A new generation of cyanide ion-selective membranes for flow injection application: part II. Comparative study of cyanide flow-injection detectors based on thin electroplated silver chalcogenide membranes.

Using induced cathodic electrodeposition a number of silver chalcogenide thin layer membranes of non-trivial composition have been synthesized and their performance as ion-selective flow-injection potentiometric detectors (FIPDs) for free cyanide has been critically estimated in the context of the stringent requirements for toxic cyanide environmental monitoring. AgSCN/Ag2S, Ag2S, Ag(2+delta)Se, Ag(2+delta)Se(1-x)Te(x) (0<delta<0.25 and x approximately = 0.13), Ag2Se and Ag2Se(1-x)Te(x) electroplated membranes were selected for the present performance-based comparative study in order to obtain a feedback information about the effect of membrane composition. Both silver selenide and Te-doped silver selenide membranes, irrespective of their stoichiometry with respect to silver, exhibit the lowest detection limit for CN- (52 ppb) with linear double-Nernstian response down to 130 ppb. The type of chalcogene anion in the membrane composition proves to exert dominant effect on the general performance characteristics of the newly developed FIPDs. The silver stoichiometry (intrinsic defects factor) and the inclusion of Te-dopant (extrinsic defects factor) have more pronounced effect on the profile of the output signal and exert moderate control on the detectors selectivity and baseline stability. This new generation of CN(-)-ion-selective membranes for FIPDs exhibits high selectivity against the common interferents present in cyanide effluents such as SCN-, S2O3(2-), Cl- and do not get poisoned in the presence of S2-. Moreover, their long-term stability and signal reproducibility, which make redundant the regular day-to-day calibration, coupled with the cost-effective technology for membranes preparation and easy re-generation make them attractive candidates for incorporation into automated in-field devices for in situ cyanide toxic species monitoring.