Abstract: The recently developed tandem technique, mass spectroscopy with atmospheric-pressure chemical ionization (APCI-MS) coupled with direct flow injection, was applied to the determination of Bitrex (denatonium benzoate) and diethyl phthalate in ethanol. The compounds were identified from their total-ion chromatograms (m/z 50-500) and, simultaneously, quantified using selected-ion chromatograms recorded at m/z 223 for diethyl phthalate and m/z 325 for Bitrex. Operating conditions were optimized for soft ionization (positive ion-mode) with fragmentation limited to that necessary for analyte identification, which was by the external-standard method. Calibration curves were rectilinear in the concentration ranges 2-30 µg mL-1 (Bitrex) and 0.075-1.2% v/v (diethyl phthalate); measurement precision (RSDs were 11.48% for Bitrex and 2.22% for diethyl phthalate), and detection limits (0.017 µg mL-1 and 0.010% v/v, respectively) were adequate for simultaneous quantitation and with high sensitivity. The lack of any sample pretreatment and the use of flow injection analysis meant that the procedure was more straightforward and rapid than previously reported methods.