Chunhong Jia

Extraction of pesticides in water samples using vortex-assisted liquid-liquid microextraction.

A simple solvent microextraction method termed vortex-assisted liquid-liquid microextraction (VALLME) coupled with gas chromatography micro electron-capture detector (GC-microECD) has been developed and used for the pesticide residue analysis in water samples. In the VALLME method, aliquots of 30 microL toluene used as extraction solvent were directly injected into a 25 mL volumetric flask containing the water sample. The extraction solvent was dispersed into the water phase under vigorously shaking with the vortex. The parameters affecting the extraction efficiency of the proposed VALLME such as extraction solvent, vortex time, volumes of extraction solvent and salt addition were investigated. Under the optimum condition, enrichment factors (EFs) in a range of 835-1115 and limits of detection below 0.010 microg L(-1) were obtained for the determination of target pesticides in water. The calculated calibration curves provide high levels of linearity yielding correlation coefficients (r(2)) greater than 0.9958 with the concentration level ranged from 0.05 to 2.5 microg L(-1). Finally, the proposed method has been successfully applied to the determination of pesticides from real water samples and acceptable recoveries over the range of 72-106.3% were obtained.

Extraction of organophosphorus pesticides in water and juice using ultrasound-assisted emulsification―mixroextraction

In this study, a microextraction method termed as ultrasound-assisted emulsification-microextraction (USAEME) has been developed for the extraction of organophosphorus pesticides (OPPs) in water and orange juice samples. In the USAEME method, aliquots of 50 microL chlorobenzene used as extraction solvent was added to 10 mL water sample in a conical glass centrifugal tube. Factors influencing the USAEME extraction efficiency such as sonication time, extraction solvent, extraction volume and salt addition were evaluated. Under the optimum conditions, enrichment factors ranged from 241 to 311, LOD varied from 5.3 to 10.0 ng/L and linearity with a coefficient of estimation (r(2)) varied from 0.9991 to 0.9998 in the concentration level range of 0.05-2.5 microg/L for the extraction of OPPs in water samples. Finally, the proposed USAEME method was used for the extraction of OPPs from water and orange juice. The recoveries were in the range of 80.0-110.0%, and the repeatability of the method expressed as RSD (n=3) varied between 1.6 and 13%. The USAEME method has the advantage of being easy to operate, low consumption of organic solvent and high extraction efficiency.

Combination of dispersive solid-phase extraction and salting-out homogeneous liquid-liquid extraction for the determination of organophosphorus pesticides in cereal grains.

A new analytical method for the determination of organophosphorus pesticides in cereal samples was developed by combining dispersive SPE (d-SPE) and salting-out homogeneous liquid-liquid extraction (SHLLE). The pesticides were first extracted from cereal grains with acetonitrile, followed by d-SPE cleanup. A 2 mL aliquot of the extract was then added to a centrifuge tube containing 9.2 mL water and 3.3 g NaCl for SHLLE. Analysis of the extract was carried out by gas chromatography coupled with flame photometric detection. The d-SPE procedure effectively provides the necessary cleanup of the extract while SHLLE is used as an efficient concentration technique. Experimental parameters influencing the extraction efficiency including amounts of added water and salt were investigated. Recovery studies were carried out at three fortification levels, yielding recoveries in the range of 57.7-98.1% with the RSD from 3.7 to 10.9%. The reported limits of determination obtained from this study were 1 μg/kg, which is better than the conventional methods. In the analysis of 40 wheat and corn samples taken from Beijing suburbs, only two wheat samples have chlorpyrifos residue over the limits of determination.

