A modified version of the classic Wiley-McLaren time-of-flight mass sp
ectrometer (TOFMS) is presented here. Owing to a second-order compensa
tion of the initial position effect, a mass resolution m/deltam higher
than 2000 is obtained with large ion volumes, of the order of 0.2 cm3
for Na55+ (1265 a.m.u.). Sodium clusters Na(n)+ with n up to 530 (con
gruent-to 12200 a.m.u.) are separated. The spectrometer can be used fo
r the analysis of ionized clusters in a mass range from 1 to about 200
00 a.m.u. as well as for the measurement of the kinetic energy of mole
clar fragments after a Coulomb explosion of a molecule. The performanc
e of this spectrometer is demonstrated with sodium clusters and molecu
les.