The alkali-metal ion extraction ability of an inert material, polytetrafluoroethylene (PTFE; empirical formula CF₂), was clarified by characterizing a partially alkali-metal ion-extracted layered compound, K_0.8(Li_0.27Ti_1.73)O₄. Washing K_0.8(Li_0.27Ti_1.73)O₄ in water extracts only 44% of the interlayer K⁺ and no intralayer Li⁺; on the other hand, 53% of the interlayer K⁺ and approximately 10% of the intralayer Li⁺ ions were extracted from K_0.8(Li_0.27Ti_1.73)O₄ by the reaction with PTFE at 350 °C under flowing Ar. A systematic decrease in the lattice parameters a and c along the intralayer directions and an increase in b along the interlayer direction were observed, consistent with the alkali-metal ion deintercalation amount as a function of the reaction temperatures and the reacted PTFE amounts. After the reaction with K_0.8(Li_0.27Ti_1.73)O₄ : CF₂ = 1 : 0.6 in mol, the lattice parameter b increased to 1.5607(3) nm from 1.5522(2) of the pristine K_0.8(Li_0.27Ti_1.73)O₄, and this change in the lattice parameter was approximately one order of magnitude larger than those in a and c.