Freeze sample enrichment highly adaptable to capillary electrophoresis

Abstract

We propose a novel sample enrichment scheme particularly suitable for capillary electrophoresis (CE). This method is based on the principle of freeze concentration. When an aqueous solution is frozen, solutes are expelled from the ice crystal phase. When an inert dopant is added to a sample, an unfrozen dopant solution is accumulated along ice grain boundaries. Analytes are also enriched in the liquid phase during this process. The liquid phase volume and in turn the enrichment factor can be controlled by adjusting the dopant concentration in an original sample solution and freezing temperature. The liquid volume is, in general, so small that it is difficult to separate it from the ice matrix for the following analysis. However, its application to CE is possible because a sample volume of nL is large enough for this method. Glycerol is a suitable dopant for the present purpose. Although disagreements between theoretical and experimental enrichment factors have been found, the addition of a low concentration of LiCl as a supporting electrolyte allows better predictions of enrichment factors. The enrichment by a factor of 1000 is possible by simple freezing of samples, and in addition, the simultaneous concentrations of anions and cations are also demonstrated.