Determination of free bile acids in pharmaceutical preparations by packed column supercritical fluid chromatography

A method was developed for the baseline separation of common free bile acids by supercritical fluid chromatography. A phenylbonded silica column, with UV detection at 210 nm, and carbon dioxide modified with methanol as the mobile phase were used. The influence of the stationary phase, modifier concentration, temperature, column pressure, and modifier identity on retention was studied. The separation obtained is at least eight times faster than those achieved for similar mixtures by the existing chromatographic techniques. This new procedure is applicable to the assay of ursodeoxycholic acid and chenodeoxycholic acid in capsule and tablet formulations. Individual dosage forms were disintegrated in methanol and an aliquot of the resulting suspension was filtered for the supercritical fluid chromatographic analysis. The method is rapid, accurate, and reproducible.