Characterization of open tubular enzyme reactors and polymer layer open tubular columns for liquid chromatography

Abstract

The structure, thickness and characteristics of liquid chromatography (LC) column materials are central factors regarding their performance. However, miniaturized capillaries (sub 20.0 μm inner diameter, typically used for small sample analysis) are difficult to characterize. The main goal of this work was to develop a simple, yet accurate, electrochemical impedance spectroscopy (EIS) method for characterization of the polymer layers of narrow open tubular (OT) columns. In situ prepared polymerized capillaries (poly(styrene-co-divinylbenzene) and poly(2-hydroxyethyl methacrylate-co-2-vinyl-4,4-dimethyl azlactone) OT capillaries were characterized. The developed EIS method proved simplicity in terms of providing layer thickness determinations compared to determination by scanning electron microscope (SEM). In addition, screening of the polymer layer homogeneity throughout the capillaries was simplified by EIS. The porosity of the polymer layer OT columns was investigated by EIS, SEM and sample loading capacity measurements (using LC). Under pore-blocking conditions, none of the polymerized capillaries could be shown to have porosity, so it was assumed that a thin polymer layer is beneficial for both types of capillaries in order to provide a high surface area, i.e. more available functional groups. EIS methods have not been published for capillary characterization by date. However, the method showed promising results and has great potential for future applications regarding characterization and preparation optimization of polymerized capillaries.