Although the theory for the rapid neutron-capture process (r-process) was developed more than 55 years ago, the astrophysical site is still under a debate. Theoretical studies predict that the r-process path proceeds through very neutron-rich nuclei with very asymmetric protonto-neutron ratios. Knowledge about the properties of neutron-rich isotopes found in similarregions of the nuclear chart and furthermore suitable for r-process studies is still little or evennot existing. The basic nuclear properties such as binding energies, half-lives, neutron-inducedor neutron-capture reaction cross-sections, play an important role in theoretical simulations andcan vary or even drastically alternate results of these studies. Therefore, a considerable effortwas put forward to access neutron-rich isotopes at radioactive ion-beam facilities like ISOLDE at CERN. The goal of this PhD thesis is to describe the experimental work done for the precision mass measurements of neutron-rich cadmium (129-131Cd) and caesium (132,146-148Cs) isotopes. Measurements were done at the on-line radioactive ion-beam facility ISOLDE by using the fourtrap mass spectrometer ISOLTRAP. The cadmium isotopes are key nuclides for the synthesis of stable isotopes around the mass peak A = 130 in the Solar System abundance
