Characterisation of the transfer of cluster ions through an Atmospheric Pressure interface Time-of-Flight mass spectrometer with hexapole ion guides
Abstract. Here we present an alternative approach of an Atmospheric-Pressure interface (APi) Time-Of-Flight mass spectrometer for the study of atmospheric ions and cluster ions, the so-called ioniAPi-TOF. The novelty is the use of two hexapoles as ion guides within the APi. As we will show, hexapoles can accept and transmit a broad mass range enabling the study of small precursor ions and heavy cluster ions at the same time. Weakly bound cluster ions can easily de-cluster during ion transfer depending on the voltages applied to the ion transfer optics. With the example system of H3O+(H2O)n=0–3, we estimate that cluster ions with higher binding energies than 17 kcal/mol can be transferred through the APi without significant fragmentation, which is considerably lower than about 25 kcal/mol estimated from the literature for APi-TOFs with quadrupole ion guides. In contrast to the low fragmenting ion transfer, the hexapoles can be set to a high fragmenting declustering mode for collision-induced dissociation (CID) experiments as well. The ion transmission efficiency over a broad mass range was determined to be in the order of 1 %, which is comparable to existing instrumentation. From measurements under well-controlled conditions during the CLOUD experiment, we demonstrate the instrument's performance and present results from an inter-comparison with a quadrupole based APi-TOF.