Preparation And Evaluation Of Carbon Quantum Dots-Bonded Silica Chromatographic Stationary Phases

Carbon quantum dots has become one of the research hotspots because of its unique physical and chemical properties.It plays an indispensable role in the fields of biosensor,catalysis and sample pretreatment.However,the application of carbon quantum dots as surface modifier of silica in chromatographic separation is still in its infancy.Based on the above research background,carbon quantum dots were synthesized from different precursor molecules and bonded to the surface of silica to synthesize high performance liquid chromatographic stationary phase,and a series of characterization and chromatographic performance evaluation were carried out.The detailed research contents are as follows:1.Octadecyl imidazolium ionic liquids was selected as carbon source to synthesize carbon quantum dots(Im C₁₈CQDs)and the carbon quantum dots were bonded on the surface of silica to synthesize mixed chromatographic stationary phase(Sil-Im C₁₈CQDs).The materials of stationary phase were characterized by transmission electron microscope,laser confocal microscope,contact angle analysis and elemental analysis,which confirmed that the Im C₁₈CQDs were successfully bonded to the surface of silica.Due to the low bonding amount of carbon quantum dots and more silicon hydroxyl groups exposed on the surface of silica,Sil-Im C₁₈CQDs can realize the separation of nine sugars,six base nucleosides,six ginsenosides and six amino acids in hydrophilic interaction chromatography（HILIC）mode.In the reversed-phase liquid chromatography（RPLC）mode,six kinds of alkylbenzene,six kinds of polycyclic aromatic hydrocarbons and five kinds of aromatic amines can be separated.After that,the stability of Sil-Im C₁₈CQDs was investigated by consecutive injections of aromatic acids.Through the investigation of chromatographic conditions,Sil-Im C₁₈CQDs shows typical mixed chromatographic characteristics of HILIC/RPLC.2.In order to increase the bonding density of silica and improve separation performance.The RPLC stationary phase(Sil-Im C₁₈/CQDs)was synthesized on the surface of silica by co-bonding between Im C₁₈CQDs and its precursor molecules.Aromatic amines,polycyclic aromatic hydrocarbons and alkylbenzene were used as analytes and compared with carbon quantum dots individually bonded silica(Sil-Im C₁₈CQDs)and precursor molecule separately bonded silica(Sil-Im C₁₈)columns.The effects of different chromatographic conditions on the retention behavior of polycyclic aromatic hydrocarbons were investigated.Tanaka,Engelhardt,SRM870,SRM869b standard test mixtures,phenols and isomers were selected as analytes to investigate the hydrophobicity,aromatic selectivity and shape selectivity of the stationary phase,and compared with C₁₈ commercial column.In addition,the content of calycosin-7-glucoside,calycosin,formononetin and ononin in Radix Astragali extract were calculated to be 0.25 mg/m L,0.13 mg/m L,0.30 mg/m L and 0.15 mg/m L by Sil-Im C₁₈/CQDs column.3.In order to further enrich the application of carbon quantum dots in HPLC,chiral carbon quantum dots（CCQDs）were synthesized by high temperature solid phase method using D-phenylalanine and anhydrous citric acid as materials,and then chiral stationary phase（Sil-CCQDs）was prepared.In order to improve the chiral resolution ability,the composite carbon quantum dots（CCQDs@β-CD）was synthesized by the combination ofβ-cyclodextrin and CCQDs,and the stationary phase（Sil-CCQDs@β-CD）was prepared.Considering that the synthesis of CCQDs@β-CD takes a long time and the steps are complex,the carbon quantum dots（β-CD-CQDs）was synthesized by grinding D-phenylalanine,anhydrous citric acid andβ-cyclodextrin in one-pot,and then the stationary phase（Sil-β-CD-CQDs）was synthesized by the same steps as above.The successful synthesis of stationary phase materials was confirmed by a variety of characterization methods.The chiral separation performance of three chromatographic columns was evaluated under the same chromatographic conditions.The chromatographic mode,repeatability and stability of Sil-CCQDs@β-CD were investigated.