FIBER OPTICAL pH-SENSOR BASED ON LASER-INDUCED FLUORESCENCE

Abstract

A fiber optical pH-sensor based on laser-induced fluorescence was developed. The fluorescence was ww. with the light of a Helium-Neon-Laser (5°mW, Polytec model PL 7504) emitting at X4 632.8 nm. The dye used was tetra-(p-sulfophenyl)-porphyrine (Ventron), ‘whieh-has in an aqueous solution an extinction coefficient at A = 632.8 nm of e = 4365 I/mol - cm. Its fluorescence behaviour changes at different-pH-values- (figure). It is a water-soluble dye and the sulfo-groups give the possibility to immobilize this dye on anion exchange resins. The fluorescence spectrum of this dye has a maximum at pH = 6.8 at A= 675 nm and A= 700 nm, respectively, which offers the advantage of a ratio-measurement.