Apparatus

In the previous chapter, we developed a set of conceptual and mathematical tools for analyzing the models and experimental data that form the subject matter of nonlinear chemical dynamics. Here, we describe some of the key items of experimental apparatus used to obtain these data so that the reader can better appreciate the results discussed in the following chapters and can learn how to begin his or her own investigations. The first several sections are devoted to measurements of temporal behavior, with emphasis on the techniques used to monitor reactions in time and on the reactors in which these reactions are studied. The final section focuses on the study of spatial patterns and waves in chemical systems. It is possible, by methods that we shall discuss later, to reconstruct the qualitative dynamics of a system from the measurement of only a single variable. However, the more species whose concentrations can be measured, the easier it is to elucidate a mechanism and the more rigorously that mechanism can be tested. The most impressive study of multiple species in a chemical oscillator was carried out by Vidal et al. (1980), who were able, by a combination of techniques, to monitor the concentrations of Ce4 + , Ce3+ , Br2, Br-, bromomalonic acid, O2, and CO2 in the BZ reaction. In the following sections, we will look at the most widely employed techniques: spectroscopic and potentiometric methods. In principle, and occasionally in practice, essentially any technique that can be used to detect changes in concentration can be utilized to monitor the systems that we are interested in. Approaches that have been employed to date include polarography, high-pressure liquid chromatography, and calorimetry. If there are absorbing species, ultraviolet and/or visible (UV/vis) spectroscopy offers rapid response time and high sensitivity for monitoring concentrations, particularly if the species of interest have spectra with relatively little overlap. Measurements can be made in a cuvette placed in a standard UV/vis spectrophotometer, but this configuration has several limitations.