First derivative of the ratio spectra method for resolving iodide and thiocyanate in binary mixtures

A new method is described to analyse the binary mixture of iodide (I(-)) and thiocyanate (SCN(-)) ions, using the first derivative of the ratio spectra obtained by mathematical treatment of the data. The method is based on the formation of mixed ligand complexes between benzohydroxamic acid (BHA), vanadium (V) and I(-) or SCN(-) and their extraction in ammonium quaternary salt dissolved in toluene. Calibration graphs for 2-9 mug/ml of I(-) and for 2-6 mug ml of SCN(-) were established by measuring the analytical signals at 376 nm for I(-) and at 400.6 nm for SCN(-). The method has been applied for determining both ions in waste water of an power station at ng/ml levels after a preconcentration step with C(18), without any separation step.