In this laboratory experiment, students follow a step-by-step procedure to prepare and study guest-host complexes in the gas phase using electrospray ionization-mass spectrometry (ESI-MS). Model systems are the complexes of hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) with the guest 4-styrylpyridine (SP). Aqueous solutions of CB7 or CB8 with SP are infused, and full scan spectra are obtained. Students analyze the ESI-MS full scan signals and discuss the structure of the guest-host complexes based on the monoisotopic masses of hosts and guest and observed "m/z" values on the charge states and on the experimental and simulated isotope distributions. Complexes are fragmented, and spectra were obtained. The assignments are further examined taking into account the fragmentation data. The structure and gas phase reactivity of the identified supramolecular associations are discussed in view of the fragmentation patterns and host size.