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J Pharm Biomed Anal. 2005 Jul 1;38(3):532-6. Epub 2005 Mar 19.

Rapid determination of trace amounts of minoxidil in hamster skin follicles with various formulations using narrow-bore LC/EC.

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Pharmaceutical Sciences, Pfizer Inc., 7000 Portage Street, Kalamazoo, MI 49001, USA.


A sensitive liquid chromatographic method with electrochemistry (LC/EC) was developed for the determination of trace of minoxidil in hamster skin follicles after topical administration of the ear using various formulations. The minoxidil in the sebaceous glands of the hamster ear was isolated from the skin and the follicles in different skin layers were treated with aqueous trichloroacetic acid followed by acetonitrile. The supernatant was directly injected into the LC/EC system and minoxidil was detected by oxidation at +800 mV versus Ag/AgCl using a glassy carbon electrode. The analytical recoveries were between 94.4 and 103.1% and the linearity was excellent up to 250 microg/ml with a regression coefficient (r(2)) of 0.9988. The LC/EC and the widely used radiolabeled scintillation methods agree well and both show high sensitivities. The LC/EC method is rapid and cost-effective with a detection limit of only 1 ng/ml.

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