A novel experimental equipment is described allowing one to perform, simultaneously and on the same electrode, ring-disk and quartz crystal microbalance measurements. Owing to the use of a still electrode and an impinging-jet cell the uniform accessibility is preserved while the critical problems of connections to a rotating quartz are overcome. The capability of the device was illustrated by an ac investigation of copper dissolution in a NaCl, HNaCO3 medium. Impedance, complex collection efficiency, and electrogravimetric transfer function were associated for elucidating unambiguously from mass and faradaic charge data the nature of the surface intermediate during copper dissolution.