No abstract

A novel method of microemulsion electrokinetic capillary chromatography (MEEKC) coupled with on-line large volume sample stacking was developed for the analysis of six plant hormones including indole-3-acetic acid, indole-3-butyric acid, indole-3-propionic acid, 1-naphthaleneacetic acid, abscisic acid and salicylic acid. Baseline separation of six plant hormones was achieved within 10 min by using the microemulsion background electrolyte containing a 97.2% (w/w) 10 mM borate buffer at pH 9.2, 1.0% (w/w) ethyl acetate as oil droplets, 0.6% (w/w) sodium dodecyl sulphate as surfactant and 1.2% (w/w) 1-butanol as cosurfactant. In addition, an on-line concentration method based on a large volume sample stacking technique and multiple wavelength detection was adopted for improving the detection sensitivity in order to determine trace level hormones in a real sample. The optimal method provided about 50-100 fold increase in detection sensitivity compared with a single MEEKC method, and the detection limits (S/N = 3) were between 0.005 and 0.02 μg mL(-1). The proposed method was simple, rapid and sensitive and could be applied to the determination of six plant hormones in spiked water samples, tobacco leaves and 1-naphthylacetic acid in leaf fertilizer. The recoveries ranged from 76.0% to 119.1%, and good reproducibilities were obtained with relative standard deviations (RSDs) less than 6.6%.

A pressure-assisted CEC with ESI-MS based on poly(1-hexadecene-co-trimethylolpropane trimethacrylate) monolithic column for rapid analysis of two beta(2)-agonists and three narcotics was established in this article. After the organic polymer-based monolithic column was prepared by an in-situ polymerization procedure, a systematic investigation of the pressure-assisted CEC separation and ESI-MS detection parameters was performed. Baseline separation of the studied analytes could be obtained using the solution containing 75% ACN v/v and 20 mmol/L ammonium acetate with pH 8.0 as running buffer, when applying separation voltage of 20 kV and assisted pressure of 5 bar. Under the optimized conditions, two beta(2)-agonists and three narcotics could be completely resolved and accurately determined within 15 min. Finally, the proposed method was successfully used for real urine samples detection.

In this work, polydopamine-coated magnetic graphene nanocomposites were synthesized by a simple solvothermal reaction and self-polymerization of dopamine, and the as-made nanocomposites were successfully applied as an effective adsorbent for the preconcentration of the four chlorophenols in environmental water samples before high-performance liquid chromatography. The polydopamine-coated magnetic graphene nanocomposites have several advantages such as a high surface area, fast separation ability, super-hydrophilicity, and high peak intensities for aromatic analytes. Various parameters, including eluting solvent and volume, the amounts of absorbents, extraction time and elution time were optimized. Validation experiments showed that the optimized method had good linearity (r(2) > 0.9990), satisfactory precision (RSD < 6.7%) and high recovery (90-105%). The limits of detection were 0.013-0.020 μg/L and the limits of quantification ranged from 0.043 to 0.070 μg/L. The results indicated that the proposed method had advantages of convenience, good sensitivity, and high efficiency. The method has been applied successfully to analyze chlorophenols in real water samples.