State-of-the-art purification of biomolecules, as well as separation of complex omic mixtures, is crucial for modern biomedical research. Mass spectroscopy (MS) represents a technique that both requires very clean biomedical samples and can substantially assist liquid chromatography (LC) separations, using either LC-MS or LC-MS/MS methods available. Here, a brief overview of the applicability of LC-MS/MS methodology for structural analyses of complex omic mixtures without prior purification of each sample component will be given. When necessary bioinformatic tools are available, these can be carried out quite quickly. However, manual data analysis of such complex mixtures is typically very slow. On the other hand, the need for high-level purity of protein samples for modern biomedical research will be discussed. Often, modification of protein purification protocols is needed, or additional purification steps may be either required or preferred. In the context of mass spectroscopy-related biomedical research, purification of pmol and subpmol amounts of biomedical samples, as well as commercial availability of pmol amounts of purified standards will be discussed.