The Influence of Ethoxylated Nonionic Surfactants on the Potentiometric Determination of Anionic Surfactants

A PVC-plasticized liquid- type anionic surfactant (AS)-responsive sensor, using 1,3-didecyl-2-methylimidazolium- tetraphenylborate (DMI-TPB) as the sensing element, has been utilized for the investigation of the influence of three ethoxylated nonionic surfactants (EONS), containing 8, 11 and 15 ethoxy (EO) groups, on the potentiometric determination of dodecyl sulfate (DS). The results demonstrate that the sensor slope (S) slowly decreased with increasing concentrations of EONS. The changes in the slope for the corresponding concentration change (DS: EONS ratios varied from 1: 1 to 1:4) were 1.62, 5.11 and 6.28 mV for EONS containing 8, 11 and 15 EO groups, respectively. The constant potential term changes for the same EONS concentration change were 18.8, 22.3 and 39.5 mV, respectively. The linear response range became more narrow as the concentration of EONS increased, and increasing numbers of EO groups were found within the EONS molecule. There was a strong correlation between E and log a(DS) for all of the DS: EONS ratios in the linear region of the sensor response. The EONS molecules significantly influenced the potentiometric titration of DS. The titration curves were seriously disturbed for EONS: DS molar ratios greater than 5 for EONS containing 8 EO groups, for ratios greater than 3 for EONS containing 11 EO groups and for ratios greater than 2 for EONS containing 15 EO groups.