依文思蓝光度法测定水样中阳离子表面活性剂

Spectrophotometric Determination of Cationic Surfactants in Water with Evans Blue

在弱酸性的NaH2PO4-Na2HPO4缓冲介质中，阳离子表面活性剂（CS）溴化十六烷基吡啶（CPB）、十六烷基三甲基溴化铵（CTAB）与依文思蓝（EB）染料反应，形成离子缔合物，溶液颜色发生明显改变，最大褪色波长位于610nm。在最大褪色波长处，CS的浓度与褪色程度呈良好线性关系，从而建立了测定阳离子表面活性剂的光度法。在最大褪色波长处，CS的浓度在5．0×10^-7～2．46×10^-5mol／L（EB-CPB）、9．0×10^-7～3．36×10^-5mol／L（EB-CTAB）范围内遵守比耳定律，表观摩尔吸光系数为1．97×10^4L·mol^-1·cm^-1（EB-CPB）、1．25×10^4L·mol^-1·cm^-1（EB—CTAB），检出限为3．6×10^-7mol／L（EB-CPB）、7．4×10^-7mol／L（EB—CTAB）。本法用于水样中阳离子表面活性剂的测定，结果满意。

In weak acidic NaH2PO4-Na2HPO4 buffer medium, cationic surfactants （CS）, cetylpyridinium bromide（CPB） and cetyl trimethyl ammonium bromide（CTAB）, react with evans blue（EB） to form ion-association complexes. The colors of solutions change obviously, and the maximum fading wavelength is at 610 nm. The fading intensity is also proportional to the concentration of CS, and a sensitive spectrophotometric method is therefore developed for determination of cationic surfactants. The concentration of CS in the range of 5.0×10^-7～2.46×10^-5 mol/L（EB-CPB） and 9.0×10^-7～3.36×10^-5 mol/L（EB-CTAB）obeys Beer＇s law at the maximum fading wavelength. The apparent molar absorptivities are 1.97×10^4 L/（mol·cm） （EB-CPB） and 1.25×10^4 L/（mol·cm） （EB-CTAB）. The detection limits are 3.6×10^-7 mol/L （EB-CPB） and 7.4×10^-7 mol/L （EB-CTAB）. The method has high sensitivity and low detection limit, and has been applied to the determination of CS in water samples with satisfactory results.