CN101362074B - Use of double-phenyl hybridization silica gel material monolithic column in chromatogram - Google Patents

Abstract

The invention relates to a chromatographic analysis technology, in particular to the application of bi-phenylene hybrid silica-gel monolithic column of bridge-bond organic-inorganic hybridization periodically meso-pore separation material in a chromatogram. The specified preparation method of bi-phenylene hybrid silica-gel material adopts a sol-gel method of acid-base catalysis. Under the condition of acid catalysis, hydrolysis reaction is carried out to a monomer, and an alkaline catalyst is added to carry out polycondensation reaction. The reaction rates of the hydrolysis reaction and the polycondensation reaction of the monomer are controlled by controlling and changing the pH value of a reaction system in the reaction process and the hydrolysis reaction and the polycondensation reaction of the monomer are effectively completely separated by the two-step catalysis method so as to obtain monolithic or particle material with uniform frame structure, suitable aperture and periodic meso-pores. Therefore, the chromatographic analysis technology meets the demands of separation, improves processing technology of the internal wall of quartz capillary, obtains stable monolithic separation material, is capable of separating acid, neutral and alkai compounds under the model of capillary electrochromatography, and shows that the material has excellent separation efficiency and separative selectivity.

Description

Application of a monolithic column of bisphenyl hybrid silica gel material in chromatography

technical field

The invention relates to chromatographic analysis technology, in particular to the application of a biphenyl hybrid silica gel material monolithic column of a bridging organic-inorganic hybrid periodic mesoporous separation material in chromatography.

Background technique

Separation materials are important components of chromatographic techniques including liquid chromatography and capillary electrochromatography, as well as the main materials for sample processing techniques such as solid phase extraction and solid phase microextraction. The characteristics of separation materials directly affect the analysis efficiency and application range. wait. In recent years, with the development of chromatographic analysis technology and the improvement of practical application requirements, higher and higher requirements have been put forward for separation materials.

Currently commonly used liquid chromatography and capillary electrochromatographic separation materials mainly include bonded silica gel materials, polymer particle materials, and monolithic materials based on silica gel or polymers. Silica gel materials have unique surface properties and can be adjusted by chemical bonding. , but it also has problems such as narrow acid-base range and non-specific adsorption on the surface; polymer materials have the advantages of wide acid-base resistance range and good biocompatibility, but the material will swell with the use of solvents, resulting in microstructure changes that affect separation. . The main solutions to the above problems include: densely bonded silica gel, end-sealing technology and composite materials, etc. to reduce the non-specific adsorption center sites on the silica gel surface, improve the acid-base tolerance range of the material, and increase the cross-linking degree of the polymer material. The material microstructure changes with the solvent.

Although the above-mentioned technologies have improved the physical and chemical properties of the material to a certain extent, improved the separation performance, expanded the scope of application, and avoided the shortcomings of the separation material, but due to the physical and chemical properties of the material itself, its shortcomings and shortcomings still exist. unavoidable to some extent. Research on new separation materials and preparation technology is the main research hotspot in related fields at home and abroad. How to obtain new materials with good separation performance and avoid the limitations of traditional separation materials is a common goal and pursuit. Inagaki (S.Inagaki, S.Guan, Y.Fukushima, T.Ohsuna, O.Terasaki, Novel Mesoporous Materials with a Uniform Distribution of OrganicGroups and Inorganic Oxide in Their Frameworks, J.Am.Chem.Soc.1999, 121, 9611-9614.), Stein (B.J.Melde, B.T.Holland, C.F.Blanford, A.Stein, Mesoporous sieves with unified hybrid inorganic/organic frameworks, Chem.Mater.1999, 11, 3302-3308.) and Ozin (T.Asefa , M.J.Maclachlan, N.Coombs, G.A.Ozin, Periodic mesoporous organosilicas with organic groups inside the channel walls, Nature 1999, 402, 867-871.) The group successively reported bridge-type organic-inorganic hybrid periodic mesoporous materials in 1999 It is referred to as the synthesis of PMOs (periodic mesoporous organosilicas). In the bridging organic-inorganic hybrid mesoporous materials, the organic functional groups are evenly distributed in the skeleton, which will not block the pores and occupy the pore volume, and the flexible organic groups can improve the mechanical strength of the material, and the surface affinity/hydrophobicity can By using different organic groups for adjustment, the organic groups can continue to participate in the reaction to derive new active centers. Studies have shown that this material has better hydrothermal and mechanical stability. Nie et al. (C.F.Nie, R.Zhao, J.S.Suo, Synthesis and characterization of bifunctional periodic silica with surface and framework benzene functionality, J.Porous Mater.2004, 11, 141-146.) used hexadecyl pyrimidine bromide as a template , Tetraethoxysilane, phenyltriethoxysilane and 1,4-bistriethoxysilylbenzene were co-condensed under acidic conditions to prepare a new type of organic-inorganic hybrid MCM-41 mesoporous molecular sieve. The material contains both bridging phenyl groups on the inner wall of the pores and terminal phenyl groups in the channels. There are also some literatures that introduce the way of structure control of this type of materials (A.Fidalgo, M.E.Rosa, L.M.Ilharco, Chemical control of highly porous silica xerogels: physical properties and morphology, Chem.Mater.2003, 15, 2186-2192.) (D.A. Loy, K.J.Shea, Bridged polysilsesquioxanes.Highly porous hybrid organic-inorganic materials, Chem.Rev.1995,95,1431-1442. porewall from a precursor with nonlinear symmetry, Chem. Mater. 2004, 16, 1209-1213.).

