18 research outputs found
Recommendations for reporting ion mobility mass spectrometry measurements
© 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc. Here we present a guide to ion mobility mass spectrometry experiments, which covers both linear and nonlinear methods: what is measured, how the measurements are done, and how to report the results, including the uncertainties of mobility and collision cross section values. The guide aims to clarify some possibly confusing concepts, and the reporting recommendations should help researchers, authors and reviewers to contribute comprehensive reports, so that the ion mobility data can be reused more confidently. Starting from the concept of the definition of the measurand, we emphasize that (i) mobility values (K0) depend intrinsically on ion structure, the nature of the bath gas, temperature, and E/N; (ii) ion mobility does not measure molecular surfaces directly, but collision cross section (CCS) values are derived from mobility values using a physical model; (iii) methods relying on calibration are empirical (and thus may provide method-dependent results) only if the gas nature, temperature or E/N cannot match those of the primary method. Our analysis highlights the urgency of a community effort toward establishing primary standards and reference materials for ion mobility, and provides recommendations to do so. © 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc
Near-Complete Structural Characterization of Phosphatidylcholines Using Electron Impact Excitation of Ions from Organics
Although
lipids are critical components of many cellular assemblies
and biological pathways, accurate descriptions of their molecular
structures remain difficult to obtain. Many benchtop characterization
methods require arduous and time-consuming procedures, and multiple
assays are required whenever a new structural feature is probed. Here,
we describe a new mass-spectrometry-based workflow for enhanced structural
lipidomics that, in a single experiment, can yield almost complete
structural information for a given glycerophospholipid (GPL) species.
This includes the lipid’s sum (Brutto) composition from the
accurate mass measured for the intact lipid ion and the characteristic
headgroup fragment, the regioisomer composition from fragment ions
unique to the sn-1 and sn-2 positions, and the positions of carbon–carbon
double bonds in the lipid acyl chains. Here, lipid ions are fragmented
using electron impact excitation of ions from organics (EIEIO)î—¸a
technique where the singly charged lipid ions are irradiated by an
electron beam, producing diagnostic product ions. We have evaluated
this methodology on various lipid standards, as well as on a biological
extract, to demonstrate this new method’s utility
Probing Electrospray Ionization Dynamics Using Differential Mobility Spectrometry: The Curious Case of 4‑Aminobenzoic Acid
Here, we present the separation of two ions that differ
only by the site of protonation of the analyte molecule using differential
mobility spectrometry (DMS). Protonated 4-aminobenzoic acid molecules
(4-ABA) generated by positive-mode electrospray ionization [ESIÂ(+)]
can exist with the proton residing on either the amine nitrogen (N-protonated)
or the carboxylic acid oxygen (O-protonated), and the protonation
site can differ on the basis of the solvent system used. In this study,
we demonstrate the identification and separation of N- and O-protonated
4-ABA using DMS, with structural assignments verified by: (1) the
presence of distinct peaks in the DMS ionogram, (2) the observed effects
resulting from altering the ESIÂ(+) solvent system, (3) the observed <sup>13</sup>C NMR chemical shifts arising from altering the solvent system,
(4) the observation of distinct MS/MS fragmentation patterns for the
two DMS-separated ions, (5) the unique hydrogen–deuterium exchange
behavior for these ions, and (6) the fundamental behavior of these
two ions within the DMS cell, linked back to the structural differences
between the two protonated forms
Distinguishing Cis and Trans Isomers in Intact Complex Lipids Using Electron Impact Excitation of Ions from Organics Mass Spectrometry
We present a mass
spectrometry-based method for the identification
of cis and trans double-bond isomers within intact complex lipid mixtures
using electron impact excitation of ions from organics (EIEIO) mass
spectrometry. EIEIO involves irradiating singly charged lipid ions
with electrons having kinetic energies of 5–16 eV. The resulting
EIEIO spectra can be used to discern cis and trans double-bond isomers
by virtue of the differences in the fragmentation patterns at the
carbon–carbon single bonds neighboring the double bonds. For
trans double bonds, these characteristic fragments include unique
closed-shell and open-shell (radical) products. To explain this fragmentation
pattern in trans double bonds, we have proposed a reaction mechanism
involving excitation of the double bond’s π electrons
followed by hydrogen atom rearrangement. Several lipid standards were
analyzed using the EIEIO method, including mixtures of these standards.
Prior to EIEIO, some of the lipid species in these mixtures were separated
from their isomeric forms by using differential mobility spectrometry
(DMS). For example, mixed cis and trans forms of triacylglycerols
and phosphatidylcholines were identified by this DMS–EIEIO
workflow. With this combined gas-phase separation and subsequent fragmentation,
we could eliminate the need for authentic standards for identification.
When DMS could not separate cis and trans isomers completely, as was
the case with sphingomyelins, we relied upon the aforementioned diagnostic
EIEIO fragment peaks to determine the relative contribution of the
trans double-bond isomer in the mixed samples. We also applied the
DMS–EIEIO methodology to natural samples extracted from a ruminant
(bovine), which serve as common origins of trans fatty acids in a
typical Western diet that includes dairy products
Electron Capture Dissociation in a Branched Radio-Frequency Ion Trap
We
have developed a high-throughput electron capture dissociation (ECD)
device coupled to a quadrupole time-of-flight mass spectrometer using
novel branched radio frequency ion trap architecture. With this device,
a low-energy electron beam can be injected orthogonally into the analytical
ion beam with independent control of both the ion and electron beams.
