Fluorimetric determination of free cyanide by flow-injection analysis

A flow-injection analysis system for the rapid and sensitive fluorimetric determination of free cyanide is developed. The determination is based on oxidation of nonfluorescent thiamine to highly fluorescent thiochrome (lambda(ex)/lambda(em) = 370/440 nm) in alkaline medium by Cu2+ when CN- is present. After designing an appropriate manifold, the effects of chemical variables, FIA system parameters and temperature on the determination of CN- were studied in detail. Under optimum experimental conditions the working range was linear from 0.02 to 2.5 mg L-1 with a high sampling throughput of 120 h(-1) at room temperature. The precision, in terms of relative standard deviations for ten replicates of analysis of 1.0 mgL(-1)CN(-), was 1.9%. Interference studies were performed with typical cations and anions in natural waters. CN- spiked in synthetic water samples was determined by this proposed FI method with good results. The composition of the reduced product [Cu+(CN-),](1-n) was determined using an indirect method. In addition, results of cyclovoltammetric measurements of thiamine are reported which throw light on the electrochemical process.