The above-mentioned organic-inorganic materials combine the characteristics of polymer materials and silica gel materials, have good physical and chemical properties, and have good prospects as separation materials. The special design of the bridge separation material makes the material have the characteristics of the stability of the polymer and the special surface properties of the silica gel material, and has good stability and separation characteristics. It is composed of various functional groups such as alkyl, alkenyl, and benzene ring The special cavity structure formed has very special significance for improving and adjusting the separation characteristics.

Contents of the invention

The object of the present invention is to provide an application of a monolithic column of bisphenyl hybrid silica gel material in chromatography.

In order to achieve the above object, the technical scheme adopted in the present invention is: the application of a biphenyl hybrid silica gel material monolithic column in chromatography. The chromatography may be capillary electrochromatography, liquid chromatography or solid phase extraction pretreatment.

The monolithic column of bisphenyl hybrid silica gel material used in chromatography is prepared according to the following steps:

1) Preparation of bisphenyl hybrid silica gel material: using acid-base catalyzed sol-gel method, add 80-150 μL of silane precursor to 120-220 μL of methanol, 12-22 μL of hydrochloric acid and 10-20 μL of aqueous solution, mix well Afterwards, vortex stirring for 1-5min, and after hydrolysis at room temperature for 3-6h, add 4-7mg of dodecylamine and mix well, stand-by, wherein the silane precursor is 60-100μL of phenyltriethoxysilane and 20 - 50 μL of 1,4-bistriethoxysilylbenzene;

2) Preparation of bisphenyl monolithic column: fill the silica gel material obtained in step 1) into the pretreated capillary, seal it, and allow the silica gel material to polymerize in the capillary at room temperature for 10-20 hours; then rinse with absolute ethanol for 3-5 hours , and then dried at 40-65°C for 48-72h to obtain a monolithic column suitable for chromatographic separation of materials.

The process of the capillary pretreatment is as follows: the capillary column is washed with 0.2-0.3mol/L hydrochloric acid and water for 30-45min in sequence, then soaked in HF with a volume concentration of 10-15% at 35-50°C for 3-5h, and then Rinse with 1.0-2.0mol/L sodium hydroxide, water and methanol for 30-45min, and finally dry it with nitrogen in a gas chromatography furnace at 160-210°C for use.

The resulting monolithic column is soaked in an acetonitrile solution of 0.1-0.3mol/L ammonia water with a volume ratio of 1:1 for 2-4h, and then washed with mobile phase; after being close to the monolithic column bed, scrape off 1-2mm The polyimide coating is used as the detection window. After the capillary is loaded into the cartridge of the electrophoresis instrument, the excess capillary at both ends is cut off.

The silane precursors used in the preparation of bisphenyl hybrid silica gel materials can be 1,4-bistriethoxysilylbenzene, 1,4-bistrimethoxysilylbenzene, bistrimethoxysilylbenzene bistriethoxysilylethane, bistrimethoxysilylpropane, bistriethoxysilylpropane, bistrimethoxysilylethylene, bistriethoxysilylethylene, bistrimethoxy Silylpropene or Bistriethoxysilylpropene.

