Differential Mobility Spectrometry-Driven Shotgun Lipidomics

Abstract

The analysis of lipids by mass spectrometry (MS) can provide in-depth characterization for many forms of biological samples. However, such workflows can also be hampered by challenges like low chromatographic resolution for lipid separations and the convolution of mass spectra from isomeric and isobaric species. To address these issues, we describe the use of differential mobility spectrometry (DMS) as a rapid and predictable separation technique within a shotgun lipidomics workflow, with a special focus on phospholipids (PLs). These analytes, ionized by electrospray ionization (ESI), are filtered using DMS prior to MS analysis. The observed separation (measured in terms of DMS compensation voltage) is affected by several factors, including the m/z of the lipid ion, the structure of an individual ion, and the presence of chemical modifiers in the DMS cell. Such DMS separations can simplify the analysis of complex extracts in a robust and reproducible manner, independent of utilized MS instrumentation. The predictable separation achieved with DMS can facilitate correct lipid assignments among many isobaric and isomeric species independent of the resolution settings of the MS analysis. This leads to highly comprehensive and quantitative lipidomic outputs through rapid profiling analyses, such as Q1 and MRM scans. The ultimate benefit of the DMS separation in this unique shotgun lipidomics workflow is its ability to separate many isobaric and isomeric lipids that by standard shotgun lipidomics workflows are difficult to assess precisely, for example, ether and diacyl species and phosphatidylcholine (PC) and sphingomyelin (SM) lipids.

Structural identification of triacylglycerol isomers using electron impact excitation of ions from organics (EIEIO)

“…Infused flow rate of working solution in this work was 0.3 ml/h, and ESI voltage was +5,500 V. The detail of DMS (SelexION ® Technology, Sciex) for lipid application was described before (19,22). Separation voltage (SV) of 3,900 V peak to peak, modifier gas of 2-propanol, and DMS temperature of 200°C were continuously applied.…”

“…1-4), the TAG molecule's structures were successfully analyzed and provided information 20% of the monoisotopic base peak of the interfering TAG, if it is present in a very large excess compared with the targeted TAG, convolution of two TAG EIEIO spectra will occur. Hence, we used DMS (22,26,27) to separate analyte TAGs from species such as interfering isotopomers, oxidized TAGs, and other unknown isobaric interferences. Such efforts reduce complexity of the EIEIO spectra and increase the confidence of the deconvolution process for separating contributions from multiple species with similar molecular structures.…”

In-depth sphingomyelin characterization using electron impact excitation of ions from organics and mass spectrometry

“…1) (10). The fundamental behavior of DMS and its application to lipid analysis are described elsewhere (11)(12)(13). Briefly, the DMS cell is mounted in the atmospheric pressure region between the ESI source (held at 5,000 V) and the spectrometer's sampling orifice.…”

“…quadrupole TOF mass spectrometer with a differential mobility spectrometry (DMS) cell (SelexION TM Technology) installed between the ion source and the mass spectrometer (11)(12)(13). The DMS was used to isolate SM from other interfering lipid classes, namely PCs and triacylglycerols (TAGs), prior to analysis.…”

Training in metabolomics research. I. Designing the experiment, collecting and extracting samples and generating metabolomics data

“…[84][85][86] This method separates lipid classes before they are subjected to quadrupole selection of molecular ions and then collision-induced formation of product ions, thereby substantially deconvoluting complex overlapping ions. It has been applied to the separation of leukotriene and protectins.…”