Spectrophotometric determination of thiocyanate by sequential injection analysis Original Research Article

A sequential injection analysis (SIA) system was developed for the spectrophotometric determination of thiocyanate as Fe(SCN)2+. The physical parameters (flow rate, sample and reagent volumes, holding coil and reaction coil internal diameter and length) which influence dispersion in a SIA system were optimized. The effect of the reagent concentration and nitric acid concentration (in the reagent solution and carrier stream, respectively), were also studied. Reagent consumption was effectively reduced by introducing the reagent as a zone into the nitric acid carrier stream, compared to flow injection analysis where the reagent itself is the carrier stream. The system is fully computerized and able to monitor thiocyanate in samples at 24 samples per hour with a relative standard deviation of <1.20% for samples and standards with thiocyanate concentrations above 10.0 mg l−1. The calibration graph is linear from 2.0 to 150.0 mg l−1 with a 3σ detection limit of 1.1 mg l−1. The system has been applied to the determination of thiocyanate in process solutions and waste waters.