Preparation and evaluation of a double-hydrophilic interaction stationary phase based on bovine serum albumin and graphene quantum dots modified silica.

The bovine serum albumin (BSA) was firstly bonded on the surface of graphene quantum dots (GQDs) functionalized silica as the stationary phase named as BSA@GQDs@SiO2 which can perform hydrophilic interaction between the stationary phase and analytes. Characteristic methods including Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), thermogravimetric analysis (TGA) and scanning electron microscope (SEM) were applied to estimate the chemical bonding results and morphological features of the prepared materials. In the chromatographic evaluation part, the BSA@GQDs@SiO2 column showed excellent separation efficiency for the analysis of hydrophilic compounds involving nucleosides and bases, acids, phenols, quinolones, vitamins and alkaloids, which proved the prepared column can exhibit hydrophilic interaction mode with other interactions including hydrogen bonding and electrostatic interaction. What's more, essential experimental approaches were designed to evaluate the retention properties of the prepared column via comparing with a commercial amino column and a prepared GQDs@SiO2 column. Results indicated the prepared column showed excellent separation ability for different kinds of hydrophilic compounds than commercial and single hydrophilic columns. The study showed that BSA@GQDs@SiO2 stationary phase with double hydrophilic materials will be a potential chromatographic material for analyzing various hydrophilic analytes.

Striped covalent organic frameworks modified stationary phase for mixed mode chromatography.

Covalent organic frameworks (COFs) have showed expected potential in chromatographic separation due to unique structure and excellent performance. Nowadays, COF materials applied as chromatographic stationary phases is still in its infancy. Here, we modified COF materials on silica using benzene-1,4,5-tetracarboxylic dianhydride (PMDA) and 1,3,5-tris-(4-aminophenyl)triazine (TAPT) monomers by one-pot synthetic method for performing mixed-mode function, named as SiO2@COF. Five characterization methods including thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FT-IR), elemental analysis (EA) and powder X-ray diffraction (XRD) verified the morphology, structure characteristics and physicochemical properties of the materials. SiO2@COF for performing the separation of polar and nonpolar analytes on high performance liquid chromatography (HPLC) achieved the desired results. Retention mechanisms of the constructed SiO2@COF were researched via observing the effects of mobile phase with retention times. Results exhibited that the prepared stationary phase can provide various interaction modes, including hydrophobic, hydrophilic, hydrogen bonding and π-π interactions. In conclusion, the prepared SiO2@COF stationary phase can execute mixed-mode separation abilities and show potential for complex samples analysis.

Preparation and evaluation of a poly(N-isopropylacrylamide) derived graphene quantum dots based hydrophilic interaction and reversed-phase mixed-mode stationary phase for complex sample analysis.

The poly(N-isopropylacrylamide) (NIPAAm) was first polymerized onto the surface of graphene quantum dots (GQDs) functionalized silica as packing materials via reversible addition-fragmentation chain transfer (RAFT) polymerization reaction, which can expand the interaction modes between stationary phase and analytes. A series of characteristic methods were selected to estimate the chemical bonding results of silica, involving Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The prepared column can exhibit reversed-phase and hydrophilic interaction modes, which were demonstrated by the retention of eight kinds of target analytes with different Log P values. The column was then applied to separate banlangen granules and further verified by HPLC tandem time-of-flight mass spectrometry (HPLC/QTOF-MS). In conclusion, Sil-GQDs-PNIPAAm stationary phase improved the analysis range and performance of traditional phases, exhibiting flexible selectivity and application prospect for both hydrophobic and hydrophilic analytes.

Preparation of an aspartame and N-isopropyl acrylamide copolymer functionalized stationary phase with multi-mode and chiral separation abilities.

A novel multi-mode and chiral separation stationary phase co-modified with copolymer composed of N-isopropyl acrylamide (NIPAM) and aspartame was synthesized by atom transfer radical polymerization (ATRP) reaction. The synthetic material was evaluated using thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FT-IR) and elemental analysis (EA). Analytes including hydrophobic, hydrophilic, alkaline and acidic compounds were separated well using the prepared stationary phase named Sil-PPAM-NIPAM. Besides, the separation of chiral compounds proved that the developed column also has the potential of chiral separation ability. In summary, the prepared column possesses excellent hydrophilic interaction, ion exchange, reversed-phase and chiral separation modes during the separation of complex and chiral compounds.

Ionic liquid functionalized ß-cyclodextrin and C18 mixed-mode stationary phase with achiral and chiral separation functions.

