4.4. Solid Phase Extraction (SPE)

SPE was used for removing the unwanted co-extracted compounds as well as for protecting the analytical column, using Sep-Pak C₁₈ cartridges (Waters Assiciates Inc., Milford, MA, USA). The cartridges were first preconditioned by flushing with 4 mL methanol, then with 4 mL ultrapure water at a flow rate of 1 mL/min [47,53]; 5 mL extracts were passed through the activated cartridges, discarding the first milliliter, then the eluates were collected in 2 mL vials, being subjected to HPLC.