Validation and uncertainty study of a comprehensive list of 160 pesticide residues in multi-class vegetables by liquid chromatography–tandem mass spectrometry

Multiresidue determination of 29 pesticide residues in pepper through a modified QuEChERS method and gas chromatography-mass spectrometry

This study describes the development and use of a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) method coupled with gas chromatography with mass spectrometry to determine 29 pesticide residues in green, red and dehydrated red peppers. Pesticides were extracted with acetonitrile (1% acetic acid), partitioned with sodium chloride and purified with primary secondary amino and octadecyl silane in acetone. The QuEChERS extraction conditions were optimized, and the matrix effects that might influence recoveries were evaluated and minimized using matrix-matched calibration curves. Under the optimized conditions, the calibration curves for 29 pesticides showed good linearity in the concentration range of 0.1-10 μg/mL with determination coefficient R(2)  > 0.998. The limits of quantification of the 29 pesticides were 0.006-0.06 mg/kg for green pepper, 0.005-0.039 mg/kg for red pepper and 0.014-0.25 mg/kg for dehydrated red pepper. These values are below the suggested regulatory maximum residue limits. The mean recoveries ranged between 70.1 and 110%, and the relative standard deviations were <13%. The developed method was successfully applied to commercial samples. Some samples were found to contain the 29 pesticides with levels below the legal limits. Copyright © 2016 John Wiley & Sons, Ltd.

Residue level and dissipation pattern of spiromesifen in cabbage and soil from 2-year field study

Spiromesifen is a new class of insecticide used for the control of whiteflies and mites which have developed resistance to the more commonly used neonicotinoids. Dissipation pattern of spiromesifen on cabbage was evaluated over 2 years by conducting supervised field studies as per good agricultural practices. Cabbage and soil samples were extracted and purified using modified QuEChERS method and analyzed through gas chromatography (GC). Confirmatory studies were carried out by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The recoveries of spiromesifen from cabbage and soil were between 85.44 and 103.37% with the relative standard deviation (RSD) between 3.2 and 9.4% (n = 6). The limit of detection (LOD) and limit of quantification (LOQ) were 0.003 μg mL(-1) and 0.01 mg kg(-1), respectively. The measurement uncertainties (MUs) were within 9.9-14.9%. Initial residues of spiromesifen on cabbage were 0.640 and 1.549 mg kg(-1) during 2013 and 0.723 and 1.438 mg kg(-1) during 2014 from treatments at standard and double doses of 125 and 250 g active ingredient (a.i.) ha(-1), respectively. Spiromesifen residue dissipation followed first-order rate kinetics, and it degraded within the half-lives of 2.9 and 3.9 days during 2013 and 3.2 and 4.5 days during 2014. The residue levels reached below the maximum residue limit (MRL; 0.02 mg kg(-1)) within 15-17 days at the standard dose and 24-27 days at the double dose. The field soil analyzed at harvest (30 days) was free from spiromesifen residues. Metabolite spiromesifen-enol was not detected in any sample which was confirmed through LC-MS/MS analysis.

Simultaneous analysis of herbicides pendimethalin, oxyfluorfen, imazethapyr and quizalofop-p-ethyl by LC-MS/MS and safety evaluation of their harvest time residues in peanut (Arachis hypogaea L.)

This paper reports a simple and rapid method for simultaneous determination of the residues of selected herbicides viz. pendimethalin, oxyfluorfen, imazethapyr and quizalofop-p-ethyl in peanut by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A modified approach of the QuEChERS methodology was used to extract the herbicides from the peanut kernel without any clean-up. The method showed excellent linearity (r(2) > 0.99) with no significant matrix effect. Accuracy of the method in terms of average recoveries of all the four herbicides ranged between 69.4 -94.4 % at spiking levels of 0.05, 0.10 and 0.25 mg kg(-1) with intra-day and inter-day precision RSD (%) between 2.6-16.6 and 8.0-11.3, respectively. Limit of quantification (LOQs) was 5.0 μg kg(-1) for pendimethalin, imazethapyr and quizalofop-p-ethyl and 10.0 μg kg(-1) for oxyfluorfen. The expanded uncertainties were <11 % for determination of these herbicides in peanut. The proposed method was successfully applied for analysis of these herbicide residues in peanut samples harvested from the experimental field and the residues were below the detection level.

Use of Combined Uncertainty of Pesticide Residue Results for Testing Compliance with Maximum Residue Limits (MRLs)

The uncertainty of pesticide residue levels in crops due to sampling, estimated for 106 individual crops and 24 crop groups from residue data obtained from supervised trials, was adjusted with a factor of 1.3 to accommodate the larger variability of residues under normal field conditions. Further adjustment may be necessary in the case of mixed lots. The combined uncertainty of residue data including the contribution of sampling is used for calculation of an action limit, which should not be exceeded when compliance with maximum residue limits is certified as part of premarketing self-control programs. On the contrary, for testing compliance of marketed commodities the residues measured in composite samples should be greater than or equal to the decision limit calculated only from the combined uncertainty of the laboratory phase of the residue determination. The options of minimizing the combined uncertainty of measured residues are discussed. The principles described are also applicable to other chemical contaminants.

