PIEZOELECTRIC SENSOR FOR DETECTION OF ORGANIC AMINES IN AQUEOUS-PHASEBASED ON A POLYSILOXANE COATING INCORPORATING ACIDIC FUNCTIONAL-GROUPS

The resonant frequency of piezoelectric quartz crystal microbalances ( QCMs), coated with a polysiloxane film containing acidic functional gr oups was studied when the pH of aqueous solutions in contact with coat ings was changed. The Delta f vs. pH curves for the polymer coating in dicated that the pK(a) values were about 7 similar to 8 (K-a is the io nization constant) and the transition region was around 3 similar to 4 pH units. The sorption characteristics of the crystal coated with pol ymer film were reported. These coated crystals were shown to behave as selective detectors for a range of organic amines in dilute aqueous s olutions. The lower limits for reliable measurement using 10 MHz cryst als coated with 15 kHz loading of OV-225 acid polymer were estimated t o be at the ppm levels for primary amines and triethylamine in a pH 7. 14 buffer solution and a water-ethanol (v/v=96/4) solution. Linear res ponses were obtained in the concentration ranges of 10-270 ppm and 10- 250 ppm for the pH 7.14 buffer and the water-ethanol solution, respect ively.