Experimental design for the study and optimization of the effect of different surfactants on the spectrophotometric determination of sulfide based on phenothiazine dye production

Abstract

In the present work the effect of three different surfactants Triton X-100, cetyltrimethylammonium bromide (CTAB) and sodium dodecylesulfate (SDS) on the spectrophotometric determination of sulfide based on phenothiazine dye production from phenyl-p-diamine (PPD) is studied. The main step for phenothiazine dye production is the oxidation of aromatic p-substituted amine to yield iminoquinone free-radical intermediary. Fe³⁺ in acidic media is used for oxidation purposes. Electron donor groups in the p-position of aromatic ring of amines are decisive for free-radical stabilization, leading to an increased dye production rate and the analytical sensitivity.

Preliminary studies showed that, the analytical signal was increased in the presence of SDS, CTAB and Triton X-100; but among the surfactants studied, SDS and Triton X-100 had a significant effect on the spectrophotometric determination of sulfide based on phenothiazine dye production. The effects of various experimental parameters in this reaction was investigated using central composite design. The experimental design was done at five levels of operating parameters. As a model surfactant, the concentration of SDS, amine, Fe³⁺ and H₂SO₄ were optimized simultaneously. The effects of Triton X-100 and CTAB as non-ionic and cationic surfactant, respectively, were investigated using a one variable at a time optimization method. The linear range for the determination of sulfide in the presence of SDS and Triton X-100 was 0.1–2 μg ml⁻¹ and that in presence of CTAB was 0.2–2.0 μg ml⁻¹. The proposed method was applied successfully for the determination of sulfide in different spiked real samples.