DOPED THIN-FILM SENSORS VIA A SOL-GEL PROCESS FOR HIGH ACIDITY DETERMINATION

An optical sensor has been developed for high-acidity ([H+] = 1-11 M) measurements. The sensor is made of thin films of silica sol-gels dope d with an acid indicator. Acid- and base-catalyzed methods to make the sol-gel films have been studied, and the properties of the sol-gel se nsors prepared by these methods are discussed. The acid-catalyzed meth od was found to give more robust films and has been optimized to prepa re thin films which are mechanically and chemically stable for a perio d of at least 3 months. The performance of the sensors resulted in a r elative standard deviation of less than 2.5%. The response time is sho rt (1 s), and a small hysteresis was observed during reproducibility m easurements with 2-10 M HCl solutions.