372 JOURNAL OF COSMETIC SCIENCE = - + + + + Y x x x 87.35 11.35x 94.41x – 8.27x 34.12x 2.16x – 2.18x – 11.94x – 87.66x 0.61x 1 2 3 1 2 1 3 2 3 1 2 2 2 3 2 (10) where x 1 , x 2 , x 3 representing three experimental variables, namely acid/alcohol molar ratio, IL molar ratio, and reaction time, respectively and Y (response) is the conversion of acid (%). Equation 10 indicates that the conversion of AA (%) increases with increasing IL molar ratio x 2 and decreases with acid/alcohol molar ratio x 1 . The most effective parameter was the IL molar ratio. ANOVA was performed to test the accuracy of the polynomial equation consisting of parameters affecting the conversion of acid (%) (Table III). With this method, the significant degree of linear, quadratic and binary interaction of each variable forming the model was determined by F-test and p F. From Table III, model terms with the p-value were important terms that affect the response. Values of “Prob F” less than 0.05 indicate model terms are significant. The Model F-value of 19.51, and The “Lack of Fit F-value” of 90.33 implied the model and the Lack of Fit was significant. In this case x 1 , x 2 , x 1 x 2 , x 2 2 are significant model terms. The fact that the regression coefficient is close to 1 indicates that the relationship between independent and dependent variables is well expressed by the model. The R-squared value Table III ANOVA for the Response Surface Quadratic Model Source Sum of squares Degrees of freedom Mean square F-value p-value Model 1926.26 9 214.03 19.51 0.0004 x 1 588.07 1 588.07 53.60 0.0002 x 2 1005.76 1 1005.76 91.68 0.0001 x 3 47.97 1 47.97 4.37 0.0748 x 1 x 2 72.76 1 72.76 6.63 0.0367 x 1 x 3 18.71 1 18.71 1.71 0.2329 x 2 x 3 4.75 1 4.75 0.43 0.5315 x 1 2 37.55 1 37.55 3.42 0.1068 x 2 2 126.39 1 126.39 11.52 0.0115 x 3 2 25.25 1 25.25 2.30 0.1730 Residual 76.79 7 10.97 Lack of fit 75.68 3 25.23 90.33 0.0004 Pure error 1.12 4 0.28 Cor. total 2003.06 16 Std Dev. 3.31 R2 0.9617 R2 adj 0.9124 Adeq R2 16.556

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