in a database ms n spectrum search , search of a known compound whose principal chain is identical to that of an unknown compound is enabled , thereby allowing analysis of an entire structure even if the entire structures of the known compound in database and that of the measured unknown compound are not identical . the ms n spectrum obtained in the ms n measurement of the unknown compound is compared with all the ms m spectra in the database regardless of ms n generation . in the ms n measurement of a series of related compounds including various types of different side chains of the same principal chain , such as in the case of biopolymers , it becomes possible to determine the structure of the principal chain using a database search even if the entire structure is not clear . and the estimation of the entire structure is made possible on the basis of the principal chain structure .