Spectrophotometric Determination of Anionic Surfactants by the Enhancing Color Reaction with Mixed Solution of Bromocresol Purple and Cetylpyridinium Bromide

It was found that in a phosphate buffer of pH 6.4,the intensity of absorption at the wavelength of 586 nm of the solution containing bromocresol purple (BCP) and cetylpyridium chloride (CPB),was increased by the addition of some anion surfactants (asf),e.g. sodium lauryl sulfonate (SLS) or sodium dodecyl sulfate (SDS). Linear relationship between values of increase in absorbance and concentration of the asf added,was obtained in the range of within 2.13×10-5mol·L-1 for SLS and within 2.15×10-5mol·L-1 for SDS. Detection limits (3S) found was 4.92×10-7mol·L-1 for SLS,and 8.54×10-7mol·L-1 for SDS. Values of molar absorptivity for these 2 asf′s found were 2.94×104L·mol-1·cm-1 and 1.58×104L·mol-1·cm-1 respectively. The proposed method has been applied to the determination of asf (expressed as SLS) in water samples,giving values of recovery in the range of 98.8%-101.9%,and values of RSD′s (n=6) less than 2%.