Micellar liquid chromatographic separation of sulfonamides in physiological samples using direct on-column injection

A mixture of twelve sulfonamides was separated by micellar liquid chromatography (MLC) using sodium dodecyl sulfate (SDS) micelles and a hydrophilic endcapped C18 column. Retention behavior and selectivity pattern of sulfonamides in MLC were examined with the change of SDS concentration and volume fraction of an organic modifier (1-propanol). The suitable condition was found to be 0.070 M SDS and 6.0% 1-propanol for the separation of these twelve sulfonamides. Under this condition, the isocratic separation of the sulfonamides was achieved within 15 min with a relatively high column efficiency for MLC (ca. 7000 plates/25 cm column). Retention times of these twelve sulfonamides were found to be very repeatable, which is due to the highly reproducible retention behavior in MLC. The same twelve sulfonamides were successfully separated in the spiked physiological fluids (human urine and cow milk) through direct on-column injection by MLC.