Separation of opium alkaloids by carbon dioxide sub- and supercritical fluid chromatography with packed columns. Application to the quantitative analysis of poppy straw extracts.

The optimization of the separation of seven opium alkaloids by sub- and supercritical fluid chromatography (SFC) using packed columns and carbon dioxide as the primary mobile phase was studied. The influence of aminated polar modifiers on bare and aminopropyl-bonded silica was investigated. It was found that the presence of an amine in the mobile phase could enhance the retention of alkaloids on aminopropylsilica. Various separation schemes were possible depending on the type of analysis needed. An aminopropyl-bonded silica used with a carbon dioxide-methanol-triethylamine-water mixture (82.95:16.25:0.50:0.30, w/w) gave a very rapid separation (2 min). A bare silica with a carbon dioxide-methanol-methylamine-water mixture (83.37:16.25:0.15:0.23, w/w) gave longer analysis (10 min) but a higher resolution. This last procedure was applied to a poppy straw extract and to the determination of three alkaloids of interest after a peak purity study using a diode-array UV detector. For these alkaloids, SFC appears to be a promising technique for the routine analysis of opium alkaloids.