ONLINE GAS-DIFFUSION SEPARATION AND FLUOROMETRIC DETECTION FOR THE DETERMINATION OF ACID DISSOCIABLE CYANIDE

A flow injection system with gas diffusion separation and spectrofluor imetric detection is described for the determination of acid dissociab le cyanide in waters, Cyanide diffuses through a microporous PTFE memb rane from an acidic donor stream into a sodium hydroxide acceptor stre am. The cyanide transferred reacts with o-phthalaldehyde and glycine t o form a highly fluorescent isoindole derivative, Complete recovery of cyanide was found for Zn(CN)(4)(2-), CU(CN)(3)(2-), Cd(CN)(4)(2-), Hg (CN)(4)(2-), Hg(CN)(2) and Ag(CN)(2)(-) complexes and low recovery fro m Ni(CN)(4)(2-). No recovery was obtained from the species that are co nsidered as non-free cyanide producing, viz., Fe(CN)(6)(4-), Fe(CN)(6) (3-) and Co(CN)(6)(3-). The sampling frequency was 10 h(-1) and the de tection limit was 0.5 mu g l(-1), The method tolerates a 40-fold exces s of sulfide. The results of cyanide determination in water samples ob tained with the proposed method are consistent with those obtained wit h APHA Method 4500 CN-I for weak acid dissociable cyanide.