Quantitation of sample extracts during validation was
done using a calibration curve based on matrix-matched standards
(blank extracts fortified with the analytes). The matrix
blank residues were fortified with a mixture of the pesticides
studied at concentrations ranging from 0.01 to 0.5 mg/kg in
order to have a wide range of concentrations. The integrated
peak area data of the selected quantification masses were
used to construct the calibration curves. The linearity in the
response was studied by using standards prepared in pure
solvent and by comparing it with matrix-matched extract
solutions to evaluate possible matrix effects. The limits of detection
(LODs) were determined as the analyte concentration
that gave a signal-to-noise of 3, as calculated by the instrument
software, and empirically verified by analyzing pesticide
mixtures at these concentration levels in matrix extracts.