This learning module is written for undergraduate chemistry researchers who are already familiar with fundamentals of separation mechanisms, separation efficiency and figures of merit for free zone capillary electrophoresis and MEKC, as well as basic aspects of operation of a capillary electrophoresis system including sample introduction, the development of operating protocol, and anticipation of experimental outcome. These concepts are covered in Learning Modules I-III. The experiment outlined in this Module may be accomplished using a commercial or custom-built capillary electrophoresis system. The first step of this learning module requires the user to develop and document experimental procedures that will lead to the determination of retention factor of MEKC separations of four NSAIDs. Step 2 requires the user to determine retention factors experimentally for four NSAIDs using the protocol formulated in Step 1. The last step (3) requires the user to perform qualitative and quantitative analyses of an unknown sample using MEKC. This exercise outlined in step 3 provides the user an opportunity to assess her or his laboratory skill and knowledge of the operation of MEKC. The experiment outlined here is performed with recommended chemicals (n-decanophenone, dimethylformamide, flurbiprofen, naproxen, sulindac, tolmetin). The experiment may be completed with other compounds, and alternative chemicals are outlined in the instructor’s manual accompanying this material. Successful completion of Learning Module IV assists the user in acquiring the skills necessary to apply MEKC to determination of samples.