Simultaneous spectrophotometric determination of cyanide and thiocyanate after separation on a melamine-formaldehyde resin

A simple indirect spectrophotometric method for the determination of cyanid e, based on the oxidation of the cyanide with chlorine (Cl-2) is described. The residual chlorine is determined by the color reaction with o-tolidine (3,3'-dimethylbenzidine). The maximum absorbance for Cl-2 is at 437 nm. A l inear calibration graph (0-4.0 x 10(-5) M CN-) is obtained under optimal re action conditions at room temperature and pH 11-12, The stoichiometric mole ratio of chlorine to cyanide is 1:1. The effective molar absorptivity for cyanide is 5.87 x 10(4) l mol(-1) cm(-1) at pH 1.6. The limit of quantifica tion (LOQ) is 3.6 x 10(-7) M or 9.4 ppb. Effects of pH, excess reagent, sen sitivity, reaction time and tolerance limits of interferent ions are report ed. The method was applied to the determination of cyanide in a real sample . The basic interferent usually accompanying CN-, i.e. thiocyanate, is sepa rated from cyanide by sorption on a melamine-formaldehyde resin at pH 9 whi le cyanide is not retained. Thiocyanate is eluted with 0.4 M NaOH from the column and determined spectrophotometrically using the acidic FeCl3 reagent . The initial column effluent containing cyanide was analyzed by both the d eveloped chlorine-o-tolidine method and the conventional barbituric acid-py ridine (Spectroquant 14800) procedure, and the results were statistically c ompared. The developed method is relatively inexpensive and less laborious than the standard (Spectroquant) procedure, and insensitive to the common i nterferent, cyanate (CNO-). (C) 2000 Elsevier Science B.V. All rights reser ved.