Packed-column supercritical fluid chromatography for the purity analysis of clevidipine, a new dihydropyridine drug.

In this paper we describe a packed column supercritical fluid chromatography method that can be used for the analysis of a new dihydropyridine substance. The method is based on methanol-modified carbon dioxide as the mobile phase and Hypersil bare silica as column support at a column temperature of 50 degrees C and 150 bar as back pressure. Using an adjusted methanol gradient the most likely by-products can be separated and detected (240 nm) within 13 min. Occasionally the column needed treatment with 4 mM citric acid in the methanol modifier in order to give a narrow peak of an acidic analogue. The present method can detect analogues at the 0.1% (w/w) level. The precision at this level for one of the analogues was 5.9% RSD. This method shows a higher selectivity than a corresponding reversed-phase liquid chromatographic method.