Stopped-flow kinetic determination of thiocyanates and thiosulphates with the application of iodine-azide reaction

A stopped-flow method for the determination of thiocyanates and thiosulphates by means of iodine-azide reaction has been elaborated. Spectrophotometric detection was applied to monitor the decrease of the absorbance of the iodine¯starch complex at 595 nm within a few seconds. It was found that the rate of decrease near zero reaction time is related to the concentration of the sulphur compounds. The initial-rate method for pseudo-first-order reaction conditions has been successfully developed for the determination of traces of thiocyanates and thiosulphates. Under the optimum reaction conditions established for stopped-flow determination, the linear calibration range depends on the concentration of iodine in the iodine-azide solution applied and for thiocyanate is from 0.03 to 15 mug ml-1 (R.S.D is from 3.6 to 1.2%) and for thiosulphate is from 0.05 to 11 mug ml-1 (R.S.D. is from 2.7 to 1.8%).