Abstract Paratungstate A adsorbed on an electrodeposited copper surface can be virtually completely decomposed to tungstate anion via contact with a basic aqueous solution. The decomposition can be monitored by observation of the SER signal in the WO stretching vibration region of the spectrum. Copper surfaces prepared by anodization in the presence of paratungstate A yield two populations of adsorbates: those than can be decomposed to tungstate anion and those that remain unchanged. It is proposed that some adsorbates are trapped under the surface, imbedded in the surface, or otherwise kept from contacting the bulk solution. The presence of such sequestered species produced by SER electrode preparation in the presence of the adsorbate must therefore be considered when interpreting the spectroscopic and electrochemical data obtained using such surface preparation procedures.