Non-isobaric time-of-flight correction for isobar resolving in MR-ToF mass spectrometry

Abstract

A development in multi-reflection time-of-flight (MR-ToF) mass spectrometry is presented with which isobars are resolved by means of an offline correction with the signal of a non-isobaric ion species. The method is demonstrated for a pair of Cr2+ isobars with a relative mass difference of 1.8∙10-5, with either an additional, non-isobaric Cr2+ or a CrO+ ion appearing in the same time-of-flight spectrum, although at a different number of revolutions during the same storage time. This is in contrast to earlier applications where ToF shift corrections are performed with ions at identical revolution numbers, typically isobars that are also acting as mass-reference ions. It is shown that ions of virtually any mass simultaneously stored in the MR-ToF analyzer can be employed. This is particularly useful in situations where both the ions of interest and the reference ions for mass calibration have only small count rates not sufficient for the ToF-shift corrections. For the present system, the resolving power increases by more than a factor of two when the offline drift correction is applied.