Reaction principle: two-step catalyzed sol-gel method, firstly under the condition of acid catalysis, the hydrolysis reaction of the monomer is faster, but the polycondensation reaction is slower, so that the silylating agent is fully hydrolyzed to produce enough silicon hydroxyl groups, and then added Alkaline catalyst to speed up the polycondensation reaction. Through this two-step catalytic method, the hydrolysis and polycondensation reactions of the monomers are effectively separated and completely separated. The reactive monomer phenyltriethoxysilane (PTES) contains phenyl groups at the end, and the phenyl groups are usually distributed in the pores after polymerization occurs. Another monomer, 1,4-bistriethoxysilylbenzene (BTEB) is a double silylated coupling agent with a rigid structure. The phenyl group in the molecule is simultaneously bonded with two triethoxysilyl After polymerization, this part of phenyl group is distributed in the silica gel skeleton. Therefore, when PTES and BTEB are hydrolyzed and polymerized, a special bifunctional hybrid material is formed. The organic groups distributed in the framework and in the pores can provide different retention behaviors and have different physicochemical properties and function simultaneously in the as-prepared materials. The bridged phenyl functional groups can improve the mechanical strength of the hybrid material. These groups also have certain activity, but due to factors such as steric resistance, π electrons and polarity of the phenyl group, the activity of the functional groups distributed at the end is higher. Small. However, due to the presence of bridging phenyl functional groups in the hybrid materials, there are special effects on the physical, chemical, and hydrophobic-hydrophilic properties of the entire material.

When the concentration of BTEB monomer in the aqueous solution containing methanol is as low as 0.2mol/L, under the catalysis of acid or base, it can still polymerize to form a gel structure. In the reaction system, another monomer PTEB was added to control the degree of polymerization and crosslinking of the gel, improve the structural properties of the gel, and obtain a capillary monolithic column with a suitable pore structure.

Advantages of the present invention:

1. The present invention uses bridged silane coupling agents with different functional groups as raw materials to prepare a separation material with special properties combining the advantages of polymers and silica gel, a bridging organic-inorganic hybrid periodic mesoporous separation material.

2. The bridging separation material of the present invention can easily obtain special pores with different physical and chemical microenvironmental characteristics by changing the type of disilane reagent, and the two functional monomers of the reaction monomer contain organic functional groups of different properties The material of the cavity structure can improve and adjust the separation characteristics to meet the needs of different separations.

3. The biphenyl hybrid silica gel material of the present invention is used as a material for capillary electrochromatography, liquid chromatography and sample processing, has good physical and chemical properties and separation characteristics, has high selectivity and separation efficiency, and has special meaning.

4. The acid-base catalyzed sol-gel method is used to prepare bisphenyl hybrid silica gel materials. Firstly, under acid catalyzed conditions, the hydrolysis reaction of the monomer is relatively fast, while the polycondensation reaction is relatively slow, so that the silanization reagent can be fully hydrolyzed and Generate enough silanol groups, and then add a basic catalyst to speed up the polycondensation reaction. By changing the pH value of the reaction system during the control reaction, the hydrolysis and polycondensation reaction rate of the monomer is controlled, and this two-step catalytic method is effective. The hydrolysis and polycondensation reactions of the monomers are completely separated, and a uniform skeleton structure and a suitable pore size with periodic mesoporous monolithic or particulate materials are obtained to meet the separation requirements. The treatment technology for the inner wall of the quartz capillary is improved to obtain a stable monolithic separation material.

5. Under capillary electrochromatography mode, the new separation material is used for the separation of acidic, neutral and basic compounds, showing that the material has good separation efficiency, good separation selectivity and application range.

6. The present invention uses phenyltriethoxysilane (PTES) and 1,4-bistriethoxysilylbenzene (BTEB) as reaction monomers, bridging organic-inorganic hybrid periodic mesoporous separation materials, Thus a novel biphenyl hybrid silica gel monolithic column is obtained, which can be applied in chromatographic analysis.

7. The present invention adopts the hydrofluoric acid etching method to pretreat the capillary. It can be seen that the integral column is closely combined with the tube wall, which is that the silicon hydroxyl density on the tube wall after the hydrofluoric acid etching treatment increases greatly, thereby The sol-gel process can achieve the purpose of fixing the column bed.

Description of drawings

Fig. 1 is a structural diagram of the raw material coupling agent of the present invention.

Fig. 2 is a 5000 times magnified electron micrograph of the bisphenyl hybrid silica gel material of the present invention.

