OPTICAL SENSORS FOR A WIDE PH RANGE BASED ON AZO DYES IMMOBILIZED ON A NOVEL SUPPORT

New reactive azo dyes are described which are useful for optical deter mination of pH. The dyes are covalently linked (via ethylsulfonyl grou ps) to a novel type of transparent solid films consisting of a thin fi lm of cellulose on top of a polyester support. The resulting membranes exhibit distinct color change when changing the pH and, in most cases , are compatible with LED light sources. Various membranes have been d eveloped with pK(a) values ranging from 0.5 to 11.28, thus practically covering the whole pH range. Because of the stability of the dyes, th e covalent bond and the solid support, the new membranes exhibit stora ge stability over years, and operational lifetimes of weeks, good repr oducibility and a fast (30-60 s) response to pH.