Liquid chromatography (LC) experiments for the undergraduate analytical laboratory course often illustrate the application of reversed-phase LC to solve a separation problem, but rarely compare LC retention mechanisms. In addition, a high-performance liquid chromatography instrument may be beyond what some small colleges can purchase. Solid-phase extraction (SPE) cartridges offer an inexpensive alternative, while still providing effective model columns for investigating LC retention mechanisms. We have shown that the four major retention mechanisms (normal-phase, reversed-phase, ion-exchange, and size-exclusion) can be investigated experimentally using two types of SPE cartridges (silica and C18) as columns. The C18 cartridges can be pre-treated with anionic or cationic polymers to produce ion-exchange columns. The concept of post-column detection is also introduced. This experiment is suitable for a first-year general chemistry course or a third-year analytical course to illustrate the importance of solvent polarity and the types of retention mechanisms employed in separation science. (Contains 2 figures and 2 tables.)