Solid-phase microextraction (SPME) for the determination of pyrethroids in cucumber and watermelon using liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection

A sensitive and efficient solid-phase microextraction (SPME) method for the determination of seven pyrethroid insecticides including fenpropathrin, λ-cyhalothrin, deltamethrin, fenvalerate, permethrin, τ-fluvalinate and bifenthrin in cucumber and watermelon samples using high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (SPME-HPLC-PIF-FD) was developed and validated. The optimum SPME conditions were used for the extraction of samples of both matrices (extraction time 30 min, stirring rate 1100 rpm, extraction temperature 65 °C, sample pH 3, soaking time 7 min, desorption time 5 min, ACN content 25%, desorption and soaking solvent was the mobile phase and in static mode). The method was validated in terms of limits of detection (LODs) and the limits of quantification (LOQs) in both IUPAC and EURACHEM criteria. LODs and LOQs were achieved in values lower than the maximum residue levels (MRLs) established in the Spanish regulations for all pesticides in this study (MRLs range between 0.01 and 0.1 mg kg⁻¹ for all pyrethroid insecticides in both matrices). LOQs according to the second criterion were between 1.5 and 5 μg kg⁻¹ for cucumber; and between 1.3 and 5 μg kg⁻¹ for watermelon samples. Precision and recovery studies were evaluated at two concentration levels for each matrix. Good precision was obtained and relative standard deviation values were less than 10% in all cases. Recovery values were calculated at 0.05 and 0.5 mg kg⁻¹ levels (n = 6) and they ranged between 93% and 108% for cucumber and between 91% and 110% for watermelon samples. Applicability of the method to pyrethroids in cucumber and watermelon of commercial samples was demonstrated.