Effectiveness of Different Organic Solvent Additions to Water Samples for Reducing the Adsorption Effects of Organic...

This study systematically investigated the effect of organic solvent addition on the detection signal intensity of 15 organic pesticides in water using ultra-high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UHPLC-ESI-MS/MS). The analysis of chromatographic peak area ratios in ultrapure water (UPW) versus 30% methanol (MeOH)-UPW showed that the adsorption effects (AEs, mainly from injection vials with weaker polarity) were the main factor influencing the detection intensity of the organic pesticides. The AEs varied with pesticide type and concentration, especially for those with high logK_ow values and longer retention times, such as malathion, triadimefon, prometryn, S-metolachlor, diazinon, and profenofos. Significant differences were observed in the ability of five organic solvents (MeOH, dimethyl sulfoxide, isopropanol, acetonitrile, and acetone) to reduce AEs, with MeOH being the most effective. Optimal solvent ratios were determined to minimize AEs in aqueous solutions. Additionally, plastic injection vials caused greater AEs than glass injection vials, but the addition of organic solvents increased the detection intensity of the analytes for vials of both materials. Density functional theory calculations of the binding energies between pesticides (diazinon, malathion, and S-metolachlor) and vial materials further confirmed the effect of AE on the detection intensity of the analytes. This study showed that the addition of MeOH to real water samples effectively reduced or eliminated the effects of AEs, achieving a good linearity of calibration curves (0.05/0.1-5 μg/L, R² = 0.9853-0.9998), high sensitivity (LOD = 5-32 ng/L), precision (RSD = 1.4-14.5%), and accuracy (average recoveries = 80.6-121.8%). These results provide technical and methodological support for mitigating the effects of AEs on pesticide detection in water using UHPLC-ESI-MS/MS.