Xiumin Yang

Dispersive liquid-liquid microextraction combined with sweeping micellar electrokinetic chromatography for the determination of some neonicotinoid insecticides in cucumber samples.

A rapid, simple and sensitive method has been developed for the analysis of some neonicotinoid insecticides in cucumber samples by using dispersive liquid-liquid microextraction (DLLME) coupled with sweeping in micellar electrokinetic chromatography (MEKC). Under optimised conditions, the enrichment factors were achieved in the range from 4000 to 10,000. The linearity of the method was in the range from 2.7 to 200 ng g(-1) for thiacloprid, acetamiprid and imidacloprid, and in the range from 4.0 to 200 ng g(-1) for imidaclothiz in cucumber samples, with the determination coefficients (r(2)) ranging from 0.9924 to 0.9968. The limits of detection (LODs, S/N=3) ranged from 0.8 to 1.2 ng g(-1). The relative standard deviations (RSDs) at the concentration levels of 10.0 and 50.0 ng g(-1) each of the neonicotinoid insecticides in cucumber samples varied from 3.8% to 6.3%. The developed method has been successfully applied to the analysis of the neonicotinoid insecticides in cucumbers with a satisfactory result.

A sensitive determination method for carbendazim and thiabendazole in apples by solid-phase microextraction−high performance liquid chromatography with fluorescence detection

A new analytical method for the determination of carbendazim (MBC) and thiabendazole (TBZ) in apples is reported, based on solid-phase microextraction (SPME) coupling HPLC with fluorescence detection. The main SPME and HPLC experimental conditions were optimized. The apples were first blended and centrifuged. Then, an aliquot of the resulting solution was subjected to SPME on a 60 µm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibre for 35 min at room temperature with the solution being stirred at 1100 rev min–1. The extracted pesticides on the SPME fibre were desorbed in the mobile phase into the SPME/HPLC interface for HPLC analysis. The method was linear over the range 0.01–1 mg kg–1 in apples for both MBC and TBZ, with detection limits of 0.005 and 0.003 mg kg–1 and correlation coefficients of 0.9995 and 0.9998, respectively. The average recoveries for MBC and TBZ were 91.5 and 92.3% with the relative standard deviations (RSD) of 4.7 and 4.1% at the 0.1 mg kg–1 level, and 94.6 and 96.1% with RSD of 3.3 and 3.8% at the 0.5 mg kg–1 level, respectively. The method is simple, sensitive, organic solvent-free and is suitable for the determination of MBC and TBZ in apples.

On-line sample concentration and determination of cationic alkaloids in human plasma by micelle to solvent stacking in capillary zone electrophoresis

A sensitive method for the determination of three cationic alkaloids (berberine, palmatine and jatrorrhizine) from human plasma samples was developed by micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE). In MSS, the sample preconcentration mainly relies on the reversal in the effective electrophoretic mobility of the analytes at the boundary zone between the sample and CZE background solution (BGS). Under the optimized conditions, the sensitivity enhancement factors achieved in terms of corrected peak area were in the range from 47 to 53 for the alkaloids. The limits of detection (LODs) (S/N=3) for berberine, palmatine and jatrorrhizine were 0.01, 0.01 and 0.02μg/mL, respectively. The intraday (n=6) and interday repeatabilities (n=12) expressed as the relative standard deviations (RSDs) were less than 6.9% in terms of peak height and less than 7.3% in terms of corrected peak area, respectively. The recoveries of the method for the three alkaloids were in the range of 95.9-101.5% with peak height as the quantitative signal, and 92.6-103.6% with corrected peak area as the quantitative signal, respectively. The MSS-CZE method proved to be suitable for the analysis of the alkaloids in human plasma samples.

