The adsorption of sulfate ions on an emersed polycrystalline platinum electrode was studied by TDS in ultrahigh vacuum (UHV). Emersion from H2SO4 solutions does not give clear evidence of sulfate adsorption due to large signal contributions of rests of bulk electrolyte remaining on the surface after transfer to UHV. Using HelO(4) as base electrolyte the surface adsorption as function of the emersion potential can clearly be followed. The results are compared with in situ radiotracer and FTIR investigations.