| Summary: | A spectrophotometric method for determination of total lactones in Andrographis paniculata was established by using dinitrobenzoic acid and potassium hydroxide solutions as colour forming agents. The absorbance of the solution was determined at 536 nm. The linearity range was 12-72 × 10-6 g.ml-1. The detection limit was 1.2 μg, the quantitation limit was 4.23 μg. The intraday variation had an average of slope 6082.97 g.ml-1, % RSD 0.10; an average intercept 0.2786, %RSD 3.66 (n=3). The interday variation had an average of 6146 g.ml-1 with the %RSD of 6.30 and an average intercept 0.2628, %RSD 4.95 (n=4). The coefficients of determination were 0.998-0.999. The total lactones content, calculated as andrographolide, determined by this method was 8.61±0.52% (n=4) and by the official method, Thai Herbal Pharmacopoeia, was 8.12±0.34% (n=2). The results of the two methods do not differ significantly at P=0.05 (P(|t|>0.903 = 0.53)
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