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 addressed. Studies on capillaries packed with a strong cation-exchange (SCX) material have shown voltage conditioning to be sufficient to produce an equilibrated column and reliable results. Storage in acetonitrile-water (80:20, v/v) for six weeks had no detrimental effect on the column performance. Columns used for capillary electrochromatography typically consist of an open and packed section, each contributing to the electroosmotic flow (EOF). Studies performed on SCX columns of varying proportions of packed section (25-100% of the total length) showed that at pH 7.5 the field strengths are similar in both sections and the linear velocity changes little with the packed section length. In contrast, at pH extremes the field strengths were greater in the packed section and the velocity decreased with length. A comparison of the conductance ratios for C-18 and SCX columns indicated little difference between them at high pH. However, at low pH results were not routinely 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.