Simultaneous determination of cytokinins by high performance liquid chromatography with resonance Rayleigh scattering and mechanism discussion.

A reliable, highly sensitive and highly selective method of high performance liquid chromatography associated with resonance Rayleigh scattering (HPLC-RRS) was developed to detect three cytokinins, namely, 6-benzylaminopurine (BA), kinetin (KT) and zeatin (ZT). In this work, Pd(ii) is added into the system to form ternary ion association complexes for the first time, which results in a lower limit of detection and extends the application of HPLC-RRS. The experimental conditions were optimized. In order to investigate the reaction mechanism, the ternary ion association complexes were characterized by ultraviolet-visible spectrophotometry, dynamic light scattering, scanning electron microscopy and density functional theory calculations. In a HAc-NaAc buffer solution (pH = 4.1), a ternary complex of cytokinin : Pd(ii) : EryB (1 : 1 : 2) was formed. The detection limits (S/N = 3) of BA, KT, and ZT were 0.9, 1.5 and 2.3 ng mL-1, respectively. In addition, this method was applied for the simultaneous detection of cytokinins in real samples with satisfactory results.

A quadruple-channel fluorescent sensor array based on label-free carbon dots for sensitive detection of tetracyclines.

A quadruple-channel fluorescent sensor array based on label-free carbon dots (CDs) was fabricated to detect and discriminate a series of tetracyclines (TCs), including chlortetracycline (CTC), oxytetracycline (OTC), tetracycline (TC) and doxycycline (DOX). Blue-emitting carbon dots (B-CDs) and green-emitting carbon dots (G-CDs) were prepared to serve as four sensing elements. When the TCs were directly mixed with CDs, the fluorescence quenching phenomenon appeared. Since different TCs exhibited different affinities for sensing elements, the sensor array displays a distinct fluorescence pattern of the fluorescence intensity variation (F0 - F)/F0 for each of these TCs, which is further analyzed by principal component analysis (PCA). The present fluorescent sensor array has the capacity to differentiate TCs at a low concentration of 1 µM. Meanwhile, quantitative detection with a lower limit (0.30 µM) for TCs could be achieved by applying a single element. Moreover, a high accuracy (100%) examination of unknown samples is acquired. Finally, the fluorescent sensor array performs well in distinguishing binary mixtures and could also recognize TCs in milk.

Facile fabrication of silica@covalent organic polymers core-shell composites as the mixed-mode stationary phase for hydrophilic interaction/reversed-phase/ion-exchange chromatography.

Covalent organic polymers (COPs) are a promising class of cross-linked polymeric networks that attracted extensive attention in separation and analysis fields. Exploring facile and convenient strategy to prepare COPs-based mixed-mode stationary phases for high performance liquid chromatography (HPLC) has seriously lagged and has never been reported. Herein, we describe a facile in-situ grow strategy for fabrication of silica@COPs core-shell composites (SiO2@TpBD-(OH)2) as a novel mixed-mode stationary phase for HPLC. Owing to the co-existing of abundant hydroxyl, carbonyl, imine, cyclohexyl groups, and benzene rings in the skeleton of COPs shell, the developed mixed-mode stationary phase exhibits hydrophilic interaction liquid chromatography (HILIC)/reversed-phase liquid chromatography (RPLC)/ion-exchange chromatography (IEX) retention mechanisms. The content of acetonitrile, pH value, and salt concentration in the mobile phase were investigated on SiO2@TpBD-(OH)2 packed column. In comparison to conventional single-mode columns, the SiO2@TpBD-(OH)2 column showed flexible selectivity, enhanced separation performance, and superior resolution for benzene homologues, polycyclic aromatic hydrocarbons, nucleosides and bases, and acidic organic compounds. The column efficiency of p-nitrobenzoic acid was up to 54440 plates per meter. The packed column also possessed outstanding chromatographic repeatability for six nucleosides and bases with the RSDs of 0.07-0.23%, 0.58-1.77%, and 0.31-1.23% for retention time, peak area, and peak height, respectively. Besides, the SiO2@TpBD-(OH)2 column offered baseline separation of multiple organic pollutants in lake water, which verified its great potential in real sample analysis. Overall, the silica@COPs core-shell composites not only provide a new candidate of mixed-mode stationary phases, but also extend the potential application of COPs in separation science.

Preparation of two ionic liquid bonded stationary phases and comparative evaluation under mixed-mode of reversed phase/ hydrophilic interaction/ ion exchange chromatography.

The present work describes the preparation of two ionic liquid and carboxyl acid silane reagents via photo-initiated thiol-ene click chemistry that have been bonded to silica to afford two mixed-mode stationary phases (Sil-C4Im-C9Co and Sil-C9Im-C4Co). The two stationary phases provided satisfactory retention repeatability and efficiencies. The influence of acetonitrile content, salt concentration and pH of the mobile phase was investigated to clarify the retention properties of the prepared stationary phases. The results showed that the prepared Sil-C4Im-C9Co and Sil-C9Im-C4Co undergo multiple interactions with solutes under different chromatographic conditions. The retention mechanisms were further studied by the linear energy solvation relationship and Van't Hoff plots. Finally, the stationary phases were employed to separate hydrophobic solutes (alkylbenzenes and polycyclic aromatic hydrocarbons) under reversed phase liquid chromatography (RPLC) mode, hydrophilic solutes (carboxylic acids, nucleosides and bases) under hydrophilic interaction liquid chromatography (HILIC) mode and inorganic anions under ion-exchange chromatography (IEC) mode, providing excellent performance and varying selectivity when compared with a commercial column. The bonding method in this work is feasible and the prepared stationary phases are promising when employed in RPLC/HILIC/IEC mixed-mode chromatography applications.