Effective separation and analysis of E- and Z-guggulsterones in Commiphora mukul resin, guggulipid and their pharmaceutical product by high performance thin-layer chromatography-densitometric method - Musharraf, S G; Iqbal, N; Gulzar, U; Ali, A; Choudhary, M I; Atta-Ur-Rahman (J Pharm Biomed Anal, 2011)