Continuous-flow extraction of colloidal components in aqueous samples

In this study we report the development and performance of a system for continuous-flow extraction of dissolved and colloidal analytes in an aqueous matrix. Initial studies, using a classical segmented-flow extraction procedure, showed poor extraction efficiency for the hydrophobic colloidally dispersed analytes. Insufficient contact between the extractant and the colloidal constituents seems to be the primary reason for poor extraction. Improved performance is obtained when mechanical energy is added to the system, to effect a forced contact between the sample and the solvent. This was accomplished by injecting the extractant, with a high velocity, into the continuous flow of analyte through a narrow-bore nozzle. In this way, the solvent stream is dispersed into fine droplets with high kinetic energies. A region of intense turbulence is created, which was studied by high-speed photography using pulsed laser fluorescence. Comparison with classical flow extraction, using a model sample of colloidal wood resin compounds in water, showed that the dissolved components extracted well with both systems, while an extraction enhancement of up to 9 times was experienced with colloidal triglycerides.