Thermo Orbitrap Fusion Series - Page 112

Glossary: mass-to-charge ratio (m/z)
94 Orbitrap Fusion Series Hardware Manual Thermo Scientific
mass-to-charge ratio (m/z) An abbreviation used to
denote the quantity formed by dividing the mass of
an ion (in Da) by the number of charges carried by
the ion. For example, for the ion C7H7
2+
,
m/z = 45.5.
molecular ion An ion formed by the removal (positive
ion) or addition (negative ion) of one or more
electrons to/from a molecule without fragmentation
of the molecular structure.
MS scan modes Scan modes where only one stage of
mass analysis is performed. The scan types used with
the MS scan modes are full-scan type and selected
ion monitoring (SIM) scan type.
MS
n
scan mode Scan modes where 2 to 10 stages of
mass analysis are performed. The scan power equals
2 to 10, where the scan power is the power n in the
expression MS
n
. MS
n
is the most general expression
for the scan mode, which can include the following:
• The scan mode corresponding to the two or more
stages of mass analysis in a two-stage full- or
narrow-scan experiment.
• The scan mode corresponding to the 3 to 10 stages
of mass analysis (n =3 to n = 10) in a multistage
full-scan experiment.
multipole A symmetrical, parallel array of (usually)
four, six, or eight cylindrical rods that acts as an ion
transmission device. An RF voltage and DC offset
voltage are applied to the rods to create an
electrostatic field that efficiently transmits ions along
the axis of the multipole rods.
multipole DC offset voltage A DC voltage applied to
a multipole rod assembly. The multipole DC offset
voltage helps to define the translational kinetic
energy of the ions within the assembly.
multipole RF voltage The amplitude of the RF
voltage applied to the multipoles.
N
nanoelectrospray ionization (nanoESI or NSI) A
type of electrospray (ESI) that accommodates very
low flow rates of sample and solvent at 1–20 nL/min
(for static nanoelectrospray) or 100–1000 nL/min
(for dynamic nanoelectrospray, which is also called
nanoESI nanoLC gradient separation).
O
Orbitrap mass analyzer A type of Fourier transform
mass analyzer. The Orbitrap mass analyzer consists of
a spindle-shaped central electrode surrounded by a
pair of bell-shaped outer electrodes. Ions inside the
mass analyzer orbit in stable trajectories around the
central electrode with harmonic oscillations along the
length of the electrode. Two detection electrodes
record an image current of the ions as they undergo
harmonic oscillations. A Fourier transformation
extracts different harmonic frequencies from the
image current.
An ion's mass-to-charge ratio (m/z) is related to the
frequency f of its harmonic oscillations and to the
instrumental constant k by:
m/z = k/f
2
P
peak threshold The minimum number of intensity
counts per sampling interval that is required before a
signal is recorded.
peak width The distance across a peak measured at a
selected peak-height level, in minutes or mass units.
The peak-height level is usually specified as a
percentage of the maximum peak height.