Anion chromatographic stationary phase based on carbon dot modified polystyrene-divinyl benzene and preparation method of anion chromatographic stationary phase

Abstract

The invention discloses an anion chromatographic stationary phase based on carbon dot modified polystyrene-divinyl benzene and a preparation method of the anion chromatographic stationary phase. The stationary phase is prepared through a CDs agglomeration method or a CDs grafting method. The CDs agglomeration method comprises the following steps: quaternizing CDs, agglomerating the CDs on the surfaces of sulfonated PS-DVB microspheres through electrostatic interaction, and then carrying out hyperbranched modification to obtain the CDs agglomeration type PS-DVB anion chromatography stationary phase. The CDs grafting method comprises the following steps: grafting CDs on the surfaces of PS-DVB microspheres through covalent bonds by taking glycidyl methacrylate as an intermediate medium, and then carrying out hyperbranched modification to obtain the CDs grafted PS-DVB anion chromatography stationary phase. The stationary phase developed by the invention shows good application potential in the field of trace analysis of complex samples, and is expected to play an important role in actual analysis and detection work.

Description

Technical Field

[0001] This invention belongs to the field of chromatographic stationary phase materials, specifically relating to an anion chromatographic stationary phase based on carbon dot modified polystyrene-divinylbenzene and its preparation method. Background Technology

[0002] In the field of ion chromatography stationary phases, traditional chromatographic stationary phases, typically represented by polystyrene-divinylbenzene (PS-DVB) stationary phases, have been widely used in numerous fields and play a vital supporting role in related analytical work due to their advantages such as good chemical stability, high mechanical strength, wide pH range, good retention capacity for nonpolar and weakly polar substances, adjustable pore size and specific surface area, and mature preparation processes. However, with the increasing complexity of analytical tasks, traditional stationary phases have revealed significant limitations when faced with challenging tasks such as the precise analysis of trace anions in complex samples and the efficient separation of anions with similar structures. These limitations include limited sensitivity, significant interference problems, high detection limits, insufficient selectivity, a single separation mechanism, and high mass transfer resistance. These shortcomings greatly restrict the development of analytical work towards higher precision and higher efficiency. Therefore, there is an urgent need to develop new solutions to overcome the current predicament and promote the further development of ion chromatography technology.

[0003] As an emerging member of the carbon nanomaterial family, carbon dots (CDs) have attracted widespread attention from researchers in the field of chromatography due to their outstanding characteristics, including nanoscale size, moderate adsorption performance, simple preparation process, abundant surface functional groups, and strong design flexibility. When CDs are used as chromatographic stationary phases, they exhibit several advantages. First, the abundant functional groups on the surface of CDs provide a large number of reactive active sites, creating favorable conditions for subsequent modification. Second, their nanoscale size ensures that they do not adversely affect the homogeneity of the chromatographic packing material, guaranteeing the stability and consistency of the stationary phase during the packing process. Furthermore, compared to some materials with large π-conjugated systems, they effectively avoid peak tailing caused by strong interactions with certain analytes, thereby improving column efficiency. This makes CDs demonstrate extremely broad application prospects in the field of chromatographic separation.

[0004] In practical applications, modifying the stationary phase with carbon dots (CDs) can enhance the ion separation selectivity of the stationary phase. This advantage has already shown initial success in the separation of inorganic anions, providing a new solution for the efficient separation of ions in complex samples. However, related research is still in its early stages, and many aspects require further in-depth exploration and improvement. Therefore, conducting in-depth and systematic research on carbon dots in the field of ion chromatography stationary phases has significant theoretical and practical implications. From a theoretical perspective, it helps to enrich and improve the theoretical system of ion chromatography stationary phases, providing a new perspective for understanding the interaction mechanism between the stationary phase and the analyte. From a practical application perspective, it is expected to develop high-performance and highly reliable stationary phase materials, powerfully promoting the widespread application and innovative development of ion chromatography technology in various fields such as environmental monitoring, food safety, and biomedicine. Summary of the Invention

[0005] The present invention aims to provide an anion chromatography stationary phase based on carbon dots (CDs) modified polystyrene-divinylbenzene (PS-DVB) and its preparation method. The present invention designs two different CDs modification strategies: CDs agglomeration and CDs grafting, both of which achieve effective modification of the PS-DVB matrix.

[0006] The technical solution of the present invention is as follows: An anion chromatography stationary phase based on carbon dot modified polystyrene-divinylbenzene was prepared by CDs agglomeration or CDs grafting. The CDs agglomeration method includes: quaternizing CDs, agglomerating them on the surface of sulfonated PS-DVB microspheres through electrostatic interaction, and then performing hyperbranching modification to obtain a CDs agglomerated PS-DVB anion chromatography stationary phase. The CDs grafting method includes: using glycidyl methacrylate (GMA) as an intermediate medium, grafting CDs onto the surface of PS-DVB microspheres via covalent bonds, followed by hyperbranching modification to obtain a CDs-grafted PS-DVB anion chromatography stationary phase.

