Radiochemical approach in studying competitive adsorption of human serum albumin and ionic surfactants at the water/p-xylene interface

The competitive adsorption and distribution in the bulk of the aqueous solution/p-xylene system was studied, using tritium labeling and the scintillation phase method, for human serum albumin (HSA) and ionic surfactants: dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS). Tritiumlabeled HSA, DTAB, and SDS of high specific radioactivity were obtained by the tritium thermal activation method and were purified by chromatography. Physicochemical studies were performed with HSA-SDS and HSA-DTAB mixtures at a protein concentration of 0.06 g l−1 and varied surfactant concentrations from 0.3 to 8.0 μM. The distribution ratio and the adsorption isotherm were obtained for each component of the mixture by the scintillation phase method. The effect of ultralow concentrations of surfactants on the competitive adsorption in mixtures with HSA and on the bulk distribution of the substances in the two-phase system was found. The parameters of intermolecular interaction in the adsorption layer were calculated, and a mechanism of formation of the adsorption layer was suggested.