Thesis (M.Sc.)--Chulalongkorn University, 2009

QuEChERS technique has been developed for the determination of pesticide residues in mangosteen using liquid chromatography – tandem mass spectrometry (LC-MS/MS) for analysis. QuEChERS parameters affecting efficiency such as extraction solvent, buffering agent and dispersive sorbent were investigated. The extraction method used acetonitrile, anhydrous magnesium sulphate, sodium chloride and acetate buffer. After shaking and centrifugation, cleanup is done by dispersive solid-phase extraction (d-SPE) using primary secondary amine (PSA) and alumina N mixed sorbent in ratio of 1:1 (25:25 mg). The optimized analytical conditions were evaluated in terms of recoveries, repeatabilities, limits of detection, and limits of quantification for 12 carbamates and 8 polar organophosphates. The matrix-matched standards provided acceptable results for all studied pesticides with overall average recoveries between 66-116%, RSDs 9-26% for carbamate and recoveries 75-97%, RSDs 5-20% for polar organophosphate. Limits of detection, limits of quantification and working range of method for all compounds are 0.005 mg/kg, 0.01 mg/kg and 0.01-0.10 mg/Kg, respectively. LC-MS/MS was performed by multiple reaction monitoring (MRM) with two mass transitions for each pesticide; one for quantification and another one for confirmation. This developed method was successfully validated and compliance to the benchmark parameters of Directive EC 396/2005.