde group includes 2,4,6-triformylphloroglucinol or 1,3,5-triformylbenzene; Step 4: The prepared chromatographic column needs to be aged on a gas chromatograph before use. The aging procedure is as follows: From room temperature to 60°C, heat up at a heating rate of 3 - 10°C / min -1 to 190 - 300°C. The final temperature after heating should be 50°C lower than the temperature for measuring the thermal stability of the material, and maintain for 2 - 12 h under this condition, with a flow rate of 0.5 - 3 mL / min -1 .

2. The preparation method of a trifluoromethyl covalent organic framework-based gas chromatography column according to claim 1, wherein The water-miscible and low-boiling organic solvent in Step 1 includes ethanol, methanol, tetrahydrofuran, or acetone; The organic solvent for diluting the amino silane coupling agent in Step 2 includes methanol, ethanol, isopropanol, or N,N-dimethylformamide; The solvent with a low boiling point and miscible with the above-mentioned organic solvent in Step 2 includes methanol, ethanol, isopropanol, tetrahydrofuran, and dichloromethane; The organic solvent with a low boiling point and miscible with the reaction solvent for rinsing the capillary column in Step 3 includes ethanol, methanol, tetrahydrofuran, or acetone.

3. The preparation method of a trifluoromethyl covalent organic framework-based gas chromatography column according to claim 1, characterized in that, The inner diameter of the fused silica capillary column in Step 1 includes any one of 0.25 mm, 0.32 mm, and 0.53 mm; The column length of the fused silica capillary column in Step 1 includes any one of 10 m, 15 m, and 30 m.

4. The preparation method of a trifluoromethyl covalent organic framework-based gas chromatography column according to claim 1, characterized in that, The reaction solvent in step 3 is a mixed solution of o-dichlorobenzene and n-butanol, a mixed solution of mesitylene and 1,4-dioxane, a mixed solution of acetonitrile and ethanol, acetonitrile, or a mixed solution of o-dichlorobenzene and N,N-dimethylacetamide.

5. The preparation method of a trifluoromethyl covalent organic framework-based gas chromatography column according to claim 1, characterized in that, The catalyst in step 3 is an aqueous acetic acid solution of 3 mol L -1 , 6 mol L -1 or 9 mol L -1 .

6. The preparation method of a trifluoromethyl covalent organic framework-based gas chromatography column according to claim 1, characterized in that, The amino ligand containing trifluoromethyl is 2,5-diaminobenzotrifluoride; the ligand containing aldehyde group is 2,4,6-triformylphloroglucinol.

7. A trifluoromethyl covalent organic framework-based gas chromatography column prepared by the method according to any one of claims 1-6.

8. The application method of the trifluoromethyl covalent organic framework-based gas chromatography column according to claim 7 or the trifluoromethyl covalent organic framework-based capillary gas chromatography column prepared by the method according to any one of claims 1-6, characterized in that It is used for gas chromatographic separation of position isomers, carbon chain isomers or cis-trans isomers.

9. The application method of a capillary gas chromatography column based on trifluoromethyl covalent organic framework according to claim 8, characterized in that, The position isomers include xylene, chlorotoluene, dichlorobenzene or nitrotoluene; the carbon chain isomers include propylbenzene; the cis-trans isomers include 1,3-dichloropropene.

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