Agriculture Reference
In-Depth Information
transform [88]. In this way, Fourier transformation of the acquired transient together
with the use of a C-shaped storage trap (called C-trap), employed to store and cool
ions before injection into the Orbitrap, allows wide mass range detection with high
resolving power, mass accuracy, and dynamic range [89]. Thus, this device performs
as a high-resolution mass analyzer, providing high mass accuracy (2
5 ppm) and a
mass resolving power up to 100,000 FWHM (
m
/
z
200) that allows a proper
discrimination between isobaric interferences and ions of interest in most cases [88]
and provides a large dynamic range over which accurate masses can be
determined [89].
The
-
first commercial form of this instrument was a hybrid analyzer, which
coupled a LIT mass spectrometer with an Orbitrap
-
MS via a RF-only trapping
quadrupole with a curved axis (LTQ
-
Orbitrap by Thermo Fisher). The combina-
MS allowed high-quality accurate mass MS
n
spectra. In
this way, the results generated by MS/MS provided important information on
structural characteristics of analytes and allowed utmost con
tion of LIT and Orbitrap
-
dence in target
analyte identi
cation. However, the main pitfall of this instrument is the scan
speed, which is sometimes insuf
cient for chromatographic analyses due to the
LIT analyzer.
A nonhybrid benchtop version of the Orbitrap mass analyzer was next commer-
cialized: the Exactive
TM
Orbitrap (single-stage Orbitrap). This instrument was reduced
in both size and cost in comparison with the
first hybrid system, facilitating its use in
routine applications. The new system is capable of generating fragmentation infor-
mation by a nonselective MS/MS mode using higher energy collision dissociation
(HCD) in a collision cell without precursor ion selection. In this way, structural
information can be obtained for compounds of interest and fragment ions can be used
for con
rmation in
nontarget or unknown analyses. The Exactive technology currently provides resolu-
tions ranging from 10,000 to 100,000 FWHM (
m
/
z
200), depending on the goal of the
analysis (Figure 6.1). The resolution is an important advantage in the area of VD
residue analysis owing to the fact that higher resolution and selectivity than TOF
instruments can be achieved. Therefore, the analyte and the matrix-related isobaric
interferences can be differentiated, allowing for more sensitive detection of analytes
in complex matrices (Figure 6.2). Furthermore, the dynamic range with accurate
mass measurements is wider than those provided by other HRMS analyzers such as
TOF
rmation in targeted analyses, as well as for identi
cation and con
-
MS or QqTOF
-
MS.
6.3.2.4 Other Analyzers
In this section, the application of other analyzers such as IT (also known as
quadrupole IT, QIT), LIT, and QqLIT is brie
y discussed. These instruments belong
to the group of LRMS detectors because they generally produce unit resolution.
Despite the fact that they are not HRMS analyzers, they can be mentioned here
because of their ability to carry out the identi
cation and structural elucidation of
target analytes, impurities, or metabolites.
