The extraction, clean-up and HPLC analysis of these three compounds
were performed simultaneously, according to the method
developed in our department (Alvarez-Vidaurre, Perez-Martinez, de
Peña, & Cid, 2005). The HPLC analysis was carried out with the same
equipment and column described above. The chromatographic
separation was achieved at 25 C by using a gradient solvent system
with acetonitrile/water adjusted to pH 2.5 with a phosphoric acid
solution according to the procedure published by Perez-Martinez
et al. (2008). The wavelengths of detection were 314 nm for caffeic
acid, 325 nm for ferulic acid and 210 nm for 4-vinylguaiacol