Fig. 2. Contour plots of the interactive effects on V extraction: (a) interaction between S/L ratio with power at constant 60% lemon juice and 20% H₂O₂, (b) interaction between power and H₂O₂ concentration at constant 0.75% S/L ratio and 50.3% lemon juice, (c) interaction between S/L ratio and lemon juice at constant 117 W power and 20% H₂O₂.