Coaxial Dielectric Spectroscopy as an In-Line Process Analytical Technique for Reaction Monitoring.

The suitability of broadband dielectric spectroscopy (DS) as a tool for in-line (in situ) reaction monitoring is demonstrated. Using the esterification of 4-nitrophenol as a test-case, we show that multivariate analysis of time-resolved DS data-collected across a wide frequency range with a coaxial dip-probe-allows reaction progress to be measured with both high precision and high accuracy. In addition to the workflows for data collection and analysis, we also establish a convenient method for rapidly assessing the applicability of DS to previously untested reactions or processes. We envisage that, given its orthogonality to other spectroscopic methods, its low cost, and its ease of implementation, DS will be a valuable addition to the process chemist's analytical toolbox.