“…In the majority of cases, separation has been performed on various C columns [ 4 , 10 , 11 , 21 , 37 , 38 , 39 ], although columns with phenyl stationary phase have also been used [ 2 , 8 , 22 ]. Usually, the mobile phase has initially a high water content and is then gradually adjusted to raise the ratio of organic solvent, this solvent being either methanol (MeOH) [ 10 , 40 ], acetonitrile (ACN) [ 22 , 32 ] or both [ 38 , 41 ]. The critical problem of the LC is the separation of 4- and 5-methyl-benzotriazole isomers, due to their similar retention.…”