Spectrophotometric determination of sodium dodecylbenzene sulphonate using congo red

Abstract

A new spectrophotometric method is developed to determine sodium dodecylbenezene sulphonate (SDBS) in natural water without the use of organic hydrophobic solvents and two-phase extraction. In BR buffer solution (pH 2.03), SDBS replaces sodium diphenyl diazo-bis--naphthylamine-4-sulphonate (Congo red, CR) in CR-cetylpyridinium chloride (CPC) system. Application of absorbance ratio difference (ARD) to this replacement reaction gives a new spectrophotometric method for the determination of SDBS. The absorbance measurements are made at 590 nm and 469 nm. Results have shown that absorbance ratio difference (ΔAr) gives linear curve in the range of 3.3 -139.4 mg/L for SDBS. The limit of determination of SDBS (3δ/k) is 1.1 mg/L. The method has been employed to determine SDBS in natural water with satisfactory results. Relative standard deviation was less than 5%, and the recovery was about 103.7%. The method is comparable to new methylene blue (NMB) method.