Qingyun Chang

Ultrasound-assisted surfactant-enhanced emulsification microextraction for the determination of carbamate pesticides in water samples by high performance liquid chromatography.

A novel ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) coupled with high performance liquid chromatography-diode array detection has been developed for the extraction and determination of six carbamate pesticides (metolcarb, carbofuran, carbaryl, pirimicarb, isoprocarb and diethofencarb) in water samples. In the UASEME technique, Tween 20 was used as emulsifier, and chlorobenzene and chloroform were used as dual extraction solvent without using any organic dispersive solvent that is normally required in the previously described common dispersive liquid-liquid microextraction method. Parameters that affect the extraction efficiency, such as the kind and volume of the extraction solvent, the type and concentration of the surfactant, ultrasound emulsification time and salt addition, were investigated and optimized for the method. Under the optimum conditions, the enrichment factors were in the range between 170 and 246. The limits of detection of the method were 0.1-0.3 ng mL(-1) and the limits of quantification were between 0.3 and 0.9 ng mL(-1), depending on the compounds. The linearity of the method was obtained in the range of 0.3-200 ng mL(-1) for metolcarb, carbaryl, pirimicarb, and diethofencarb, 0.6-200 ng mL(-1) for carbofuran, and 0.9-200 ng mL(-1) for isoprocarb, with the correlation coefficients (r) ranging from 0.9982 to 0.9998. The relative standard deviations varied from 3.2 to 4.8% (n=5). The recoveries of the method for the six carbamates from water samples at spiking levels of 1.0, 10.0, 50.0 and 100.0 ng mL(-1) were ranged from 81.0 to 97.5%. The proposed UASEME technique has demonstrated to be simple, practical and environmentally friendly for the determination of carbamates residues in river, reservoir and well water samples.

Developments in Liquid-phase Microextraction Method Based on Solidification of Floating Organic Drop

Abstract The liquid-phase microextraction based on solidification of floating organic drop (LPME-SFO), which incorporated sampling, extraction, and concentration into a single step, has been developed to be a new environmentally benign sample-preparation technique. This novel technique has proved to be low-cost and virtually organic solvent-free and could provide a high enrichment factor. It can be easily integrated with gas chromatography (GC), high-performance liquid chromatography (HPLC), and atomic absorption spectrometry (AAS). The basic principles and the main parameters that affect the extraction efficiency and recent applications of the LPME-SFO are briefly reviewed in this paper.

A graphene-coated magnetic nanocomposite for the enrichment of fourteen pesticides in tomato and rape samples prior to their determination by gas chromatography-mass spectrometry

A graphene-based magnetic nanocomposite (Fe3O4@SiO2–G) was synthesized and used as the adsorbent for the extraction of fourteen pesticides in tomato and rape samples prior to their gas chromatography-mass spectrometry (GC-MS) detection. Various experimental parameters affecting the extraction efficiencies, such as the amount of Fe3O4@SiO2–G, extraction time, the pH and salt concentration of the sample solution and desorption conditions were investigated. Under optimized experimental conditions, good linearity existed in the range of 1.0–100.0 ng g−1 for all the analytes with the correlation coefficients (r) ranging from 0.9972 to 0.9996. The limits of detection (S/N = 3) of the method for the compounds were between 0.005 and 0.030 ng g−1 for the vegetable samples. Good reproducibilities were obtained with the relative standard deviations (RSDs) below 12.5% (n = 5). The recoveries of the method were in the range between 83.2% and 110.3%.

Metal-organic framework UiO-67-coated fiber for the solid-phase microextraction of nitrobenzene compounds from water.

