The electrochemical behaviors of n-decanethiolate-protected gold (C10Au) nanoparticles that had been exchanged with p-nitrothiophenolate (NTP) ligands at varied feed ratios were investigated in an external magnetic field (0-0.5 T). It was found that the NTP voltammetric currents are dependent on the electrode orientation and the intensity of the magnetic field. When the concentration of NTP in the particle is low (e.g., 10 or 30% exchange ratio), the currents at angles of 0 and 180degrees are greater than those at 90 and 270degrees. However, when the initial feed ratio is increased to 50%, the currents at angles of 0 and 180degrees are smaller than those at 90 and 270degrees. While these observed phenomena are ascribed to the magnetic field effects on nanoparticle mass transfer, their mechanistic origins are different. The former is attributable to the field-enhanced magnetoconvection due to the formation of an interfacial gradient of magnetic susceptibility concentration), and the latter arises from magnetohydrodynamic interactions.