4.3.1. Sample Preparation and Extraction
Phenolic compounds were extracted in urine using Waters OASIS HLB μElution plates (Milford, MA, USA), which were preconditioned with 250 μL methanol and 250 μL 0.2% acetic acid. After urine collection, the samples were immediately acidified with trifluoracetic acid. Aliquots of the samples were applied to the μ Columns of the plates and the phenolic compounds were eluted with methanol acidified with 0.2% acetic acid. The eluate was dried using CentriVap Benchtop Vacuum Concentrators (Labconco, Kansas City, MO, USA), reconstituted with methanol acidified with 5% acetic acid, and filtered with a 0.43 μm PTEF filter (Millipore, Bedford, MA, USA).