A sol-gel coating technique was applied for the preparation of a solid-phase microextraction fiber by coating the metal-organic framework UiO-67 onto a stainless-steel wire. The prepared fiber was explored for the headspace solid-phase microextraction of five nitrobenzene compounds from water samples before gas chromatography with mass spectrometric detection. The effects of the extraction temperature, extraction time, sample solution volume, salt addition, and desorption conditions on the extraction efficiency were optimized. Under the optimal conditions, the linearity was observed in the range of 0.015-12.0 μg/L for the compounds in water samples, with the correlation coefficients (r) of 0.9945-0.9987. The limits of detection of the method were 5.0-10.0 ng/L, and the recoveries of the analytes from spiked water samples for the method were in the range of 74.0-102.0%. The precision for the measurements, expressed as the relative standard deviation, was less than 11.9%.

Metal organic framework MIL-101 coated fiber for headspace solid phase microextraction of volatile aromatic compounds

A sol–gel coating technique was applied for the preparation of metal organic frameworks (MOFs)-based solid phase microextraction (SPME) fibers by coating MIL-101 onto stainless steel wires. The prepared fiber was explored for the headspace SPME (HS-SPME) of seven volatile aromatic compounds (VACs) from water samples followed by gas chromatography-mass spectrometric analysis. Several important experimental parameters, such as extraction temperature, extraction time, sample volume, salt addition and desorption conditions, were investigated. Under the optimized experimental conditions, the developed HS-SPME method with MIL-101 coated fiber had a good linearity in the range of 0.05–50.0 μg L−1 for the analytes with the correlation coefficients (r) ranging from 0.9974 to 0.9988. Based on a signal-to-noise ratio (S/N) of 3, the limits of detection (LODs) for the seven analytes ranged from 1.0 to 5.0 ng L−1. Compared with two commercial SPME fibers, the laboratory-made MIL-101 coated fiber showed a higher extraction efficiency for the seven VACs. The established method was successfully applied for the determination of the VACs in real local tap and lake water samples. The recoveries for the method of the seven VACs at spiking levels of 0.1 and 5.0 μg L−1 were in the range from 76.4% to 116.1%.

Graphene grafted magnetic microspheres for solid phase extraction of bisphenol A and triclosan from water samples followed by gas chromatography-mass spectrometric analysis

Graphene grafted magnetic microspheres were prepared and used as the adsorbent for magnetic solid phase extraction (MSPE) of bisphenol A and triclosan from water samples prior to their determination by gas chromatography-mass spectrometric (GC-MS) detection. A new customized ground-glass stoppered conical flask with a side tube was used for MSPE operations to simplify the separation of the magnetic adsorbent from the sample solution. The main experimental factors affecting the extraction recoveries of the analytes including the amount of adsorbent, pH of the sample solution, extraction time, salt concentration, desorption conditions, and derivatization conditions were investigated. Under the optimal conditions, a linear response was observed in the concentration range of 0.05–2.50 μg L−1 for bisphenol A and 0.10–5.00 μg L−1 for triclosan. The limits of detection (S/N = 3) were 10.0 ng L−1 for bisphenol A and 20.0 ng L−1 for triclosan. The established method was applied to the determination of bisphenol A and triclosan residues in environmental water samples with satisfactory results. The recoveries of the analytes using this method from lake, river, bottled and tap water samples were in the range from 93.9% to 104.3% (intra-day), and from 93.5% to 99.5% (inter-day) with the relative standard deviations varying from 2.1% to 5.8% (intra-day), and from 3.1% to 5.7% (inter-day).

Solid phase microextraction using a graphene composite-coated fiber coupled with gas chromatography for the determination of acetanilide herbicides in water samples

A graphene composite-coated stainless steel solid-phase microextraction fiber was prepared. The applicability of the fiber was evaluated through the solid-phase microextraction of five acetanilide herbicides (alachlor, acetochlor, pretilachlor, butachlor and metolachlor) in water samples followed by gas chromatography-electron capture detection. Parameters that affect the extraction efficiency, including the extraction time, extraction temperature, pH of the sample solution, stirring rate and desorption conditions were investigated and optimized. The linear response for the analytes was observed in the range from 0.8 to 150.0 μg L−1 with the correlation coefficients (r) ranging from 0.9933 to 0.9970 and the limits of detection (LODs) between 0.06 and 0.10 μg L−1. The single fiber repeatability and fiber-to-fiber reproducibility were less than 6.2% and 11.2%, respectively. The recoveries of acetanilides from water samples by the current method at spiking levels of 10.0 and 100.0 μg L−1 fell in the range from 81.8% to 112.0%.

