The adsorption of carbon monoxide (CO) on platinum (Pt) nanoparticles under the influence of a low electrical field (E-field) is studied. The adsorption of CO is monitored by attenuated total reflection infrared (ATR-IR) spectroscopy, while an external electrical field is applied over the microreactor. Linearly (on top; COL), bridged (two-fold hollow; COB), and multiply (three-fold hollow; CO) adsorbed CO species were found on the Pt nanoparticles. In a sequence of adsorption experiments the integrated ATR-IR intensity of the absorption band of the linearly adsorbed COL was found to reach steady-state values after an initial decrease, which is attributed to a loss of Pt surface area due to sintering of the Pt metal nanoparticles. The application of electrical fields results in changes in the ratio between linearly adsorbed CO, on top of Pt, versus CO adsorbed on multiple Pt atoms.