Abstract

Coexistence curves of two different aqueous micellar two-phase systems (AMTPS) were determined by potentiometric titration. The nonionic surfactants Triton X-114 and Eumulgin ES were quantified by means of the Metrohm NIO Surfactant Electrode with excellent correlations coefficients. The influence of different media on the titration end-point was ascertained.

Measurement in the presence of commonly used biotechnological buffers 2-(N-morpholino)ethanesulfonic acid (MES), sodium phosphate, and 2-(Bis(2-hydroxyethyl)amino)acetic acid (bicine) as well as in the supernatant of an E. coli fermentation exhibited deviations below 5%. Coexistence curves of Triton X-114 AMTPS and Eumulgin ES AMTPS were investigated in a temperature range of 25–40 °C by measuring the surfactant concentration of both, the detergent-rich (coacervate) and the detergent-depleted (aqueous) phase after phase separation.

The resulting coexistence curves are in good agreement with those published by authors who have employed the cloud point method. Yet, potentiometric titration outranges the cloud point method as it provides direct information about the compositions of the coacervate and the aqueous phase, which form when an AMTPS is shifted up to a temperature at which it splits.