\n\tSummary
\n\tImprovement of the Method for Simultaneous Determination of Indirubin and Indigo by UV-Visible Spectrophotometry
\n\tA direct quantitative method has been improved for the simultaneous determination of indigo and indirubin using UV-visible spectrophotometry. The method is based on the measurements of the sulfatd derivatives of indigo and indirubin at wavelengths of 610 nm and 541 nm, respectively. Calibration curves show excellent linearity (r2>0.9998 for indigo at 610 nm) and (r2>0.9996 for indirubin at 541 nm) in the range of 0.6 - 20.8 mg/ml. The method has high precision with the standard deviation of 0.410 and 0.057, and the relative standard deviation of 1.63 % and 0.76 % for indigo and indirubin, respectively. The accuracy of method is good with recoveries greater than 99 %. The proposed method is high of precision, rapid and inexpensive. Application of this method to a natural indigo powder produced from the leaves of Strobilanthes cusia, resulted in indigo and indirubin contents of 35.4% and 15.6%, respectively.
\n\tKeywords: indirubin, indigo, UV-Vis spectrophotometry, quantitative determination.
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