Kinetic Methods of Analysis

methods of qualitative and quantitative chemical analysis based on the relationship between the reaction rate and the concentration of the reactants. Kinetic mehods of analysis may be applied to the identification of both relatively large and small quantities of materials; catalytic reactions, in which the material to be identified is either consumed during the reaction or serves as its catalyst, are used in the latter case.

The sensitivity of kinetic methods of analysis based on such reactions is comparable to that of activation analysis. For example, the use of catalytic reactions makes possible the identification of manganese and cobalt at ion concentrations of 10^-5 and 10^-6 micrograms per milliliter, respectively. The reaction whose rate is used to determine the concentration is called the indicator reaction.

Reactions of the following types are usually used in kinetic methods of analysis: oxidation-reduction reactions (for example, oxidation of Mn²⁺ to MnO₄^- by hypobromite in an alkaline medium), isotope exchange reactions between ions of like charges (for example, Ce⁴⁺—Ce³⁺), substitution reactions in the inner coordination sphere of complex compounds [for example, replacement of CN^- in Fe(CN)₆^4- by water], and various heterogeneous catalytic reactions. The reaction rates are determined by titrimetric, gas-volumetric, photometric, polaro-graphic, and potentiometric methods. Measurements should be performed with careful regulation of the temperature of the reaction vessels, and high-purity reagents should be used, since the rate of catalytic reactions depends strongly on temperature and on the presence of impurities. Kinetic methods of analysis are used mainly to determine impurities in semiconductor elements and trace elements in biological materials and underground waters, as well as in the analysis of ultrapure reagents and materials.