Monitoring Pb2+ with optical sensing films

A new lipophilic ionophore, N,N,N,N'-tetradodecyl-3,6-dioxaoctane-1-thio-8-oxodiamide (ETH 5493), is characterized in optical sensing films with a view to being used for environmental monitoring. It sufficiently discriminates all alkali and alkaline earth metal ions and, contrary to what is observed with the corresponding dithioamide, does not suffer from irreversible changes upon contact with Ag+ and Hg2+ salts. Different response functions are found for bulk optodes with ratios of chromoionophore/ion exchanger above and below 1.0. The data obtained fit the theoretical response function with a standard deviation of the residuals of 0.0012 absorbance units (AU) without any systematic error. When comparing different membranes, the precision is still high (+/-0.0029 AU) but the residuals show a certain systematic trend. (C) 1999 Elsevier Science B.V. All rights reserved.