Review of recent advances in development and applications of organic-silica hybrid monoliths

Organic-silica hybrid monoliths attracted attention as an alternative to extensively researched organic polymer-based and silica-based counterparts. The development and applications of these materials as extraction and separation media in capillary liquid chromatography and capillary electrochromatography were previously reviewed in several manuscripts. In this review, we will concentrate on work published since mid-2016 focusing on advances in their development using sol-gel chemistry of tetra- and trialkoxysilanes and subsequent surface modification with organic monomers, and "one-pot" strategy incorporating sol-gel chemistry of alkoxysilanes and free-radical polymerization, ring-opening polymerization, or thiol-based click polymerization with organic monomers. Approaches adapted to the preparation of hybrid monoliths made with polyhedral oligomeric silsesquioxanes will be covered as well.

Recent developments of monolithic and open-tubular capillary electrochromatography (2017-2019)

Capillary electrochromatography, which combined the high selectivity of high-performance liquid chromatography and the high separation efficiency of capillary electrophoresis, is an attractive separation tool. In this review, the developments on monolithic and open tubular capillary electrochromatography during 2017 to August 2019 are summarized. Considering the development of novel stationary phases is the most active research field in capillary electrochromatography, monolithic capillary electrochromatography is classified according to the polymer-based and hybrid monolithic columns, while open-tubular capillary electrochromatography is categorized by cyclodextrin, silica, polymer, nanomaterials, microporous materials, and biomaterials-based open tubular columns.

Determination of sulfamerazine in aquatic products by molecularly imprinted capillary electrochromatography

A molecularly imprinted monolith was prepared and evaluated for the special selective separation of sulfamerazine (SMR) by capillary electrochromatography (CEC). The single-step in situ polymerization method was applied through thermally immobilized vinyl groups of itaconic acid and a derivatization capillary column using SMR as the template. The monolith with optimal selectivity and permeability was performed at 45°C for 7 h according to the molar ratios of 1 : 4 : 10 (template/functional monomer/cross-linker). Under the optimized separation conditions of 75% acetonitrile in 20 mM phosphate buffer with pH 5.0, 15 kV applied voltage and 20°C column temperature, the imprinted monolith showed strong recognition ability for SMR and high column performance. Finally, the molecularly imprinted monolith coupled with the CEC method was successfully developed for the quantification of SMR in aquatic products, which was properly validated by a good linear relationship, recoveries and limit of detection. The coupling technique of the molecularly imprinted technology and CEC achieved pre-treatment enrichment and separation analysis in only one miniaturized chromatographic column.

Rapid Separation and Determination of Metronidazole Benzoate and Other Antiprotozoal Drugs by Pressurized Capillary Electrochromatography

A novel method for the rapid separation and determination of five polar 5-nitroimidazoles in water from different sources by pressurized capillary electrochromatography has been developed. Compared with the gradient elution mode and the packed nonpolar columns which were usually utilized for the separation of 5-nitroimidazoles, a simple isocratic elution mode and low-cost homemade polar molecularly imprinted polymer monolith were used in the experiment. Electrochromatographic conditions such as pH of buffer, organic modifier, concentration of buffer, and separation voltage were optimized. At 320 nm UV wavelengths, the five 5-nitroimidazoles could be baseline-separated rapidly in less than 11 min with the separation voltage of +20 kV in 10 mmol/L sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution (pH 4.82) containing 30% acetonitrile. Under the optimum conditions, the linear ranges of the metronidazole, secnidazole, tinidazole, ornidazole, and metronidazole benzoate were 0.50–100.00, 0.50–100.00, 0.80–500.00, 0.80–100.00, and 5.00–500.00 μg/mL, respectively, and the detection limits of these analytes were 0.11–0.73 μg/mL. Column efficiencies of 43 000, 36 000, 34 000, 14 000, and 29 000 plates/m were obtained for metronidazole, secnidazole, tinidazole, ornidazole, and metronidazole benzoate, respectively. The recoveries of different water samples were about 85.0–95.8%. Additionally, the proposed method has been successfully applied to the rapid separation of 5-nitroimidazoles in the locally available pure milk sample by simple pretreatment.