Dissipation behaviour, processing factors and risk assessment for metalaxyl in greenhouse-grown cucumber

BACKGROUND

Cucumber is widely cultivated in Iran, and the application of systemic and protective fungicides is the main choice of disease treatment, particularly in greenhouse-grown systems. In this research, cucumber fruits were harvested at 1 h to 25 days after the last application to determine the residue and dissipation behaviour of metalaxyl. The effects of peeling and storage (at 3 °C for 4 days) on metalaxyl residue reduction were also assessed. Samples were extracted by the QuEChERS procedure then analysed using liquid chromatography-tandem mass spectrometry.

RESULTS

The dissipation of metalaxyl residues approximately fitted a first-order kinetic model, obtaining half-life values of 2.2 and 3.8 days and preharvest interval values of 5.2 and 12.5 days at the recommended dose (2 kg ha(-1) ) and double (4 kg ha(-1) ) dose respectively. The processing factor values for peeling and storage were 0.50 and 0.93 respectively, showing that storage had little effect on residue reduction compared with peeling.

CONCLUSION

The higher content of metalaxyl residues in flesh showed its penetration from the skin into the flesh. The results provided more understanding of fungicide distribution as well as the effective role of peeling in reducing residues in cucumber fruits.

High-resolution mass spectrometry associated with data mining tools for the detection of pollutants and chemical characterization of honey samples

Analytical methods for food control are mainly focused on restricted lists of well-known contaminants. This paper shows that liquid chromatography-high-resolution mass spectrometry (LC/ESI-HRMS) associated with the data mining tools developed for metabolomics can address this issue by enabling (i) targeted analyses of pollutants, (ii) detection of untargeted and unknown xenobiotics, and (iii) detection of metabolites useful for the characterization of food matrices. A proof-of-concept study was performed on 76 honey samples. Targeted analysis indicated that 35 of 83 targeted molecules were detected in the 76 honey samples at concentrations below regulatory limits. Furthermore, untargeted metabolomic-like analyses highlighted 12 chlorinated xenobiotics, 1 of which was detected in lavender honey samples and identified as 2,6-dichlorobenzamide, a metabolite of dichlobenil, a pesticide banned in France since 2010. Lastly, multivariate statistical analyses discriminated honey samples according to their floral origin, and six discriminating metabolites were characterized thanks to the MS/MS experiments.

Second-order advantage maintenance with voltammetric data modeling for quantitation of ethiofencarb in the presence of interferences

This work presents the development of a method based on a voltammetric determination coupled to second-order data modeling with multivariate curve resolution-alternating least-square (MCR-ALS) and unfolded partial least squares regression followed by residual bilinearization (U-PLS/RBL) for the quantitation of the pesticide ethiofencarb in the presence of interferences in tap water. The determination of ethiofencarb by voltammetry is possible on the basis that this pesticide is hydrolysed in alkaline media giving rise to a compound which shows an oxidation peak at Ep=0.80 V. But some other pesticides belonging to the same family can be considered as interferences due to the high overlapping in their signals. The two such interferences are fenobucarb and bendiocarb, which have not been included in the calibration step. The possibility of second-order multivariate calibration was studied by using the hydrolysis time as the third variable, and MCR-ALS and U-PLS/RBL. Good results were obtained in this determination in spite of the high overlapping in voltammetric signals.

Residues and dissipation kinetics of triazole fungicides difenoconazole and propiconazole in wheat and soil in Chinese fields

An analytical method for simultaneously determining the residues of difenoconazole and propiconazole in wheat straw, wheat grain and soil was developed. Mean recoveries and relative standard deviations in all samples ranged 86.2-101.3% and 3.1-12.1% for propiconazole and difenoconazole. The half-lives of difenoconazole and propiconazole were 3.6-5.5days and 5.1-6.9days in wheat straws, and 4.9-5.8days and 6.1-8.4days in soil, respectively. The residues in wheat grain were found to be <0.01mg/kg, based on the application rate (135g a.i./ha) and the pre-harvest interval (PHI=28days) recommended by the manufacturer. The results suggest that the use of difenoconazole and propiconazole on wheat is considered to be safe under the Good Agricultural Practices (GAP) in the Chinese fields, and the main factors for pesticide residue in crops are application times, rates and pre-harvest intervals.

Water-based extraction and liquid chromatography-tandem mass spectrometry analysis of neonicotinoid insecticides and their metabolites in green pepper/tomato samples

This paper proposes an environmentally friendly method involving water-based extraction of the samples, cleanup of the extracts by solid-phase extraction, and subsequent liquid chromatography coupled with tandem mass spectrometry, which was used for simultaneous determination of seven hydrophilic neonicotinoid insecticides as well as their metabolites in agricultural samples. The effects of sample matrix on detection of the target compounds were negligibly small. Mean recoveries obtained at spiked concentrations between 0.01 and 1.00 mg/kg were 71.2-122.3% with relative standard deviations of ≤ 7.5%. When the method was applied to crop samples sprayed with commercial formulations of the target compounds, the residual concentrations of the compounds determined by the proposed method (0.015-0.27 mg/kg in green peppers and 0.017-0.31 mg/kg in tomatoes) were equivalent to those determined by the official Japanese method (0.017-0.26 mg/kg in green peppers and 0.013-0.30 mg/kg in tomatoes).

