Shuqing Dong

Simultaneous determination of oleanolic acid, ursolic acid, quercetin and apigenin in Swertia mussotii Franch by capillary zone electrophoresis with running buffer modifier

The method of capillary zone electrophoresis (CZE) with direct UV detection was developed for the determination of oleanolic acid, ursolic acid, quercetin and apigenin. and then for the first time successfully applied to the analysis of four analytes in Swertia mussotii Franch and its preparations. Various factors affecting the CZE procedure were investigated and optimized, and the optimal conditions were: 50 × 10(-3) mol/L borate-phosphate buffer (pH 9.5) with 5.0 × 10(-3) mol/L β-cyclodextrin, 15 kV separation voltage, 20 °C column temperature, 250 nm detection wavelength and 5 s electrokinetic injection time (voltage 20 psi). Under the conditions, oleanolic acid, ursolic acid, quercetin and apigenin could be determined within the test ranges with a good correlation coefficient (r(2) > 0.9991). The limits of detection for conditions, oleanolic acid, ursolic acid, quercetin and apigenin were 0.3415, 0.2003, 0.0062 and 0.2538 µg/mL, respectively, and the intra- and inter-day relative standard deviations were no more than 4.72%. This procedure provided a convenient, sensitive and accurate method for simultaneous determination of oleanolic acid, ursolic acid, quercetin and apigenin in S. mussotii Franch.

Electrochemical sensor for discrimination tyrosine enantiomers using graphene quantum dots and β-cyclodextrins composites

An electrochemical sensor using the composites of graphene quantum dots (GQDs) and β-cyclodextrins (β-CDs) functionalized glassy carbon electrode (GCE) was developed for determination and recognition of tyrosine (Tyr) enantiomers which are biomarker of depression. The modified electrode is simple to fabricate and rapid, sensitive, selective to detect the Tyr enantiomers. In order to further validate the feasibility of the electrochemical sensor in real samples, the sensor was applied to the detection of L-Tyr in blood serum samples of healthy people and depression patients, and found that the quantities of L-Tyr of depression patients in serum is less than healthy people. The β-CDs-GQDs composites were fabricated as modification layer of electrodes. GQDs were used as substrate and functionalized with β-CDs. The β-CDs-GQDs composites utilized nanosize of GQDs and enantioselectivity of β-CDs to realize chiral recognition of Tyr. The β-CDs-GQDs modified electrode presented significant difference in the oxidation peak current with ratio of L to D-Tyr reaching 2.35. The detection limits of L-Tyr and D-Tyr were 6.07×10-9 M and 1.03×10-7 M, respectively and superior to detection limits of the reported methods. In addition, the stability and reproducibility of the prepared modified electrode were investigated, and achieved good results.

Nanocellulose 3, 5‐Dimethylphenylcarbamate Derivative Coated Chiral Stationary Phase: Preparation and Enantioseparation Performance

Nanocrystalline cellulose (NCC) with high surface area and high ordered crystalline structure was prepared from microcrystalline cellulose (MCC) under the hydrolysis of sodium hypochlorite. NCC was further reacted with 3,5-dimethylphenyl isocyanate to obtain the nanocellulose derivative, and then coated successfully on the surface of silica gel to a prepared NCC-coated chiral stationary phase (CSP) as a new kind of chiral separation material. Similarly, MCC derivative-coated CSP was also prepared as contrast. The chiral separation performance of NCC-based CSP was evaluated and compared with MCC-based CSP by high-performance liquid chromatography. Moreover, the effects of the alcohol modifiers, mobile phase additives, and flow rates on chiral separations were investigated in detail. The results showed that 10 chiral compounds were separated on NCC-based CSP with better peak shape and higher column efficiency than MCC-based CSP, which confirmed that NCC-based CSP was a promising packing material for the resolution of chiral compounds.Chirality 28:376-381, 2016.

Spherical β-cyclodextrin-silica hybrid materials for multifunctional chiral stationary phases.

