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Abstract
Two thiazine dyes were used for quantitation of anionic surfactants. The analytical procedure consists in titration of surfactant solution with cationic dye, registering absorbance at specific wavelength. Optimal wavelengths are 640 nm for the o-Toluidine Blue dye and 666 nm for the Methylene Blue dye. The registered absorbance values are dependent on surfactant concentration because of formation of low-soluble ion pairs. Analytical signal is titrant volume needed to reach the previously selected absorbance value. The main advantage of the proposed method is that no toxic chloroorganic solvents are used. The additional advantage is that the spectrophotometric titrations may be carried out in semi-automatic mode.