Fluorimetric flow injection and flow-through sensing systems for cyanide control in waste water

The high toxicity of cyanide and its great variety of uses in industrial processes make it necessary to develop sensitive and selective on-line methods for its determination in natural and waste waters. In this work, a flow injection analysis (FIA) system for cyanide determination was first developed and then experiments were performed in order to develop a flow-through sensing approach. Both systems are based on the interaction between the non-fluorescent copper-calcein complex and cyanide. The analytical features of the FIA system are: linear dynamic range from the quantification limit up to 0.4 mM CN- , detection limit 4 x 10(-3) mM CN-, relative standard deviation 1.2% and sampling frequency 30 h(-1) in the FIA system. The analytical figures for the flow-through approach were linear dynamic range from the quantification limit up to 0.2 mM CN-, detection limit 5 x 10(-4) mM CN-, relative standard deviation 3.7% and sampling frequency 10 h(-1). Interference studies were performed with typical cations and anions present in natural and waste waters. The proposed methodologies were applied to cyanide determination in natural water samples and in samples coming from an industrial bioreactor in order to evaluate its effectiveness in the biological cyanide degradation process of metallurgical waste waters.