We measured absolute partial and total cross sections for the electron ionization of hexafluoroethane (C₂F₆) from threshold to 900eV using a time-of-flight mass spectrometer (TOF-MS), which can be operated in a linear and in a reflection mode. Measurements were also made for tetrafluoromethane (CF₄), which is perhaps the most thoroughly investigated complex polyatomic molecule in terms of ionization cross sections, in an effort to demonstrate the reliable performance of our apparatus. Our measurements for both CF₄ and C₂F₆ are compared with other available experimental data and with calculated cross sections.