Spherical β-CD-silica hybrid materials have been prepared successfully by simple one-pot polymerization, which provide a new strategy to construct new type of HPLC chiral stationary phases. Various β-CD, ethane, triazinyl and 3,5-dimethylphenyl functional groups that can provide multiple interactions were introduced into the pore channels and pore wall framework of mesoporous materials, respectively. The materials towards some chiral, acidic, anilines and phenols compounds showed multiple chromatographic separation functions including racemic resolution, anion exchange and achiral separations with a typical feature of normal/reversed phase chromatography. Multi-tasking including racemic resolution and achiral separations for selected compounds were performed simultaneously on a chiral chromatographic column. The multifunctional character of materials arises from the multiple interactions including hydrophobic interaction, π-π interaction, anion exchange, inclusion interaction and hydrogen bonding interaction.

Multi-mode application of graphene quantum dots bonded silica stationary phase for high performance liquid chromatography.

Graphene quantum dots (GQDs), which possess hydrophobic, hydrophilic, π-π stacking and hydrogen bonding properties, have great prospect in HPLC. In this study, a novel GQDs bonded silica stationary phase was prepared and applied in multiple separation modes including normal phase, reversed phase and hydrophilic chromatography mode. Alkaloids, nucleosides and nucleobases were chosen as test compounds to evaluate the separation performance of this column in hydrophilic chromatographic mode. The tested polar compounds achieved baseline separation and the resolutions reached 2.32, 4.62, 7.79, 1.68 for thymidine, uridine, adenosine, cytidine and guanosine. This new column showed satisfactory chromatographic performance for anilines, phenols and polycyclic aromatic hydrocarbons in normal and reversed phase mode. Five anilines were completely separated within 10min under the condition of mobile phase containing only 10% methanol. The effect of water content, buffer concentration and pH on chromatographic separation was further investigated, founding that this new stationary phase showed a complex retention mechanism of partitioning, adsorption and electrostatic interaction in hydrophilic chromatography mode, and the multiple retention interactions such as π-π stacking and π-π electron-donor-acceptor interaction played an important role during the separation process. This GQDs bonded column, which allows us to adjust appropriate chromatography mode according to the properties of analytes, has possibility in actual application after further research.

Chromatographic Evaluation of Octadecyl-Bonded SiO2/SiO2-Based Stationary Phase for Reversed-Phase High Performance Liquid Chromatography

A new type of octadecyl-bonded SiO2/SiO2 (ODSS) core–shell monodisperse silica spheres was prepared as a high performance liquid chromatography stationary phase. The chromatographic performance was evaluated and compared with totally porous octadecyl-bonded SiO2. Various methods were used for characterization of the two column packings for reversed-phase chromatography in terms of permeability, hydrophobic selectivity, sensitivity, stability and hydrophobicity. The results showed that the ODSS-based stationary phase has enhanced permeability, good hydrophobic selectivity, high chemical stability and sensitivity. Acidic, basic and neutral aromatic compounds were separated on the two types of stationary phases. The ODSS-based stationary phase has good selectivity and gives symmetrical narrow peaks under reversed-phase conditions.

Nanocellulose crystals derivative-silica hybrid sol open tubular capillary column for enantioseparation

Broad spectrum separation of chiral compounds is a challenge task for analysts. It is significant for preparation of chiral stationary phase and selection of separation technology in the field. Here, we present a novel nanocellulose crystals (NCCs) which were derivation with 3,5-dimethylphenyl isocynate (DMPC) and silane with 3-triethoxysilylpropylisocyanate form sol in tetraethylorthosilicate (TEOS) and layer-by-layer self-assembly in the inner of capillary to fabricate the organic-inorganic hybrid open tubular capillary column (DMPC/NCCs-OTC) for enantiomers separation by capillary electrochromatography technology (CEC). The experimental results verified that this coating column has the broad spectrum separation ability and high resolution efficiency for thirteen different enantiomers at the optimal CEC conditions. The mechanizations of DMPC/NCCs-OTC modified layer numbers and structure effect on chiral separation performance have been investigated and compared. Although the limitation and difficulty in fabrication of open tubular coating column, this work provided the preparation method of stability, controlled, long column life, adequate repeatability and satisfied enantioseparation performance.

