We obtained the nearly complete structural elucidation of oligosaccharide components, including sequence, linkage, and even stereochemistry in the picomolar levels. The "catalog-library" approach is used for elucidating the structures of minor components in a mixture of oligosaccharides. Oligosaccharides released from a family of glycoproteins are often composed of a small finite set of monosaccharides. In this regard, the numerous oligosaccharide species are analogous to the products found in syntheses involving combinatorial libraries. The great structural diversity in the library is the result of the nearly infinite combinations in which even a small number of monosaccharides can be arranged. Fortunately, structural similarities exist between different oligosaccharides, as specific substructural motifs are preserved among different compounds. We propose that a catalog of substructural motifs can be identified and characterized by collision-induced dissociation mass spectrometry. The catalog is constructed from a set of known compounds that have been fully structurally elucidated by, for example, nuclear magnetic resonance. The catalog consists of the characteristic fragmentation patterns belonging to a set of specific substructural motifs. Collision-induced dissociation is used to determine the presence of these motifs and reconstruct the structures of less abundant components.