Spectrophotometric Method for the Direct Determination of Anionic Surfactant Sodium Dodecyl Benzenesulfonate (SDBS) Using a Hydrophobic Near‐Infrared (NIR) Cationic Cyanine Dye Without Solvent Extraction

Abstract

A new hydrophobic near‐infrared (NIR) cationic cyanine dye was synthesized and evaluated as a new reagent for the determination of anionic surfactant sodium dodecyl benzenesulfonate (SDBS). The cyanine dye with an absorption maximum at 770 nm reacted with SDBS, causing significant hypochromism. Under the optimal conditions, the decreased absorption is proportional to the concentration of SDBS over the range 2.9 × 10⁻⁷–1 × 10⁻⁵ mol/L. The detection limit was 1.9 × 10⁻⁷ mol/L. The relative standard deviation for 1.43 × 10⁻⁶ mol/L SDBS was 1.3% (n = 9). The proposed method was applied to determination of anionic surfactant in the river with 93–106% recovery levels. Preliminary research shows that the hypochromism is due to the formation of dye aggregate facilitated by SDBS.