OBJECTIVE

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To evaluate the quality of Indigo Naturalis， and to provide reference for the quality control of Indigo Naturalis.

METHODS

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UPLC-MS/MS method was used to determine the contents of 6 indole alkaloids （indigo， indirubin， isatin， tryptanthrin， indole and indole-3-carboxaldehyde） in Indigo Naturalis from different origins. Cluster analysis， principal component analysis and partial least squares-discriminant analysis （PLS-DA） were used to evaluate the quality of Indigo Naturalis from different origins.

RESULTS

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The contents of indigo， indirubin， isatin， tryptanthrin， indole and indole-3-carboxaldehyde in Indigo Naturalis from different origins were 20 320.83-26 585.01， 1 327.69-3 102.25， 141.69-894.50， 2.17-5.27， 2.14-5.93 and 1.69-4.34 μg/g，

respectively. The Indigo Naturalis from different areas were clustered into two categories by cluster analysis. Samples S1， S2， S4， S6， S7， S9 and S10 were clustered into category Ⅰ， and samples S3， S5， S8， S11 and S12 were clustered into category Ⅱ. Indigo Naturalis from different origins was evaluated with 3 principal components. The results showed that category Ⅰ sample scored higher and had better quality， while category Ⅱ sample scored lower and had worse quality. PLS-DA showed that indigo， indirubin， tryptanthrin and isatin were the main substances that reflected the quality difference of Indigo Naturalis.

CONCLUSIONS

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The quality of Indigo Naturalis from different origins is different， and the quality of Indigo Naturalis of different batches from the same area is not stable. The quality evaluation method of Indigo Naturalis established in this paper is stable and reliable， which can provide a basis for the quality control of Indigo Naturalis.