Abstract: A two-step procedure was used to optimize instrumental parameters in the cited techniques (details given). Surface or drinking water (3-5 mL) was injected into a carrier solution (1.5 ml/min) of 0.1 M ammonium acetate/acetonitrile (9:1) and analyzed by MS with a thermospray interface at vaporizer and source block temperature 105 and 200°C, respectively. The parent ion intensities were obtained in the single-scan Q3-MS scan mode and daughter ions after collision with Ar at 3-4 mTorr and collision offset voltage l8 and 22 eV, respectively, for phenoxyacid herbicides and bentazone (I). Multiple-reaction monitoring was used with monitoring of two parent ion-daughter ion pairs for the phenoxyacids and one parent and three daughter ions for I (m/e values given). Calibration graphs were linear for 50 µg/l of each analyte with detection limits of 0.2 µg/l for 2,4,5-(trichlorophenoxy)propionic acid to 0.8 µg/l for 2,4,5-(trichlorophenoxy)acetic acid. The method was fully automated with a sample analysis time of 10 min. Results obtained agreed well with those of LC with UV detection.