Assessment of Different Fluorimetric Reactions for Cyanide Determination in Flow Systems

Several fluorimetric reactions for the determination of cyanide by means of flow injection systems were tested. The first reaction is based on the displacement of 8-hydroxyquinoline-5-sulfonic acid (HQS) from the Pd(HQS) 2 complex by cyanide ion and the subsequent reaction of free HQS with Mg II to form a fluorescent species. Secondly, the inhibitory effect of cyanide on the reaction between iodine and fluorescein was also evaluated as a method to quantify cyanide. The third method is based on the detection of an isoindole derivative formed by the reaction of o-phthalaldehyde (OPA) or 2,3-naphthalenedialdehyde (NDA) with glycine in the presence of cyanide. Chemical and hydrodynamic parameters were optimized for each system and the analytical performance of the methods was established. Detection limits of 5 µg l - 1 (fluorescein–iodine method), 0.40 µg l - 1 (Pd–HQS–Mg method), 0.25 µg l - 1 (OPA method) and 0.03 µg l - 1 (NDA method) were obtained.