DEVELOPMENT OF REDOX SENSORS FOR ENVIRONMENTAL APPLICATIONS BASED ON IMMOBILIZED REDOX INDICATORS

Two redox indicators, thionine and phenosafranine, were successfully i mmobilized on an affinity chromatography gel and were shown to retain their redox activity, The formal potentials (versus the standard hydro gen electrode) near pH 7 were determined to be 52 mV for immobilized t hionine and -286 mV for immobilized phenosafranine. It was demonstrate d that the immobilized indicators can be packed in a now cell and moni tored spectrophotometrically to determine their speciation, The absorp tion spectra and electrochemical behavior of the indicators were only slightly affected by immobilization on the gel, For both indicators, i mmobilization caused the formal potential to decrease (15-20 mV) and t he absorption spectrum to shift to higher wavelengths (20-40 mm) with respect to the free (unbound) indicators, These immobilized redox indi cators couple with some redox-active species [Cr(VI), O-2, and Fe(II)] that are important in environmental samples.