Tandem column coupling in supercritical fluid chromatography-mass spectrometry for the multiresidue analysis of pesticides in complex Allium vegetables.

Supercritical fluid chromatography coupled with tandem mass spectrometry (SFC-MS/MS) has established itself as a powerful, environmentally sustainable alternative to conventional liquid chromatography for the multiresidue analysis of pesticides in food matrices. While single-column SFC-MS/MS configurations based on C18 stationary phases have demonstrated clear analytical advantages, their performance can be severely compromised in difficult matrices such as Allium vegetables, where dense co-extractive backgrounds cause significant ion suppression and limit method sensitivity. The serial coupling of columns with complementary selectivities is an inherently SFC-compatible strategy to improve chromatographic resolution without the pressure constraints that restrict analogous approaches in liquid chromatography. In this study, two tandem column configurations were evaluated for the SFC-MS/MS determination of 216 pesticides in onion, leek, and garlic: a 15 cm Silica column coupled upstream to a 25 cm C18 column, and a 15 cm Fluorophenyl column coupled to the same C18 column. Method performance was assessed by comparing limits of quantification (LOQ), matrix effects (ME), and reproducibility (RSD) against a reference single-C18 configuration across the three matrices. The assessment of method performance revealed that both tandem configurations effectively mitigated matrix effects relative to the single C18 setup, though with distinct trade-offs. The Fluorophenyl + C18 coupling provided a meaningful reduction in signal suppression across all matrices but this came at the cost of deteriorated reproducibility and a compound-dependent effect on sensitivity (in garlic it improved the LOQ of 27 compounds while worsening 23). Conversely, the Silica + C18 configuration proved to be the most balanced and robust strategy. It dramatically improved matrix effect mitigation (up to 78.7% of compounds showing negligible effects in onion), lowered LOQs for 38 compounds in garlic, and successfully preserved method precision by reducing the fraction of compounds with highly variable RSDs (> 20%) from 7.4% to just 1.4% in garlic. Finally, this Silica + C18 configuration was utilized for the analysis of real vegetable samples.