Sequential Oscillations in the Ferroin-Catalyzed Belousov-Zhabotinsky Reaction: The Case of Oxalacetic Acid Substrate

A novel sequential, dual-frequency oscillations were found in the Ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction when oxalacetic acid was employed as the substrate. The reactions were followed spectrophotometrically at a wavelength of 490 nm. The reaction revealed a "trumpet"-shape oscillation pattern at relatively low oxalacetic acid (OAA) concentration, while at higher OAA concentration oscillation splits into a low and a high frequency region separated by a short second "induction period". Furthermore, the effect of the initial reactant concentrations such as those of bromate, ferroin, sulfuric acid and oxalacetic acid were also investigated. It was observed that oscillation started to appear at shorter reaction time upon increasing the concentrations of bromate and ferroin, while it changed according to a minimum curve as a function of sulfuric acid concentration. However, in the case of OAA increasing its concentration resulted in increasing "induction periods", i. e., the onset of oscillation shifted to longer reaction times. The origin of the "trumpet"-shape oscillation patterns and the two-phase oscillation was interpreted by means of the Oregonator model.