Colorimetric estimation of total iridoid content of Picrorhiza kurrooa

A colorimetric method has been developed for the selective analysis of the total iridoid content of the rhizomes of Picrorhiza kurrooa in terms of catalpol. The method of analysis is based on the reaction between iridoid compounds and primary amine. The iridoid glycosides present in P. kurrooa are mainly the esters of catalpol, and can be easily converted into catalpol by saponification. Catalpol thus obtained by hydrolysis is treated with glycine in acidic medium to give a purple color with a maxmimum absorption of 542 nm. The method was validated as per the ICH guidelines for linearity, accuracy and precision. Several other rhizome samples of the plant were also assayed using this method. The method developed is precise, sensitive, reproducible and easy to perform and can be used for the standardization of crude drug.