Methods Based on Chemical Kinetics
The earliest examples of analytical methods based on chemical kinetics, which date from the late nineteenth century, took advantage of the catalytic activity of en- zymes. Typically, the enzyme was added to a solution containing a suitable sub- strate, and the reaction between the two was monitored for a fixed time. The en- zyme’s activity was determined by measuring the amount of substrate that had reacted. Enzymes also were used in procedures for the quantitative analysis of hy- drogen peroxide and carbohydrates. The application of catalytic reactions contin- ued in the first half of the twentieth century, and developments included the use of nonenzymatic catalysts, noncatalytic reactions, and differences in reaction rates when analyzing samples with several analytes.
Despite the variety of methods that had been developed, by 1960 kinetic meth- ods were no longer in common use. The principal limitation to a broader accep- tance of chemical kinetic methods was their greater susceptibility to errors from un- controlled or poorly controlled variables, such as temperature and pH, and the presence of interferents that activate or inhibit catalytic reactions. Many of these limitations, however, were overcome during the 1960s, 1970s, and 1980s with the development of improved instrumentation and data analysis methods compensat- ing for these errors.