Species Tracking And Kinetic Analysis In The Oxidation Reaction Of Thiocyanate

The hydrogen peroxide/thiocyanate system (pH=8.86-10.18) andchlorite/thiocyanate system (pH=6.10-7.10) were studied in the thesis. Capillaryelectrophoresis (CE) and high performance liquid chromatography (HPLC) were usedto track the species simultaneously.The species in the reaction have weak ultraviolet absorption in the range of200nmto400nm. Thus indirect ultraviolet detection method was used to detecte anions inthe system. The analysis and separation conditions of CE were optimized by adjustingthe composition of the background electrolyte (pH and electroosmotic flow modifier)and the separation voltage. By modifying the composition and the pH of mobile phase,an HPLC optimized separation method was developed. With the optimized conditions,each anion in the oxidation reaction of SCN-can be completely separated in less than8minunits and concentration calibration curves can be obtained.The H2O2/SCN-reaction was reinvestigated by means of CE and HPLC. It has beenclearly demonstrated that OxSCN-(where x=1,2and3) cannot be accumulated indetectable amount. The reaction rate increases with the concertration of ClO2-andSCN-increasing; the the pH has no effect on the reaction rate.It has been shown thatthe overall rate law is first-order with respect to both reactants, but no pH-dependencewas observed within the pH range of8.86-10.08. Buffers strongly affect the rate ofreaction in the order of ammonia, phosphate, carbonate and borate. A3-step kineticmodel has been proposed to fit all the concentration–time curves simultaneously atfive different pHs (pH8.86,9.18,9.53,9.84and10.08) demonstrating the powerfulcombination of the experimental techniques CE and HPLC with simultaneousevaluation of kinetic curves. The average deviation was found to be4.9%.By varying the initial concentration of the reactants and the pH of the reactionbuffer solution, the effects of pH and the initial concertration of ClO2-on theClO2-/SCN-system were studied by CE. The results indicated that several products,including chloride, cyanate and sulfate can be detected; the reaction rate increases asdecreasing the pH value of the solution and increasing the initial concertration ofClO2-. The ultraviolet spectrophotometry result shows that ClO2generates when SCN-is consumed. Combined with previous studies and the results of this experiment,mechanism of the ClO2-/SCN-reaction can be proposed.