THE DETERMINATION OF SILVER IN PHOTOGRAPHIC-EMULSIONS BY DISCONTINUOUS FLOW-ANALYSIS

An investigation of the use of the flow-based procedure of discontinuo us flow analysis (DFA) for the determination of silver in photographic emulsions is described. It is shown that a procedure used by the phot ographic industry which involves the complexation of a silver halide w ith the thiosulfate ion followed by titration with thioacetamide produ ces poor repeatability when applied in DFA. Evidence is presented to d emonstrate that this is due to a slowing of the response of the silver sensor used to detect the end-point in the titration which is caused by the formation of a loosely bound layer of silver sulfide on the sen sor surface. This surface layer has been identified using scanning ele ctron microscopy and cyclic voltammetry. An alternative procedure is p roposed for the determination using DFA which involves complexing the silver halide (bromide) with the cyanide ion followed by titration wit h sodium sulfide. The results from this method are within 2% compared with those obtained by AAS.