[0007] Furthermore, the CDs aggregation method is operated as follows: (1) Quaternization of CDs The CDs solution was heated to 60°C, and BDDE (1,4-butanediol diglycidyl ether) aqueous solution was added. The mixture was stirred for 10 min, followed by MA (methylamine) aqueous solution. The mixture was stirred for another 60 min, and then filtered through a Buchner funnel. The filtrate was a quaternized CDs solution. Specifically, the CDs solution was prepared as follows: citric acid was dissolved in deionized water, ethylenediamine was added, the mixture was ultrasonically mixed, and the mixture was placed in a hydrothermal reactor and reacted at 200°C for 4 hours. After that, it was naturally cooled to room temperature, filtered through a Buchner funnel (to remove large particles produced in the reaction), and the filtrate was collected and dialyzed through a 1000 Da dialysis bag at room temperature for 48 hours to obtain the CDs solution; wherein, the feed ratio of citric acid, deionized water, and ethylenediamine was 1 g: 60 mL: 200 μL. The preferred concentration of the BDDE aqueous solution is 7.2%, g / mL; The preferred concentration of the MA aqueous solution is 2.8%, g / mL; The preferred volume ratio of CDs solution, BDDE aqueous solution, and MA aqueous solution is 20~60:20:20; (2) Sulfonation of PS-DVB At room temperature, PS-DVB microspheres were mixed with glacial acetic acid and stirred for 10 min. Dichloromethane was added to swell the mixture for 30 min. Then, concentrated sulfuric acid (98wt%) was added to sulfonate the mixture for 3 min. The mixture was then quenched with 1 mol / L glacial sulfuric acid (0~5 ℃), filtered, and washed with deionized water to obtain sulfonated PS-DVB microspheres. The preferred feed ratio of PS-DVB microspheres, glacial acetic acid, dichloromethane, and concentrated sulfuric acid is 2.5 g: 15 mL: 3 mL: 7 mL; (3) Agglomeration reaction The sulfonated PS-DVB microspheres obtained in step (2) were dispersed in a solvent, heated to 40°C under stirring, and the quaternized CDs solution obtained in step (1) was added. The reaction was carried out for 12 h, filtered, and washed with deionized water to obtain PS-DVB microspheres with agglomerated CDs. Specifically, the solvent is water or a eutectic solvent, preferably water; the eutectic solvent is prepared by mixing choline chloride and ethylene glycol in a molar ratio of 1:3. (4) Hyperbranching modification The PS-DVB microspheres with CDs agglomerated obtained in step (3) were dispersed in water, BDDE aqueous solution was added at 60°C, stirred for 30 min, filtered, washed with deionized water, and then the microspheres were dispersed in water. MA aqueous solution was added at 60°C, stirred for 30 min, filtered, and washed with deionized water to complete one hyperbranching modification process. The hyperbranching modification process was repeated several times (preferably 1 to 3 times) to obtain the CDs agglomerated PS-DVB anion chromatography stationary phase. The preferred concentration of BDDE aqueous solution is 10%, g / mL; The preferred concentration of the MA aqueous solution is 4%, g / mL.

[0008] Furthermore, the CDs grafting method is operated as follows: (1) Covalent grafting PS-DVB microspheres were dispersed in a solvent, and glycidyl methacrylate (GMA) and azobisisobutyronitrile (AIBN) were added. The mixture was heated to 70°C under a nitrogen atmosphere and reacted for 12-24 h (preferably 24 h). Then, a CDs solution was added and reacted at 60°C for 12-24 h (preferably 12 h). The mixture was then filtered through a Buchner funnel and washed with ethanol and water to obtain CDs-grafted PS-DVB microspheres. The preparation method of CDs solution is the same as described above; The preferred feed ratio of PS-DVB microspheres, glycidyl methacrylate, azobisisobutyronitrile, and CDs solution is 2.5 g: 0.3~0.8 g: 0.2 g: 40 mL, and more preferably 2.5 g: 0.3~0.5 g: 0.2 g: 40 mL; Specifically, the solvent is ethanol or a eutectic solvent, preferably a eutectic solvent; the eutectic solvent is prepared by mixing choline chloride and ethylene glycol in a molar ratio of 1:3. The preferred mass-to-volume ratio of PS-DVB microspheres to solvent is 2.5:100, g / mL; (2) CDs amination The CDs-grafted PS-DVB microspheres obtained in step (1) were dispersed in water, BDDE aqueous solution was added at 60°C, stirred for 10 min, MA aqueous solution was added, stirred for 60 min, filtered, and washed with deionized water to obtain CDs-amined PS-DVB microspheres. The preferred concentration of the BDDE aqueous solution is 7.2%, g / mL; The preferred concentration of the MA aqueous solution is 2.8%, g / mL; The purpose of this step is to introduce a large number of amine groups onto the surface of CDs, providing active sites for the next step of hyperbranching modification; (3) Hyperbranching modification The CDs-amined PS-DVB microspheres obtained in step (2) were dispersed in water, BDDE aqueous solution was added at 60°C, stirred for 30 min, filtered, washed with deionized water, and then the microspheres were dispersed in water again. MA aqueous solution was added at 60°C, stirred for 30 min, filtered, and washed with deionized water to complete one hyperbranching modification process. The hyperbranching modification process was repeated several times (preferably 1 to 3 times) to obtain the CDs-grafted PS-DVB anion chromatography stationary phase. The preferred concentration of BDDE aqueous solution is 10%, g / mL; The preferred concentration of the MA aqueous solution is 4%, g / mL.

