Silver(I)-mediated separations by capillary zone electrophoresis and micellar electrokinetic chromatography:...

The addition of Ag(I) to the run buffer in capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC), containing sodium dodecyl sulfate, applies the principles of argentation chromatography to electrophoretic separations and is termed "argentation electrophoresis". This technique is shown to provide a complementary method to CZE and MEKC for the separation of specific types of solutes that selectively complex with Ag(I). Baseline resolution in the CZE separation of nine sulfonamides is achieved by the addition of 50 mM silver nitrate to the run buffer. Retention mechanisms in MEKC separations can also be manipulated by the addition of Ag(I) to the micellar solution. Only slight resolution of a pair of sulfonamides was achieved under normal MEKC conditions. Upon the addition of Ag(I) to the mobile phase containing SDS micelles, baseline resolution of the compounds is shown. The retention order and resolution of five sulfonamides changed significantly when 25 mM Ag(I) was added to the SDS-containing buffer. The use of Ag(I) addition in MEKC is also applied to the separation of various other compounds that show selectivity toward Ag(I) complexation, including S-containing heterocycles and vitamin D compounds. The effect of the addition of Ag(I) on the elution range in MEKC is also investigated. A steady increase in the elution range is seen upon increasing the concentration of Ag(I). With a constant percentage of organic modifier (15%), the addition of higher concentrations of silver nitrate (25-50 mM) results in elution ranges greater than 12. The results using Ag(I) as buffer additives in MEKC are also compared to studies utilizing a mixed counterion surfactant of sodium/silver dodecyl sulfate.