Chromatographic efficiency comparison of polyhedral oligomeric silsesquioxanes-containing hybrid monoliths via photo- and thermally-initiated free-radical polymerization in capillary liquid chromatography for small molecules

Facile DNA adsorption enabling ammonium-based hydrophilic affinity monolithic column for high-performance online selective microextraction of ochratoxin A

Herein, a facile protocol of simple DNA adsorption on UV-initiated polymerization supports was proposed for effectively fabricating aptamer-based affinity monolithic column. Hydrophilic cationic monolith with an excellent mechanical stability was achieved within 7 min and then massive aptamers were directly bound by DNA charge-dependent adsorption. Strong cationic quaternary ammonium-based monomer was employed to provide effective and stable positive charge surface for aptamer immobilization in a wide range of pH. An ultra-high aptamer coverage density of 6813 pmol/μL was achieved to gain a highly specific online recognition performance. Limitations such as low aptamer capacity, tedious modification and time-consuming reactions in the traditional biological or covalent modification strategies were avoided. By using ochratoxin A (OTA) as the given analyte, the selective recognition and high recoveries were successfully achieved, and little cross-reactivity towards OTB analogue was only 0.5% even if the content of OTB got up to 125 folds of OTA. Applied to sample analysis, the satisfactory discriminations of trace OTA were obtained at 93.9 ± 1.9% - 96.5 ± 1.7%（n = 3）in beer, wheat and chicken liver samples. It might light a cost-effective access to efficiently preparing high-performance affinity monoliths towards the selective in-tube microextraction of OTA.

Towards highly specific aptamer-affinity monolithic column by efficient UV light-initiated polymerization in "one-pot"

Time-consuming or tedious operation in multiple-step process might is the obstacle for efficiently preparing aptamer-affinity monolithic column. Here, a new and facile strategy to prepare aptamer-based hybrid affinity monolith in "one-pot" at room temperature was exploited, in which UV light-initiated free-radical polymerization and "thiol-ene" click reaction were implemented simultaneously. Only 7 min was cost for finishing the polymerization reaction, which was only 1/100 of that for the traditional thermal polymerization. Using ochratoxin A (OTA) as the model analyte, the recipe for photo-initiated polymerization was optimized, and SEM morphology, FTIR, EDS, pore size distribution and specific recognition performance were also studied. Compared with traditional thermal polymerization, the resultant monolith was achieved more facilely and displayed better results such as more homogeneous skeleton structure, higher reaction efficiency of aptamer (>88.2%) and better specific selectivity to OTA. Besides, an extremely low nonspecific adsorption of analogues was obtained and showed a level at only 1/25 of that in the similar aptamer-affinity monolith prepared by thermal polymerization. Applied to beer and red wine samples, good recovery yields about 99.7 ± 4.0% -101.2 ± 2.3% (n = 3)was achieved with the acceptable RSDs. It would open up a rapid and promising access to efficiently preparing high-performance aptamer-based affinity monolithic columns for online specific recognition.

Ternary thiol-ene photopolymerization for facile preparation of ionic liquid-functionalized hybrid monolithic columns based on polyhedral oligomeric silsesquioxanes

A simple thiol-ene photopolymerization approach was developed for the rapid preparation of ionic liquid-functionalized hybrid monolithic column based on polyhedral oligomeric silsesquioxane (POSS). "One-pot" polymerization was realized in the UV-transparent fused-silica capillary by using octanethiol, 1-allyl-3-methylimidazolium hexafluorophosphate as functional monomers and methacryl-substituted POSS as a crosslinker. The thiol-vinyl-methacrylate ternary system uniquely exhibits a mixed step-chain growth polymerization regime that combining the thiol-ene reaction and free-radical reaction mechanisms, which provides a simple route to prepare novel POSS-based functionalized hybrid monoliths. The pore property, permeability, and electroosmotic flow (EOF) of the hybrid monoliths can be tailored by proper adjustment of the feeding composition and initiation condition. Morphologic and spectroscopic characterizations of monolithic columns clearly indicate that utilization of the photo-initiated approach in thiol-vinyl polymerization can generate a more homogeneous porous structure, smaller domain size and higher column efficiency (53,800-60,300 plates/m for alkylbenzenes) than the thermally-initiated one (32,800-49,300 plates/m). Significant improvements in mechanical stability, anti-swelling property and tailorability of hybrid polymer were achieved in a simple manner, owing to the photopolymerization of rigid nanoscale POSS units and imidazolium-based ionic liquids in ternary thiol-vinyl system for the first time. The resulting hybrid monolith possessed controllable EOFs at pH values from 2 to 10, and showed a multimode separation mechanism in capillary electrochromatography, including π-π interaction, ion exchange, electrophoretic migration, electrostatic and hydrophobic interaction. Satisfactory separation ability was achieved for the analysis of different types of small molecules.

One-step fabrication of cinchona-based hybrid monolithic chiral stationary phases via photo-initiated thiol-ene polymerization for cLC enantioseparation

Although various click polymerization reactions (thiol-ene, thiol-yne, thiol-Michael, thiol-epoxy and amine-epoxy) have been utilized to prepare either hybrid or organic monolithic columns with homogeneous network structures, there were few reports on fabrication of monolithic CSPs via click polymerization. Herein, a fast and robust approach was explored to fabricate cinchona-based monolithic hybrid CSPs via photo-initiated thiol-ene polymerization within 10 min in one step. A self-synthesized octakis(3-mercaptopropyl) octasilsesquioxane (POSS-SH) was polymerized with phenylisocyanate cinchonidine (PCD) and (+)-N,N'-diallyl-L-tartardiamide (DATDA) or 1,2,4-trivinylcyclohexane (TVCH). The resulting two kinds of as-synthesized monolithic CSPs, poly(POSS-co-DATDA-co-PCD) and poly(POSS-co-TVCH-co-PCD), were evaluated for cLC enantioseparation of acidic racemates. It was found that they exhibited different enantioseparation ability due to using different multivinyl crosslinkers. The influence of ACN content in mobile phase on the enantioseparation of acidic racemates was investigated. The separation mechanism was also discussed on the basis of a comparison of enantioseparation on two kinds of hybrid monolithic CSPs.

Highly hydrophilic polyhedral oligomeric silsesquioxane (POSS)-containing aptamer-modified affinity hybrid monolith for efficient on-column discrimination with low nonspecific adsorption

A highly hydrophilic aptamer-modified POSS-containing hybrid affinity monolith is presented for efficient on-column discrimination with low non-specific adsorption.