[0009] The present invention has the following advantages: 1. Two different CDs modification strategies were designed: CDs aggregation and CDs grafting. During the preparation process, the reaction conditions were optimized, and anion exchange stationary phases based on CDs modification were successfully prepared. The influence of different synthesis parameters on separation performance was investigated.

[0010] 2. In-depth research on anion exchange chromatography stationary phases based on CDs-modified PS-DVB matrix provides a novel approach for the design of carbon-based functionalized chromatographic packing materials. The developed stationary phase demonstrates excellent application potential in the trace analysis of complex samples and is expected to play an important role in practical analytical detection work. Attached Figure Description

[0011] Figure 1 : Schematic diagram of the synthesis of the anion chromatography stationary phase of the present invention; (a) is a schematic diagram of CDs synthesis, (b) is a schematic diagram of CDs quaternization, and (c) is a schematic diagram of CDs grafted stationary phase synthesis.

[0012] Figure 2 Example 3: Chromatographic separation spectra of seven common anions of CDs agglomerated stationary phases prepared with different volumes of CDs solution after two hyperbranching grafts; (a) CDs solution volume is 20 mL, (b) CDs solution volume is 40 mL, (c) CDs solution volume is 60 mL.

[0013] Figure 3 Example 4: Chromatographic separation spectra of seven common anions of CDs agglomerated stationary phases prepared with different agglomerating solvents after two hyperbranching grafts; (a) agglomerating solvent is DESs, (b) agglomerating solvent is water.

[0014] Figure 4 Example 5: Chromatographic separation spectra of CDs agglomerated stationary phases relative to seven common anions prepared with different grafting times (one graft and two grafts).

[0015] Figure 5 Example 6: Chromatographic separation spectra of CDs grafted stationary phases prepared with different reaction solvents relative to seven common anions; (a) reaction solvent is DESs, (b) reaction solvent is ethanol.

[0016] Figure 6 Example 7: Chromatographic separation spectra of CDs grafted stationary phases with different amounts of GMA prepared relative to seven common anions; (a) GMA amount is 0.3g, (b) GMA amount is 0.5g, (c) GMA amount is 0.8g.

[0017] Figure 7Example 8: Chromatographic separation spectra of CDs grafted stationary phases with seven common anions prepared at different reaction times; (a) copolymerization reaction time of 12 h, epoxy ring-opening reaction time of 12 h, (b) copolymerization reaction time of 24 h, epoxy ring-opening reaction time of 12 h, (c) copolymerization reaction time of 24 h, epoxy ring-opening reaction time of 24 h. Detailed Implementation

[0018] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0019] In the following embodiments, PS-DVB microspheres: Take PS-DVB microsphere emulsion (Suzhou Nanomicro Technology Co., Ltd., 10 μm, 100 Å), filter it, wash it three times with anhydrous ethanol, and then dry it in a 60℃ oven for later use.

[0020] The specific steps for synthesizing CDs are as follows: Dissolve 1.00 g of citric acid in 60 mL of deionized water, add 200 μL of ethylenediamine, and sonicate for 5 min to ensure the solution is homogeneous. Then, place the solution in a 100 mL hydrothermal reactor and react at 200 °C for 4 h. After removal, allow it to cool naturally to room temperature, filter using a Buchner funnel to remove large particles generated during the reaction, and finally dialyze through a 1000 Da dialysis bag at room temperature for 48 h to obtain 60 mL of CDs solution for later use.

[0021] Preparation method of eutectic solvent (DESs): Mix choline chloride and ethylene glycol at a ratio of 1:3 (molar ratio), stir at 60°C until the solution is completely clear and transparent, and obtain DESs for later use.

