The objectives of this project are twofold and range from fundamental understanding of the separation process of isomers using differential mobility spectrometry (DMS) hyphenated to tandem mass spectrometry (MS/MS) to developing robust methodologies for isomer identification and quantification for targeted metabolomics analyses. Our ambition is thus to bridge gap between development of gas phase physical chemists (partner 1) and clinical biology (partner 2). Our idea is to couple three orthogonal techniques: DMS, MS/MS, and an isomer-selective ion fragmentation based on infrared absorption, which could be considered as a « selective multiple reaction monitoring » (IR-MRM) method. Proof of principle of the application of our DMS-MS/MS(IR) approach for the identification of metabolite isomers has been published in 2018. Current standard protocols based on the coupling of liquid chromatography to tandem mass-spectrometry (LC-MS/MS) have some drawbacks which could be overcome with DMS-MS/MS(IR): large volume of (toxic) solvents to be recycled, and the fact that only a set of molecules with comparable polarities can be isocratically separated. In adding, separation of relevant metabolites from isobaric and/or isomeric compounds is often difficult. Through systematic studies of sets of targeted metabolites, relevant for different MDs, we want to challenge the robustness of DMS. Our analytical targets are biomarkers of metabolic diseases (MDs), which are life-threatening inherited metabolic defects that irremediably lead to significant organ dysfunctions (i.e. brain, liver, cardiac, kidney, muscle...). Two applications dedicated to MD diagnosis will be performed in order to address the topics of emergency in metabolic diagnosis and newborn screening from blood samples.