Attempt to define the role of the length of the packed section in capillary electrochromatography

The problems of memory effects when using ion-exchange columns have been ad dressed. Studies on capillaries packed with a strong cation-exchange (SCX) material have shown voltage conditioning to be sufficient to produce an equ ilibrated column and reliable results. Storage in acetonitrile-water (80:20 , v/v) for six weeks had no detrimental effect on the column performance. C olumns used for capillary electrochromatography typically consist of an ope n and packed section, each contributing to the electroosmotic flow (EOF). S tudies performed on SCX columns of varying proportions of packed section (2 5-100% of the total length) showed that at pH 7.5 the field strengths are s imilar in both sections and the linear velocity changes little with the pac ked section length. In contrast, at pH extremes the field strengths were gr eater in the packed section and the velocity decreased with length. A compa rison of the conductance ratios for C-18 and SCX columns indicated little d ifference between them at high pH. However, at low pH results were not rout inely obtained for the C-18 column, whereas the short SCX column gave rise to far higher EOF than expected. (C) 1999 Published by Elsevier Science B.V . All rights reserved.