Impact of injection solvent composition on 90 pesticides by LC-MS/MS: A data-driven framework for initial method...

The composition of the injection solvent is a critical, yet often underestimated, parameter in liquid chromatography-tandem mass spectrometry (LC-MS/MS). This study systematically evaluates the influence of injection solvent on the analysis of 90 pesticides by comparing mixtures of acetonitrile (ACN) with water and buffered mobile phase A (5 mM ammonium formate, 0.1% formic acid) across various ratios (10/90 to 50/50, v/v). The investigation, conducted using solvent-based standards, explicitly focuses on chromatographic and ionization effects in the absence of sample matrix. Results reveal distinct, polarity-dependent response patterns. Early-eluting, polar compounds (e.g., methamidophos) demonstrated up to a 14-fold signal enhancement in highly aqueous solvents (10/90 ACN/water), attributed to improved on-column focusing. Conversely, late-eluting, non-polar analytes (e.g., spinosad) required higher organic content (50/50 ACN/water) to ensure solubility and maximize response. A 30/70 ACN/aqueous ratio emerged as a robust compromise for most mid-polarity compounds. ANOVA confirmed that solvent ratio significantly impacts MS response (p < 0.001). While matrix effects were not within the scope of this study, the research provides a foundational framework and practical guidelines for selecting an optimal injection solvent during initial method development, thereby enhancing the sensitivity and chromatographic integrity of multi-residue pesticide analyses.