[0022] Preparation of seven anion standard solutions: Weigh sodium fluoride, sodium chloride, sodium nitrite, sodium bromide, sodium nitrate, sodium phosphate decahydrate, and sodium sulfate reagents. Transfer each reagent to a separate volumetric flask, add ultrapure water to prepare a 1000 mg / L single-standard solution, and store at 4°C for later use. Dilute and mix each ion single-standard solution to prepare a mixed standard solution of the required concentration, wherein the concentrations of each ion are as follows: F - 2 mg / L, Cl - 5 mg / L, NO2 - 10 mg / L, Br - 20 mg / L, NO3 - 20 mg / L, PO4 3- 30 mg / L, SO4 2- The concentration is 10 mg / L.

[0023] The stationary phase was packed into a column using a high-pressure homogenization method to test chromatographic performance. The specific column packing process is as follows: First, disperse 2.5g of the prepared stationary phase in 60 mL of deionized water, then pour it into a homogenizing tank. Use deionized water as the displacement liquid, adjust the flow rate in the pipeline to keep the pressure constant at 10 MPa, and press the homogenate into a stainless steel column (4.6 mm × 150 mm). Stop packing the column when the outflow reaches 500 mL.

[0024] When testing chromatographic performance, the seven anion elution conditions were as follows: mobile phase: a mixed solution of 2 mmol / L sodium carbonate and 2 mmol / L sodium bicarbonate; flow rate: 1.0 mL / min; injection volume: 25 μL; suppression current: 25 mA; column temperature: 30 ℃; conductivity detector.

[0025] Example 1: Preparation of CDs-agglomerated PS-DVB anion chromatography stationary phase

[0026] (1) Quaternization of CDs

[0027] CDs solutions (20 mL, 40 mL, 60 mL) were added to a 250 mL three-necked flask, heated to 60 °C, and 20 mL of BDDE aqueous solution (7.2%, m / v) was added. After stirring for 10 min, 20 mL of MA aqueous solution (2.8%, m / v) was added and the reaction was continued to be stirred for 60 min. The mixture was then filtered through a Buchner funnel, and the filtrate was a quaternized carbon dot solution.

[0028] (2) Sulfonation of PS-DVB

[0029] Weigh 2.5 g of PS-DVB microspheres into a 100 mL three-necked flask, add 15 mL of glacial acetic acid at 30 °C, stir for 10 min, then add 3 mL of dichloromethane to swell for 30 min, and finally slowly add 7 mL of concentrated sulfuric acid to sulfonate for 3 min. After the reaction is complete, immediately quench the reaction with 1 mol / L glacial sulfuric acid, and then repeatedly wash the microspheres with deionized water until the filtrate is neutral.

[0030] (3) Agglomeration reaction

[0031] Disperse the sulfonated microspheres in 100 mL of water or DESs, turn on the stirrer, heat to 40°C, slowly add the quaternized carbon dot solution obtained above, react for 12 h, then filter, and wash repeatedly with deionized water until the filtrate is neutral.

[0032] (4) Hyperbranching modification

[0033] The aggregated microspheres were dispersed in 100 mL of water, and 20 mL of BDDE aqueous solution (10%, m / v) was added at 60 °C. The mixture was stirred and reacted for 30 min. Then, the microspheres were washed with deionized water until the filtrate was neutral. The microspheres were dispersed again with water, and 20 mL of MA aqueous solution (4%, m / v) was added at 60 °C. The mixture was reacted for 30 min and then filtered. The filtrate was washed with deionized water until it was neutral to obtain a stationary phase that had been grafted once. The above steps were repeated alternately to obtain a stationary phase that had been grafted multiple times.

[0034] Example 2: Preparation of CDs-grafted PS-DVB anion chromatography stationary phase

[0035] (1) Covalent grafting

[0036] Disperse 2.5 g of PS-DVB in 100 mL of DESs or ethanol, then add GMA (0.3 g, 0.5 g, 0.8 g) and 0.2 g of AIBN. React at 70 °C under a nitrogen atmosphere for 12 h and 24 h. Then add 40 mL of CDs solution and react at 60 °C for 12 h and 24 h. After the reaction is complete, filter through a Buchner funnel and wash three times successively with ethanol and water.

[0037] (2) CDs amination

[0038] The obtained microspheres were dispersed in 40 mL of water. At 60 °C, 20 mL of BDDE (7.2%, m / v) was added, and the reaction was allowed to proceed for 10 min. Then, 20 mL of MA aqueous solution (2.8%, m / v) was added, and the reaction was allowed to proceed for another 60 min. The mixture was filtered and then washed three times with deionized water.

