Impact of molecular surface characteristics on the reversed-phase retention behaviour of synthetic dyes

The lipophilicity and specific hydrophobic surface area of 42 synthetic dyes were determined on reversed-phase alumina layers using water-methanol mixtures as eluents, and their relationship with the molecular surface characteristics was elucidated by principal component analysis followed by a two-dimensional nonlinear map and cluster analysis. Four dyes remained on the origin in each eluent system. Except for two dyes, the majority showed regular retention behaviour with their retention decreasing steadily with increasing concentration of methanol in the mobile phase. Calculations indicated that both hydrophobicity parameters decrease with increasing polar surface area of the molecules.