An effective methodology for simultaneous quantification of thiophanate-methyl, and its metabolite carbendazim in...

Herein we have developed an optimized analytical method for the simultaneous quantification of a fungicide, thiophanate-methyl, and its metabolite, carbendazim, in pear cultivated under open-field conditions using liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS). Due to the problem of partitioning associated with using acetonitrile and salts, methanol was used for sample extraction; the extract was then filtered using a vacuum filter, and cleaned-up using C₁₈ QuEChERS bulk sorbent following dispersive solid-phase extraction (d-SPE) procedure. Since a common problem, "matrix effect", associated with the matrix was observed in LC-MS/MS, calibration curves for both thiophanate-methyl and carbendazim were constructed in the matrix using seven different concentration levels. Excellent linearity was observed, with determinant coefficient (R²) ≥ 0.9990. The limits of quantification (LOQs) were ≤0.02 mg/kg, satisfactory in terms of the maximum residue limits. Methods were validated at two fortification concentrations (10 × LOQ and 50 × LOQ); the experiments were repeated three times for each level and the average recoveries were 75.00-84.92%, with the coefficient of variation (CV) being ≤5.78%. The developed analytical method was applied to pear samples previously sprayed with commercial thiophanate-methyl formulation four times on different days during pre-harvest treatment. The parent compound was converted to its metabolites and the total residues degraded continuously until harvest. The data obtained in this study could help set safety guidelines for thiophanate-methyl in pear.