Jul 08, 2005 · The column was a Discovery RP Amide C16 150 mm × 4.6 mm with 5 μm pore size, and a Vaco precolumn frit filter, 5 μm, and a Discovery RP Amide C16 Guard column 20 mm × 4.0 mm, 5 μm, were used to protect the column (all purchased from Sigma-Aldrich, Stockholm, Sweden).