(CCD) approach. In this work, the full CCD consisted of (1) a com-plete two-factorial design; (2) n0, center point (n0> 1), and (3) twoaxial points on the axis of each design variable at a distance of˛ = 2.000 from the design center. Hence, a total number of designpoints of N = 2k+ 2k + n0was used. The actual variable was codedto facilitate multiple regression analysis. The complete design con-sisted of 30 combinations including seven replicates of the centerpoint with five degrees of freedom for calculation of errors in theexperiments. The optimal values of response Y (individual recov-ery of interest compounds) were obtained by solving the regressionequation and by analyzing the response surface contour plots.Table 1 indicates the coded and CCD-processed variables for theoptimization of the QuEChERS method for samples. The resulting30 experiments were carried out randomly. The goodness of fit ofthe regression model and the significance of parameter estimateswere determined through appropriate statistical methods. DesignExpert trial version 8.0.6.0 was used (Stat-Ease Inc., Minneapolis,MN).