OPTIMIZATION OF RESOLUTION OF 13 DIURETICS IN CZE BY CONTROLLING CAPILLARY LENGTH AND ELECTROOSMOTIC FLOW VELOCITY

The separation of diuretics in CZE can be further improved by controlling the capillary length and the analysis times independently, while other parameters are kept constant. This can be done by using a modifier in the electrolyte solution which has a strong effect on the electroosmosis, but negligible effect on the selectivity of the electrolyte system. In this work, [Cu(NH3)(4)](2+) was used at low concentration (O - 140 mu M) to control the electroosmotic flow velocity (v(eo)) and hence the analysis time, determined as the migration time of the last migrating compound (t(fin)) With other parameters, especially V, kept constant, the use of shorter capillaries enables the use of high electric field strength for the separation. The use of quadratic regression models proved to be an effective way to study the effect of L(tot) and t(fin) on the R(s) of each analyte pair. The theoretical values for the separation of peak maxima correlated well with the values predicted by the empirical regression models. The actual band broadening was much stronger, however, than what was predicted by the overly simplified theoretical calculations based on the electrophoretic mobilities as well as the self diffusion coefficients of the diuretics, determined by the two marker technique. Further study is needed on theoretical modelling of the band broadening, while the use of regression models and desirability functions provided a convenient way to determine the optimal conditions. The results showed that independent control of L(tot) and t(fin) offers an effective way to further optimize capillary electrophoretic separation. This method should prove important in cases where sufficient separation is difficult to achieve.