    Investigation of Solute–Wall Interactions in Separation of ( ) Uranium VI and Lanthanides by Capillary Electrophoresis Using On-Capillary Complexation with Arsenazo III Miroslav Macka, Pavel Nesterenko, Paul R. Haddad Department of Chemistry, Uni  ersity of Tasmania, GPO Box 252C, Hobart, Tasmania 7001, Australia Ž . Abstract: The separation of uranium VI and lanthanides by capillary elec- Ž . trophoresis CE in the form of anionic complexes with arsenazo III in aqueous background electrolytes was found to depend strongly on the chemistry of the surface of the internal wall capillary. A recently developed separation scheme for these complexes was used as a model for the evaluation of the solute  wall interactions in which a number of capillaries with different charge, polarity, hydrophobicity, and structure of bonded layer of the internal wall surface were Ž . compared. Pretreatment of bare fused silica FS capillaries with acid or alkali was found to be very important: After treatment with sodium hydroxide, the observed adsorption of the analytes was higher than for untreated FS capillaries. Capillaries with a chemically bonded neutral hydrophilic layer also showed considerable adsorption of the analytes. Strong adsorption of the negatively charged amphiphilic molecules of ligand or metal complexes was observed for coated capillaries with a positively charged wall, as well as for capillaries with a hydrophobic wall. Dynamic coating of the bare FS capillary with Carbowax 20M provided better peak shapes and shorter migration times owing to suppression of electroosmotic flow and blockage of adsorption sites on the internal capillary wall. The best separation of complexes of uranium and lanthanides with arsenazo III was achieved using an Ž untreated bare FS capillary dynamically coated with Carbowax 20M 350,000 . theoretical plates for uranyl and 63,000 theoretical plates for lanthanum .  1999 John Wiley & Sons, Inc. J Micro Sep 11: 1 9, 1999 Key words: capillary electrophoresis; solute  wall interactions; adsorption; metal- lochromic ligands; metal complexes INTRODUCTION Ž . It is well known in capillary electrophoresis CE that an interaction of a solute with the capillary wall Ž . solute adsorption can have a detrimental effect on the solute’s peak shape andor its quantification, depending on the adsorption isotherm and sorp-   tiondesorption kinetics 1,2 . Solute adsorption may also lead to baseline disturbances or increased noise; and in addition, an irreversible adsorption of a so- lute is likely to cause a change of the  potential of the wall and consequently of the electroosmotic flow Ž . EOF . This can adversely affect the reproducibility of migration times and peak areas, and consequently  the precision of analysis 3 . Although the ideal case Correspondence to: P.R. Haddad Contract grant sponsor: Australian Research Council Contract grant sponsor: Department of Industry, Sci- ence, and Tourism, Australia of a complete absence of solute  wall interactions may never be achieved, those interactions which are present can often be suppressed effectively by judi- Ž . cious choice of the background electrolyte BGE composition and the capillary wall chemistry, as nu- merous examples of separations of proteins and   other biopolymers have shown 4  8. Although metal ions and metal complexes are generally known to adsorb onto the surface of silica  particles 9 , the question of the extent to which they Ž . adsorb onto fused silica FS CE capillaries has   gained only limited attention. Salomon et al. 10   and Dickens et al. 11 investigated the adsorption of group I and II metals onto the FS capillary inner wall and the influence of this adsorption upon the   EOF. Gassner et al. 12 showed the adsorption of Ž . Fe III onto the FS and also the detrimental effect on the separation of some analytes owing to their Ž . complexation with the adsorbed Fe III . Macka et al. Ž. Ž . J. Microcolumn Separations , 11 1 1  9 1999  1999 John Wiley & Sons, Inc. 1 CCC 1040-768599010001-09