BACKGROUND
Ion mobility spectrometry (IMS) is a rapid separation tool that can be coupled with several sampling/ionization methods, other separation techniques (e.g., chromatography), and various detectors (e.g., mass spectrometry). This technique has become increasingly used in the last 2 decades for applications ranging from illicit drug and chemical warfare agent detection to structural characterization of biological macromolecules such as proteins. Because of its rapid speed of analysis, IMS has recently been investigated for its potential use in clinical laboratories.
CONTENT
This review article first provides a brief introduction to ion mobility operating principles and instrumentation. Several current applications will then be detailed, including investigation of rapid ambient sampling from exhaled breath and other volatile compounds and mass spectrometric imaging for localization of target compounds. Additionally, current ion mobility research in relevant fields (i.e., metabolomics) will be discussed as it pertains to potential future application in clinical settings.
SUMMARY
This review article provides the authors' perspective on the future of ion mobility implementation in the clinical setting, with a focus on ambient sampling methods that allow IMS to be used as a “bedside” standalone technique for rapid disease screening and methods for improving the analysis of complex biological samples such as blood plasma and urine.
Lipidomics has great promise in various applications; however, a major bottleneck in lipidomics is the accurate and comprehensive annotation of high-resolution tandem mass spectral data. While the number of available lipidomics software has drastically increased over the past five years, the reduction of false positives and the realization of obtaining structurally accurate annotations remains a significant challenge. We introduce Lipid Annotator, which is a user-friendly software for lipidomic analysis of data collected by liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS). We validate annotation accuracy against lipid standards and other lipidomics software. Lipid Annotator was integrated into a workflow applying an iterative exclusion MS/MS acquisition strategy to National Institute of Standards and Technology (NIST) SRM 1950 Metabolites in Frozen Human Plasma using reverse phase LC-HRMS/MS. Lipid Annotator, LipidMatch, and MS-DIAL produced consensus annotations at the level of lipid class for 98% and 96% of features detected in positive and negative mode, respectively. Lipid Annotator provides percentages of fatty acyl constituent species and employs scoring algorithms based on probability theory, which is less subjective than the tolerance and weighted match scores commonly used by available software. Lipid Annotator enables analysis of large sample cohorts and improves data-processing throughput as compared to previous lipidomics software.
Novel
synthetic anabolic androgenic steroids have been developed not only
to dodge current antidoping tests at the professional sports level,
but also for consumption by noncompetitive bodybuilders. These novel
anabolic steroids are commonly referred to as “designer steroids”
and pose a significant risk to users because of the lack of testing
for toxicity and safety in animals or humans. Manufacturers of designer
steroids dodge regulation by distributing them as nutritional or dietary
supplements. Improving the throughput and accuracy of screening tests
would help regulators to stay on top of illicit anabolic steroids.
High-field asymmetric-waveform ion mobility spectrometry (FAIMS) utilizes
an alternating asymmetric electric field to separate ions by their
different mobilities at high- and low-fields as they travel through
the separation space. When coupled to mass spectrometry (MS), FAIMS
enhances the separation of analytes from other interfering compounds
with little to no increase in analysis time. Here we investigate the
effects of adding various cation species to sample solutions for the
separation of structurally similar or isomeric anabolic androgenic
steroids. FAIMS-MS spectra for these cation-modified samples show
an increased number of compensation field (CF) peaks, some of which
are confirmed to be unique for one steroid isomer over another. The
CF peaks observed upon addition of cation species correspond to both
monomer steroid–cation adduct ions and larger multimer ion
complexes. Notably, the number of CF peaks and their CF shifts do
not appear to have a straightforward relationship with cation size
or electronegativity. Future directions aim at investigating the structures
for these analyte–cation adduct ions for building a predictive
model for their FAIMS separations.
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