A miniaturized time-of-flight (TOF) mass spectrometer utilizes an end-cap r
eflectron to achieve high kinetic energy focusing and improved mass resolut
ion. However, the coaxial geometry gives rise to considerable losses in sen
sitivity resulting from reflected ion trajectories close to the center. The
se trajectories were modeled, using initial ion velocity distributions in t
he radial direction up to 300 m s(-1), and the portion of the active area o
f the detector that is utilized was evaluated experimentally using a variab
le diameter iris diaphragm. The sensitivity was improved by modification of
the reflectron by tilting the end-cap electrode 4 degrees and redirecting
the ions to a portion of the detector active area. Sensitivity was then mea
sured as 3 fmol of the peptide substance P. Copyright (C) 2000 John Wiley &
Sons, Ltd.