Determining Low Concentrations of Silver Ions from measurements of DC Conductivity of Highly Insulating Liquid Media by the Alternate Polarization Current Method^*

Driven by many applications, the development of new biomaterials has considerably increased in the last decade. Silver, and particularly silver nanoparticles (AgNPs) have gained popularity in the biomedical domain due to their inherent antimicrobial properties. Beyond the validation of their efficiency, achievement of sustainable applications of AgNPs-tailored antimicrobial surfaces implies knowledge on the released amount of ionic silver $\left(\mathrm{Ag}^{+}\right) / \mathbf{A g N P s}$ in order to control their biocidal/toxicity level and prevent from users and environmental risks. To that end, we propose here a reliable approach for measuring DC conductivity of highly insulating liquid media (water solutions containing low concentrations of silver ions) by using the alternate polarization current method. The current, which is related to the conductivity of the media, is measured in the $10^{-14}$ to $10^{-5} \mathrm{~A}$ range with high accuracy (dispersion less than 2%). The amount of silver ions $\left(\mathbf{A g}^{+}\right)$ is then determined.