EFFECT OF ALKALI-METALS AND METAL-AMMONIA COMPLEXES ON ELECTROOSMOSIS, EFFECTIVE-FIELD STRENGTH, AND RESOLUTION IN THE SEPARATION OF DIURETICS BY CZE

The counter ion in CZE separation systems affects resolution, effectiv e field strength and electroosmosis. Alkali metals (lithium, sodium, p otassium, and cesium), the ammonium ion, and several complexes of meta ls with ammonia ([Ag(NH3)2]+, [Cu(NH3)4]2+, [Zn(NH3)4]2+, [Cd(NH3)4]2, [Ni(NH3)6]2+, and [Co(NH3)6]2+) have been studied for their effect o n the separation of diuretics. With the alkali metals the electroosmot ic flow velocity decreased and the effective field strength and resolu tion increased as the hydrated radius of the alkali metal decreased. A ll the metal-ammonia complexes except that with silver greatly reduced the electroosmotic flow velocity (v(eo) and had only a slight effect on the effective field strength (E(eff)). Because these complexes had a negligible effect on the ionic strength of the buffer, they enabled high separating power to be maintained during the separation, and henc e the use of more energy in the separation system. This yielded better resolution of the compounds, but the analysis time was then compromis ed. A simultaneous reduction in capillary length and v(eo) while maint aining the high voltage enabled increased resolution without an increa se in analysis time. The ability to control v(eo) by adding small conc entrations (< 100 muM) of metal complexes to the buffer solution makes it possible to adjust the analysis time and capillary length independ ently while employing high separation power.