[0039] (3) Hyperbranching modification

[0040] The aggregated microspheres were dispersed in 100 mL of water, and 20 mL of BDDE aqueous solution (10%, m / v) was added at 60 °C. The reaction was allowed to proceed for 30 min, and the mixture was then repeatedly washed with deionized water until the filtrate was neutral. The microspheres were then dispersed again in 100 mL of water, and 20 mL of MA aqueous solution (4%, m / v) was added at 60 °C. The reaction was allowed to proceed for 30 min, and the mixture was then filtered. The mixture was repeatedly washed with deionized water until the filtrate was neutral, yielding a stationary phase grafted once. The above hyperbranching grafting steps were repeated to perform alternating reactions, resulting in a stationary phase grafted multiple times.

[0041] Example 3: Effect of different volumes of CDs solution on the chromatographic performance of CDs agglomerated stationary phase

[0042] Using the method described in Example 1 for preparing the CDs-agglomerated PS-DVB stationary phase, quaternization was performed using different volumes of CDs solution (20 mL, 40 mL, and 60 mL), followed by agglomeration in water. Hyperbranching grafting was then performed twice, and the resulting microspheres were packed into a column using a high-pressure homogenization method to prepare the stationary phase. The ion chromatography performance of the prepared stationary phase was tested, and the results are as follows: Figure 2 As shown.

[0043] from Figure 2 As can be seen in (b), the stationary phase prepared using 40 mL of CDs solution exhibits more symmetrical chromatographic peaks. This is likely because the appropriate amount of CDs agglomerated on the microsphere surface optimizes the charge distribution and chemical environment of the stationary phase surface. The electrostatic interaction between the quaternized CDs and anions becomes more uniform in this optimized environment, resulting in more consistent retention and elution behavior of different ions on the stationary phase. This effectively reduces peak tailing or forward projection caused by unevenness on the stationary phase surface, thus making the chromatographic peaks more symmetrical and sharp.

[0044] Example 4: Effect of different agglomeration solvents on the chromatographic performance of CDs agglomerated stationary phases

[0045] Using the method described in Example 1 for preparing the CDs-agglomerated PS-DVB stationary phase, 40 mL of CDs solution was quaternized, and then water and DESs were used as solvents for the agglomeration reaction to agglomerate them onto sulfonated microspheres. Hyperbranching modification was then performed, followed by two grafting processes, and the column was packed using a high-pressure homogenization method. The chromatographic performance test results of the prepared stationary phase are as follows: Figure 3 As shown.

[0046] Table 1. Chromatographic performance of stationary phases synthesized in different agglomeration solvents.

[0047] from Figure 3As shown in (a), the CDs agglomerate stationary phase prepared in DESs can achieve baseline separation of all seven conventional anions, and the chromatographic performance of the two is not significantly different from that of the stationary phase prepared in water. The data in Table 1 also show that the asymmetry factors of the chromatographic peaks of the CDs agglomerate stationary phase in different solvents are all close to 1 when separating the seven anions, and the peak shapes in the chromatograms are also very symmetrical. This may be because the amount of CDs used has reached the optimal level. At this point, the coverage of the agglomerate layer on the surface of the microspheres is close to saturation, almost completely covering the surface of the microspheres. Under these conditions, the original influence of the solvent on the agglomeration density is greatly weakened. Because the formation of the agglomerate layer mainly depends on the interaction between CDs and microspheres and the concentration of CDs themselves, when the amount of CDs is optimal and the agglomerate layer is basically saturated, changes in the solvent can hardly have a substantial impact on the agglomeration process, thus leading to the fact that changing the solvent cannot significantly improve the chromatographic performance of the stationary phase. Therefore, water is used as the agglomeration solvent in the preparation of CDs agglomerate stationary phases.

[0048] Example 5: Effect of different grafting times on the chromatographic performance of CDs agglomerated stationary phases

[0049] Using the method for preparing the CDs agglomerated stationary phase in Example 1, 40 mL of CDs solution was quaternized and then agglomerated onto sulfonated microspheres in water. The resulting agglomerated microspheres were subjected to hyperbranching grafting once and twice, respectively, to obtain two types of stationary phases. The results of chromatographic performance testing are as follows: Figure 4 As shown.

[0050] Grafted stationary phases offer certain advantages, enabling rapid separation of seven anions within 10 minutes. This rapid separation characteristic improves separation efficiency and saves time in practical chromatographic analysis applications. However, its shortcomings are also apparent. Firstly, it does not achieve baseline separation of all ions; the chromatographic peaks of phosphate and sulfate still overlap, which may lead to decreased accuracy and hinder quantitative analysis in practical applications. Secondly, the column efficiency of this stationary phase is significantly low, meaning the column's ability to separate different substances during the separation process is limited, potentially resulting in less than ideal separation outcomes.

