title: Microemulsion electrokinetic chromatography of corticosteroids. Effect of surfactants and cyclodextrins on the separation selectivity.
abstract: The separation of neutral hydrophobic corticosteroids (cortisone, cortisone acetate, hydrocortisone, hydrocortisone acetate, prednisolone and prednisolone acetate) by microemulsion electrokinetic chromatography (MEEKC) was studied. In the preparation of microemulsion, heptane was the solvent, n-butanol the co-surfactant and, as anionic surfactants, sodium dodecyl sulfate (SDS) or taurodeoxycholic acid sodium salt (STDC) were employed. Using an acidic running buffer, (phosphate pH 2.5) a strong suppression of the electroosmotic flow (EOF) was observed; this resulted in a fast anodic migration of the analytes partitioned into the negatively charged microemulsion droplets. Under these conditions, STDC showed better separation of corticosteroids than the conventional SDS; however, the use of a single anionic surfactant did not provide the required selectivity. The addition of the neutral surfactant polyoxyethylene glycol octadecyl ether (Brij 76) significantly altered the migration of each analytes allowing a better tuning of separation; however, in order to obtain adequate resolution between couples of adjacent critical peaks, the addition of neutral cyclodextrins (CDs) was found to be essential. This apparently complex system (CD-MEEKC), was optimized by studying the effect of the most important parameters affecting separation: STDC concentration, Brij 76 concentration, nature and concentration of cyclodextrins. Following a rational step-by-step approach, the optimised conditions providing the complete separation of the analytes were found to be: 4.0% STDC, 2.5% Brij 76, 6.6% n-butanol, 1.36% heptane and 85.54% of a solution 5 mM beta-CD in 50 mM phosphate buffer (pH 2.5). The optimized system was preliminary applied to the detection of corticosteroids related substances at impurity level and it could be considered a useful orthogonal alternative to HPLC methods.
authors: Dipartimento di Scienze Farmaceutiche, Alma Mater Studiorum--Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy.
authors: Romeo
authors: R
authors: Pomponio
authors: Roberto
authors: R
authors: Gotti
authors: Jessica
authors: J
authors: Fiori
authors: Vanni
authors: V
authors: Cavrini
mesh_terms: D000305:Adrenal Cortex Hormones / Q000302:isolation & purification*; D020374:Chromatography, Micellar Electrokinetic Capillary / Q000379:methods*; D003348:Cortisone / Q000031:analogs & derivatives / Q000302:isolation & purification; D003505:Cyclodextrins; D004655:Emulsions; D011239:Prednisolone / Q000031:analogs & derivatives / Q000302:isolation & purification; D013501:Surface-Active Agents; D013657:Taurodeoxycholic Acid
chemical_list: D000305:Adrenal Cortex Hormones; D003505:Cyclodextrins; D004655:Emulsions; D013501:Surface-Active Agents; D013657:Taurodeoxycholic Acid; C009935:prednisolone acetate; D011239:Prednisolone; D003348:Cortisone