While ions and electrons can interact in a “flow-through”
mode, we observed a large enhancement in ECD efficiency by introducing
a short ion trapping period at the region of ion and electron beam
intersection. This simultaneous trapping mode still provides up to
five ECD spectra per second while operating in an information-dependent
acquisition workflow. Coupled to liquid chromatography (LC), this
LC-ECD workflow provides good sequence coverage for both trypsin and
Lys C digests of bovine serum albumin, providing ECD spectra for doubly
charged precursor ions with very good efficiency
Characterizing the Tautomers of Protonated Aniline Using Differential Mobility Spectrometry and Mass Spectrometry
The
site of protonation for gas-phase aniline has been debated
for many years, with many research groups contributing experimental
and computational evidence for either the amino-protonated or the <i>para</i>-carbon-protonated tautomer as the gas-phase global
minimum structure. Here, we employ differential mobility spectrometry
(DMS) and mass spectrometry (MS) to separate and characterize the
amino-protonated (N-protonated) and <i>para</i>-carbon-protonated
(<i>p</i>-protonated) tautomers of aniline. We demonstrate
that upon electrospray ionization (ESI), aniline is protonated predominantly
at the amino position. Similar analyses are conducted on another three
isotopically labeled forms of aniline to confirm our structural assignments.
We observe a significant reduction of the relative population of the <i>p</i>-protonated tautomer when a protic ESI solvent is employed
(methanol/water) compared to when an aprotic solvent (acetonitrile)
is employed. We also observe conversion of the <i>p</i>-protonated
species into the N-protonated species upon clustering with protic
solvent vapor post-DMS selectionî—¸a finding supported by previous
experimental data acquired using DMS-MS
Identifying Fenton-Reacted Trimethoprim Transformation Products Using Differential Mobility Spectrometry
A transformation
product of trimethoprim, a contaminant of emerging
concern in the environment, is generated using an electro-assisted
Fenton reaction and analyzed using differential mobility spectrometry
(DMS) in combination with MS/MS techniques and quantum chemical calculations
to develop a rapid method for identification. DMS is used as a prefilter
to separate positional isomers prior to subsequent identification
by mass spectrometric analyses. Collision induced dissociation of
each DMS separated species is used to reveal fragmentation patterns
that can be correlated to specific isomer structures. Analysis of
the experimental data and supporting quantum chemical calculations
show that methylene-hydroxylated and methoxy-containing phenyl ring
hydroxylated transformation products are observed. The proposed methodology
outlines a high-throughput technique to determine transformation products
of small molecules accurately, in a short time and requiring minimal
sample concentrations (<25 ng/mL)
Direct Interface between Digital Microfluidics and High Performance Liquid Chromatography–Mass Spectrometry
We introduce an automated method
to facilitate in-line coupling
of digital microfluidics (DMF) with HPLC-MS, using a custom, 3D-printed
manifold and a custom plugin to the popular open-source control system,
DropBot. The method was designed to interface directly with commercial
autosamplers (with no prior modification), suggesting that it will
be widely accessible for end-users. The system was demonstrated to
be compatible with samples dissolved in aqueous buffers and neat methanol
and was validated by application to a common steroid-labeling derivatization
reaction. We propose that the methods described here will be useful
for a wide range of applications, combining the automated sample processing
power of DMF with the resolving and analytical capacity of HPLC-MS
Rapid Characterization of Naphthenic Acids Using Differential Mobility Spectrometry and Mass Spectrometry
To
analyze the naphthenic acid content of environmental waters
quickly and efficiently, we have developed a method that employs differential
mobility spectrometry (DMS) coupled to mass spectrometry (MS). This
technique combines the benefits of infusion-based MS experiments (parallel,
on-demand access to individual components) with DMS’s ability
to provide liquid chromatography-like separations of isobaric and
isomeric compounds in a fraction of the time. In this study, we have
applied a DMS-MS workflow to the rapid gas-phase separation of naphthenic
acids (NAs) within a technical standard and a real-world oil sands
process-affected water (OSPW) extract. Among the findings provided
by this workflow are the rapid characterization of isomeric NAs (i.e.,
same molecular formulas) in a complex OSPW sample, the ability to
use DMS to isolate individual NA components (including isomeric NAs)
for in-depth structural analyses, and a method by which NA analytes,
background ions, and dimer species can be characterized by their distinct
behaviors in DMS. Overall, the profiles of the NA content of the technical
and OSPW samples were consistent with published values for similar
samples, such that the benefits of DMS technology do not detract from
the workflow’s accuracy or quality
Direct Interface between Digital Microfluidics and High Performance Liquid Chromatography–Mass Spectrometry
We introduce an automated method
to facilitate in-line coupling
of digital microfluidics (DMF) with HPLC-MS, using a custom, 3D-printed
manifold and a custom plugin to the popular open-source control system,
DropBot. The method was designed to interface directly with commercial
autosamplers (with no prior modification), suggesting that it will
be widely accessible for end-users. The system was demonstrated to
be compatible with samples dissolved in aqueous buffers and neat methanol
and was validated by application to a common steroid-labeling derivatization
reaction. We propose that the methods described here will be useful
for a wide range of applications, combining the automated sample processing
power of DMF with the resolving and analytical capacity of HPLC-MS