Fengmao Liu

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.

Use of graphitic carbon black and primary secondary amine for determination of 17 organophosphorus pesticide residues in spinach.

Graphitized carbon black (GCB) and primary secondary amine (PSA) as dispersive-SPE sorbents were applied to optimize the method for the determination of 17 organophosphorus pesticides in spinach which contained so many pigments using GC with flame photometric detector (FPD). The sample was extracted with ACN, and an aliquot of the extract was concentrated to near dryness. Ethyl acetate or acetone was chosen as the dissolving solvent. Subsequently, dispersive-SPE was used for cleanup, and the type and quantity of sorbents (GCB, PSA and activated carbon) were tested in the experiments. The best results were when acetone was used to dissolve and 30 mg each of GCB and PSA for cleanup. In this condition, recoveries of pesticides analyzed were between 52-117% with RSD below 10%, and LOQ ranged from 10 to 20 microg/kg. This method was simple, effective and efficient, and can protect the GC system to some extent.

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 and residue of dimethomorph in pepper and soil under field conditions

The dissipation and residual levels of dimethomorph in pepper and soil under field conditions were determined by gas chromatography with an electron capture detector (GC-ECD). The dissipation rates of dimethomorph were described using first-order kinetics and its half-life ranged from 1.7 to 3.8 days in pepper and 11.5-18.5 days in soil. At harvest time, the terminal residues of dimethomorph were below the EUs maximum residue limit (MRL, 0.5 mg kg⁻¹) in pepper when measured 7 days after the final application, which suggested that the use of this fungicide was safe for humans. The collected field samples were stable for up to two months when refrigerated at -20°C. The residues persistence varied among three geographically separated experimental fields, suggesting that it might be affected by climatic, soil properties and local microorganisms. These results will be helpful in setting MRL guidance for dimethomorph in pepper in China.

Stereoselective separation and determination of triadimefon and triadimenol in wheat, straw, and soil by liquid chromatography-tandem mass spectrometry

A sensitive and rapid analytical method was developed for simultaneous determination of triadimefon (TF) and triadimenol (TN) stereoisomers in wheat, straw, and soil by liquid chromatography coupled with triple quadrupole mass spectrometry (LC-MS/MS). The direct enantioseparation of TF and TN was performed on a Lux cellulose-1 column packed with cellulose-tris-(3,5-dimethylphenylcarbamate). The effects of mobile-phase composition on the separation were investigated and stereoisomeric elution orders were confirmed with a polarimeter detector. The pesticides were extracted from samples with acetonitrile and cleaned up by solid-phase extraction or activated carbon. Based on the developed stereoselective LC-MS/MS method, for TF and TN stereoisomers, good linearities were obtained over the concentration range of 0.003-4 mg/L; recoveries were 84.2-102.7% in wheat, 84.0-104.0% in straw, and 85.2-106.8% in soil at spiked concentrations of 0.007-2.0 mg/kg; intra-day and inter-day assay precisions were below 12.2%. Limits of detection (LODs) and limits of quantification (LOQs) in wheat, straw, and soil were 0.001-0.005 mg/kg and 0.007-0.02 mg/kg, respectively. Finally, the method was successfully applied to detect TF and TN stereoisomers in wheat, straw, and soil samples from residual trials in farm.

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.

Rapid and sensitive analysis of nine fungicide residues in chrysanthemum by matrix extraction-vortex-assisted dispersive liquid–liquid microextraction

A simple sample pretreatment for simultaneous determination of nine fungicides (triadimefon, picoxystrobin, kresoxim-methyl, diniconazole, epoxiconazole, trifloxystrobin, triticonazole, difenoconazole, and azoxystrobin) in chrysanthemum was developed using matrix extraction-vortex-assisted dispersive liquid-liquid microextraction (ME-VADLLME) prior to gas chromatography with electron capture detection. The target fungicides were firstly extracted with acetonitrile and cleaned with the mixture of primary secondary amine and graphite carbon black. The VADLLME procedure was performed by using toluene with lower density than water as the extraction solvent and the acetonitrile extract as the dispersive solvent, respectively. After vortexing and centrifugation, the fine droplet of toluene was collected on the upper of the mixed toluene/acetonitrile/water system using a 0.1-mL pipettor. Under the optimum conditions, the relative recoveries ranged from 73.9 to 95.1% with relative standard deviations of 3.5-9.7% for all of the analytes. The limits of detection were in the range of (0.005-0.05)×10(-3) mg kg(-1). In the proposed method, the ME step provides more effective cleanup for the chrysanthemum matrix, and VADLLME introduces higher sensitivity with the remarkable enrichment factors up to 88-fold compared with the conventional QuEChERS or SPE. The good performance has demonstrated that ME-VADLLME has a strong potential for application in the multi-residue analysis of complex matrices.

Transfer of difenoconazole and azoxystrobin residues from chrysanthemum flower tea to its infusion

Investigations of the transfer of pesticide residues from tea to its infusion can be important in the assessment of the possible health benefits of tea consumption. In this work the transfer of difenoconazole and azoxystrobin residues from chrysanthemum tea to its infusion was investigated at different water temperatures, infusion intervals and times. The transfer percentages were in the range of 18.7–51.6% for difenoconazole and of 38.1–71.2% for azoxystrobin, and increased considerably with longer infusion intervals. The results indicated that azoxystrobin with a lower octanol–water partition coefficient of 2.5, showed a higher transfer than that of difenoconazole with a relatively high octanol–water partition coefficient of 4.4. Water temperature had no significant effect on the transfer of the two residues, and no obvious loss of difenoconazole and azoxystrobin occurred during the infusion process. The concentrations in the infusions decreased gradually from 0.67 to 0.30 μg kg−1 for difenoconazole and from 2.3 to 0.46 μg kg−1 for azoxystrobin after five infusions. To assess the potential health risk, the values of estimate expose risk were calculated to be 0.016 for difenoconazole and 0.0022 for azoxystrobin, meaning the daily residue intake of the two analytes from chrysanthemum tea was safe. This research may help assure food safety and identify the potential exposure risks from pesticides in chrysanthemum that may be health concerns. Graphical Abstract