SIMULTANEOUS DETERMINATION OF SODIUM DODECYL-SULFATE AND SODIUM LINEAR-DODECYLBENZENESULPHONATE WITH 1-STEARYL-4-(4-AMINONAPHTHYLAZO)-PYRIDINIUM BROMIDE BY SPECTROPHOTOMETRY

A rapid and sensitive spectrophotometric method for the simultaneous determination of sodium dodecyl sulphate (SDS) and sodium linear-dodecylbenzenesulphonate (DBS) with 1-stearyl-4-(4-aminonaphthylazo)-pyridinium bromide (SAPB) is described using the difference at the maximum absorption wavelength of the SDS- and the DBS-ion associate. SDS and DBS have been determined independently by measuring their respective absorbances at the maximum absorption wavelength. The apparent molar absorptivities of the SDS- and the DBS-ion associate are 8.0 x 10(4) l mol(-1) cm(-1) at 445 nm and 4.5 x 10(4) l mol(-1) cm(-1) at 424 nm, respectively. The calibration graph for SDS is linear in the range from 0.1 to 1.0 x 10(-6) mol/l in the presence of 1.2 x 10(-6) mol/l DBS and for DBS from 0.8 to 2.0 x 10(-4) mol/l in the presence of 8.0 x 10(-7) mol/l SDS. The relative standard deviation (n = 15) for 8.0 x 10(-7) mol/l SDS is 3.4% and for 1.6 x 10(-6) mol/l DBS 2.1%. The proposed method has been applied to the simultaneous determination of SDS and DBS in river water samples.