Using post source decay technique, matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) is not only a method to determine the molecular weight but also a useful tool to obtain structural information of biomacromolecular compounds. The way to optimize a gridless reflectron for post source decay analysis is demonstrated. A window-independent mass calibration function for fragment ions is described. Delayed ion extraction to improve the resolution of precursor ion selection is also presented.