An in-vial simple method for the combined derivatization and extraction of phenolic acids and flavonoids from plant extracts and their direct determination with GC-MS, is described. The method is taking advantage of the beneficial potentials of phase transfer catalysis (PTC). Catalysts in soluble and polymer-bound form were tested with the latter being the format of choice due to its high reaction yield and facile separation from the rest of the reaction system. Optimization of experimental conditions was established. Chromatographic separation of eight phenolic acids and four flavonoids methylated via the PTC derivatization step was achieved in 45 min. The detection limits for the described GC-MS(SIM) method of analysis ranged between 2 and 40 ng/ml whereas limits of quantitation fall in the range 5-118 ng/ml, with flavonoids accounting for the lowest sensitivity due to their multiple reaction behavior. Four methanolic extracts from Tilia europea, Urtica dioica, Mentha spicata and Hypericum perforatum grown wild in north-western Greece and four aquatic infusions from commercially available Mentha spicata, Origanum dictamnus, Rosemarinus officinalis and Sideritis cretica were analyzed. Good trueness of the method was demonstrated as no matrix effects were found for the analytes concerned.