Influence of light scattering of residual silica particles on the estimation of surfactants adsorption by spectrometry

The adsorption of a surfactant mixture, based on a cationic surfactant (cetylpyridinium chloride, CPC) and a non-ionic surfactant (Triton X-100, or TX-100), on silica particles was determined by solution depletion method combined with spectrometric measurement. It is shown that the light scattering, originated from the residual adsorbent silica particles in the supernatant after centrifugation separation, interferes with the measurements of absorbance of the surfactant molecules, and therefore constitutes an error source for determination of the surfactant concentration in the supernatant by spectrometric means. The intensity of this light scattering, namely the influence of the residual silica particles upon the surfactant adsorption, was related to the surfactant adsorption and its equilibrium concentration and varied among a batch. In this paper, we report a multiple linear regression (MLR) method in order to eliminate the variational scattering background caused by non-separated residual silica particles in each supernatant. This method is of interest as it is simple, easy to carry out and of high precision.