Xiangwei You

Ultrasound-assisted surfactant-enhanced emulsification microextraction based on the solidification of a floating organic droplet used for the simultaneous determination of six fungicide residues in juices and red wine.

A novel ultrasound-assisted surfactant-enhanced emulsification microextraction technique based on the solidification of a floating organic droplet followed by high performance liquid chromatography with diode array detection was developed for simultaneous determination of six fungicide residues in juices and red wine samples. The low-toxicity solvent, 1-dodecanol, was used as an extraction solvent. For its low density and proper melting point near room temperature, the extractant droplet was collected easily by solidifying it at a low temperature. The surfactant, Tween 80, was used as an emulsifier to enhance the dispersion of the water-immiscible extraction solvent into an aqueous phase, which hastened the mass-transfer of the analytes. Organic dispersive solvent typically required in common dispersive liquid-liquid microextraction methods was not used in the proposed method. Some parameters (e.g., the type and volume of extraction solvent, the type and concentration of surfactant, ultrasound extraction time, salt addition, and volume of samples) that affect the extraction efficiency were optimized. The proposed method showed a good linearity within the range of 5μgL(-1)-1000μgL(-1), with the correlation coefficients (γ) higher than 0.9969. The limits of detection for the method ranged from 0.4μgL(-1) to 1.4μgL(-1). Further, this simple, practical, sensitive, and environmentally friendly method was successfully applied to determine the target fungicides in juice and red wine samples. The recoveries of the target fungicides in red wine and fruit juice samples were 79.5%-113.4%, with relative standard deviations that ranged from 0.4% to 12.3%.

Air-assisted liquid–liquid microextraction used for the rapid determination of organophosphorus pesticides in juice samples

A novel and simple air-assisted liquid-liquid microextraction (AALLME) is introduced to analyze the organophosphorus pesticide (OPP) residues in fruit juice samples, using the gas chromatography-flame photometric detection (GC-FPD). In this method, fine extraction solvent drops are rapidly formed and dispersed into the aqueous samples, by using a syringe to withdraw and push-out the mixture of aqueous sample solution and extraction solvent several times. The parameters affecting the extraction efficiency were investigated including the type and volume of the extraction solvent, salt addition, extraction times, and pH. Under optimized conditions, the method showed good linearities with the correlation coefficients (γ) higher than 0.9988, and the sensitivity with the limits of detection (LODs) between 0.02μgL(-1) and 0.6μgL(-1). The method was applied to determine the OPP residues in juice samples and the recoveries were ranged from 79% to 113% with relative standard deviations (RSDs) of 0.4-9.9%. The feasibility of the method in real samples was proved.

Multi-residue determination of plant growth regulators in apples and tomatoes by liquid chromatography/tandem mass spectrometry.

A sensitive and rapid multi-residue analytical method for plant growth regulators (PGRs) (i.e., chlormequat, mepiquat, paclobutrazol, uniconazole, ethephon and flumetralin) in apples and tomatoes was developed using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). A homogenised sample was extracted with a mixture of methanol/water (90:10, v/v) and adjusted to pH <3 with formic acid. Primary secondary amine (PSA) adsorbent was used to clean up the sample. The determination was performed using electrospray ionisation (ESI) and a triple quadrupole (QqQ) analyser. Under the optimised method, the results showed that, except for ethephon, the recoveries were 81.8-98.1% in apples and tomatoes at the spiked concentrations of 0.005 to 2 mg/kg, with relative standard deviations (RSDs) of less than 11.7%. The limits of quantification (LOQs) were lower than their maximum residue limits (MRLs). The procedure was concluded as a practical method to determine the PGR residues in fruit and vegetables and is also suitable for the simultaneous analysis of the amounts of samples for routine monitoring. The analytical method described herein demonstrates a strong potential for its application in the field of PGR multi-residue analysis to help assure food safety.

Air-assisted liquid–liquid microextraction by solidifying the floating organic droplets for the rapid determination of seven fungicide residues in juice samples

A novel air assisted liquid-liquid microextraction using the solidification of a floating organic droplet method (AALLME-SFO) was developed for the rapid and simple determination of seven fungicide residues in juice samples, using the gas chromatography with electron capture detector (GC-ECD). This method combines the advantages of AALLME and dispersive liquid-liquid microextraction based on the solidification of floating organic droplets (DLLME-SFO) for the first time. In this method, a low-density solvent with a melting point near room temperature was used as the extraction solvent, and the emulsion was rapidly formed by pulling in and pushing out the mixture of aqueous sample solution and extraction solvent for ten times repeatedly using a 10-mL glass syringe. After centrifugation, the extractant droplet could be easily collected from the top of the aqueous samples by solidifying it at a temperature lower than the melting point. Under the optimized conditions, good linearities with the correlation coefficients (γ) higher than 0.9959 were obtained and the limits of detection (LOD) varied between 0.02 and 0.25 μgL(-1). The proposed method was applied to determine the target fungicides in juice samples and acceptable recoveries ranged from 72.6% to 114.0% with the relative standard deviations (RSDs) of 2.3-13.0% were achieved. Compared with the conventional DLLME method, the newly proposed method will neither require a highly toxic chlorinated solvent for extraction nor an organic dispersive solvent in the application process; hence, it is more environmentally friendly.