Nanocellulose Derivative/Silica Hybrid Core-Shell Chiral Stationary Phase: Preparation and Enantioseparation Performance

Core-shell silica microspheres with a nanocellulose derivative in the hybrid shell were successfully prepared as a chiral stationary phase by a layer-by-layer self-assembly method. The hybrid shell assembled on the silica core was formed using a surfactant as template by the copolymerization reaction of tetraethyl orthosilicate and the nanocellulose derivative bearing triethoxysilyl and 3,5-dimethylphenyl groups. The resulting nanocellulose hybrid core-shell chiral packing materials (CPMs) were characterized and packed into columns, and their enantioseparation performance was evaluated by high performance liquid chromatography. The results showed that CPMs exhibited uniform surface morphology and core-shell structures. Various types of chiral compounds were efficiently separated under normal and reversed phase mode. Moreover, chloroform and tetrahydrofuran as mobile phase additives could obviously improve the resolution during the chiral separation processes. CPMs still have good chiral separation property when eluted with solvent systems with a high content of tetrahydrofuran and chloroform, which proved the high solvent resistance of this new material.

Graphene quantum dots-functionalized C18 hydrophobic/hydrophilic stationary phase for high performance liquid chromatography

Graphene quantum dots (GQDs) were chosen as functional material to improve the separation performance of C18 column since GQDs could provide multiple interactions such as hydrophilic, π-π stacking and hydrogen bonding interactions. In this study, a novel octadecyl modified GQDs-bonded silica (C18/GQDs/SiO2) stationary phase was prepared and applied in reversed-phase and hydrophilic interaction liquid chromatography. This column showed satisfactory separation performance for both hydrophobic, polar and hydrophilic compounds including polycyclic aromatic hydrocarbons, alkylbenzenes, anilines, phenols, aromatic acids, alkaloids, nucleosides and nucleobases. Through investigating the impact of organic solvent content on retention, it was found this new stationary phase had typical characteristics of hydrophobic/hydrophilic chromatography. Compared with commercial C18 column, this column showed better separation performance for polar aromatic compounds because the introduction of GQDs provided more interactions such as π-π stacking, hydrophilic and hydrogen bonding interaction with analytes. To get an in-depth understanding of the retention mechanism, linear solvation energy relationship model was established for both C18/GQDs/SiO2 and C18 columns, theoretically calculated data indicated that C18/GQDs/SiO2 column had higher π-π stacking and hydrogen-bonding acceptance ability. C18/GQDs composite stationary phase equipped with hydrophobic/hydrophilic properties has great prospect in separation science.

Ionic liquid-functionalized graphene quantum dot-bonded silica as multi-mode HPLC stationary phase with enhanced selectivity for acid compounds

Graphene quantum dots (GQDs), which can form hydrophobic, π–π stacking, hydrogen bond and hydrophilic interactions with analytes, are a type of multifunctional separation materials. GQD-based stationary phases have great prospects in HPLC. In this study, 1-aminoethyl-3-methylimidazolium bromide ionic liquids (ILs) were chosen as functional molecules to improve the chromatographic performance of GQD-bonded silica stationary phase. This new phase could be applied in multiple separation modes including normal phase, reverse phase, ionic exchange and hydrophilic chromatography modes. Anilines, phenols and polycyclic aromatic hydrocarbons were efficiently separated on the IL/GQD/SiO2 column within 10 minutes in the normal phase and reverse phase modes. Five inorganic anions were baseline separated in the ionic exchange mode. Hydrophilic compounds including alkaloids, glycosides, amino acids and aromatic acids achieved satisfactory resolutions on this stationary phase in the hydrophilic chromatography mode. The separation performance of the IL/GQD/SiO2 column was compared to those of GQD/SiO2 column and IL/SiO2 column; it was found that the IL/GQD/SiO2 column showed better separation performance than the other two columns, which indicated ILs and GQDs had certain synergistic and complementary effects. Introduction of ILs enhanced the separation performance of the GQD-based phase, especially for acid compounds. By investigating the effects of buffer pH, buffer concentration and water content in the mobile phase, it was found that the electrostatic adsorption retention mechanism played a major role in the hydrophilic chromatography mode. This stationary phase, which allows the selection of appropriate separation modes on the basis of analytes, possesses practical prospects after further improvement.