The tube was shaken for 3 min on vortex and then 6.0 g of anhydrous MgSO4 and 1.5 g of NaCl were added,following 1 min of vortex shaking. After this, the tube was centrifuged at 2,200 × g for 8 min to obtain good separation of the phases and 2 mL of the supernatant (organic phase) was used for the clean-up step by d-SPE. This step was performed in a 15 mL polypropylene tube with cap, containing 120 mg of anhydrous MgSO4 and 100 mg of the sorbent PSA, which was vortexed for 3 min and centrifuged for 8 min at 1,800 × g to obtain a clean extract (upper phase).