EFFECTS OF ORGANIC MOBILE-PHASE MODIFIERS ON ELUTION AND SEPARATION OF BETA-BLOCKERS IN MICELLAR ELECTROKINETIC CAPILLARY CHROMATOGRAPHY

A study was made of the effect of organic modifiers (acetone, acetonit rile, ethanol, ethylene glycol, methanol and 2-propanol) in phosphate buffer (0.08 M) containing 15 mM cetyltrimethylammonium bromide as sur factant on the elution and separation of eleven common beta-adrenergic blocking agents. The amount of the modifier was varied from 0.1 to 10 .0% (v/v). At maximum addition, the organic solvents increased the vis cosity of the buffer solution as follows: acetone 16%, acetonitrile 9% , ethanol 26%, ethylene glycol 27%, methanol 20% and 2-propanol 29%. I n contrast to the migration time of the other beta-blockers, that of l abetalol was not increased by the addition of organic solvent to the b uffer solution. Rather, labetalol eluted more quickly with increase in the amount of modifier, and thereby effected changes in the elution o rder of the beta-blockers. The addition of modifiers also affected the resolution, and the best resolution values were achieved with the fol lowing amounts of organic solvent in MEKC buffer: acetone 0.1%, aceton itrile 0.1-0.5%, ethanol 5.0-7.5%, ethylene glycol 1.0-2.5%, methanol 5.0% and.-propanol 1.0-2.5% (v/v). No significant relationship was fou nd between the elution order and separation and the structure of the b eta-blockers in micellar electrokinetic capillary chromatography with an organic modifier in buffer solutions.