This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The capability for accurate mass measurements is an important attribute of Fourier transform mass spectrometry (FTMS). Unlike other instrumental methods in mass spectrometry, FTMS still offers significant opportunities to improve mass measurement accuracy (MMA), making it an area of research. Although FTMS can measure ion frequencies to nine significant figures, the conversion of frequency to m/z is difficult because frequency depends on the electric field and the space charge in the ion trap. We are working on methods to shim the electric field (electrical compensation) and to correct for space charge effects. We are also interested in the relation of mass calibration and the fundamentals of ion motion and space-charge effects, and we wish to to improve the basic calibration procedure particularly those that correct for effects of space charge. The advent of matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) have opened the door for FTMS to be used for analyzing at high performance biopolymers, including proteins, oligodeoxynucleotides (ODNs), oligosaccharides, and synthetic polymers. We will pursue accurate mass measurement in these areas and some practical ways to improve MMA.