Dissipation of pyraclostrobin and its metabolite BF-500-3 in maize under field conditions

The dissipation and residue of pyraclostrobin and its metabolite BF-500-3 in maize under field conditions were investigated. A sensitive, simple and fast method for simultaneous determination of pyraclostrobin and BF-500-3 in maize matrix was established by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The average recoveries of pyraclostrobin and BF-500-3 were found in the range of 83.6-104.9% with relative standard deviations (RSDs) of 2.3-10.0%. The results showed that pyraclostrobin dissipated quickly in maize plant with half-lives of 1.6-1.7 days. Its metabolite BF-500-3 showed a tendency of rapid increasing initially and decreasing afterwards. At harvest time, the terminal residues of pyraclostrobin were below the maximum residue limit (MRL) set by USA and Canada in maize grain when measured 7 days after the final application, which suggested that the use of this fungicide was safe for humans. The results could provide guidance to safe and reasonable use of pyraclostrobin in agriculture.

Ionic-liquid-based, manual-shaking- and ultrasound-assisted, surfactant-enhanced emulsification microextraction for the determination of three fungicide residues in juice samples.

A novel manual-shaking- and ultrasound-assisted surfactant-enhanced emulsification microextraction method was developed for the determination of three fungicides in juice samples. In this method, the ionic liquid, 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, instead of a volatile organic solvent was used as the extraction solvent. The surfactant, NP-10, was used as an emulsifier to enhance the dispersion of the water-immiscible ionic liquid into an aqueous phase, which accelerated the mass transfer of the analytes. Organic dispersive solvent typically required in common dispersive liquid-liquid microextraction methods was not necessary. In addition, manual shaking for 15 s before ultrasound to preliminarily mix the extraction solvent and the aqueous sample could greatly shorten the time for dispersing the ionic liquid into aqueous solution by ultrasound irradiation. Several experimental parameters affecting the extraction efficiency, including type and volume of extraction solvent, type and concentration of surfactant, extraction time, and pH, were optimized. Under the optimized conditions, good linearity with the correlation coefficients (γ) higher than 0.9986 and high sensitivity with the limit of detection ranging from 0.4 to 1.6 μg/L were obtained. The average recoveries ranged from 61.4 to 86.0% for spiked juice, with relative standard deviations from 1.8 to 9.7%. The proposed method was demonstrated to be a simple, fast, and efficient method for the analysis of the target fungicides in juice samples.

Simultaneous determination of five strobilurin fungicides and the metabolite BF-500-3 in cereals, fruits and vegetables

A rapid and sensitive method for the simultaneous determination of five strobilurin fungicides and the metabolite BF-500-3 in cereals (maize and wheat), fruits (grape and apple) and vegetables (cucumber and tomato) was developed by a Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method using high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS). The five strobilurin fungicides (kresoxim-methyl, picoxystrobin, pyraclostrobin, azoxystrobin and trifloxystrobin) and the metabolite BF-500-3 were extracted from six matrices using acetonitrile and subsequently cleaned up by dispersive solid phase extraction (d-SPE) using octadecylsilane (C18) as sorbent prior to HPLC-MS/MS analysis. The determination of the six compounds was achieved in less than 6.0 min using an electrospray ionisation source in positive mode (ESI+). This method showed the linearity with the coefficients of determination (R2) higher than 0.9929. The limits of quantification (LOQs), defined as the lowest spiking level, were 5 μg/kg for all the fungicides in all matrices. Recovery studies were performed at three fortification levels (5, 10 and 100 μg/kg) and the overall average recoveries ranged from 76.9% to 114.2% with the relative standard deviation (RSD) less than 13.6% for all the analytes. The method is demonstrated to be convenient and reliable for the routine monitoring of five strobilurin fungicides and the metabolite BF-500-3 in cereals, fruits and vegetables.

Ionic liquid-based air-assisted liquid–liquid microextraction followed by high performance liquid chromatography for the determination of five fungicides in juice samples

A novel and simple ionic liquid-based air-assisted liquid-liquid microextraction technique combined with high performance liquid chromatography was developed to analyze five fungicides in juice samples. In this method, ionic liquid was used instead of a volatile organic solvent as the extraction solvent. The emulsion was formed by pulling in and pushing out the mixture of aqueous sample solution and extraction solvent repeatedly using a 10mL glass syringe. No organic dispersive solvent was required. Under the optimized conditions, the limits of detection (LODs) were 0.4-1.8μgL-1 at a signal-to-noise ratio of 3. The limits of quantification (LOQs) set as the lowest spiking levels with acceptable recovery in juices were 10μgL-1, except for fludioxonil whose LOQ was 20μgL-1. The proposed method was applied to determine the target fungicides in juice samples, and acceptable recoveries ranging from 74.9% to 115.4% were achieved.

Low-density solvent based vortex-assisted surfactant enhanced emulsification microextraction with a home-made extraction device for the determination of four herbicide residues in river water

A vortex-assisted surfactant-enhanced emulsification microextraction method was developed for the determination of four acetanilide herbicides in river water. Non-chlorinated solvents with a lower density than water were used as the extraction solvent. With the help of vortex assistance and surfactant emulsification, the extraction solvent could be dispersed into the sample solution without the use of an organic dispersive solvent. After centrifugation, the extraction solvent drop floating on the top of the sample solution was collected using the unique home-made device based on a flexible plastic Pasteur pipette and iron stands. The factors which might affect the extraction efficiencies were investigated including the type and volume of extraction solvent, the type and concentration of surfactant, the vortex time, and pH of the sample. Under optimized conditions, the proposed method provided a good linearity in the range of 0.5–20 μg L−1 and 1–40 μg L−1, respectively. The limit of detection of the method was in the range of 0.15–0.30 μg L−1 and the limit of quantification was in the range of 0.5–1.0 μg L−1. Recoveries for each target herbicide were 85.7–113.3% with good repeatability (RSDs below 9.9%, n = 5) in the river water sample.