Objective: To investigate effects of different chromogenic agents on determining the content of total saponins from Achyranthis Bidentatae Radix by UV spectrophotometry. Method: Total saponins were determined by UV with five different chromogenic agents namely method A as 5% vanillin-glacial acetic acid:perchloric acid:glacial acetic acid(2:8:50)

method B as 5% vanillin-glacial acetic acid:perchloric acid:ethyl acetate(2:8:50)

method C as perchloric acid

method D as sulfuric acid:methanol(7:3)

method E as vanillin-sulfuric acid(2:58).With absorbance as index

chromogenic time and temperature was investigated by single factor tests. Result: Methdod C and D had not the maximun absorption at 400-800 nm;The maximum absorption wavelength of method E was at 544 nm

but absorbance value was too small which was not suitable for determination of standard curve;The maximum absorption wavelengths of method A and B were at (548±1)

(554±1) nm

respectively

these two methods were suitable for determination of total saponins from Achyranthis Bidentatae Radix

whereas peak pattern and sample recovery of method A were better than method B. Conclusion: Method A was optimal chromogenic method of total saponins from Achyranthis Bidentatae Radix.