Selection of Separation Conditions for HPLC and HPLC/MS of Aromatic Sulphonic Acids and Acid Azo Dyes

Liquid chromatography of organic anionic compounds usually cannot be performed without ionic additives to the mobile phase. Buffered mobile phases usually do not provide sufficient suppression of the ionization of strong acids, such as anionic dyes and aromatic sulfonic acids used in the dye production, or as whitening agents or detergents in various industrial and household applications. Hence, other modes are usually necessary for successful separation of these compounds, including ion‐exchange chromatography, ion‐interaction reversed‐phase chromatography, or ion‐pair chromatography. The retention mechanisms in these modes are still a controversial issue. In the present work, various theoretical models describing the retention of strong organic acids with bulky hydrophobic structural elements are reviewed.