Ionophores based on 1,3-dithiole-2-thione-4,5-dithiolate (DMIT) as potentiometric silver sensors

A range of acyclic compounds based on 1,3-dithiole-2-thione-4,5-dithiolate (DMIT), functionalised with a silver binding chain and an alkyl chain, were synthesised and assessed as silver ionophores suitable for incorporation into potentiometric ion-selective electrodes as sensors for silver ions in photographic emulsions. The new ionophores were compared with a commercially available ionophore and a 14-crown-4-based ionophore. The membrane compositions were optimised for silver ion selectivity over a range of ions of relevance in the photographic process. 4-(Butylsulfanyl)-5-(phenylmethylthioethylsulfanyl)-1,3-dithiole-2-one was shown to be the most suitable ionophore in plasticised membrane electrodes, with a Nernstian response in the range 10(-1)-10(-6) mol dm(-3) and selectivity coefficients of the order of log K-Ag/M(POT) less than or equal to -4.0.