Biology Reference
In-Depth Information
collision cross-section. A novel method of ion mobility, called
“traveling-wave” ion mobility spectrometry (TWIMS), has been
recently reported [
81
]. Unlike the traditional drift-time IMMS,
a DC pulse is applied sequentially through the ion mobility cell
one segment at a time causing the ions to move forth to the next
potential groove. When ions differing either in charge state or
collision cross sections, or both, are entering the traveling wave
ion guides (TWIG), the less mobile ones may occasionally trans-
verse a wave in backward direction. Those ions lagging behind
the traveling wave will exit later than those surfing on the wave.
This makes the TWIG become an ion mobility separator [
82
].
A hybrid instrument comprising a mass-selecting quadrupole, a
traveling wave ion mobility separator, and an oaTOF analyzer
has been marketed by Waters as Synapt™ mass spectrometry sys-
tems [
81
]. An advantage of this Q-IM-oaTOF MS configuration
is that the sensitivity of the mass analyzer is not compromised by
the duty cycle of the ion mobility cell, as is the case with drift-
tube instruments in which the ion gate is only open for about 1 %
of the duty cycle [
81
]. Continuous introduction of mobility-
selected ions (referred to as SelexION™ technology) has also
been implemented in ABSciex Triple Quad™ and QTRAP
®
plat-
forms [
83
-
85
].
Ion mobility cells have been interfaced to TOF, quadrupole,
ion trap, and FTICR mass spectrometers [
78
], indicating the
analytical power of coupling mobility with mass measurements.
Ion mobility delivers a new dimension of selectivity and perfor-
mance for applications requiring the separation of isobaric spe-
cies. The application of ion mobility in biological research is
gaining more and more popularity. Size, mass, and position are
important parameters that describe a molecule in a biological sys-
tem [
86
]. Ion mobility is capable of separating ions of the same
size on the basis of their cross-section area (shape), whereas imag-
ing MS is used to visualize the spatial distribution of molecules.
The evolution of ion-mobility-based imaging mass spectrometry,
reviewed by Kiss and Heeren [
86
], provides examples of its appli-
cation in analytical studies enabling the simultaneous determina-
tion of size, mass, and position of molecules in biological surfaces.
Advances in the field of proteomics parallel technological advances
in mass spectrometry techniques. The unique capabilities of ion
mobility offer a useful analytical tool for bottom-up [
87
] and
top-down [
88
] proteomics. For instance, an increased ability to
disperse peptide ion signals in the ion mobility dimension facili-
tates parallel tandem mass spectrometry experiments on mobil-
ity-separated b-type and y-type sequence-specific peptide ions.
An approach that combines mass spectrometry, CID, and ion
mobility for top-down proteomics has been recently described
[
88
]. Using this approach, CID product ions are dispersed in two
dimensions, specifically size-to-charge (IM) and mass-to-charge
