Shifting the Measuring Range of Chloride Selective Electrodes and Optodes Based on the Anticrown Ionophore [9]Mercuracarborand-3 by the Addition of 1-Decanethiol

摘要

Ion-selective electrodes and optodes based on the anticrown ionophore mercuracarbo-rand-3 (MC-3) exhibit excellent selectivity to halide ions but suffer from a low upper detection limit because of very strong complexation in the sensing phase.In this work,we have successfully improved the upper detection limit and widened the working range of chloride selective electrode based on MC-3 by introducing 1-decanethiol into the membrane cocktail.With an assumed 1:2 stoichiometry between chloride and MC-3 the apparent complex formation constant was reduced from log beta=13.4 as reported for the membrane without the addition of 1-decanethiol to log beta=12.13,log beta=10.84 and log beta=5.67 with the addition of a 1:1,1:2 and 1:4 molar ratio of 1-decanethiol to MC-3.Besides these values,obtained with the sandwich membrane method,similar shifts in the measuring range of thin optode film responses to lower chloride concentrations were observed as well.The selectivity of the modified membrane was found to be very good,with hydroxide and the other halides:bromide and iodide,as the main interferences.Based on these results,corresponding iodide selective electrodes were prepared that showed a near-Nernstian iodide slope,rather than a cationic slope as observed without thiol additive.