On-line ion-pair solid-phase extraction–liquid chromatography–mass spectrometry for the analysis of quaternary ammonium herbicides

An ion-pair on-line solid-phase extraction procedure using C8 extraction disks, suitable for liquid chromatography–mass spectrometry analysis is developed to determine quaternary ammonium herbicides (quats) in water samples. The separation of these compounds was performed using ion-pair chromatography with heptafluorobutyric acid (15 mM, pH 3.3) and acetonitrile gradient elution. Detection was carried out using a quadrupole mass spectrometer. Water sample volumes up to 50 ml can be preconcentrated with recoveries higher than 70%. Good precision and accuracy (day-to-day and run-to-run) were obtained and the detection limits ranged from 6 to 85 ng l−1. The proposed on-line ion-pair solid-phase method enables compliance with European Community directives for drinking waters (100 ng l−1).