Determination of pesticide residues in honeybees using modified QUEChERS sample work-up and liquid chromatography-tandem mass spectrometry

Increasing emissions of chemical compounds to the environment, especially of pesticides, is one of factors that may explain present honeybee colony losses. In this work, an analytical method employing liquid chromatography-tandem mass spectrometry (LC-MS/MS) was optimized for the simultaneous screening of 19 pesticides which have not been yet determined in honeybee samples from northern Poland (Pomerania). The sample preparation, based on the QuEChERS method combining salting-out liquid-liquid extraction to acetonitrile and a dispersive-SPE clean-up, was adjusted to honeybee samples by adding a small amount of hexane to eliminate beeswax. The recovery of analytes ranged from 70% to 120% with relative standard deviation ≤20%. The limits of detection were in the range of 0.91–25 ng/g. A total of 19 samples of honeybees from suspected pesticide poisoning incidents were analyzed, in which 19 different pesticides were determined.

Fast and easy extraction combined with high resolution-mass spectrometry for residue analysis of two anticonvulsants and their transformation products in marine mussels

Environmental field studies have shown that carbamazepine (Cbz) is one of the most frequently detected human pharmaceuticals in different aquatic compartments. However, little data is available on the detection of this substance and its transformation products in aquatic organisms. This study was thus mainly carried out to optimize and validate a simple and sensitive analytical methodology for the detection, characterization and quantification of Cbz and oxcarbazepine (Ox), two anticonvulsants, and six of their main transformation products in marine mussels (Mytilus galloprovincialis). A modified QuEChERS extraction method followed by analysis with liquid chromatography coupled to high resolution mass spectrometry (HRMS) was used. The analyses were performed using two-stage fragmentation to reveal the different fragmentation pathways that are highly useful for the identification of isomeric compounds, a common problem when several transformation products are analyzed. The developed analytical method allowed determination of the target analytes in the lower ng/g concentration levels. The mean recovery ranged from 67 to 110%. The relative standard deviation was under 11% in the intra-day and 18% in the inter-day analyses, respectively. Finally, the method was applied to marine mussel samples collected from Mediterranean Sea cultures in southeastern France. Residues of the psychiatric drug Cbz were occasionally found at levels up to 3.5ng/g dw. Lastly, in this study, other non-target compounds, such as caffeine, metoprolol, cotinine and ketoprofen, were identified in the real samples analyzed.

Analytical considerations on the use of a fruit-specific and representative matrix in pesticide residue analysis by LC-ESI-MS/MS

One of the quantification methods frequently applied to pesticide residue analysis in food by liquid chromatography — mass spectrometry (LC-MS) involves matrix-matched calibrations with a representative matrix used for all commodities belonging to one group. This approach, although very practical, is deemed to generate analytical errors. The effect of the application of a representative-matrix calibration curve on the pesticide quantification result was examined. Extractions of 56 pesticides from five soft fruits (strawberries, blackberries, raspberries, black currant and red currant) were carried out using QuEChERS method. Pesticide determinations were performed by LC-MS/MS in multiple reaction monitoring mode. Quantification difference functions and parameters were proposed and calculated. At the concentration of 0.05 mg kg−1 for ca. 90% of examined pesticides the quantification difference arising from the use of a representative matrix calibration curve (raspberries) instead of a specific fruit matrix calibration curve was below 20% for black and red currents, and below 30% and 35% in the case of strawberries and blackberries, respectively. The 25% difference limit was not exceeded for 51 pesticides in black and red currents, 46 pesticides in blackberries and 45 pesticides in strawberries. Quantification difference functions and parameters such as relative standard deviation of corrected process efficiencies were found to be helpful in data-driven decision-making on the applicability of a representative matrix; the former may be also used as a tool for data correction to ensure the reliability and accuracy of analyses.

Ability of NIRS technology to determine pesticides in liquid samples at maximum residue levels

BACKGROUND

Pesticide residues remaining on food represent a potential risk to consumer's health. Determination of these pesticide residues involves tedious procedures of analysis with regard to time and laboratory work. Near-infrared spectroscopy (NIRS) is a possible alternative to these methods. The aim of this research was to evaluate the ability of NIRS to classify two pesticides used for controlling apple fruit pests according to their concentration. Different solutions were prepared, based on the dose recommended by the pesticide producers for apple pest treatments. Spectra were acquired on a spectrophotometer from liquid samples belonging to these solutions.

RESULTS

Calibration models were developed from liquid samples, following the soft independent modelling of class analogy (SIMCA) analysis method. These models classified between 99 and 100% of the validation samples belonging to different pesticide concentration solutions even at the maximum residue limit level of these products in apple fruit.

CONCLUSIONS

NIRS technology shows a high potential for identifying pesticides in liquid samples, according to their concentration, at the levels required by the legislation.