A rapid multi-residue method for the determination of pesticide residues in choi sum, yardlong beans and aubergines

Development and comparison of two multi-residue methods for the analysis of select pesticides in honey bees, pollen, and wax by gas chromatography-quadrupole mass spectrometry

One of the hypotheses that may help explain the loss of honey bee colonies worldwide is the increasing potential for exposure of honey bees to complex mixtures of pesticides. To better understand this phenomenon, two multi-residue methods based on different extraction and cleanup procedures have been developed, and compared for the determination of 11 relevant pesticides in honey bees, pollen, and wax by gas chromatography-quadrupole mass spectrometry. Sample preparatory methods included solvent extraction followed by gel permeation chromatography (GPC) cleanup and cleanup using a dispersive solid-phase extraction with zirconium-based sorbents (Z-Sep). Matrix effects, method detection limits, recoveries, and reproducibility were evaluated and compared. Method detection limits (MDL) of the pesticides for the GPC method in honey bees, pollen, and wax ranged from 0.65 to 5.92 ng/g dw, 0.56 to 6.61 ng/g dw, and 0.40 to 8.30 ng/g dw, respectively, while MDLs for the Z-Sep method were from 0.33 to 4.47 ng/g dw, 0.42 to 5.37 ng/g dw, and 0.51 to 5.34 ng/g dw, respectively. The mean recoveries in all matrices and at three spiking concentrations ranged from 64.4% to 149.5% and 71.9% to 126.2% for the GPC and Z-Sep methods, with relative standard deviation between 1.5-25.3% and 1.3-15.9%, respectively. The results showed that the Z-Sep method was more suitable for the determination of the target pesticides, especially chlorothalonil, in bee hive samples. The Z-Sep method was then validated using a series of field-collected bee hive samples taken from honey bee colonies in Virginia.

Rapid analysis of multi-pesticide residues in lotus seeds by a modified QuEChERS-based extraction and GC-ECD

A modified quick, easy, cheap, efficient, rugged and safe method (QuEChERS) coupled to gas chromatography with electron capture detector (GC-ECD) was developed for rapid extraction and simultaneous determination of 36 pesticides in lotus seeds. The extraction solvent (acetone, ethyl acetate, acetonitrile, n-hexane and n-hexane in combination with ethyl acetate) and purifying agent (neutral alumina, primary secondary amine, graphite carbon block and florisil) for QuEChERS extraction were optimized. The GC-ECD method was in-house validated in terms of linearity, selectivity, reproducibility, stability and recovery. The limits of detection (LODs) of the developed GC-ECD method for all investigated pesticides ranged from 0.01 to 3.0μgL(-1) and limits of quantification (LOQs) from 0.05 to 10.0μgL(-1). The satisfactory data demonstrated the good reproducibility and stability of the method with relative standard deviations (RSDs) lower than 15%. Recoveries for spiked lotus seed samples were from 60.84% to 119.91% with RSDs lower than 13.06%. Two out of 24 batches of lotus seeds collected in China were found to be contaminated with trans-chlordane, which were below LOQ. This is the first attempt in China using QuEChERS to GC-ECD to determine 36 major pesticides with differences in physio-chemical properties in lotus seeds. The method described here was found to be practicable in the routine residue analysis of pesticides in lotus seeds.

A robust GC-MS/MS method for the determination of chlorothalonil in fruits and vegetables

Chlorothalonil is a non-systemic fungicide that is easily degraded in contact with plants and soil or even by the effect of light and pH. A method for the determination of chlorothalonil in courgettes, strawberries, oranges, leeks and tomato by solvent extraction followed by GC-MS/MS with a triple quadrupole analyser was developed. The causes of chlorothalonil degradation during sample treatment were studied and minimised. The final method was based on extraction with acetone in the presence of 0.1 M EDTA sodium salt solution, and clean-up by SPE using OASIS HLB cartridges. Isotope-labelled hexachlorobenzene (HCB-(13)C(6)) was added as an internal standard to the SPE extracts before analysis by GC-MS/MS (EI) (QqQ) analysis in order to correct for instrumental deviations. Quantification was performed by matrix-matched standard calibration using relative responses to the internal standard. Two MS/MS transitions were used for mass spectrometric determination of chlorothalonil to ensure reliable quantification and confirmation. The method was validated using blank samples (for all matrices) spiked at two levels. Recoveries between 77% and 110% and an RSD below 20% were obtained for 0.1 and 0.01 mg kg(-1) spiking levels (n = 5). The validated method was applied to treated and untreated samples collected from an experimental field where a chlorothalonil formulated was applied.

Analysis of pesticide residues in fresh peppermint, Mentha piperita L., using the quick easy cheap effective rugged and safe method (QuEChERS) followed by gas chromatography with electron capture and nitrogen phosphorus detection

A new analytical method for the determination of 14 pesticide residues in fresh peppermint was developed based on the QuEChERS sample preparation technique followed by gas chromatography coupled to electron capture and nitrogen phosphorus detectors (GC/ECD/NPD). The validation study clearly demonstrated suitability of the method for its intended application. The overall recoveries of the pesticides from peppermint, at the three spiking levels of 0.01, 0.1 and 1.0 mg kg(-1), were 100% ± 10% with relative standard deviations of 6% ± 5% on average. The limit of quantification was 0.01 mg kg(-1) for all the pesticides. The expanded uncertainties were in the range between 7% and 30% (14% on average), which was distinctively less than a maximum default value of ±50%. Compared with our previous method, that entailed dichloromethane/acetone extraction and florisil column cleanup with collection of four fractions, the new method was more straightforward, less time and labour intensive as well as more sensitive, selective and accurate, simultaneously.