Sono-electroanalysis of copper: enhanced detection and determination in the presence of surfactants

Abstract

Surfactant adsorption has been shown to have a passivating effect on the electrode surface during anodic stripping voltammetric measurements. In the present work the feasibility of sono-anodic stripping analysis for the determination of copper in aqueous media contaminated with surfactant has been studied at an unmodified bare glassy carbon electrode. We illustrate the deleterious effect of three common surfactants, sodium dodecyl sulfate (SDS), dodecyl pyridinium chloride (DPC) and Triton-X 100 (TX-100) on conventional electroanalysis. The analogous sono-electroanalytical response was investigated for each surfactant at ultrasound intensities above and below the cavitation threshold. The enhancement in the stripping signal observed is attributed to the increased mass transport due to acoustic streaming and above the cavitation threshold the intensity of cavitational events is significantly increased leading to shearing of adsorbed surfactant molecules from the surface. As a result accurate analyses for SDS concentrations up to 100 ppm are possible, with analytical signals visible in solutions of SDS and TX-100 of 1000 ppm. Analysis is reported in high concentration of surfactant with use of sono-solvent double extraction. The power of this technique is clearly illustrated by the ability to obtain accurate measurements of copper concentration from starting solutions containing 1000 ppm SDS or TX-100. This was also exemplified by analysis of the low concentration 0.3 microM Cu(II) solution giving a percentage recovery of 94% in the presence of 1000 ppm SDS or TX-100.

Sonoelectroanalysis in Acoustically Emulsified Media: Zinc and Cadmium

“…Typical voltammograms are shown in Figure 1C, but were found to be un-reproducible with much reduced currents as compared to the surfactant free case. We have shown elsewhere [56] that for low concentrations of surfactants that this problem can be overcome via the in-situ cleaning action of ultrasound; in particular at the micromolar concentration level this is possible using a mercury modified glassy carbon working electrode [57]. However, for higher levels this has limited success.…”

Ultrasonically Enhanced Voltammetric Analysis and Applications: An Overview

“…For a concentration of 1 000 ppm SDS, a 94.1% percentage recovery was observed. Consequently for the 1 000 ppm of TX-100 a 94% recovery was observed [115].…”

“…In particular, the behavior in the presence of 1 000 ppm SDS was non-linear precluding the determination of apparent copper. Similarly, analysis with Triton X-100 was indicative of complete passivation of the electrode [115]. This observed behavior precludes meaningful analysis at unmodified electrode surface via traditional electrochemical techniques.…”

“…Employing a silent preconcentration for 60 s at À 1.5 V (vs. SCE) followed by voltammetric stripping step in 0.1 M nitric acid, a standard addition plot was constructed for increasing concentrations of sodium dodecyl sulfate (SDS). The additions plots of peak area against copper concentration were indicative of passivation with surfactant concentration with depreciating peak heights and lower overall percentage recovery of copper [115]. In particular, the behavior in the presence of 1 000 ppm SDS was non-linear precluding the determination of apparent copper.…”

“…and Determination in the Presence of Surfactants [115] Surfactant adsorption has been shown to have a passivating effect on the electrode surface during anodic stripping measurements. This can result in decreased electron transfer rates and impeded diffusion of analytes to the electrode surface, ultimately decreasing peak heights, increasing peak broadness and causing shifts in peak potentials [116 ± 118].…”