Tandem-trapped ion mobility spectrometry/mass spectrometry (TIMS/MS): a promising analytical method for investigating heterogenous samples.

Ion mobility spectrometry/mass spectrometry (IMS/MS) is widely used to study various levels of protein structure. Here, we review the current state of affairs in -trapped ion mobility spectrometry/mass spectrometry (TIMS/MS). Two different TIMS/MS instruments are discussed in detail: the first TIMS/MS instrument, constructed from coaxially aligning two TIMS devices; and an orthogonal TIMS/MS configuration that comprises an ion trap for irradiation of ions with UV photons. We discuss the various workflows the two TIMS/MS setups offer and how these can be used to study primary, tertiary, and quaternary structures of protein systems. We also discuss, from a more fundamental perspective, the processes that lead to denaturation of protein systems in TIMS/MS and how to soften the measurement so that biologically meaningful structures can be characterised with TIMS/MS. We emphasize the concepts underlying TIMS/MS to underscore the opportunities tandem-ion mobility spectrometry methods offer for investigating heterogeneous samples.