Shuaihua Zhang

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.

Application of dispersive liquid–liquid microextraction combined with sweeping micellar electrokinetic chromatography for trace analysis of six carbamate pesticides in apples

A rapid and sensitive method for the multiresidue analysis of six commonly used carbamate pesticides in apples was developed by using dispersive liquid–liquid microextraction (DLLME) coupled with sweeping micellar electrokinetic chromatography (MEKC). Parameters that affect the extraction and sweeping efficiency, such as the kind and volume of the extraction and disperser solvent, extraction time, salt addition, sample matrix and concentration of organic modifiers in the separation buffer were investigated and optimized. Under optimized conditions, the enrichment factors were achieved in the range from 491 to 1834. The linearity of the method for methiocarb, diethofencarb, carbaryl and isoprocarb was in the range of 6–500 ng g−1, and for fenobcarb and tsumacide in the range of 9–500 ng g−1, with the correlation coefficients (r) ranging from 0.9952 to 0.9990. The limits of detection (LODs) at a signal-to-noise ratio of 3 ranged from 2.0 to 3.0 ng g−1. The recoveries of the six carbamates for apple samples at spiking levels of 20.0 and 100.0 ng g−1 were 85.5–108.1% and 85.4–113.3%, respectively. The proposed method has been successfully applied to the analysis of the target carbamate residues in apple samples with satisfactory results.

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.

A novel Schiff base network-1 nanocomposite coated fiber for solid-phase microextraction of phenols from honey samples

A novel covalent organic framework, Schiff base network-1 (SNW-1), was synthesized and used as a solid-phase microextraction (SPME) fiber coating material. The SNW-1 coated SPME fiber was fabricated by a covalent chemical cross-linking between the SNW-1 nanocomposite and a silanol-functionalized stainless steel wire substrate. Scanning electron microscopy and nitrogen isothermal adsorption results indicate that the new fiber coating exhibited a porous, homogenous surface with the Brunauer-Emmett-Teller surface of 668m2g-1. The prepared fiber was explored for the SPME of phenols from honey samples prior to their determination by gas chromatography-mass spectrometry. The developed method had large enrichment factors (136-816), low limits of detection (0.06-0.2ngg-1), good linearity (0.1-100.0ngg-1) and repeatability (<9.7%) for phenols. The recoveries for spiked phenols (1.0ngg-1 and 10.0ngg-1) in Wolfberry, Robinia and Codonopsis honey samples were in the range of 84.2-107.2% with the relative standard deviations ranging from 3.8% to 12.7%. The developed method was suitable for the determination of phenols from honey samples.

Covalent Bonding of Metal–Organic Framework-5/Graphene Oxide Hybrid Composite to Stainless Steel Fiber for Solid-Phase Microextraction of Triazole Fungicides from Fruit and Vegetable Samples

A hybrid material of the zinc-based metal-organic framework-5 and graphene oxide (metal-organic framework-5/graphene oxide) was prepared as a novel fiber coating material for solid-phase microextraction (SPME). The SPME fibers were fabricated by covalent bonding via chemical cross-linking between the coating material metal-organic framework-5/graphene oxide and stainless steel wire. The prepared fiber was used for the extraction of five triazole fungicides from fruit and vegetable samples. Gas chromatography coupled with microelectron capture detector (GC-μECD) was used for quantification. The developed method gave a low limit of detection (0.05-1.58 ng g(-1)) and good linearity (0.17-100 ng g(-1)) for the determination of the triazole fungicides in fruit and vegetable samples. The relative standard deviations (RSDs) for five replicate extractions of the triazole fungicides ranged from 3.7 to 8.9%. The method recoveries for spiked fungicides (5, 20, and 50 ng g(-1)) in grape, apple, cucumber, celery cabbage, pear, cabbage, and tomato samples were in the range of 85.6-105.8% with the RSDs ranging from 3.6 to 11.4%, respectively, depending on both the analytes and samples. The metal-organic framework-5/graphene oxide coated fiber was stable enough for 120 extraction cycles without a significant loss of extraction efficiency. The method was suitable for the determination of triazole fungicides in fruit and vegetable 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.

Micellar Electrokinetic Chromatographic Determination of Triazine Herbicides in Water Samples

Dispersive liquid-liquid microextraction combined with online sweeping preconcentration in micellar electrokinetic chromatography was developed for the simultaneous determination of five triazine herbicides (atrazine, simazine, propazine, prometon and simetryn) in water samples. Several experimental parameters affecting the extraction efficiencies such as the type and volume of both the extraction and dispersive solvents, the addition of salt to sample solution, the extraction time and the pH of the sample solution were investigated. Under optimum conditions, the linearity of the method was good in the range from 0.33 to 20 ng mL(-1) for simazine, propazine, atrazine and simetryn, and from 0.17 to 20 ng mL(-1) for prometon, respectively. The sensitivity enrichment factors were in the range from 1750 to 2100, depending on the compound. The limit of detection (S/N = 3) ranged from 0.05 to 0.10 ng mL(-1). The developed method was successfully applied to the analysis of the five triazines in river, ground and well waters.

Cyclodextrin‐functionalized reduced graphene oxide as a fiber coating material for the solid‐phase microextraction of some volatile aromatic compounds

A novel solid phase microextraction fiber was prepared for the first time by using a sol-gel technique with hydroxypropyl-β-cyclodextrin-functionalized reduced graphene oxide as the fiber coating material. The results verified that the β-cyclodextrin was successfully grafted onto the surface of reduced graphene oxide and the coating possessed a uniform folded and wrinkled structure. The performance of the solid phase microextraction fiber was evaluated by using it to extract nine volatile aromatic compounds from water samples before determination with gas chromatography and flame ionization detection. Some important experimental parameters that could affect the extraction efficiency such as the extraction time, extraction temperature, desorption temperature, desorption time, the volume of water sample solution, stirring rate, as well as ionic strength were optimized. The new method was validated to be effective for the trace analysis of some volatile aromatic compounds, with the limits of detection ranging from 2.0 to 8.0 ng/L. Single fiber repeatability and fiber-to-fiber reproducibility were in the range of 2.5-9.4 and 5.4-12.9%, respectively. The developed method was successfully applied to the analysis of three different water samples, and the recoveries of the method were in the range from 77.9 to 113.6% at spiking levels of 10, 100, and 1000 ng/L, respectively.