Determination of Glycan structure use MS/MS. • Problem • Structure of glycan is diverse- complex tree structure, isomeric molecules, number of glycan. • Glycan is secondary gene products, hard to predict from genome sequence. • Double counting peaks. • Current method • De novo sequencing from tandem MS data. • Generate candidate glycan structure then score with experimental spectrum. • 24 spectra identified 58% glycan topologies, each topologies in Top 4 ranking. • Our method • Using biology prior knowledge to limit the number of candidate glycan. Reduce sample space. • Incorporate with HCD data to determinate the linkage.