“…Concerning liquid chromatography, the first study [21] was performed on a C30 column with a MeOH based gradient while the second study [1] used a C18 column with an ACN based gradient. We made first standard solutions in MeOH at 10, 1 and 0.1 ng L −1 and investigated the MeOH gradient (from 5% to 100% in 10 min) on a Waters BEH C18 column (100 mm × 2.1 mm, 1.7 m).…”