Zinc detection in oil-polluted marine environment by stripping voltammetry with mercury-free nanoporous gold electrode

Abstract

Detection of Zn(II) in oil-polluted seawater via square-wave anodic stripping voltammetry (SW-ASV) utilizing thin gold electrodes sputtered onto nanoporous poly(acrylic acid)-grafted-poly(vinylidene difluoride) (PAA-g-PVDF) membrane is herein reported. Prior to SW-ASV, PAA grafted nanopores demonstrated to efficiently trap Zn(II) ions at open circuit. This passive adsorption followed a Langmuir law. An affinity constant of 1.41 L $\mathrm{\mu }$mol${}^{-1}$ and a maximum Zn(II) adsorbed mass q${}_{\mathit{max}}$ of 1.21 $\mathrm{\mu }$mol g${}^{-1}$ were found. Applied SW-ASV protocol implied an accumulation step (− 1.2 V for 120 s) followed by a stripping step (− 1.2 to 1 V; 25 Hz; step: 4 mV; amplitude: 25 mV; acetate buffer (pH 5.5)). It revealed a Zn redox potential at − 0.8 V (Ag/AgCl pseudo-reference). Multiple measurements in synthetic waters close to the composition of production waters exhibited a decreasing precision with the number of readings R (1.65$\%$ (R = 2) and 6.56$\%$ (R = 3)). These membrane-electrodes should be used as disposable. The intra-batch mean precision was 14$\%$ (n = 3) while inter-batches precision was 20$\%$ (n = 15). Linear and linear-log calibrations allow exploitation of Zn(II) concentrations ranging from 10 to 500 $\mathrm{\mu }$g L${}^{-1}$ and 100 to 1000 $\mathrm{\mu }$g L${}^{-1}$ respectively. The LOD was 4.2 $\mathrm{\mu }$g L${}^{-1}$ (3S/N). Thanks to obtained calibration, a detected Zn(II) content of 1 ppm in a raw production water from North Sea oil platform was determined.