Complementing Matrix-Assisted Laser Desorption Ionization-Mass Spectrometry Imaging with Chromatography Data for Improved Assignment of Isobaric and Isomeric Phospholipids Utilizing Trapped Ion Mobility-Mass Spectrometry

Abstract

Lipids, such for example the multifaceted category of glycerophospholipids (GP), play a major role in many biological processes. High-resolution mass spectrometry is able to identify these highly diverse lipid species in combination with fragmentation experiments (MS/MS) on the basis of the accurate m/z and fragmentation pattern. However, for the differentiation of isomeric lipids or isobaric interferences, more elaborate separation methods are required. Especially for imaging techniques, such as matrixassisted laser desorption/ionization (MALDI)-MS imaging, the identification is often exclusively based on the accurate m/z. Fragmentation via MS/MS increases the confidence in lipid annotation in imaging approaches. However, this is sometimes not feasible due to insufficient sensitivity and significantly prolonged analysis time. The use of a separation dimension such as trapped ion mobility spectrometry (TIMS) after ionization strengthens the confidence of the identification based on the collision cross section (CCS). Since CCS libraries are limited, a tissue-specific database was initially generated using hydrophilic interaction liquid chromatography-TIMS-MS. Using this database, the identification of isomeric lipid classes as well as isobaric interferences in a lipid class was performed using a mouse spleen sample in a workflow described in this study. Besides a CCS-based identification as an additional identification criterion for GP in general, the focus was on the distinction of the isomeric GP classes phosphatidylglycerol and bis(monoacylglycero)phosphate, as well as the differentiation of possible isobaric interferences based on the formation of adducts by MALDI-TIMS-MS imaging on a molecular level.

LPS-induced lipid alterations in microglia revealed by MALDI mass spectrometry-based cell fingerprinting in neuroinflammation studies

“…4e www.nature.com/scientificreports/ deviation < 1%) with those predicted and previously reported in CCS databases and the literature where available (Suppl. Table ST4) [34][35][36][37][38] .…”

An Organ-Specific Metabolite Annotation Approach for Ambient Mass Spectrometry Imaging Reveals Spatial Metabolic Alterations of a Whole Mouse Body

“…While additional LC–MS/MS analysis after MSI experiments targeting the preselected features allows for metabolite identification with relatively high confidence, the whole workflow may be inefficient and time-consuming. Prebuilt databases support efficient putative identification; for example, the collision cross section database has been used in lipid analysis, which is practicable but limited in MS with ion mobility. , Establishing metabolite databases with LC–MS/MS is believed to greatly enhance the annotation efficiency, in which LC–MS/MS is utilized to acquire mounting identified metabolites and provide a comprehensive reference for MSI analysis. Considering the differences in sample preparation, solvent system composition, and ionization process, the MS signals would be distinct between the two techniques and need to be adapted for MSI.…”

Ion Mobility Mass Spectrometry for the Separation and Characterization of Small Molecules

“…In order to better understand the physiological and pathological processes, it is vital to capture and present this spatiotemporal change. Matrix-assisted laser desorption ionization (MALDI), − infrared matrix-assisted laser desorption electrospray ionization, , DESI, − nano-DESI, ,, LESA, , LAESI, and other ionization techniques equipped with imaging platform and software can achieve this goal, which is helpful to determine the spatiotemporal correlation between metabolites. Like ambient ionization MS, it faces the challenges of dynamic range, peak capacity, and the ability to identify observed species structurally due to the lack of separation process .…”