pH Oscillations in the Bromate−Sulfite−Marble Semibatch and Flow Systems

Abstract

A self-accelerating oxidation of an unbuffered aqueous sodium sulfite-hydrogen sulfite solution by sodium bromate and a selective removal of the hydrogen ion by solid marble chips from the reaction mixture have been used to construct an oscillatory system. The system exhibits large-amplitude oscillations between pH 3.5 and 7.5 at 25.0°C in a continuous-flow stirred tank reactor and in a semibatch configuration. The shape, the periodic time (from 10 min to 2 h), and the region of oscillations can be controlled by using different amounts and grade size of marble. A simple reaction scheme, consisting of the protonation equilibria of SO 3 2-and HSO 3 -, the oxidation of HSO 3 -and H 2 SO 3 by BrO 3 -, and a removal of H + by the CaCO 3 in marble in the form of HCO 3 -has successfully been used to simulate the observed dynamical behavior.

Ionizable drugs and pH oscillators: Buffering effects

“…A proposed mechanism for the RH oscillator involves three relatively slow reactions 17,20,22 that are essentially irreversible in the CSTR configuration. Equations R1-R3 list these reactions, along with expressions for reaction velocities, V i , taken from the literature.…”

“…Because the first of these steps is rate limiting, reaction R1 is apparently first order in HSO 3 The rate constants for reactions R1 and R2 are published by RH 17 as…”

“…Outside these conditions, the system may find stationary points at high or low pH. 17,20 For example, when flow is extremely slow, the series of steps outlined above can run their course completely, with virtually all produced H þ consumed by the marble reaction, and pH settles to a high value.…”

“…Moreover, the period of oscillation should be tuned to physiologic demand, and many pH oscillators, including the mixed Landolt oscillator, have rather specific oscillation frequencies. Since the initial work of Giannos et al, Rá bai and Hanazaki (RH) 17 constructed a relatively simple bromatesulfite-marble pH oscillator that exhibits longperiod oscillations in which periodicities are more readily adjusted. The ingredients of this oscillator are also somewhat less toxic.…”

“…For this study, we used the RH oscillator because of its relative simplicity, its controllable periodicity, and because Rá bai and Hanazaki have proposed a mathematical model that accounts semiquantitatively for its behavior. 17,20 This model provides a basis for mathematical analysis of the observed drug effects on the oscillator. In section II of this article, we report results of experiments in which drug concentration and pK D were systematically varied.…”