Fig. 3 is a pore size distribution diagram of the bisphenyl hybrid silica gel material of the present invention.

Fig. 4 is the spectrogram (wherein, experimental conditions: mobile phase, 5mM Tris-HCl (pH 8.0)+70%ACN; voltage, 10kV. Sample: (1) naphthalene; (2) acenaphthene; (3) fluorene; (4) acenaphthene; (5) phenanthrene; [a] anthracene; (10) chrysene; (11) benzo [b] fluoranthene; (12) benzo [k] fluoranthene; (13) benzo [a] pyrene; (14) dibenzo [a, h] anthracene; (15) indeno[1,2,3-cd]pyrene; (16) benzo[g,h,l]pyrene)

Fig. 5 is the spectrogram (wherein, experimental condition: 5mM Tris-HCl (pH 8.0)+70%ACN; voltage: 10kV. Sample: (1). Acetanilide (pK _b 13.39); (2). Aniline (pK _b 9.42); (3). o-toluidine (pK _b 9.52); (4). 3,4-dimethylaniline (pK _b 8.83); (5).1-naphthylamine (pK _b 10.08); (6).N,N-dimethylaniline (pK _b 8.92); (7).Diphenylamine (pK _b 13.12); (8 ).N,N-diethylaniline (pK _b 7.43).)

Fig. 6 is the spectrogram (wherein, experimental condition: 5mM Tris-HCl (pH 8.0)+50%ACN; Voltage: 18kV. Solute: 1 .m-nitrophenol (pKa8.36); 2. p-nitrophenol (pKa 7.15); 3.o-nitrophenol (pKa 7.23).)

Detailed ways

The present invention will be described in further detail in conjunction with the accompanying drawings.

Example 1

1) Capillary pretreatment

The capillary column was washed successively with 0.2mol/L hydrochloric acid and water for 30 minutes, then soaked in 10% HF at 35°C for 3 hours, then washed with 1.0mol/L sodium hydroxide, water and methanol for 30 minutes, and finally placed in a gas chromatography furnace. Blow dry with nitrogen at 160°C and set aside.

2) The monolithic column of bisphenyl hybrid silica gel material is prepared according to the following steps:

①Preparation of biphenyl hybrid silica gel material: Using acid-base catalyzed sol-gel method, add 110 μL of silane precursor to 220 μL of methanol, 22 μL of hydrochloric acid and 20 μL of aqueous solution, mix well, vortex for 3 minutes, and After hydrolysis at room temperature for 4 hours, add 4 mg of dodecylamine and mix well, and the silane precursors are 60 μL of phenyltriethoxysilane (PTES) and 50 μL of 1,4-bistriethoxysilylbenzene (BTEB) (see Figure 1);

②Preparation of bisphenyl monolithic column: fill the silica gel material obtained in step ① into the capillary, connect the two ends of the capillary with polytetrafluoroethylene tubes, make the silica gel material in the capillary, react at room temperature for 10h; then use absolute ethanol Rinse for 3 hours, and then dry at 40°C for 48 hours to obtain a monolithic column suitable for separating materials in chromatography.

The obtained monolithic column was soaked in acetonitrile solution of 0.1M ammonia water with a volume ratio of 1:1 for 4 hours, and then washed with the mobile phase commonly used for samples to be analyzed. After being close to the integral column bed, use a blade to scrape off 1-2mm of polyimide coating as the detection window, put the capillary into the cartridge of the electrophoresis instrument, and cut off the excess capillary at both ends.

3 Overall material characterization conditions

A capillary monolithic column with a length of 5 mm was intercepted, and gold was sprayed on its cross section, and a JSM-6360LV scanning electron microscope (JEOL, Japan) was used to characterize the microstructure of the monolithic column. The large-volume monolithic material is prepared by the same method as in the specific embodiment 2), the reaction volume is enlarged by 10 times, and the reaction solution is injected into a 100×2.0mm i.d. stainless steel liquid chromatography column tube, and the biphenyl hybrid silica gel material The reaction was carried out under the operation steps of the monolithic column. After the reaction was completed, rinse with absolute ethanol for 4 hours, then flush the monolithic column out of the chromatographic column tube, cut into small pieces, and finally dry in vacuum at 80°C overnight. A Poresizer 9310 mercury intrusion pore size tester (Micromeritics, USA) was used to determine the pore size distribution of the bulk material (see Figure 2). Infrared spectrum was determined by Spectrum GX Fourier Transform Infrared Spectrometer (Perkin Elmer, USA) by KBr tablet method (see Figure 3).

