Variable-Ionic Strength Kinetic Experiments in Drug Stability Studies

The dependence of the pseudo-first-order rate constant on the ionic strength for the alkaline hydrolysis of indomethacin has been obtained, for the first time, in a single kinetic experiment carried out by varying with time the salt concentration inside the reaction vessel. The kinetic profile obtained was processed using as a mathematical model the variable-parameter kinetic equation containing the Bronsted–Bjerrum equa-tion as the dependence function. The results are in good agreement with those obtained by the traditional method but the experimental time is reduced to about one-tenth.