Mass selective blanking in a compact multiple reflection time-of-flight mass spectrometer

In a time-of-flight mass spectrometer with a reflectron (RTOF), an additional small ion mirror, named Hardmirror, is used to increase the mass resolution and to efficiently blank out selected mass lines. Since the mass resolution of a RTOF spectrometer mainly depends on the effective ion driftpath, an increase in mass resolution is achieved by enlarging the driftpath, either by expanding the distance between the ion source and the reflectron or by using multiple reflections. The overall dimension of the instrument was severely constrained so that an elongation of the driftpath was not an option. Using multiple reflections, facilitated by the Hardmirror, we found a way to double the flight path without doubling the distance between the source and the reflectron. In addition with this design we were able to blank out selected mass lines by reducing its intensities by a factor of more than 1000. Blanking out mass lines is performed with an electrical pulse temporarily added to the potential of the Hardmirror's backplane electrode. The effect of this blank pulse is to geometrically defocus ions so they do not reach the detector. (C) 1999 Elsevier Science B.V.