A preliminary voltammetric investigation of silver ions in food simulants

Abstract

In this paper, the voltammetric behavior of the Ag+/Ag0 system was investigated in milli-Q water, 3% v/v acetic acid/milli-Q water, 10% v/v, 20% v/v and 50% v/v ethanol/milli-Q water media, which, according to the European Commission recommendations, can be employed as simulants of liquid foods for tests regarding the release of contaminants from plastic food packaging. Cyclic voltammetric measurements were performed using AgNO3, as source of Ag+ ions, and the various media without and with KNO3 or CH3COONa (for the aqueous acetic acid solution) as supporting electrolyte. Media with no deliberately added supporting electrolytes were investigated to better adhering to the experimental conditions used in conventional tests for establishing the amounts of Ag+ released from food packaging, loaded with silver nanoparticles (AgNPs), in the simulant media. To avoid strong distortions of the voltammetric responses, especially in the solutions without supporting electrolyte, the measurements were performed using a microdisk electrode. Diffusion coefficient values of Ag+, evaluated by the quasi steady-state limiting currents obtained from the Ag+ reduction process, depended mainly on viscosity of the specific food simulant investigated. The ionic strength of the medium affected diffusivity parameters to a lower extent. However, current values in the media without supporting electrolyte were larger than those recorded with excess electrolyte due to migration, which adds to diffusion in the mass transport. This contribution was observed when the Ag+ concentration levels were larger than a few tens of micromolar. Preliminary anodic stripping voltammetric measurements performed in milli-Q and 3% HAc, containing commercially available AgNPs (30–90nm diameter), incubated for about 6h in ambient conditions (i.e., temperature 24°C and air saturated media), provided Ag+ ion concentrations of 1.1×10−7molL−1 and 2.4×10−7molL−1, respectively.