Use of System Peaks in Liquid Chromatography for Continuous Online Monitoring of Chemical Reactions

Abstract

System peaks, which occur in chromatophy with multicomponent mobile phases, car be used for the continuous on-line monitoring of chemical reactions. The mobile phase reservoir is the chemical reactor, and the mobile phase, which contains the reaction mixture, is recycled continuously through the column. At predetermined times, a neat solvent, normally the solvent of the reaction, is injected. The system peaks that result reflect the status of the reaction. We describe here the use of system peaks to follow the progress of two reactions: titration of aniline and hydrolysis of aspirin. In the case of aniline titration, we obtained a titration curve by plotting the capacity ratio of the aniline system peak versus the acid volume added during the titration. The experimental endpoint agreed very well with the theoretical equivalence point. A plot of the capacity factor as a function of mobile phase pH behaves similarly to such plots in conventional chromatography. In the hydrolysis of aspirin, we followed the progress of the reaction by monitoring the formation of salicylic acid via its system peak. The data allowed us to calculate the apparent hydrolysis rate constant. The value obtained is in excellent agreement with literature values