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 addition al small ion mirror, named Hardmirror, is used to increase the mass resolut ion and to efficiently blank out selected mass lines. Since the mass resolu tion of a RTOF spectrometer mainly depends on the effective ion driftpath, an increase in mass resolution is achieved by enlarging the driftpath, eith er by expanding the distance between the ion source and the reflectron or b y using multiple reflections. The overall dimension of the instrument was s everely constrained so that an elongation of the driftpath was not an optio n. Using multiple reflections, facilitated by the Hardmirror, we found a wa y to double the flight path without doubling the distance between the sourc e and the reflectron. In addition with this design we were able to blank ou t selected mass lines by reducing its intensities by a factor of more than 1000. Blanking out mass lines is performed with an electrical pulse tempora rily added to the potential of the Hardmirror's backplane electrode. The ef fect of this blank pulse is to geometrically defocus ions so they do not re ach the detector. (C) 1999 Elsevier Science B.V.