Improved Methylene Blue Two-Phase Titration Method for Determining Cationic Surfactant Concentration in High-Salinity Brine

摘要

The methylene blue ( two-phase titration method is a rapid and efficient method for determining the concentrations of anionic surfactants. The point at which the aqueous and chloroform phases appear equally blue is called Epton's end point. However, many inorganic,an ions e.g., Cl-, NO3-, Br-, and I-, can form ion pairs with MB+ and interfere with Epton's end point, resulting in the failure of the hase titration in high-salinity brine. Here we present a method to extend the MB two-phase titration method lordete g inin the concentration of various cationic surfactants in both deionized water and high-salinity brine (22% total-dissOtvect Acolorless end point, at which the blue color is completely transferred from the aqueous phase to the chloroform phase, tis,perotr the as titration end point. Light absorbance at the characteristic wavelength of MB is measured using a spectrophotometer. m r. When e absorbance falls below a threshold value of 0.04, the aqueous phase is considered colorless, indicating ot the end point has been reached. By using this improved method, the overall error for the titration of a permanent cationic limits surfactant, e. dodec-ethyl monium bromide, in deionized (DI) water and high-salinity brine is 1.274% and 1.322% with of. detection (LOD) of 0.149 and 0.215 mM, respectively. Compared to the traditional acid base titration method, the error of this improved mhod for a switch able cationic surfactant, e.g., tertiary amine with surfactant (Ethomeen C12), is 2.22% in DI water and 0.106% LOD of 0.369 and 0.439 mM, respectively.