On-line two-step stacking in capillary zone electrophoresis for the preconcentration of strychnine and brucine

An on-line sample preconcentration method by two-step stacking i.e., sweeping and micelle to solvent stacking, in capillary zone electrophoresis (CZE) has been developed for the determination of strychnine and brucine in traditional Chinese herbal medicines. After experimental optimizations, the best separation was achieved by using 75 mM phosphate buffer (pH 2.5) with 30% methanol (v/v). Compared with normal CZE injection, 51- and 38-fold improvement in concentration sensitivity was achieved for strychnine and brucine, respectively. The calibration curve was linear in the range of 0.1-5.0 μg mL(-1) for both strychnine and brucine, with the correlation coefficients of 0.9998 and 0.9997, respectively. The limits of detection (S/N=3) for both alkaloids were 0.01 μg mL(-1). The inter-day (n=8) and intra-day (n=5) reproducibilities expressed as the relative standard deviations for corrected peak area were less than 9.5%. The method was applied to determine strychnine and brucine in two Chinese herbal medicines, with recoveries ranging from 94.2% to 105.4%. The results indicated that the method is simple, rapid, reliable, and can be applied to determine strychnos alkaloids in traditional Chinese herbal medicines.

A zeolitic imidazolate framework based nanoporous carbon as a novel fiber coating for solid-phase microextraction of pyrethroid pesticides

A high-surface-area nanoporous carbon (NPC) has been successfully synthesized by using the metal-organic framework ZIF-90 as both the template and precursor together with furfuryl alcohol as a secondary carbon source. The prepared ZIF-90 templated NPC (ZIF-90-NPC) was then coated onto a stainless steel wire by a simple physical adhesion approach to prepare solid-phase microextraction (SPME) fiber. By coupling the ZIF-90-NPC coated fiber-based SPME with gas chromatography-microelectron capture detection (GC-μECD), the developed method gave a large enhancement factor (984-2869), low limit of detection (0.1-0.5ngg-1) and good linearity (0.3-50ngg-1) for the determination of some pyrethroid pesticides (bifenthrin, fenpropathrin, cyhalothrin, permethrin, cyfluthrin, flucythrinate, fenvalerate and deltamethrin) from different fruits and vegetables. The relative standard deviations (RSDs) for six replicate extractions of the pyrethroids by the ZIF-90-NPC coated fiber ranged from 4.3% to 8.0%. The recoveries of the spiked pyrethroids (5ngg-1 and 20ngg-1) from fruit and vegetable samples were in the range of 88.0-104.0% and 86.0-103.5% with the RSDs ranging from 4.8% to 12.9% and 5.0-10.8%, respectively. Besides, the ZIF-90-NPC coated fiber was stable enough for 100 extraction cycles without a significant loss of extraction efficiency. The method was successfully applied to the determination of the pyrethroids in fruit and vegetable samples.

Fabrication of a three-dimensional graphene coating for solid-phase microextraction of polycyclic aromatic hydrocarbons

A novel three-dimensional graphene (3D-G) coated fiber for solid-phase microextraction (SPME) was fabricated via a sol–gel coating method on stainless steel wires. The 3D-G was obtained by connecting graphene oxide (GO) sheets with Ca2+ and water molecules by hydrothermal treatment. Due to the π–π stacking and hydrophobic interactions between the 3D-G and the analytes, the 3D-G fibers showed high extraction efficiencies for the polycyclic aromatic hydrocarbons (PAHs). The developed method, which combined the 3D-G coated fiber-based SPME with gas chromatography-flame ionization detection, had large enhancement factors (842–2458), low limits of detection (2.0–10.0 ng L−1) and good linear range (10.0–1000.0 ng L−1) for the PAHs in water samples. Single fiber repeatability and fiber-to-fiber reproducibility were in the range of 4.7–8.8% and 6.4–11.9%, respectively. The recoveries of the analytes for the method were in the range from 76.5% to 102.6%. The fiber exhibited an excellent durability and can be reused more than 150 times without a significant loss of the extraction performance. The method was successfully applied to the determination of PAHs in water and soil samples.

