Determination of pesticides in lettuce using solid–liquid extraction with low temperature partitioning

• New method for pesticides determination in lettuce samples.
• SLE/LTP-GC/ECD is selective, accurate and precise.
• The LOQs were either comparable to or better than those reported previously.
• The residual concentrations of the pesticides in lettuce were below the MRLs.

This work describes the optimization and validation of a method employing solid–liquid extraction with low temperature partitioning (SLE/LTP) together with analysis by gas chromatography with electron capture detection (GC/ECD) for the determination of nine pesticides (chlorothalonil, methyl parathion, procymidone, endosulfan, iprodione, λ-cyhalothrin, permethrin, cypermethrin, and deltamethrin) in lettuce. The method was found to be selective, accurate, and precise, with means recovery values in the range of 72.3–103.2%, coefficients of variation ⩽12%, and detection limits in the range 0.4–37 μg kg−1. The matrix components significantly influence the chromatographic response of the analytes (above 10%). The optimized and validated method was applied to determine the residual concentrations of the fungicides iprodione and procymidone that had been applied to field crops of lettuce. The maximum residual concentrations of the pesticides in the lettuce samples were 13.6 ± 0.4 mg kg−1 (iprodione) and 1.00 ± 0.01 mg kg−1 (procymidone), on the day after application of the products.