Salt effects in capillary zone electrophoresis V. Adsorption and retentionof electrically neutral analytes

Two electrically neutral analytes previously observed to be separated from the neutral marker in capillary zone electrophoresis (CZE) experiments [sul phanilamide (SAA) and sulphaguanidine (SGW)] have been examined to determin e the basis for separation. The degree of separation increases markedly wit h buffer concentration and improves with increasing field strength. On the basis of the apparent electrophoretic mobilities in conventional CZE, migra tion times in a zero EOF environment were calculated for SAA, SGW and six o ther sulphonamides that were known to be ionized. These six markers were us ed to test the legitimacy of our predictions and to correct for small discr epancies between the predicted and observed migration times. It was conclud ed that SAA and SGW have negligible electrophoretic mobilities and that the y are retained in the electrical double layer close to the capillary wall. A mechanism for adsorption is proposed and the generality of the phenomenon is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.