A method identifies glycopeptides in a sample. The method includes converting a mass spectrum of MS1 precursors of the sample into a plurality of nodes in a graph, each node corresponding to one mass and one retention time of a glycopeptide to be identified in the sample; calculating differences in the mass and/or retention time between all combinations of pairs of the nodes; generating a graph theoretic network of the nodes; and predicting compositions of the glycopeptides in the sample based on the graph theoretic network of the nodes so as to identify the glycopeptides.