And the capillary was separated in the electrochromatographic mode, and the repeatability test results (see Table 1) showed that the material had good separation reproducibility.

Table 1

Example 2

The difference from Example 1 is:

1) The process of capillary pretreatment is as follows: wash the capillary column with 0.3mol/L hydrochloric acid and water for 45min, then treat it with HF with a volume concentration of 15% at 50°C for 5h, and then wash it with 1.0mol/L sodium hydroxide and water Rinse with methanol for 45 minutes, and finally blow dry in a gas chromatograph oven at 210°C with nitrogen for use.

2) The monolithic column of bisphenyl hybrid silica gel material is prepared according to the following steps:

①Preparation of biphenyl hybrid silica gel material: Using acid-base catalyzed sol-gel method, add 120 μL of silane precursor to 120 μL of methanol, 12 μL of hydrochloric acid and 10 μL of aqueous solution. After hydrolysis for 6 hours, add 7 mg of dodecylamine and mix well, and set aside, the silane precursors are 100 μL of phenyltriethoxysilane and 20 μL of 1,4-bistriethoxysilylbenzene;

②Preparation of bisphenyl monolithic column: fill the silica gel material obtained in step ① into the pretreated capillary, seal it tightly, and allow the silica gel material to polymerize in the capillary at room temperature for 20 hours; then rinse with absolute ethanol for 5 hours, and then incubate at 65°C After drying for 72 hours, a monolithic column suitable for chromatographic separation materials was obtained.

Example 3

The difference from Example 1 is:

1) The process of capillary pretreatment is as follows: wash the capillary column with 0.2mol/L hydrochloric acid and water for 40 minutes, then treat it with HF with a volume concentration of 13% at 46°C for 4 hours, and then wash it with 1.5mol/L sodium hydroxide and water Rinse with methanol for 40 minutes, and finally blow dry in a gas chromatograph oven at 190°C with nitrogen for use.

2) The monolithic column of bisphenyl hybrid silica gel material is prepared according to the following steps:

①Preparation of bisphenyl hybrid silica gel material: Using acid-base catalyzed sol-gel method, add 140 μL of silane precursor to 160 μL of methanol, 18 μL of hydrochloric acid and 15 μL of aqueous solution. After hydrolyzing for 3 hours, add 5 mg of dodecylamine and mix well, and set aside, the silane precursors are 90 μL of phenyltriethoxysilane and 50 μL of 1,4-bistriethoxysilylbenzene;

②Preparation of bisphenyl monolithic column: fill the silica gel material obtained in step ① into the pretreated capillary, seal it tightly, and polymerize the silica gel material in the capillary at room temperature for 15 hours; then rinse with absolute ethanol for 4 hours, and then incubate at 50°C After drying for 65 hours, a monolithic column suitable for chromatographic separation materials was obtained.

Example 4

The silane precursor can be replaced by 90 μL 1,4-bistriethoxysilylbenzene or 100 μL 1,4-bistrimethoxysilylbenzene.

Example 5

The silane precursor can be replaced by 80 μL of bistrimethoxysilylethane or 130 μL of bistriethoxysilylpropane.

Example 6

The silane precursor can be composed of 140 μL of bistrimethoxysilylethylene or 150 μL of bistriethoxysilylpropylene.

Application example 1:

The total length of the capillary column is 27cm, and the effective length is 20cm. Prepare the monolithic column of bisphenyl hybrid silica gel material according to the steps of Example 1, then at a temperature of 20° C., with a detection wavelength of 214 nm and a data acquisition frequency of 16 Hz, using thiourea as an electroosmotic flow marker. Before the experiment, the monolithic column was first used with a mobile phase ( 5mM Tris-HCl (pH 8.0)+70% ACN) was washed for 30min, and then balanced for 30min with low voltage on the electrophoresis instrument. In the actual analysis process, when changing the mobile phase, first wash with the mobile phase for 30 minutes, and then use the separation voltage to balance for 30 minutes before measuring.

