Determination of pesticides and their metabolites in processed cereal samples.

Fifteen pesticides including some of their metabolites (disulfoton sulfoxide, ethoprophos, cadusafos, dimethoate, terbufos, disulfoton, chlorpyrifos-methyl, malaoxon, fenitrothion, pirimiphos-methyl, malathion, chlorpyrifos, terbufos sulfone, disulfoton sulfone and fensulfothion) were analysed in milled toasted wheat and maize as well as in wheat flour and baby cereals. The QuEChERS (quick, easy, cheap, effective, rugged and safe) methodology was used and its dispersive solid-phase extraction procedure was optimised by means of an experimental design with the aim of reducing the amount of co-extracted lipids and obtaining a clean extract. Gas chromatography with nitrogen phosphorus detection were used as the separation and detection techniques, respectively. The method was validated in terms of selectivity, recoveries, calibration, precision and accuracy as well as matrix effects. Limits of detection were between 0.07 and 34.8 µg kg(-1) with recoveries in the range of 71-110% (relative standard deviations were below 9%). A total of 40 samples of different origin were analysed. Residues of pirimiphos-methyl were found in six of the samples at concentrations in the range 0.08-0.47 mg kg(-1), which were below the MRLs established for this pesticide in cereal grains. Tandem mass spectrometry confirmation was also carried out in order to identify unequivocally the presence of this pesticide.

Evaluation of multi-walled carbon nanotubes as solid-phase extraction adsorbents of pesticides from agricultural, ornamental and forestal soils.

A new, simple and cost-effective method based on the use of multi-walled carbon nanotubes (MWCNTs) as solid-phase extraction stationary phases is proposed for the determination of a group of seven organophosphorus pesticides (i.e. ethoprophos, diazinon, chlorpyriphos-methyl, fenitrothion, malathion, chlorpyriphos and phosmet) and one thiadiazine (buprofezin) in different kinds of soil samples (forestal, ornamental and agricultural) using gas chromatography with nitrogen phosphorus detection. Soils were first ultrasound extracted with 10 mL 1:1 methanol/acetonitrile (v/v) and the evaporated extract redissolved in 20 mL water (pH 6.0) was passed through 100 mg of MWCNTs of 10-15 nm o.d., 2-6 nm i.d. and 0.1-10 microm length. Elution was carried out with 20 mL dichloromethane. The method was validated in terms of linearity, precision, recovery, accuracy and selectivity. Matrix-matched calibration was carried out for each type of soil since statistical differences between the calibration curves constructed in pure solvent and in the reconstituted soil extract were found for most of the pesticides under study. Recovery values of spiked samples ranged between 54 and 91% for the three types of soils (limits of detection (LODs) between 2.97 and 9.49 ngg(-1)), except for chlorpyrifos, chlorpyrifos-methyl and buprofezin which ranged between 12 and 54% (LODs between 3.14 and 72.4 ngg(-1)), which are the pesticides with the highest soil organic carbon sorption coefficient (K(OC)) values. Using a one-sample test (Student's t-test) with fortified samples at two concentration levels in each type of soil, no significant differences were observed between the real and the experimental values (accuracy percentages ranged between 87 and 117%). It is the first time that the adsorptive potential of MWCNTs for the extraction of organophosphorus pesticides from soils is investigated.