Determination of silver in photographic emulsion: comparison of traditional solid-state electrodes and a new ion-selective membrane electrode

The performance of a new ion-selective membrane electrode as a suitable probe for measuring silver ions in photographic emulsions was compared with traditional silver/silver halide electrodes and silver bars used by Kodak. The ion-selective membrane was assembled using conventional 10−3 mol dm−3 AgNO3 inner filling solutions and silver ion buffered (at 10−7.2 mol dm−3) solutions in an attempt to achieve lower limits of detection. Membrane fouling on the inner side of the membrane (on storage in conditioning solution) was observed for the latter. Although this prevented the use of the electrode in photographic emulsions, the observation is significant as it implies Donnan exclusion failure due to extraction of primary ions. The behaviour of the conventional membrane electrode was similar to that of silver/silver chloride electrodes in both aqueous solutions and photographic emulsion. This showed that a suitable membrane ion-selective electrode is eminently suitable for the direct measurement of silver ions in photographic emulsion media.