Silver nanoparticles (AgNPs) were detected and characterized in several silver colloidal products available on the market. The relationship of the diameter of the nanoparticle with the corresponding peak potential was used to determine the dimensions of AgNPs in real samples. Quantitative analysis was carried out by voltammetry of immobilized particles on screen printed and glassy carbon electrodes. Screen printed electrodes were used prior to modification of the reference electrode to attain stable readings of peak potential. The repeatability of the modification as well as the quantitative results was checked and found satisfactory.