[0051] The double-grafted stationary phase exhibits superior performance, clearly separating the chromatographic peaks of each anion, providing a solid foundation for accurate quantitative analysis. Furthermore, compared to a single-grafted stationary phase, the double-grafted stationary phase demonstrates significantly improved column efficiency, with an improvement ranging from 27.0% to 54.0%.

[0052] Example 6: Effect of different reaction solvents on the chromatographic performance of CDs-grafted stationary phases

[0053] Using the method described in Example 2 for preparing the CDs-grafted stationary phase, ethanol or DESs was used as the reaction solvent. 0.5 g GMA was reacted with 2.5 g PS-DVB at 70°C for 24 hours, followed by reaction with 40 mL of CDs solution at 60°C for 12 hours, and then subjected to quaternization and hyperbranching modification once. The synthesized stationary phase was subjected to chromatographic performance testing, and the results are as follows: Figure 5 As shown.

[0054] from Figure 5 As can be clearly seen in (b), when ethanol is used as the reaction solvent, the synthesized stationary phase exhibits significant defects in separation performance, especially in the separation of phosphate and sulfate ions, where their chromatographic peaks completely overlap, making effective separation difficult. This indicates that the stationary phase lacks sufficient separation selectivity for these two anions with similar structures and properties.

[0055] Replacing the reaction solvent with DESs yielded the following results: Figure 5 As shown in (a), the seven anions prepared at this time can be effectively separated, which is in stark contrast to the case when ethanol is used as the reaction solvent.

[0056] The difference in separation selectivity exhibited by the two stationary phases may stem from the different physicochemical properties of the solvents themselves. Ethanol, as a common organic solvent, has relatively low polarity. In systems where ethanol is used as the reaction solvent, the solubility and activity of GMA may be limited to some extent, resulting in inconsistent polymerization rates between GMA and PS-DVB, and uneven distribution of CDs grafted onto the PS-DVB surface. In contrast, the unique physicochemical properties of DESs, such as high polarity, good solubility, and low volatility, allow GMA to dissolve fully and disperse uniformly in the reaction system. This provides ideal conditions for the polymerization reaction of GMA and PS-DVB, enabling a more stable and efficient polymerization process. Therefore, CDs can be grafted onto the PS-DVB surface in a more ordered and uniform manner, allowing the stationary phase surface to form regular functionalized structures. This provides a good foundation for subsequent interactions with sulfate and phosphate ions, thus significantly improving the separation selectivity of the stationary phase and achieving effective separation of seven anions.

[0057] Example 7: Effect of different GMA dosages on the chromatographic performance of CDs-grafted stationary phases

[0058] In Example 2, the preparation method of the CDs-grafted PS-DVB stationary phase, GMA, as the intermediate medium connecting PS-DVB and CDs, directly affects the final chromatographic performance of the stationary phase. Therefore, to investigate the correlation between the amount of GMA and chromatographic performance, comparative experiments were conducted using different amounts of GMA (0.3 g, 0.5 g, 0.8 g). Different amounts of GMA were reacted with 2.5 g of PS-DVB at 70°C for 24 hours, and then with 40 mL of CDs at 60°C for 12 hours, followed by quaternization and hyperbranching modifications. The prepared stationary phase was tested for chromatographic performance, and the results are as follows: Figure 6 As shown.

[0059] from Figure 6 (a) (GMA dosage is 0.3 g) and from Figure 6 As can be seen in (b) (GMA dosage 0.5 g), both stationary phases are basically able to achieve effective separation of the seven anions. Under these two dosage conditions, GMA plays a good bridging role between PS-DVB and CDs, enabling the construction of a relatively suitable functional group structure on the stationary phase surface. These functional groups can specifically interact with the seven anions, thereby separating them one by one and presenting clearly distinguishable chromatographic peaks on the chromatogram. By measuring the exchange capacity of the two stationary phases, it was found that when the amount of GMA used increased from 0.3 g to 0.5 g, the column capacity increased slightly, from 0.181 mmol / column to 0.205 mmol / column. This indicates that the amount of GMA grafted increases with the increase in dosage, thereby increasing the number of functional groups.

[0060] However, according to Figure 6 In section (c), a significant change occurred when the amount of GMA increased to 0.8 g. Excessive GMA grafted onto the PS-DVB surface, further connecting a large number of CDs. This process led to a sharp increase in the density of functional groups on the stationary phase surface, causing the originally ordered surface structure to become crowded and disordered. Under these circumstances, the microenvironment of the stationary phase surface changed, especially for nitrate and phosphate ions. Due to the excessive density of functional groups, their adsorption and desorption behaviors on the stationary phase surface were severely interfered with. The interaction between the stationary phase and nitrate and phosphate ions became overly complex and chaotic, failing to form an effective differential separation mechanism. Ultimately, the chromatographic peaks of nitrate and phosphate ions could not be separated on the chromatogram, resulting in overlap and severely affecting the separation selectivity of the stationary phase and the accuracy of chromatographic analysis. Therefore, when preparing CDs-grafted stationary phases, a GMA dosage of 0.5 g is more suitable.

