Determination of fungicides' residues and their degradation kinetics in orange tree fruits using liquid chromatography-Tandem mass spectrometry coupled with QuEChERS method

A new, sensitive, selective and validated LC-MS/MS method has been developed for the determination of five fungicides namely; Carbendazim, Thiabendazole, Metalaxyl, Imazalil and Propiconazole in orange samples. Sample pretreatment was performed using the QuEChERS technique where orange samples were extracted using acetonitrile and were centrifuged for 5 min. Procedural standard calibration was applied to compensate for signal suppression due to the matrix effect. LC-MS/MS parameters were optimized to quantify the least concentration of the studied fungicides below maximum residue limits. Isocratic elution using 10 mM ammonium formate buffer pH 4 (10%), and methanol (90%) on Agilent C18 column ZORBAX Eclipse plus was applied with total elution time of 5 min. Trueness results, according to SANTE guideline, ranged from 101.04% to 104.51% with average % RSD < 7.01%, The method detection limit and limit of quantification were in the range of (0.67-1.25 ng/g) and (2.24-4.15 ng/g) respectively. The proposed method was successfully used to quantify the residuals amounts of the selected fungicides in different market and organic orange samples. It is the first time to study the degradation kinetics of these fungicides in citrus fruits, as well as their half-lives and their predicted preharvest interval, in the real orange samples from orange trees after their treatment with the studied fungicides.