A novel reversed-phase/hydrophilic interaction/ion-exchange (RPLC/HILIC/IEC) and chiral recognition mixed-mode stationary phase material was synthesized using 3-n-octadecyl-1-vinylimidazolium bromide and 6-(1-allylimidazolium)-cyclodextrin tosylate as functional monomers. After identifications of intermediates and stationary phase materials using nuclear magnetic resonance analysis, Fourier transform infrared spectrometer, element analysis and thermogravimetric analysis, the synthesized Sil-VMBD material was packed into an empty column under high pressure. The mixed-mode retention performance was researched by hydrophobic, hydrophilic and ionic compounds. And the retention mechanism of the multi-mode stationary phase was studied via changing the mobile phase composition and pH value. Moreover, the enantiomers of 1-phenyl-1-propanol, warfarin and styrene oxide were separated rapidly under reverse-phase mode. Fast enantioseparation of ibuprofen and ketoprofen were obtained within 4 min under polar organic mode. The experimental results show that the as-prepared mixed-mode column possesses reversed-phase, hydrophilic and ion-exchange interactions with various analytes, and these interactions also enable the stationary phase with multi-mode and chiral separation abilities.

Preparation of an aminophenylboronic acid and N-isopropyl acrylamide copolymer functionalized stationary phase for mixed-mode chromatography.

A novel stationary phase co-modified with N-isopropyl acrylamide (NIPAM) and 3-aminophenylboronic acid copolymer on the silica was synthesized through atom transfer radical polymerization (ATRP) reaction for performing mixed-mode and boronate affinity chromatography. The prepared functionalized silica was characterized using Fourier transform infrared spectrometry (FT-IR), elemental analysis (EA) and thermogravimetric analysis (TGA), scanning electron micrographs (SEM) and Brunauer-Emmett-Teller (BET) measurements. The prepared column named Sil-PBA-NIPAM showed great separation performance for hydrophobic, hydrophilic, positional isomer, acidic and alkaline compounds. Besides, the mixture of cis-diol and non-cis-diol compounds was used to prove that the developed column also has potential to capture and enrich cis-diol compounds. The prepared column possesses merits of time-saving, high selectivity to cis-diol compounds and molecular-planarity selectivity compared with two commercial single-mode columns. The theoretical plates of material can reach to 57472 and the column has good hydrolysis stability and batch-to-batch reproducibility. In summary, the prepared column possesses good hydrophilicity, hydrophobicity, molecular-planarity selectivity and boronate affinity abilities for the analysis of various compounds.

Thermoresponsive chiral stationary phase functionalized with the copolymer of ß-cyclodextrin and N-isopropylacrylamide for high performance liquid chromatography.

A novel chiral stationary phase (CSP) was prepared through the reaction of surface-initiated atom transfer radical polymerization (ATRP) by the copolymerization of thermoresponsive N-isopropylacrylamide (NIPAM) and ß-cyclodextrin (ß-CD) on the silica beads for high performance liquid chromatography (HPLC). X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), Fourier transform infrared spectrometry (FT-IR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were applied to characterize the surface property of modified silica. Thermoresponsive modulation for the effect on enantioselectivity were investigated with chiral reagents including 1-phenyl-1-propanol, styrene oxide, 2-phenylpropionic acid and commercial chiral drugs comprising ibuprofen and labetalol hydrochloride. The column efficiency was evaluated by chromatographic parameters including retention factor (k), selective factor (α), resolution (Rs), plate number (N) and peak tailing factor (Tf). The results showed that five chiral solutes could be separated on the prepared smart column. And the selectivity of these compounds could be modulated by regulating the column temperature. It was contributed to the thermoresponsive NIPAM assisting ß-CD to separate these chiral compounds. These results indicated that the thermoresponsive CSP would be a potential tool for separation of hydrophilic and hydrophobic chiral drugs and this paper provided a novel method for chiral separation in the future.

Preparation and evaluation of a molybdenum disulfide quantum dots embedded C18 mixed-mode chromatographic stationary phase.

Molybdenum disulfide quantum dots (MoS2 QDs) were chosen as a functional two-dimensional material to improve the separation performance of a traditional C18 column. In this work, MoS2 QDs were synthesized by the combination of sonication and solvothermal treatment of bulk MoS2. The prepared MoS2 QDs were characterized by transmission electron microscope (TEM), Zeta potential measurement, UV-visible absorption and fluorescence spectroscopy. Then, a novel MoS2 QDs embedded C18 (Sil-MoS2-C18) stationary phase was prepared for performing mixed-mode liquid chromatography. The results of elemental analysis (EA), thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) measurements indicated the stationary phase was prepared successfully. Five types of compounds including alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), nucleosides and nucleobases, anilines and flavonoids were utilized to evaluate reversed phase, weak cation exchange and hydrophilic interaction of the new column. To a certain extent, the column could achieve separation for different properties of samples on one column, with less organic solvent and shorter time than conventional alkyl and amino columns. Furthermore, the mechanism for separation was studied by investigating effects of mobile phase composition and pH on retentions. In summary, the Sil-MoS2-C18 stationary phase was deemed able to serve the performance of various types of phases, which revealed the prepared mixed-mode column could be potentially applied for the analysis of complex samples. Graphical abstract.