Stability-indicating RP-HPLC method for the determination of 6-gingerol in polyherbal formulations

Background: Among different systems medicine practiced worldwide, Unani medicine is the classical one and still commonly practiced in India and abroad for centuries. As it is widely used by a majority of population, it is necessary to come up with a systematic approach to develop well-designed methodologies for the quality control of different polyherbal formulations which are used for treatment of various diseases in this system of medicine. Methods: A reverse phase stability indicating HPLC method was developed for the determination of 6-gingerol in polyherbal formulations. Separation of 6-gingerol was achieved on reverse phase C18 (250 × 4.6 mm) column with a mobile phase containing methanol: 0.05% orthophosphoric acid in water (60:40, v/v) at 280 nm using UV-visible detector. The flow rate was kept as 1 mL/min. The proposed method was validated according to ICH guidelines for accuracy, precision, robustness, LOD, and LOQ, and statistical analysis proved method was accurate, precise, and robust. Results: The linear regression analysis data showed a good linear relationship (r² = 0.9989 ± 0.0010) for 6-gingerol in the concentration range of 0.5 μg to 500 μg/mL. This proved the method can be employed for the determination 6-gingerol even in nanogram levels. The detection (LOD) and quantification (LOQ) limits were found to be 0.05 μg and 0.18 μg/mL, respectively. Satisfactory recovery results were observed from the herbal compound formulations (98.5 to 101%). Intra- and inter-day precisions of the method were found convincing, with relative standard deviation (%RSD) values in the range of 0.5 to 1.9%. Forced degradation studies of 6-gingerol was also carried out under different stress conditions which showed that the drug is stable in acidic and basic conditions whereas unstable against dry heat. Conclusions: Hence, newly validated HPLC method can be used for the quality control and standardization of different herbal formulations which contain Zingiber officianalis as one of the ingredients.