Capillary electrophoresis applied to the analysis of pharmaceutical compounds

Abstract

Abstract Separations by capillary zone electrophoresis (CZE) in plain, uncoated fused silica capillaries were compared with those in electroendosmosis‐free coated capillaries. For small ions, exemplified by some anti‐inflammatory drugs, resolution and analysis times were comparable in the two types of capillaries. The advantage of the coated capillary was that it predictably eluted all negative analytes regardless of electrolyte pH. The uncoated capillary, on the other hand, allowed separation of both positive and negative species in one run, provided that the electroendosmotic flow was sufficiently high to elute all negatively charged analytes. Because electrolyte conditions were established that eluted all sample analytes, subsequent analyses were performed in uncoated capillaries. Antibiotics such as sulfonamides, cephalosporins, and penicillins were separated by zone electrophoresis. Optimal separation conditions were established by varying the pH and ionic strength of the electrolyte. For the separation of structurally similar peptides and barbiturates, micellar electrokinetic capillary chromatography (MECC) was the method of choice because the structural differences conferred differences in hydrophobicity. The feasibility of using CZE in pharmaceutical analysis was shown in the evaluation of over‐the‐counter pain, cold, and allergy medications. These typically gave relative standard deviations of 1% for retention times and 3% for peak areas.