ELECTRICAL-CONDUCTIVITY AS A TOOL FOR CHARACTERIZING PACKING STRUCTURE IN CAPILLARY ELECTROCHROMATOGRAPHY

Electroosmotic flow in packed capillary electrochromatography (CEC) ma y deviate considerably from the assumed flat velocity profile due to t hermal and electrical double-layer overlap effects occurring in sectio ns of poor permeability. It is thus highly desirable to devise a metho d for proper characterization of the flow permeability of packed colum ns used in CEC. Here we describe such a method which is based on the w ell-known relationships between the electrical properties and structur al factors of a porous medium. The approach involves the measurement o f electrical conductivity for columns with and without chromatographic packing and the calculation of relative conductivity lambda. The lamb da value is then used to indicate the flow permeability of the packed column. Experiments with three well-packed capillary columns found the lambda values ranging from 0.31 to 0.34. These results appear to conf irm the theoretical prediction that relative conductivity is essential ly a structural constant and thus independent of column dimensions, pa rticle size, and field strength.