Tensammetry with accumulation on the hanging mercury drop electrode : Part 4. The behaviour of oxyethylated alcohols (polyoxyethylene n-alkyl monoethers)

Abstract

The behaviour of polydispereed oxyethylated alcohols having a well-defined n-alkyl radical is described. Surfactants 6-14, 10-10, 10-14, 18-14, 18-10 and 18-6 (the first number denotes the number of carbon atoms in the n-alkyl radical, and the second one the average number of oxyethylene subunits) were examined. The conditions included 5 or 10 min of adsorptive preconcentration of surfactants at concentrations lower than the c.m.c value. Only negative tensammetric peaks were examined. The relationships between the peak height and the preconcentration potential were investigated for potentials more negative than - 1.0 V vs. SCE. More hydrophilic surfactants (i.e., 6-14, 10-10 and 10-14) form one wide tensammetric peak. The relationship of this peak to the preconcentration potential is simple and is similar to the negative branch of the adsorption isotherm. More hydrophobic surfactants (i.e., 18-6, 18-10 and 18-14) form a narrow peak, caused by the monomer form of the surfactant. If the threshold concentration of surfactants 18-6 and 18-10 is exceeded, a second very narrow peak appears, which is caused by the premicellar form of the surfactant formed at concentrations lower than the c.m.c. The dependences of the peak height on the preconcentration potential for surfactants 18-6, 18-10 and 18-14 are complicated; each plot shows a maximum, but the curves greatly depend on the surfactant concentration, which makes the choice of preconcentration potential difficult. Within the 10-(30-50) μg l −1 range of surfactant concentration, the plots of peak height vs. surfactant concentration are approximately linear. Results for the lowest concentrations are very imprecise because of strong adsorption of the surfactants on the surface of the cell.