where X2 is the sorbent amount (C18-NPs), X3 is the elutionsolvent volume (Vsolv) and X4 is the elution time (Telut).The model coefficient of determination (R2= 0.9600) is in
reasonable agreement with the experimental results. The adjusted determination coefficient (adjusted R2= 0.8881) also advocates for a high significance of the model. Both values ensured a satisfactory correlation between the experimental and predicted values. Moreover, the lack of fit, which measures the failure of the model to