Flow injection spectrophotometric determination of andrographolide from Andrographis paniculata

A simple flow injection colourimetric procedure for determining andrographolide was proposed. It is based on the reaction between andrographolide with 3,5-dinitrobenzoic acid, resulting in an intense purplish red complex with a suitable absorption at 536nm. A standard or sample solution was injected into the 3,5-dinitrobenzoic acid stream (flow rate of 1.0mlmin(-1)) which was then merged with potassium hydroxide stream with the same flow rate. Optimum conditions for determining andrographolide were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 5.0-150.0mugml(-1) and the detection limit was 1.50mugml(-1) (3sigma). The relatives standard deviation of the proposed method calculated from 10 replicate injections of 10.0 and 80.0mugml(-1) andrographolide were 0.66% and 1.64%, respectively. The sample throughput was 50h(-1). The proposed method has been satisfactorily applied to the determination of andrographolide in herb plant samples.