QuEChERS method. Phase separation and pesticide partitioning were performed by the addition of the extraction kits based on the EN-QuEChERS methodology. The LC-MS/MS analysis was conducted using an Agilent HPLC 1260 along with API 6500 QTRAP mass spectrometer and electro spray ionization (ESI) interface. The chromatographic separation was achieved using an Agilent C18 reverse-phase column ZORBAX Eclipse plus 4.6 × 150 mm with 5.0 μm particle size. The ESI was operated in the positive mode. A gradient elution program was used at 500 μL/min flow rate using 10 mM ammonium formate in 1% methanol and methanol.
The obtained results showed that, more than 34 pesticides have been detected in most of examined samples collected from different companies in the Egyptian market. Limit of quantitation for the studied pesticides was10µg/kg. It was found that some pesticide residues exceed Maximum Residue Level (MRL).
The optimized QuEChERS was validated according to accuracy, precision ,detection limit (LOD), quantification limit (LOQ) and it was successfully applied for detection of 34 pesticide residues in tea bags samples collected from the Egyptian market.