Solid‐phase extraction combined with dispersive liquid–liquid microextraction for the determination of pyrethroid pesticides in wheat and maize samples

A rapid, selective and sensitive sample preparation method based on solid-phase extraction combined with the dispersive liquid-liquid microextration was developed for the determination of pyrethroid pesticides in wheat and maize samples. Initially, the samples were extracted with acetonitrile and water solution followed phase separation with the salt addition. The following sample preparation involves a solid-phase extraction and dispersive liquid-liquid microextraction step, which effectively provide cleanup and enrichment effects. The main experimental factors affecting the performance both of solid-phase extraction and dispersive liquid-liquid microextration were investigated. The validation results indicated the suitability of the proposed method for routine analyze of pyrethroid pesticides in wheat and maize samples. The fortified recoveries at three levels ranged between 76.4 and 109.8% with relative standard deviations of less than 10.7%. The limit of quantification of the proposed method was below 0.0125 mg/kg for the pyrethoroid pesticides. The proposed method was successfully used for the rapid determination of pyrethroid residues in real wheat and maize samples from crop field in Beijing, China.

Determination of oxathiapiprolin concentration and dissipation in grapes and soil by ultrahigh-performance liquid chromatography-tandem mass spectrometry.

BACKGROUND The residue concentrations and dissipation rate of a new oxathiapiprolin fungicide in grapes and soil were investigated to provide an evaluation for the safe use of oxathiapiprolin in grapes. Pesticide residue was extracted by acetonitrile, then purified by solid-phase extraction with an Envi-Carb cartridge and determined by ultrahigh-performance liquid chromatography-tandem mass spectrometry. RESULTS The fortified recoveries ranged from 85.2% to 99.0%, with relative standard deviations of 1.7-4.5%. The limit of quantitation for oxathiapiprolin in grapes and soil was 0.002 mg kg-1 . The mean initial deposits of oxathiapiprolin in grapes were 0.345-0.565 mg kg-1 , with half-lives of 8.6-9.2 days. The mean initial deposits of oxathiapiprolin in soil were 0.078-0.273 mg kg-1 , with half-lives of 7.6-12.0 days. The oxathiapiprolin residue in grapes and soil was 0.002-0.022 mg kg-1 and 0.002-0.123 mg kg-1 when sampling 14 days after application, respectively. CONCLUSION The residue in the grapes was less than 0.01 mg kg-1 when sampling 28 days after application, which suggested that the application rate of 20 mg a.i. kg-1 for this fungicide should be used to ensure that treated grapes can be considered safe for humans to consume when sampling 28 days after the final application.

Residue behavior and dietary intake risk assessment of carbosulfan and its metabolites in cucumber

ABSTRACT The residue behavior and dietary intake risks of carbosulfan and its metabolites in cucumbers were investigated. A quick and reliable method for determining carbosulfan and its metabolite residues in cucumbers was established using ultrahigh performance liquid chromatography–tandem mass spectrometry. The fortified recoveries ranged from 87.2% to 91.0% with relative standard deviations of 3.2%–8.1%. The dissipation results showed that carbosulfan was transformed into carbofuran and 3‐hydroxy carbofuran in cucumbers. The half‐life of carbosulfan was 1.5 days, and the half‐life of carbofuran was 45 days. The final residues of carbosulfan varied from 0.245 to 0.005 mg/kg and carbofuran varied from 0.123 to 0.008 mg/kg. After a 5‐day application period the residues of carbosulfan was 0.113 mg/kg that was below the maximum residue limit set by China (0.2 mg/kg), and the residues of carbofuran was 0.055 mg/kg that was higher than the maximum residue limit set by China (0.02 mg/kg). The risk assessment results indicated that the dietary intake risks of carbosulfan and carbofuran from cucumber consumption were safe for Chinese consumers, but pre‐harvest intervals should be strictly recommended for 7 days at the recommended dose to ensure that food quality conforms to the MRL standard. This study provides a method and data for scientifically evaluating dietary intake risks of carbosulfan and its more toxic metabolites. HighlightsEstablished a quick method for determining carbosulfan and its metabolite.Studied the dissipation of carbosulfan and its metabolite in cucumber.Researched the final residues of carbosulfan and its metabolite in cucumber.Provided a method for scientifically evaluating carbosulfan and its metabolites.Provided data for the safe and rational use of carbosulfan in cucumber.