1. USPCI (United States Pharmacopeial Convention Inc.). The 25. Tyihak E, Held G. Thin-layer chromatography in pharmacog-United States Pharmacopeia, NF 22. Toronto, ON: Webcom nosy. In Niederwieser A, Pataki G, eds. Thin-layer Chromatog-Limited, 2004: 2004-5 raphy and Related Methods Vol. II. Ann Arbor, MI: Ann Arbor