Effects of Sodium Dodecyl Sulfate, Sodium Laureth Sulfate, Surfactin, and Polyoxyethylene Sorbitan Monooleate (Tween 80) on Poly(ethylene oxide) (PEG 8000) and Dipotassium Hydrogen Phosphate Aqueous Two-Phase Systems

Aqueous two-phase(ATP) systems are useful in the separation of,particularly, biomolecules. These two-phase systems form when an aqueoussolution's concentrations of phase-forming compounds (suchas polymers like polyethylene glycol and salts) are within the two-phaseenvelope. Various physical and chemical conditions affect ATP phaseformation, such as temperature, pH, and composition. One set of chemicalswhich has not been characterized in terms of impact on polymer-saltaqueous two-phase separation (ATPS) are surfactants. It is importantto quantify the effects of surfactants, as they may be in solutionwith compounds to be extracted with an ATP system. In this study fourmodel surfactants (surfactin, Tween 80, sodium dodecyl sulfate (SDS),and sodium laureth sulfate (SLS)) were added to PEG 8000-PO4 (3-) ATP systems, and the impact on phaseformation was recorded and modeled using the Merchuk equation. Theaddition of the surfactants reduced the size of the two-phase envelopein all cases, particularly affecting the salt-rich bottom phase byincreasing the polymer concentration found therein. Little impactwas seen on the composition of the polymer-rich top phases. The slopeof the tie-lines was impacted, by the slopes being increased, modifyingthe phase-volume distributions and changing the critical point(w/w) from (0.076; 0.016) salt and polymer concentrations respectivelywith no additions to (0.077; 0.069) with Tween 80, (0.075; 0.091)with SDS, (0.101; 0.036) with SLS, and (0.072; 0.092) with surfactin.The impact of surfactants on ATP separations is demonstrated here,and therefore extractions where there will be surfactants presentmay need to construct modified phase diagrams, in order to properlyoperate the separation system.