Sodium lauryl sulphate (LS) has been the subject of extensive studies in interfacial adsorption. The adsorption of lauryl sulphate at the mercury-solution interface has been studied by tensammetric 1 and double-layer capacity measurements 2 . The capacitancepotential curves are marked by a large frequency dependent peak at about -1.0 V (with respect to SCE) and a small sharp peak in the range -0.3 to -0.5 V. The peaks are obtained even with very small concentrations of LS and peak potentials shift to cathodic potentials with concentrations. The large peak at negative potentials is supposed to result from the desorption of lauryl sulphate. The small peak, for which the capacitance is less than that in the supporting electrolyte at the peak potential, is variously interpreted as due to phase transitions within the adsorbed fdm, due to multimolecular layer formation or even micel formation. Drop time studies show that the lauryl sulphate is strongly adsorbed in the range of potentials when the small peak is observed. One of us (R.N.) a carried out d.c. polarographic studies with the system and suspected that oxygen may play a role in the formation of peaks. D.c. polarographic experiments were repeated carefully with various concentrations of 02 and lauryl sulphate in a 0.1 M NaC104 solution. A drop-detaching device was used to ensure a constant drop time in the presence of surfactant. The oxygen wave is shifted by about 200 mV and is split into two portions even in the presence of very small concentrations of LS. The relative wave heights vary with the concentration of LS and 02 and a small maximum is generally present beyond the first wave (Fig. l). The limiting current after the second wave is equal to the current obtained with 02 alone. Larger additions of LS shift the reduction by more than 300 mV and results in a single irreversible wave. The reduction of H202 (second wave of O~ starting at -0.6 V and extending to -1.1 V) is suppressed totally by the presence of small quantities of LS. The H202 wave appears when the LS is desorbed. This is confirmed by an independent study of the reduction of H 2 02 in presence of LS. Similar results are obtained in acidic buffer solution and in 0.1 M NaOH.
The d.c. polarograms obtained in the presence of lauryl sulphate may be interpreted as follows. Lauryl sulphate is strongly adsorbed at the metal solution interphase.