On the combination of a linear field free trap with a time-of-flight mass spectrometer

Abstract

A new instrument has been developed which combines a rf ring electrode trap and a time-of-flight mass spectrometer (TOF-MS). The wide field free storage volume of such a trap enables the study of low temperature ion-molecule collisions; however it is not straightforward to match the nonlocalized ion cloud to the TOF-MS. For obtaining sufficient mass resolution, a special pulse sequence has been developed to transfer the ions from the whole trap volume to a small region in the vicinity of the exit electrode. Additional compression is achieved via buffer gas relaxation prior to extracting the ions. Using a linear flight path of 57 cm, a mass resolution of about 50 is routinely achieved. The mass range of the whole instrument, which is determined by the operating conditions both of the trap and the TOF-MS, has been estimated to be 3–700 u. The actual characteristics of the instrument such as mass range, resolution, and dynamical range have been determined and the results have been analyzed. As a typical application of the new instrument, the growth of (CO)n+ cluster ions is investigated at 80 K. The simultaneous detection of all masses of interest as a function of storage time allows one to follow in detail the kinetics of the reaction and loss processes involved. Limitations of the method are discussed together with ways to overcome them in an improved setup.