The interactions of arsenic species with platinum and porous carbon electrodes were investigated with an electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry in alkaline solutions. It is shown that the redox reactions in arsenic-containing solutions electrocatalyzed by Pt can be readily distinguished with the EQCM. This approach was used to show that the porous carbon electrode electrocatalyzes the redox reactions of arsenic species in a manner analogous to that of the bare Pt electrode. This could not be ascertained with just classical cyclic voltammetry alone due to the obfuscation of the faradaic features with the large capacitative effects of the carbon double layer. For the porous carbon electrode, a continual mass loss was always observed during potential cycling, with or without arsenic in the solution. This was attributed to electrogasification of the carbon. The apparent mass loss per cycle was observed to decrease with increasing arsenic concentration. This was attributed to a net mass increase in adsorbed arsenic per cycle that increased with arsenic concentration, offsetting the carbon mass loss. Apparently, additional carbon adsorption sites involved in arsenic species interactions seem to be created during electrogasification, thereby augmenting the net uptake of arsenic per cycle. It is demonstrated that EQCM is a very useful technique for distinguishing arsenic species interactions with carbon electrodes. It may also prove to be effective for investigating redox/adsorption desorption characteristics of other species in solution with carbon materials as well. ; This work was partially supported by grant number 5 P42 (2006) ES013660 from the U.S. National Institute of Environmental Health Sciences (NIEHS), NIH, and by the Generalitat Valenciana (RED ARVIV/2007/076) and Ministerio de Educación y Ciencia (Project CTQ2006-08958/PPQ). The authors also wish to acknowledge the following: E. Morallon to the Generalitat Valenciana for a travel grant (BEST/2007/038); J.M. Calo for support from the Programa de Ayuda para Investigadores Senior, 2006, from the Universidad de Alicante; and D. Cazorla-Amorós for a travel grant (PR2007-177) from the MEC (Spain).