Nitrite is diazotized with sulfanilamide (SAM) in the pH range 2.0–5.0, sulfamethizole (SM) in pH 1.8–5.6 and sulfadimidine (SD) in pH 1.8–4.0 in a hydrochloric acid medium to form water-soluble colourless diazonium cations. These cations were coupled with sodium 1-naphthol-4-sulfonate (NS) in the pH range 9.0–12.0 for the SAM–NS system, pH 8.6–12.0 for the SM–NS system and pH 9.4–12.0 for the SD–NS system to be retained on naphthalene-tetradecyldimethylbenzylammonium (TDBA)–iodide (I) adsorbent packed in a column.