[0061] Example 8: Effect of different reaction times on the chromatographic performance of CDs-grafted stationary phases

[0062] In Example 2, the preparation method of the CDs-grafted PS-DVB stationary phase, the copolymerization reaction of PS-DVB and GMA, and the oxidative ring-opening reaction of GMA and CDs are the core reaction steps of the entire preparation process. The time of these two key reactions directly affects the grafting density, surface chemical properties, and chromatographic performance of the stationary phase. This experiment set different reaction times to prepare the stationary phase, and the specific conditions are shown in Table 2, thereby exploring the correlation between reaction time and chromatographic performance of the stationary phase. Three stationary phases were prepared according to the different reaction times in Table 2, and the chromatographic performance was tested, with the results as follows: Figure 7 As shown.

[0063] Table 2 Reaction time of microsphere grafting modification

[0064] pass Figure 7 (a) and Figure 7 A comparison of the chromatograms in (b) shows that when the copolymerization reaction time is short, some ions are difficult to separate at the baseline. This may be because the chain growth stage is not fully carried out during the free radical polymerization process, which prevents the GMA monomer from being effectively grafted onto the PS-DVB surface. This results in insufficient epoxy groups on the stationary phase surface, leading to a lower grafting density of CDs and a decrease in the number of quaternary ammonium groups on the microsphere surface. Consequently, the charge density on the stationary phase surface is insufficient, weakening the electrostatic interaction difference in ion exchange and causing the selectivity factor to approach 1, thus making baseline separation impossible. Increasing the copolymerization reaction time of PS-DVB and GMA is beneficial for grafting more GMA onto the microsphere surface, providing sufficient epoxy groups for subsequent modification.

[0065] according to Figure 7 (b) and Figure 7Comparing the chromatograms in (c), increasing the epoxy ring-opening time reduces the retention time of anions. This is mainly because, with prolonged reaction time, the epoxy groups of GMA can undergo more complete ring-opening reactions, forming more hydroxyl and carboxylic acid groups. This significantly increases the hydrophilicity of the stationary phase surface, making it easier for a hydration layer to form. This weakens the electrostatic interaction between anions and quaternary ammonium groups, thus shortening the retention time of anions in the stationary phase. Simultaneously, this may cause excessive densification of the hyperbranched structure, hindering anions from approaching deeper quaternary ammonium groups, reducing the effective exchange sites that can participate in ion exchange. Furthermore, the densification of the hyperbranched structure may inhibit the swelling of the PS-DVB matrix, thereby reducing the internal pore size of the stationary phase and limiting the permeation path of large anions. However, for small anions (such as chloride and nitrate ions), the dense structure actually shortens the migration distance in the stationary phase, allowing them to pass through more quickly. Although increasing the epoxy ring-opening reaction time reduces the analysis time, the overall column efficiency is not significantly improved, and the peak symmetry is worse. In summary, a copolymerization reaction time of 24 hours and an epoxy ring-opening reaction time of 12 hours are suitable reaction times.

Claims

1. A carbon dot-modified polystyrene-divinylbenzene-based anion chromatography stationary phase, characterized in that, Prepared by a CDs agglomeration method or a CDs grafting method; The CDs agglomeration method comprises: quaternization of CDs, agglomeration on the surface of sulfonated PS-DVB microspheres by electrostatic interaction, and hyperbranched modification to obtain a CDs agglomeration type PS-DVB anion chromatography stationary phase; The CDs grafting method comprises: taking glycidyl methacrylate as an intermediate medium, grafting CDs on the surface of PS-DVB microspheres by a covalent bond, and then performing hyperbranched modification to obtain a CDs grafting type PS-DVB anion chromatography stationary phase.

