Ion mobility spectrometry combined with ultra-performance liquid chromatography/mass spectrometry for the study of natural products

The major goal in natural products (NP) research is to interrogate complex extracts for the purposes of metabolic exploration and molecular discovery. In order to achieve this objective, NP studies rely on accurate and selective acquisition of all possible chemical information, which include the maximization of the number of detected metabolites and their correct molecular assignments. These requirements however, are intrinsically subordinate upon the employed analytical method and its capabilities considering chemical coverage and structural information. LC-MS has been recognized as the most powerful strategy to explore the chemical diversity of crude extracts. It is orders of magnitude more sensitive than nuclear magnetic resonance (NMR) and provides important chemical information in an extended selective analysis due to the pre-ionization chemical separation. Nonetheless, NP characterization by LC-MS is still a massive task, with two major drawbacks: the difficulty in achieve high chemical coverage due to the complex and convoluted nature of biological samples, and the limitations of MS in terms of structural assignment involving high dependence on the chemical behavior in the gas-phase, from ionization efficiency to distinct fragmentation expression. Here we demonstrate the value of combining UHPLC-MS/MS with ion mobility spectrometry (IMS) to separate and identify natural products. IMS-MS adds an orthogonal dimension of separation based on ion gas-phase conformation. Together with the UPLC separation and high-resolution MS/MS, it is possible to enhance peak capacity, spectral clarity and fragmentation specificity.