Development of Micellar to Solvent Stacking On-line Preconcentration Technique in Capillary Electrophoresis

Abstract Micellar to solvent stacking (MSS) is a novel on-line preconcentration technique in capillary electrophoresis. MSS is fast, inexpensive, and easy to be operated. Moreover, it can be used in different capillary electrophoresis modes including capillary zone electrophoresis, micellar electrokinetic chromatography and non-aqueous capillary electrophoresis. MSS has been widely applicated in the analysis of medicines, biological samples and environmental samples. In this paper, the basic principles of MSS, the main experimental parameters involved and its latest applications are reviewed.

On-line micelle to solvent stacking in capillary electrophoresis for the preconcentration of three antihistamines from human plasma

A new on-line concentration method of micelle to solvent stacking in capillary electrophoresis was developed for the determination of three antihistamine drugs (chlorpheniramine, diphenhydramine and promethazine) in human plasma. Palmatine was used as an internal standard. The main parameters that affect the ability of the developed method to detect and separate the three drugs were investigated and optimized. Under the optimized conditions, the sensitivity enhancement factors obtained by this method for diphenhydramine, chlorpheniramine and promethazine were 63, 43 and 111, respectively. The method showed good linearity in the range of 0.6–60.0 μg mL−1 for the three antihistamines with the correlation coefficients varying from 0.9971 to 0.9996. The limits of detection (S/N = 3) were 0.1–0.2 μg mL−1. The relative standard deviations for intra-day (n = 8) and inter-day (n = 5) analysis were found to be less than 9.1%. The recoveries of the method for the analytes were in the range from 89.7% to 108.0%. The method is feasible for fast screening of the antihistamine drugs in plasma.

On-line two-step stacking for the preconcentration and determination of quinolizidine alkaloids by capillary electrophoresis

In this research, a novel on-line two-step stacking preconcentration method by sweeping and micelle to solvent stacking in capillary zone electrophoresis was developed and validated for the simultaneous determination of quinolizidine alkaloids (sophocarpine, matrine and oxymatrine) in traditional Chinese medicines. Strychnine was used as an internal standard. The main parameters that affect the separation and sensitivity were investigated and optimized. Under the optimum conditions, the sensitivity enhancement factors obtained by the developed method for the analytes were from 42- to 52-fold. The method showed a good linearity over the range of 0.1–10.0 μg mL−1 for sophocarpine, matrine and oxymatrine with the correlation coefficients (r) varying from 0.9992 to 0.9996. The limits of detection (S/N = 3) were 0.02–0.03 μg mL−1. The intra-day (n = 8) and inter-day (n = 5) precisions of the method expressed as the relative standard deviation (RSD) were found to be less than 10%. The recoveries of the analytes by the method for the analysis of traditional Chinese medicines were in the range from 87.5% to 109.0% with RSDs (n = 3) less than 8.9%.

Sweeping-micelle to solvent stacking for the on-line preconcentration and determination of organic acids in Angelica sinensis by capillary electrophoresis

A novel on-line two-step stacking preconcentration method by sweeping plus micelle to solvent stacking in capillary zone electrophoresis was developed for the simultaneous determination of three organic anions (vanillic acid, ferulic acid and cinnamic acid) in Angelica sinensis. Hexadimethrine bromide was used for electroosmotic flow reversal. The main experimental parameters that affected the separation and sensitivity were investigated and optimized. The best separation was achieved in 50 mM ammonium acetate (pH 12.0) containing 50% methanol (v/v) under a negative voltage of 20 kV. The micellar solution was a mixed solution comprised of 12 mM cetyltrimethyl ammonium bromide and 20 mM ammonium acetate. After injecting a short plug (0.5 psi, 30 s) of micellar solution, the sample was introduced into the capillary at 0.5 psi for 45 s. Under the optimal conditions, the sensitivity enhancement factors obtained by the developed method were between 42 and 77. The intra-day (n = 6) and inter-day (n = 5) precisions of the method expressed as their relative standard deviations were found to be less than 7.2%. The Angelica sinensis sample was pulverized and then refluxed in 95% ethanol and filtered. After an aliquot of the extractant was dried, it was reconstituted in 20 mM ammonium acetate for capillary electrophoresis analysis. The recoveries of the analytes by this method for the analysis of Angelica sinensis were in the range of 94.4% to 108.4%.