WALL ADSORPTION IN CAPILLARY ELECTROPHORESIS - EXPERIMENTAL STUDY AND COMPUTER-SIMULATION

A semi-quantitative model based on non-linear equilibrium chromatography coupled with diffusion-driven sample sorption at the wall was developed to account for and predict potential binding of an analyte to the wall in It was then used for computer simulation of sample concentration profiles corresponding tal conditions (sorption kinetics, capillary length, wall capacity and initial sample concentration). The binding phenomena were also studied experimentally by means of analysis of the sample peak shape (including peak height and area). Contrary to expectations, it was found that the interaction of small monovalent cations with the charged capillary wall does not lead to strong adsorption, as the sample mass is not lost during experiment and the peak shape remains close to that which one could expect in the absence of interaction. For polycations (e.g., poly-L-histidine) at any pH above 3, sample adsorption is evident by a lack of return of the baseline to zero, after peak passage, with progressively higher levels at progressively increasing buffer pH values. Upon several runs with a polycation, the surface charge on the wan changes from negative to positive, as evidenced by reversal of electroosmotic flow. However, it was discovered that even under these last conditions, the sample-wall interaction was rather strong. The influence of NaOH washing and the addition of different substances (urea, Tween-20, sodium chloride) on adsorption was studied. The comparison between simulated results and experimental data is discussed.