Determination of volatile organic compounds in pen inks by a dynamic headspace needle trap device combined with gas chromatography–mass spectrometry

Some harmful volatile organic compounds (VOCs), such as methylbenzene, ethylbenzene, xylene, chlorobenzene and bromobenzene, are the commonly found chemicals in pen inks. In this work, a dynamic headspace needle-trap device (D-HS-NTD) with a ZIF-8-derived nanoporous carbon (ZIF-8-NPC) as the adsorbent was developed for the extraction of some VOCs in different pen inks prior to GC-MS detection. The main important influencing experimental parameters including the flow rate of the purge gas N2, extraction temperature, extraction time, desorption temperature and desorption time for the extraction were optimized to obtain a high extraction efficiency. Under the optimized conditions, a good linearity was obtained in the concentration range of 0.1-400μgkg-1 with the correlation coefficients (r) ranging from 0.9911 to 0.9990 for the eleven VOCs. The LODs at a signal-to-noise ratio of 3 (S/N=3) were measured to be 10-20ngkg-1 for the VOCs. The developed method was applied to determine the VOCs from 20 pen inks. The recoveries of the VOCs for the method at the spiking levels of 0.5 and 20.0μgkg-1 fell in the range from 80.0% to 108%.

Application of liquid phase microextraction based on solidification of floating organic drop for the determination of triazine herbicides in soil samples by gas chromatography with flame photometric detection

A simple and efficient liquid phase microextraction based on solidification of floating organic drop coupled with gas chromatography–flame photometric detection was developed for the extraction and determination of some triazine herbicides (metribuzin, simetryn, ametryn and prometryn) in soil samples. The type and volume of the extraction solvent, sample solution temperature, salt addition, stirring rate, and the extraction time were optimized. Under the optimal conditions, the linear response was observed over the range of 10–2000 µg kg−1 for metribuzin and 2–500 µg kg−1 for simetryn, ametryn, and prometryn, respectively, with the correlation coefficients (r) varying from 0.9990 to 0.9992. The limits of detection were in the range between 0.2 and 1.0 µg kg−1 (S/N = 3 : 1). The recoveries of the target analytes for the spiked soil samples ranged from 75.5% to 97.3%, with the relative standard deviation values less than 7.2% (n = 5). The enrichment factors were achieved ranging from 122 to 336. The developed method was applied for the preconcentration and determination of triazine herbicides in real soil samples and a satisfactory result was obtained.

Cyclodextrin-functionalized magnetic graphene as solid-phase extraction absorbent coupled with flame atomic absorption spectrophotometry for determination of cadmium in water and food samples

ABSTRACT A magnetic hydroxypropyl-β-cyclodextrin-functionalized reduced graphene oxide was synthesized and used as a magnetic solid-phase extraction adsorbent for the enrichment of cadmium from water and food samples before its determination by flame atomic absorption spectrometry. The effects of pH, amount of adsorbent, extraction time, desorption condition, and coexisting ions on the extraction efficiency were investigated and optimized. Under the optimal conditions, the limit of detection was 0.23 µg L−1 for water samples and 0.015 µg g−1 for food samples, respectively. The linear range was between 0.50 and 100.0 µg L−1 with a good correlation coefficient of 0.9986 in water samples, and between 0.050 and 5.0 µg g−1 with a correlation coefficient of 0.9975 in food samples. The method recoveries for the spiked samples were in the range of 87.5–102.4%, with the relative standard deviations ranging from 4.7% to 6.2% and enrichment factors ranging from 38 to 41, respectively. The adsorbent could be reused over 50 times without a significant change of extraction capability. The established method provides a promising environmentally friendly alternative for the determination of cadmium in complex matrix samples with no need of additional chelating reagents during the extraction process.