Drift tube ion mobility-mass spectrometry

Measurements to obtain experimental collision cross sections (^DTCCS_He) have been conducted on an in-house-constructed DT-IM-MS instrument (iMob), which is described in detail elsewhere.26 Briefly, ions are generated using a nano-electrospray ionization (nESI) source and subsequently pulsed into an ion mobility cell in which they travel under the influence of a weak electric field (10–15 V cm^–1) through helium buffer gas (∼5 mbar). After ion separation in the ion mobility cell, the ions of interest are m/z-selected using a quadrupole mass filter and their arrival time distributions (ATDs) are recorded by measuring their time-dependent ion current. ATDs have been recorded at six different drift voltages (950–1200 V) and were fitted by Gaussian functions. The center of each Gaussian corresponds to the drift time of a single species and is further converted into a ^DTCCS_He using the Mason–Schamp equation.21,22