We employ reversed-phase ion-pair high-performance liquid chromatography to quantitatively characterize the oxidation kinetics of thiourea oxidation by hydrogen peroxide. The HPLC technique makes it possible to monitor the concentrations of a variety of sulfur-containing species with different oxidation states and to elucidate the relative phase relations among them. The experimental results are in good agreement with simulations from an 8-step reaction mechanism.Oxidation reactions of sulfur(-II) compounds such as thiourea (TU) can be quite complex, yielding species with oxidation states ranging from -1 to +6. [1][2][3][4] Researchers have investigated the dynamics of these reactions from several perspectives: First, the mechanism of the nonlinear reaction between various oxidants and TU is of considerable interest for explaining such exotic phenomena as oscillations, chaos and spatiotemporal patterning seen in such systems. [5][6][7][8] Secondly, the physiological effects of thiourea oxides have attracted scientists to explore the biofunction of these sulfur species. 9,10 Finally, sulfur abatement is a key technology in alleviating environmental pollution. 4,11 To tackle the above challenges, understanding the basic sulfur chemistry, i.e., the kinetics and mechanism of the changes of sulfur oxidation state, is essential. A major obstacle is the difficulty of tracking the different oxidation states of sulfur during the reaction. Standard methods of chemical analysis, which typically involve multiple steps and intensive experimental efforts, generally fail for most intermediates in these systems. UV-visible spectroscopy cannot quantify the sulfur intermediates, because their absorption spectra overlap.Thiourea (λ max )196 nm and 236 nm, ε ) 11273 and 11048 M -1 cm -1 ), is a typical sulfur(-II) compound that is widely used in industrial production. Its oxidation involves the formation of such reagents as formamidine disulfide (TU 2 , λ max ) 218 nm, ε ) 21523 M -1 cm -1 ), thiourea dioxide (TUO 2 , λ max ) 269 nm, ε ) 489 M -1 cm -1 ), thiourea trioxide (TUO 3 , λ max ) 202 nm, ε ) 7295 M -1 cm -1 ), sulfite (λ max ) 205 nm, ε ) 3548 M -1 cm -1 ) and sulfate. The overlap of the UV-vis absorption spectra prevents simultaneous detection of these intermediates. Using high-performance liquid chromatography (HPLC), Grigorova and Wright 12 separated thiourea, formamidine disulfide and cyanamide from a hydrogen peroxide-thiourea reactive mixture. In this report, we describe a new approach for directly tracking the evolution of multiple sulfur species and performing kinetic analysis.We employ reversed-phase ion-pair high-performance liquid chromatography to quantitatively characterize the oxidation kinetics of TU oxidation by hydrogen peroxide. Indeed, the capability to monitor simultaneously the time evolution of multiple sulfur species allows us not only to study the reaction kinetics but also to characterize the relative phase relations of the different species. Our results demonstrate that HPLC is a unique and effec...
