Sodium dodecyl sulfate-coated alumina and C18 cartridge for the separation and preconcentration of cationic surfactants prior to their quantitation by spectrophotometric method

a new solid phase extraction method has been developed to the separation and preconcentration of trace amounts of cationic surfactants i.e. dodecyltrimethylammonium bromide (dtab), cetyltrimethylammonium bromide (ctab) and cetylpyridinium chloride (cpc). this method is based on the sorption of anionic surfactant (as-) of sodium dodecyl sulfate (sds) on the γ-alumina surface and c18 cartridge is used for preconcentration of cationic surfactants (cs+). spectrophotometric determination method used for the determination of cationic surfactants is based on the competition between the cationic dye of methylene blue (mb+) and cs+ for association complex formation with sds. the mb+ in the ion associate complex can be quantitatively substituted by cs+ leading to an increase in the absorbance measured at 662 nm. optimum experimental conditions for separation, preconcentration and determination of cationic surfactants have been reported. under the selected optimal conditions, preconcentration factor of two-fold was achieved and the results showed that determination of cpc, dtab and ctab could be performed in concentration ranges of 1×10-5-2×10-4, 4×10-5-5×10-4 and 5×10-5-5×10-4 mol l-1, respectively. eleven determinations of 10.0 mg ml-1 of cpc, dtab and ctab solutions led to rsd's of 4.3, 3.7 and 4.0%, respectively. method was validated using a set of different samples containing cationic surfactants.