DIRECT AND CONTINUOUS DETERMINATION OF PH VALUES IN NONTRANSPARENT W O SYSTEMS BY MEANS OF EPR SPECTROSCOPY/

The change of the pH value induced by the decomposition of hydrolyzabl e drugs with ester structure was monitored directly and continuously i n nontransparent w/o systems by means of EPR spectroscopy using the pH sensitivity of the spectral parameters of imidazoline-derived spin pr obes. This nondestructive method makes it possible to perform measurem ents in nontransparent w/o systems without the need of any preparatory steps. While the hydrolysis of acetylsalicylic acid caused a rapid de crease of the pH value during 5 h at room temperature (25 degrees C) w ithin the emulsion, benzocain exhibited a relatively higher stability.