Spectrophotometric determination of anionic surfactants in water samples based on inhibition of fading reaction

In weak acidic HCl-NaOAC buffer medium,the mixed solution of cetylpyridinium bromide(CPB) and eosin Y(EY) discolored,Two kinds of AS SDS and SDBS were respectively added into above solution,and the colors of solutions changed.Maximum absorption wavelengths were all at 514 nm,and obvious discoloration occurred at 548 and 546 nm respectively.Adding or fading color intensity is also proportional to the concentration of anionic sufactant at the maximum absorption on fading,a sensitive spectrophotometric method is developed for the determination of anionic surfactant.In SDBS and SDS system,the concentration of AS in the range of 0～2.06×10~(-5) mol/L and 0～2.63×10~(-5) mol/L obeys Beer′s law at the maximum absorption wavelength,the apparent molar absorptivity e is 1.30×10~4(L/(mol·cm)) and 1.01×10~4 (L/(mol·cm),) the detection limit is 8.14×10~(-7) mol/L and 9.96×10~(7) mol/L.If the determination process is dealt with double wavelength,the apparent molar absorptivity is 2.07×10~4 and 1.78×10~4(L/mol~(-1)·cm~(-1),) the detection limit is 4.82×10~(-7) mol/L and 8.34×10~(-7)mol/L.The method has better sensitivity and selectivity,and has been applied to the determination of AS in water samples,with satisfactory results.