The Penning trap mass spectrometer SHIPTRAP at GSI Darmstadt allows high-accuracy mass spectrometry of fusion-evaporation residues, produced and separated at the velocity filter SHIP. The production technique gives access to nuclei far off the beta stability line. To match the energy of the products to the energy acceptance of the trap a buffer gas stopping cell is used. In the experiment described here, Sn, In, Cd and Ag isotopes were produced in the reaction ⁵⁰Cr + ⁵⁸Ni and the masses of 13 nuclides could be measured with an accuracy better than 10^-7. Our results agree well with the data derived from β⁺-decay studies but allow for a more accurate determination of the proton separation energies and Q _β-values. This is important to improve reaction network calculation of the rp-process.