The bridging separation material of the present invention was used to separate 16 kinds of fused-ring aromatic hydrocarbon compounds under capillary electrochromatography mode. Measurement conditions: experimental conditions: mobile phase, 5mM Tris-HCl (pH 8.0)+70% ACN; voltage, 10kV (A). Sample: (1) naphthalene; (2) acenaphthene; (3) fluorene; (4) acenaphthene; (5) phenanthrene; (6) anthracene; (7) fluoranthene; (8) pyrene; (9) benzo[a ] anthracene; (10) chrysene; (11) benzo [b] fluoranthene; (12) benzo [k] fluoranthene; (13) benzo [a] pyrene; (14) dibenzo [a, h] anthracene; (15) indeno[1,2,3-cd]pyrene; (16) benzo[g,h,l]pyrene) (see Figure 4).

Under the mobile phase condition of 70% ACN, except for two pairs of samples, phenanthrene and anthracene, benz[a]anthracene and chrysene, the other samples were separated well. When the operating voltage was 10kV, thiourea peaked at about 4.8 minutes, and the required migration time for 16 samples was 28 minutes.

Application example 2

Separation of 8 kinds of basic compounds, wherein the experimental conditions: 5mM Tris-HCl (pH 8.0) + 70% ACN; voltage: 10kV (A) and 25kV (B). Sample: (1). Acetanilide (pK _b 13.39); (2). Aniline (pK _b 9.42); (3). o-Toluidine (pK _b 9.52); (4). 3,4-Dimethylaniline (pK _b 8.83); (5).1-naphthylamine (pK _b 10.08); (6).N,N-dimethylaniline (pK _b 8.92); (7).Diphenylamine (pK _b 13.12); (8). N, N-diethylaniline (pK _b 7.43).)

Figure 5 Separation spectrum of aniline compounds on bisphenyl monolithic column, the mobile phase is 5mM Tris-HCl (pH 8.0) buffer solution containing 70% ACN, the operating voltage is 10kV, the separation time is 10.5min, eight kinds Aniline compounds can be separated well.

Application example 3

Separate the spectra of three acidic compounds, wherein, the experimental conditions: 5mM Tris-HCl (pH8.0) + 50% ACN; voltage: 18kV. Solute: 1. m-nitrophenol (pKa8.36); 2. p-nitrophenol (pKa 7.15); 3.o-nitrophenol (pKa 7.23).) See Figure 6.

It can be seen from Figure 6 that the phenol derivatives were completely separated on the monolithic column, and the peak order was m-nitrophenol, p-nitrophenol and o-nitrophenol. Since the migration behavior of nitrophenol samples on the monolithic column is controlled by both the electrophoresis mechanism and the retention mechanism of reversed-phase chromatography, it exhibits different separation selectivities in electrochromatography.

Claims (1)

1. The application of a monolithic column of bisphenyl hybrid silica gel material in chromatography, characterized in that: the monolithic column of bisphenyl hybrid silica gel material applied in chromatography is prepared according to the following steps: 1) Preparation of bisphenyl hybrid silica gel material: using acid-base catalyzed sol-gel method, add 80-150 μL of silane precursor to 120-220 μL of methanol, 12-22 μL of hydrochloric acid and 10-20 μL of aqueous solution, mix well Afterwards, vortex stirring for 1-5min, and after hydrolysis at room temperature for 3-6h, add 4-7mg of dodecylamine and mix well, stand-by, wherein the silane precursor is 60-100μL of phenyltriethoxysilane and 20 - 50 μL of 1,4-bistriethoxysilylbenzene; 2) Preparation of bisphenyl monolithic column: fill the silica gel material obtained in step 1) into the pretreated capillary, seal it, and allow the silica gel material to polymerize in the capillary at room temperature for 10-20 hours; then rinse with absolute ethanol for 3-5 hours , and then dried at 40-65°C for 48-72h to obtain a monolithic column suitable for chromatographic separation materials; The process of capillary pretreatment is as follows: wash the capillary column with 0.2-0.3mol/L hydrochloric acid and water for 30-45min, then soak it with HF with a volume concentration of 10-15% at 35-50℃ for 3-5h, and then wash it with 1.0 -2.0mol/L sodium hydroxide, water and methanol rinse for 30-45min, and finally dry in a gas chromatography furnace with nitrogen at 160-210°C, and set aside; The resulting monolithic column is soaked in an acetonitrile solution of 0.1-0.3mol/L ammonia water with a volume ratio of 1:1 for 2-4h, and then washed with mobile phase; after being close to the monolithic column bed, scrape off 1-2mm The polyimide coating is used as the detection window. After the capillary is loaded into the cartridge of the electrophoresis instrument, the excess capillary at both ends is cut off.

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