Indirect conductivity detection in size exclusion chromotography of small molecules

Abstract

Size Exclusion Chromatography (SEC) is a liquid chromarographic technique used for the characterization of polymers and polymer related materials and also for the separation of small molecules. The major drawback of SEC is the lack of availability of a universal and true mass detector for providing a homogeneous response for all samples. Indirect detection methods have demonstrated to supply an alternative way to obtain a universal, sensitive and mass response in liquid chromatography.

This research evaluated the indirect conductivity detection method for the size exclusion chromatographic separation of small molecules. Several studies were developed in order to understand the performance of this novel indirect detection mode. The evaluation of the initial experimental conditions snowed a dependence on the response, efficiency and elution time with the concentration of the conductivity probe added to the mobile phase. The SEC calibration curves developed for a series of standards indicated that selected conditions do not affect the separation by size. Response factors revealed a slight increase with molecular weight when they are expressed in volume or mass. Limits of detection were in the order of 20 nanoliters for small molecules. The effect of different conductivity probes on the separation and response was also studied. A modification of the original detector cell design resulted in improvement in the signal to noise ratio.