In this study, it is shown that calibration solutions prepared in control matrix extract can be used to compensate for matrix-induced chromatographic response enhancement observed for certain pesticides. This phenomenon is characterized by enhanced chromatographic response for certain pesticides in the presence of matrix due to reduced analyte loss during injection. Unacceptably high recoveries are seen for affected pesticides when matrix-free solutions are used for reference and calibration. The effects of matrix concentration on overall enhancement and linear response were determined. When used as reference standards for the determination of recovery, matrix-standard solutions were found to provide acceptable recoveries for pesticides subject to matrix-induced chromatographic response enhancement along with other pesticides. General guidelines are presented for using matrix-standard calibration solutions in pesticide residue analysis.

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Pressurized hot water was used to extract two fungicides, thiabendazole (TBZ) and carbendazim (MBC), from agricultural commodities including banana pulp, whole lemons, orange pulp, mushrooms, and rice at extraction temperatures below 100 °C and an extraction pressure of 50 atm. The extraction parameters that were studied include temperature, equilibration time, flow rate, pH, and collection volume. Liquid−liquid partitioning using ethyl acetate was then used to partition MBC and TBZ from the aqueous extractant and concentrate the analytes for final analysis and the determination of recovery. Residues of TBZ were also determined in incurred matrixes which had already been analyzed by another laboratory using validated methodology. Reversed-phase ion-pairing HPLC with UV absorbance and fluorescence detection was used to determine the recoveries of TBZ and MBC from fortified homogenates. Using an extraction temperature of 75 °C, the average recoveries of MBC and TBZ ranged 80.9−100.5% at fortification levels ranging from 0.14 ppm in fresh mushrooms to 10 ppm in whole lemon homogenates. The relative standard deviations were 10% or less. Keywords: Thiabendazole; carbendazim; benomyl; subcritical; water; extraction; ion-pairing HPLC

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