On the basis of results of the BBD, two 2D contour plots are illustrated in Fig. 6, which portray the interaction effects between the volume of elution solvent (n-hexane) and the elution time (Fig. 6a) and between the sorbent amount and the elution solvent volume(Fig. 6b). When low amounts of n-hexane are introduced (Fig. 6a),the extraction efficiency declines irrespectively of the contact time between n-hexane and Fe3O4@SiO2@C18 (elution time). Higher yields were obtained when higher amounts of sorbent were used for the extraction. The reflected interaction effects between sorbent amount and n-hexane volume (Fig. 6b), demonstrated that the highest recovery of the target analytes was observed at the highest values of both variables.