CHARACTERIZATION OF AN OPTODE MEMBRANE FOR ZINC(II) INCORPORATING A LIPOPHILIZED ANALOG OF THE DYE 4-(2-PYRIDYLAZO)RESORCINOL

A chemical optical sensing system (optode) for Zn(II) based on a lipophilized metal ion indicator dye [1-octadecyloxy-4-(2-pyridylazo)resorcinol; ETH 2464] dissolved in a plasticized poly(vinyl chloride) membrane has been developed. In the measuring range from 1 x 10(-6) to 3 x 10(-3) mol dm-3 Zn2- (pH 4.8), the absorbance response shows a good correlation with the theoretically derived formulae. The optode membranes were found to reach 95% of the final signal within 5 min (t95). When exposed to a continuous sample flow (1 ml min-1), the optode membrane did not lose a perceptible amount of the indicator over a period of 10 h. The selectivity of the optode membrane for the response towards Zn2+ ions in pH-buffered solutions is described.