F. J. Egea González

Assessment of uncertainty in pesticide multiresidue analytical methods: main sources and estimation

Abstract The estimation of the uncertainty associated to analytical methods is necessary in order to establish the comparability of results. Multiresidue analytical methods lack very often of information about uncertainty of results with likely implications when results are compared with maximum residue levels (MRL) established by regulations. An adequate identification and estimation of each uncertainty source allows to laboratories to establish the accuracy of results and to balance with time-consuming and costs.

Analysis of lindane, α- and β-endosulfan and endosulfan sulfate in greenhouse air by gas chromatography

Abstract A method to sample and analyse lindane and three endosulfan isomers in greenhouse air has been studied. The behaviour of Chromosorb 102, Porapak R, Supelpak-2, Amberlite XAD-2, Amberlite XAD-4 and polyurethane foam (PUF) as sorbents has been studied. Atmospheres containing known concentrations of these pesticides were generated. The desorption process of the analytes and the behaviour of sorbents in atmospheres with different relative humidities have been tested. No breakthrough was observed in the range of concentration studied. Personal samplers have been used with the selected sorbent (PUF), in order to sample lindane, α- and β-endosulfan and endosulfan sulfate in an experimental greenhouse. GC—electron-capture detection analysis and MS confirmation of the pesticides have been carried out. The dissipation process of the analytes in the 24 h period after application has been studied.

Determination of imidacloprid and its metabolite 6-chloronicotinic acid in greenhouse air by high-performance liquid chromatography with diode-array detection.

A method is described for analysing and sampling imidacloprid and its metabolite 6-chloronicotinic acid in greenhouse air by high-performance liquid chromatography (HPLC) with diode-array detection (DAD). The trapping efficiency of two solid sorbents, Amberlite XAD-2 and Amberlite XAD-4 and the use of different desorption procedures have been tested. To validate the methodology, standard atmospheres containing known concentrations of these pesticides and with different relative humidities were generated. No breakthrough was observed in the range of concentrations studied. Dissipation of analytes was investigated in a 24 h period after application by using personal samplers in a field experiment.

Matrix-effects of vegetable commodities in electron-capture detection applied to pesticide multiresidue analysis

The influence of the sample matrix in the analysis of pesticides in vegetable samples has been studied in order to determine if the matrix content introduces a systematic or proportional (or both) bias in the measurements. Experiments have been carried out during a 4-month period, in which calibration curves, prepared in solvent and in vegetable matrix, were prepared and analysed. A statistical treatment has been applied in order to: (i) check the stability of such calibrations during the period studied; (ii) compare both solvent and matrix-matched calibrations; and (iii) obtain a correction function. Applying the correction function to the results obtained with a solvent calibration it is possible to make a prediction of the values obtained applying a matrix-matched calibration. The performance of the correction function has been validated with recovery data. Finally the uncertainty derived from the use of each calibration plot and the correction function has been calculated.

Analysis of biogenic volatile organic compounds in zucchini flowers: identification of scent sources.

An analytical method has been applied to determine volatile organic compounds in zucchini flowers. In a first step, the analytical method was applied to characterize the main scents emitted by whole male and female living flowers of three main commercial cultivars of zucchini (Tosca, Chapin, and Consul). In a second step, the compounds were quantified in different parts of the living flowers to identify the contribution of nectar, petals, anther, and stigma to the aroma profile of the flower. The analytical method is based on headspace solid-phase microextraction coupled on-line with GC and tandem MS detection (HS-SPME-GC-MS/MS). A reference compound is added to samples as part of the field quality control procedure to check for likely analyte losses or sample decomposition. The reference compound also acts as an internal standard for quantification purposes. Results have been statistically studied applying principal component analysis (PCA), which shows that three components explain more than 91% of the variance. PCA emphasizes the great importance of nectar as being the main source of 1,4-dimethoxybenzene and 1,2,4-trimethoxybenzene, which influence the aroma profile of flowers. The remaining components can be accounted for by emissions from petals and sexual organs (adroecium and gynoecium anthers or stigmas).An analytical method has been applied to determine volatile organic compounds in zucchini flowers. In a first step, the analytical method was applied to characterize the main scents emitted by whole male and female living flowers of three main commercial cultivars of zucchini (Tosca, Chapin, and Consul). In a second step, the compounds were quantified in different parts of the living flowers to identify the contribution of nectar, petals, anther, and stigma to the aroma profile of the flower. The analytical method is based on headspace solid-phase microextraction coupled on-line with GC and tandem MS detection (HS-SPME-GC-MS/MS). A reference compound is added to samples as part of the field quality control procedure to check for likely analyte losses or sample decomposition. The reference compound also acts as an internal standard for quantification purposes. Results have been statistically studied applying principal component analysis (PCA), which shows that three components explain more than 91% of the variance. PCA emphasizes the great importance of nectar as being the main source of 1,4-dimethoxybenzene and 1,2,4-trimethoxybenzene, which influence the aroma profile of flowers. The remaining components can be accounted for by emissions from petals and sexual organs (adroecium and gynoecium anthers or stigmas).

