A Validated Stability-Indicating TLC Method for Determination of Forskolin in Crude Drug and Pharmaceutical Dosage Form

A simple, accurate, selective, precise, economical and stability-indicating high-performance thin-layer chromatographic method for analysis of forskolin in crude drug and in pharmaceutical dosage form was developed and validated. The method was developed on TLC aluminium plates precoated with silica gel 60F-254 using solvent system benzene:methanol (9:1, v/v), which gives compact spot of forskolin (R _f value 0.25 ± 0.02). Densitometric analysis of forskolin was carried out in the absorbance mode at 545 nm after spraying with anisaldehyde sulphuric acid. The linear regression analysis data for the calibration plots showed good linear relationship with r = 0.994 and 0.994 with respect to peak height and peak area, respectively, in the concentration range 100–1,000 ng per spot. The limits of detection and quantification were 8.1 and 26.9 ng per spot, respectively. The proposed method was applied for determination of forskolin in Coleus forskohlii root and in capsule dosage forms, which showed 0.18 and 0.57% w/w of forskolin. Forskolin was subjected to acid and alkali hydrolysis, oxidation, photodegradation and heat degradation. It was observed that the drug is susceptible to acid, base hydrolysis, oxidation, photo-oxidation and heat degradation. Statistical analysis proves that the method is repeatable, selective and accurate for the estimation of forskolin in crude drug and in pharmaceutical dosage forms. The developed method effectively resolved the forskolin from components of C. forskohlii root, from excipients of capsule as well as the degradation products of forskolin hence, it can be employed for routine analysis and as a stability-indicating method.