Ion mobility spectrometry-mass spectrometry (IMS–MS) can be used for the simultaneous characterization of the chemical composition and molecular structures of compounds in the gas phase. It can be used in conjunction with chemical ionisation, similar to the nitrate CIMS, or it can be equipped with an electrospray inlet for offline measurements.

The instrument employs a mass spectrometer to determine the mass to charge ratio of molecules. Before the sample flow is passed into the mass spectrometer however, the molecular structure is investigated by passing the flow containing the ions through a drift tube subjected to an electric field. Compared to normal mass spectrometry, this technique allows resolution of isomeric structures and the investigation of molecular clusters under atmospheric conditions. The IMS-measurement technique is described by Krechmer et al 2016.

The IMS-MS maintained by the smog chamber group is built by TOFWERK.
Ion mobility spectrometry–mass spectrometry (IMS–MS) for on- and offline analysis of atmospheric gas and aerosol species.
Krechmer, J. E., Groessl, M., Zhang, X., Junninen, H., Massoli, P., Lambe, A. T., Kimmel, J. R., Cubison, M. J., Graf, S., Lin, Y.-H., Budisulistiorini, S. H., Zhang, H., Surratt, J. D., Knochenmuss, R., Jayne, J. T., Worsnop, D. R., Jimenez, J.-L., and Canagaratna, M. R., 2016:
Atmos. Meas. Tech., 9, 3245-3262,