A bioinspired polydopamine approach toward the preparation of gold-modified magnetic nanoparticles for the magnetic solid-phase extraction of steroids in multiple samples.

In this work, a simple, facile, and sensitive magnetic solid-phase extraction method was developed for the extraction and enrichment of three representative steroid hormones before high-performance liquid chromatography analysis. Gold-modified Fe3 O4 nanoparticles, as novel magnetic adsorbents, were prepared by a rapid and environmentally friendly procedure in which polydopamine served as the reductant as well as the stabilizer for the gold nanoparticles, thus successfully avoiding the use of some toxic reagents. To obtain maximum extraction efficiency, several significant factors affecting the preconcentration steps, including the amount of adsorbent, extraction time, pH of the sample solution, and the desorption conditions, were optimized, and the enrichment factors for three steroids were all higher than 90. The validity of the established method was evaluated and good analytical characteristics were obtained. A wide linearity range (0.8-500 µg/L for all the analytes) was attained with good correlation (R2  ≥ 0.991). The low limits of detection were 0.20-0.25 µg/L, and the relative standard deviations ranged from 0.83 to 4.63%, demonstrating a good precision. The proposed method was also successfully applied to the extraction and analysis of steroids in urine, milk, and water samples with satisfactory results, which showed its reliability and feasibility in real sample analysis.

The application of functional silica nanoparticles to fulfill the rapid and improved enantioselective capillary electrophoresis separation of amino acid derivatives.

In this study, diamino moiety functionalized silica nanoparticles with the size of 118 ± 12 nm were successfully synthesized and directly introduced into a chiral capillary electrophoresis system to improve the enantioseparation of 9-fluorenyl methoxycarbonyl derivatized amino acids using norvancomycin as chiral selector. Under acidic background electrolyte conditions, functional silica nanoparticles can be readily adsorbed onto the inner surface of bare silica capillary column through electrostatic interaction to form a dynamic coating, resulting in a reversed anodic electro-osmotic flow (i.e. from cathode to anode). As expected, chiral amino acid derivatives (usually negatively charged) can be rapidly separated under co-electro-osmotic flow conditions in the current separation system. Furthermore, the column performance and detection sensitivity for the enantioseparation were also obviously improved because the adsorption of chiral selector of norvancomycin to the capillary wall was greatly suppressed. Some important factors influencing the separation, such as the coating thickness, background electrolyte concentration, functional silica nanoparticles concentration, and the organic modifier were also investigated and the optimized separation conditions were obtained.

Preparation of polydopamine-coated magnetic nanoparticles for dispersive solid-phase extraction of water-soluble synthetic colorants in beverage samples with HPLC analysis.

A facile and sensitive dispersive solid-phase extraction (D-SPE) method for the extraction and enrichment of four representative synthetic colorants prior to high performance liquid chromatography analysis was introduced. As highly efficient adsorbents, polydopamine-coated Fe3O4 nanoparticles (Fe3O4@PDA NPs) were prepared by a simple and green procedure. Several factors affecting the extraction efficiency, mainly including the polymerization time of dopamine, pH of the sample solution, the amount of adsorbent, extraction time and the desorption conditions, were systematically studied. Under the optimized conditions, the enrichment factors for the four colorants were both higher than 176. The limits of detection (LODs) for the established d-SPE-HPLC method were found to be 0.20-0.25µgL(-1), which were lower than most chromatographic methods previously reported for synthetic colorant analysis. When used for quantitative analysis, wide linearity ranges (1-500µgL(-1) for amaranth and Ponceau 4R, and 0.80-500µgL(-1) for sunset yellow and allure red) were achieved with good correlation (R(2)≥0.9995). The developed method was also successfully applied to the analysis of colorants in beverage samples with satisfactory results, demonstrating its reliability and feasibility in real sample analysis.

[Application of coating technology in capillary electrophoresis for chiral separation].

Chirality is one of the intrinsic attributes of the nature. Chiral separation and analysis are of great importance in many research fields, such as life science, environmental science, biological engineering and pharmaceutical engineering. Currently, chiral capillary electrophoresis technique used for the enantioselective resolution of different kinds of racemates has become one of the most distinctive research and application fields. However, the adsorption of the analytes (or chiral selectors) on the inner wall of the capillary is a common problem in capillary electrophoresis chiral separation. Coating technology, namely modification of the inner wall of the capillary, is the simplest and most effective way to suppress disadvantageous adsorption, and to improve the separation efficiency and analysis repeatability. In this review, the recent applications of different coating procedures in chiral analysis are presented, and the future developments in this field are also prospected.