The homologous tallow fatty alcohol and oleyl alcohol ethoxylates were investigated using a PVC liquid surfactant sensor based on 1, 3-didecyl-2-methylimidazolium-tetraphenylborate as a sensing element and bis(2-ethylhexyl) phthalate as a plasticizer. The sensor responded to the tetraphenylborate (TPB) ion according to the Nernst equation (slope = -59.1 mV/decade of activity) in the region of 5 × 10-6 to 1 × 10-2 M, and it reached 95 % of its equilibrium response for the TPB ion within 10 s for the concentration change of 1×10−6 M→1×10−5 M, and in 5 s for the concentration change of 1×10−5 M → 1 × 10−3 M. The sensor was successfully used for the potentiometric titration of the homologous tallow fatty alcohol and oleyl alcohol ethoxylates. The accuracy of the determination was 98.6 % - 100.8 % for both alcohol ethoxylates investigated. The reaction stoichiometry of the potentiometric titration of ethoxylated nonionic surfactants (EONS) investigated was also studied.

Chemistry