Determination of Sodium Dodecyl Sulfate by Means of Photometric Titration with o-Toluidine Blue Dye

A convenient technique for the determination of sodium dodecyl sulfate is titration with a metachromatic dye using in situ absorbance measurements. A suitable color reagent is ortho-Toluidine Blue dye. Commercially available immersion optical probe Optrode (R) possesses a working wavelength of 640 nm, well matching the dye spectrum. The surfactant concentration is linearly related to the titrant volume at a certain solution absorbance. Optimal values of end point absorbance fall in the range from 0.7 to 2. The lower limit of quantitation is equal to 29 mg L-1. The highest concentration determined in this study was 52 g L-1. The required determination range may be adjusted by the appropriate selection of analyte volume and titrant concentration. The developed method is intended for routine process control in the surfactant industry. This method needs minimal manual efforts due to the lack of the dilution stage. Application of an automatic titrator looks to be a suitable solution for any industrial lab.