Multiresidue method for determining multiclass acidic pesticides in agricultural foods by liquid chromatography-tandem mass spectrometry†
A reliable multiresidue method was developed for determining multiclass acidic pesticides in cereal grains, legumes, vegetables, and fruits. The target pesticides comprise 75 compounds, including phenoxy acid, sulfonylurea, imidazoline, and triazolopyrimidine herbicides, with acidic dissociation constant (pKa) values of 1.9–5.9. The method includes extraction with acidified acetonitrile, salting out, cleanup with octadecyl silica and primary secondary amine cartridges, and subsequent liquid chromatography-tandem mass spectrometry. The analytical performance of the developed method was validated for nine foods (i.e., brown rice, soybeans, peanuts, spinach, cabbage, eggplant, potatoes, apples, and oranges) at a concentration of 0.01 mg kg−1. Because matrix effects were negligible for most pesticide and food combinations, solvent-based calibration curves were used for quantification purposes. Most of the target compounds exhibited satisfactory analytical performance with trueness values of 70–100% and relative standard deviations below 14%. The high selectivity of the developed method was evidenced by the absence of interfering peaks near those of the target analytes. With the exception of 1-naphthaleneacetic acid, for which linearity was observed at 2.5–100 ng mL−1, linear calibration curves were constructed for the target compounds in the 1–100 ng mL−1 range, with coefficients of determination exceeding 0.995. The limits of detection were 3 μg kg−1 or below in the examined matrices. The results demonstrate that the developed method is suitable for monitoring acidic pesticides in a variety of foods.