Acidified Acetonitrile Extraction and Ultra-High Performance Liquid Chromatography–Tandem Mass Spectrometry for Multiresidue Determination of 136 Pesticides in Tahiti Lime (Citrus latifolia)

The determination of pesticide residues in citrus fruits remains analytically challenging due to their high acidity and complex chemical compositions, which can compromise extraction efficiency and promote significant matrix effects, particularly for acidic compounds. In this study, an acidified acetonitrile-based QuEChERS method was developed and validated for the multiresidue determination of 136 pesticides in Tahiti lime (Citrus latifolia) using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC–MS/MS). The proposed approach employs 1% formic acid in acetonitrile and omits the conventional clean-up step, aiming to improve analyte recovery and analytical throughput. Method validation was performed according to SANTE guidelines, demonstrating satisfactory linearity (R2 ≥ 0.99 for all analytes), limits of quantification of 0.01 mg kg−1, and recoveries within 70–120%, with relative standard deviations ≤ 20% for the vast majority of compounds. Notably, the method achieved consistent and reliable performance for 12 acidic pesticides, which are typically problematic in conventional QuEChERS approaches. Application to 22 real samples revealed the presence of 14 pesticide residues, with some compounds exceeding European Union (EU) maximum residue limits. The proposed method provides a simple, efficient, and robust alternative for comprehensive pesticide monitoring in citrus fruits, with particular advantages for the determination of acidic compounds in highly complex matrices.