Electrochemical silver sensors for photographic processes

Abstract

A range of novel silver ionophores was synthesised based on the l,3-dithiole-2- thione-4,5-dithiolate (DMIT) building block. These were incorporated in ion-selective electrodes (ISEs) and applied to the determination of silver ion in photographic process solutions of interest to Kodak. Two classes of compounds were synthesised incorporating acyclic silver binding sites. The first class of compounds were 1,3 dithiole-2-ones functionalised with (i) a silver binding chain, and (ii) an alkyl chain, the latter allowing a range of compounds to be synthesised of varying lipophilicity. These compounds were applied as silver ionophores in plasticised PVC membranes and incorporated in ion-selective electrodes. The newly synthesised ionophores were compared to silver ionophores in the literature and to those previously used by Kodak. The membrane composition was optimised for silver ion selectivity over a range of metal cations of relevance to photographic process solutions. Samples of photographic emulsions were supplied by Kodak and subsequent analysis demonstrated successful detection of silver ion to micromolar levels with the ISE incorporating the newly synthesised ionophores. The second class of compounds was based on the tetrathiafulvalene (TTF) building block. A TTF derivative was synthesised incorporating two acyclic silver binding chains and a hydrophobic domain. The reversible redox properties of this compound enabled it to be applied as a transducer suitable for voltammetric analysis of silver ion. Titration of a solution of the new TTF compound with silver ion revealed that it was very sensitive; an equimolar quantity of silver ion resulting in a marked change in voltammetric behaviour. A silver ion binding constant was determined by ultraviolet spectrophotometry.