Partitioning between organic solvents is used in the extraction of analytes from oily excipients such as in the extraction of steroid creams prior to HPLC analysis. The most commonly used systems are methanol/hexane, aqueous ethanol/hexane or acetonitrile/hexane. In the case of analysis of corticosteroids in creams, the cream is usually dispersed by heating in hexane and then extracted with an equal volume of methanol. Methanol and hexane mix only very slightly and the oily excipients remain in the predominantly hexane layer, while the more polar corticosteroid partitions into the methanol layer. Use of an internal standard with a structure closely related to that of the analyte is essential in order to achieve good precision in this type of analysis through compensating for incomplete recovery of the analyte. Examples of pharmacopoeial methods using this type of partitioning include assays of: hydrocortisone acetate cream, fluocinolone cream and beclomethasone cream.
Was this article helpful?
Everything you wanted to know about. How To Cure Tennis Elbow. Are you an athlete who suffers from tennis elbow? Contrary to popular opinion, most people who suffer from tennis elbow do not even play tennis. They get this condition, which is a torn tendon in the elbow, from the strain of using the same motions with the arm, repeatedly. If you have tennis elbow, you understand how the pain can disrupt your day.