2. The anion chromatography stationary phase based on carbon dot modified polystyrene-divinylbenzene of claim 1, wherein, The operation of the CDs agglomeration method is as follows: (1) Quaternization of CDs The CDs solution is heated to 60 DEG C, and then BDDE aqueous solution is added, followed by stirring for 10 min, and then MA aqueous solution is added, followed by continuous stirring for 60 min, and then the mixture is filtered through a Buchner funnel, and the filtrate is a quaternized CDs solution; (2) Sulfonation of PS-DVB At room temperature, the PS-DVB microspheres are mixed with glacial acetic acid, stirred for 10 min, swelled in dichloromethane for 30 min, then sulfonated by adding concentrated sulfuric acid for 3 min, quenched by 1 mol / L ice sulfuric acid, filtered, and washed with deionized water to obtain sulfonated PS-DVB microspheres; (3) Agglomeration reaction The sulfonated PS-DVB microspheres obtained in step (2) are dispersed in a solvent, heated to 40 DEG C under stirring, and then the quaternized CDs solution obtained in step (1) is added, and the mixture is reacted for 12 h, filtered, and washed with deionized water to obtain agglomerated CDs PS-DVB microspheres; The solvent is water or a low eutectic solvent; the low eutectic solvent is prepared by mixing choline chloride and ethylene glycol at a molar ratio of 1:3; (4) Hyperbranched modification The agglomerated CDs PS-DVB microspheres obtained in step (3) are dispersed in water, and then BDDE aqueous solution is added at 60 DEG C, followed by stirring for 30 min, filtering, washing with deionized water, and then dispersing the microspheres in water, and then MA aqueous solution is added at 60 DEG C, followed by stirring for 30 min, filtering, and washing with deionized water to complete one hyperbranched modification process; the hyperbranched modification process is repeated for several times to obtain a CDs agglomeration type PS-DVB anion chromatography stationary phase.

3. The anion chromatography stationary phase based on carbon dot modified polystyrene-divinylbenzene of claim 2, wherein, In step (3), the solvent is water.

4. The anion chromatography stationary phase based on carbon dot modified polystyrene-divinylbenzene of claim 1, wherein, The operation of the CDs grafting method is as follows: (1) Covalent bond grafting The PS-DVB microspheres are dispersed in a solvent, and then glycidyl methacrylate and azobisisobutyronitrile are added, and the mixture is heated to 70 DEG C under a nitrogen atmosphere for 12-24 h, and then a CDs solution is added, and the mixture is reacted at 60 DEG C for 12-24 h, and then the mixture is filtered through a Buchner funnel, and washed with ethanol and water to obtain grafted CDs PS-DVB microspheres; The solvent is ethanol or a low eutectic solvent; the low eutectic solvent is prepared by mixing choline chloride and ethylene glycol at a molar ratio of 1:3; (2) Amination of CDs The grafted CDs PS-DVB microspheres obtained in step (1) are dispersed in water, and then BDDE aqueous solution is added at 60 DEG C, followed by stirring for 10 min, and then MA aqueous solution is added, followed by stirring for 60 min, filtering, and washing with deionized water to obtain aminated CDs PS-DVB microspheres; (3) Hyperbranched modification The amine-modified PS-DVB microspheres obtained in step (2) are dispersed in water, a BDDE aqueous solution is added at 60 ℃, stirring is performed for 30 min, filtration is performed, deionized water is used for cleaning, the microspheres are dispersed in water, a MA aqueous solution is added at 60 ℃, stirring is performed for 30 min, filtration is performed, deionized water is used for cleaning, and one hyperbranched modification process is completed; the hyperbranched modification process is repeated for several times, and a CDs grafted PS-DVB anion chromatographic stationary phase is obtained.

5. The anion chromatography stationary phase based on carbon dot modified polystyrene-divinylbenzene of claim 4, wherein, In step (1), the first-stage reaction time is 24 h, and the second-stage reaction time is 12 h.

6. The anion chromatography stationary phase based on carbon dot modified polystyrene-divinylbenzene of claim 4, wherein, In step (1), the feeding ratio of the PS-DVB microspheres, glycidyl methacrylate, azobisisobutyronitrile and the CDs solution is 2.5 g: 0.3-0.5 g: 0.2 g: 40 mL.

7. The anion chromatography stationary phase based on carbon dot modified polystyrene-divinylbenzene of claim 4, wherein the carbon dots are covalently bonded to the polystyrene-divinylbenzene. In step (1), the solvent is a eutectic solvent.

8. The anion chromatography stationary phase based on carbon dot modified polystyrene-divinylbenzene of any one of claims 2 or 4, wherein the carbon dots have a diameter of 1 to 10 nm. The CDs solution is prepared in the following manner: citric acid is dissolved in deionized water, ethylenediamine is added, ultrasonic mixing is performed, the mixture is placed in a hydrothermal reactor, reaction is performed at 200 ℃ for 4 h, then natural cooling to room temperature is performed, filtration is performed by using a Buchner funnel, the filtrate is collected, dialysis is performed in a 1000 Da dialysis bag at room temperature for 48 h, and the CDs solution is obtained; wherein the feeding ratio of the citric acid, the deionized water and the ethylenediamine is 1 g: 60 mL: 200 μL.

9. The carbon dot modified polystyrene-divinylbenzene based anion chromatography stationary phase of any one of claims 2 or 4, wherein, The hyperbranched modification process is repeated for 1-3 times.

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