Table 6.
Statistical parameters of ANOVA and obtained regression coefficients for different degradation.
| R2 | R2 Predicted | R2 Adjusted | Adequate precision | Regression coefficients | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| b0 | b1 | b2 | b3 | b12 | b23 | b13 | b123 | |||||
| Acid degradation | ||||||||||||
|
| ||||||||||||
| y 1 | 0.9736 | 0.8943 | 0.9537 | 16.724 | 20.75 | 8.60 | / | 8.35 | / | / | 2.76 | / |
| y 2 | 0.9823 | 0.9293 | 0.9691 | 23.526 | 0.17 | / | 0.066 | / | / | 0.029 | 0.026 | / |
| y 3 | 0.9701 | 0.8806 | 0.9477 | 15.756 | 20.21 | 8.53 | / | 8.33 | / | / | 2.53 | / |
|
| ||||||||||||
| Alkali degradation | ||||||||||||
|
| ||||||||||||
| y 1 | 0.9810 | 0.9241 | 0.9668 | 22.878 | 38.79 | 4.43 | 9.51 | 14.39 | / | / | / | / |
| y 2 | 0.9590 | 0.8362 | 0.9283 | 15.000 | 0.13 | / | / | 8.7E−3 | 0.016 | 0.031 | / | |
| y 3 | 0.9730 | 0.8920 | 0.9527 | 17.544 | 30.31 | 3.32 | 5.34 | 14.69 | / | / | / | / |
|
| ||||||||||||
| Oxidative degradation | ||||||||||||
|
| ||||||||||||
| y 1 | 0.9328 | 0.7312 | 0.8824 | 9.504 | 2.73 | / | 0.79 | 1.41 | / | 0.61 | / | / |
| y 2 | 0.9595 | 0.8382 | 0.9292 | 14.839 | 0.10 | 0.017 | 0.017 | 0.050 | / | / | / | / |
| y 3 | 0.9943 | 0.9771 | 0.9900 | 29.558 | 1.28 | / | 0.16 | 1.14 | / | 0.15 | / | / |
|
| ||||||||||||
| Thermal degradation | ||||||||||||
|
| ||||||||||||
| y 1 | 0.9439 | 0.7755 | 0.9158 | 8.203 | 14.05 | 8.90 | / | / | / | / | / | / |
| y 2 | 0.9918 | 0.9672 | 0.9877 | 22.000 | 0.16 | 0.11 | / | / | / | / | / | / |
| y 3 | 0.9383 | 0.7531 | 0.9074 | 7.797 | 12.06 | 7.45 | / | / | / | / | / | / |
Linear mathematical model of the measured response y = b0 + b1x1 + b2x2 + b3x3 + b12x1x2 + b13x1x3 + b23x2x3 + b123x1x2x3,
where y is the response [y1: amount of total impurities (%); y2: amount of impurity with RRT 1.16 (%); y3: amount of Simvastatin impurity A (%)], xi is investigated factors [for acid, alkali, and oxidative degradation; x1 represents stressor strength (0.01 M and 0.1 M HCl/NaOH or 3% and 30% H2O2 for hydrolysis and oxidative degradation respectable); x2 represents temperature and x3 represents time of exposure. For thermal degradation x1 is temperature and x2 is time of exposure]; b0 is the intercept b1, b2 and b3, b12, b23, b12, and b123 as regression coefficients for the variables and interaction between the variables.