Characterization of an optode membrane for zinc(II) incorporating a lipophilized analogue of the dye 4-(2-pyridylazo)resorcinol

A chemical optical sensing system (optode) for ZnII 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 × 10–6 to 3 × 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.