Dermal exposure to pesticides in greenhouses workers: Discrimination and selection of variables for the design of monitoring programs

Dermal exposure to pesticides is one of the main sanitaryproblems which greenhouses workers face. With the dual aimsof establishing both the body part that receives the greatestexposure and the variable that has greatest influence on this exposure level, 22 pesticide application trials were performed. Trials were carried out in different greenhouse vegetable crops,using different pesticides and different spray diameters from the spray gun. In order to determine dermal exposure, the wholebody method was used. Pieces of the applicator suit were subject to an extraction procedure and their pesticide contentdetermined using GC-NPD analysis. Multivariate analysis were applied to the data obtained. Principal component analysis showed that all trials produced a high exposure level on lowerleft leg and lower right leg. Cluster analysis distinguished between three sample groups. The most and the least affectedparts were clearly distinguished. Discriminant analysis indicated that the thin drop size of the spray gun is responsible for both the differences between groups and the minimum or maximum exposure level measured on the applicatorsuit. Therefore, selecting the variables, lower legs and thindrop size, is considered fundamental in designing programs formonitoring pesticide exposure.

Analytical method for assessing exposure of greenhouse applicators to procymidone by gas chromatography and whole body dosimetry

SummaryAn analytical method for the determination of the potential and actual exposure of agricultural workers to procymidone has been developed. The methodology is based on the whole body technique, using Tyvek Pro-Tech and Sontara as sampling media, and uses hexane extraction, GC-ECD analysis and GC-MSD confirmation. The validation of the analytical method has been carried out incorporating the matrix of coverall in all steps when calculating parameters such as retention time window, limits of detection and quantification, linear ranges and precision. A field sampling strategy has also been developed and the method has been applied to the evaluation of the potential and actual dermal exposure of an applicator and an assistant in normal working conditions.

Estimation and correction of matrix effects in gas chromatographic pesticide multiresidue analytical methods with a nitrogen–phosphorus detector

The assessment of matrix effects in the quantification of organophosphorus pesticides in fruit and vegetables by GC-NPD, were studied applying ANCOVA. Calibration curves prepared in solvent were compared with calibration curves prepared in a blank matrix extract for eight different commodities, establishing whether the matrix induces systematic or proportional errors in the quantification of the pesticides. In such cases correction functions were obtained and validated by quantifying spiked samples using solvent calibrations and applying the correction functions to the data obtained. The results were compared with those obtained by quantification using matrix-matching calibrations and with those from 100% recovery experiments. It was found that the matrix effects can be avoided using the correction functions. Finally the contribution of the correction functions to the uncertainty of the results was estimated as well as their stability during a four month period.

Gas chromatographic method and whole body dosimetry for assessing dermal exposure of greenhouse applicators to chlorpyrifos-methyl and fenitrothion

An analytical method has been developed in order to determine potential and actual dermal exposure to chlorpyrifos-methyl and fenitrothion of greenhouse agricultural workers using whole body dosimetry. The validation of the methodology has been established following standards requirements, performance parameters such as limits of detection and quantification, linear ranges, recovery rates and precision were determined. The matrix effect in the quantification and recovery steps and the spiking procedure has been considered. A field sampling strategy has been developed including a procedure for collecting samples, which included field spikes and field blanks to ensure the stability of samples during transport, storage and analysis. Quality control criteria have been established for checking that in routine analyses all data are under statistical control. Finally, the methodology has been applied to assess the potential and actual dermal exposure of two applicators and their assistants after greenhouse application to chlorpyrifos-methyl and fenitrothion founding total dermal exposure levels close to 63 and 60 ml/h, respectively, in the case of applicators and ranging between 13 and 20 ml/h in the case of assistants.

Levels of metamidophos in air and vegetables after greenhouse applications by gas chromatography

The diminution of metamidophos residue levels with time in vegetables and greenhouse air was investigated after treatment of tomatoes and green beans. A gas chromatographic method using dichloromethane as an extraction solvent has been developed to analyse metamidophos in vegetables, with obtained recoveries higher than 89%. The reliability of several sorbents for air sampling was tested using standard atmospheres resulting in recoveries higher than 90% from PUF, XAD-2, XAD-4 and Supelpak using Soxhlet extraction with acetone. The dissipation of metamidophos in greenhouse air was studied 52 h after application. Finally the effect of crop, type of greenhouse, season and dose applied on the dissipation kinetic of metamidophos in vegetables, was statistically studied by analysis of variance resulting in crop and season being the most significant factors.