Front propagation in the bromate-sulfite-ferrocyanide-aluminum (III) system: Autocatalytic front in a buffer system

We study the propagation of pH fronts in a narrow, pseudo-one-dimensional strip of gel containing bromate, sulfite, ferrocyanide and aluminum ions. The front propagation speed v decreases with [ Al3+] as 1/v=1/v0+c[Al3+], where c is a constant. We determine the diffusion coefficients of protons and ferricyanide ions and find that Al(OH)3 loaded in agarose or acrylamide gels binds protons reversibly, thereby slowing the propagating fronts without significantly affecting the diffusion of ferricyanide ions. We present a model that qualitatively reproduces the experimental behavior, and we suggest some general principles governing autocatalytic fronts in buffered systems.