Fig. 3. Response surface plots (three-dimensional) showing the effect of the ethanol concentration (X1, %), microwave temperature (X2, °C) and microwave power (X3, W) on the yield of chrysophanol (Y) in rhubarb. (A) represents the effects of X2, X3 and their reciprocal interactions on the yield of chrysophanol in rhubarb. (B) shows the three-dimensional plot of the response surface for the chrysophanol yield as related to X1 and X2. (C) shows the 3D plot of the response surface for the chrysophanol yield as related to X1 and X3. Contour plots (D–F) shows the effect of variables (X1, X2 and X3) on the chrysophanol yield.
