Agriculture Reference
In-Depth Information
Nielen et al. [118] discussed the mass resolution and accuracy for LC
-
MS
screening and con
cation of
unknown compounds employing HRMS detectors. The experiments were based
on the screening of the anabolic steroid stanozolol and the designer
rmation of targeted analytes and for
the identi
β
-agonist
“
Clenbuterol-R
”
using screening resolutions of 10,000 FWHM or higher with
mass windows of
50 mDa, employing different HRMS analyzers. It was observed
that accurate mass determination without proper mass resolving power criteria led to
false negative results in MS screening as well as in MS/MS con
±
rmation. Finally, the
authors concluded that only resolutions of 70,000 FWHM or higher allowed reliable
accurate masses of elemental compositions differing in one CO, C
2
H
4,
or N
2
substructure to distinguish between the analytes and coeluting substances. A lack
of mass resolving power was demonstrated for anabolic steroid stanozolol analyzed
using the LC
MS.
Recently, two HRMS techniques, QqTOF
-
QqTOF
-
-
MS and single-stage Orbitrap
-
MS,
were compared with the traditional LRMS detector, QqQ
MS/MS [64], to evaluate
their ability to serve as screening tools. In this work, two screening methods based on
the use of UHPLC
-
-
QqTOF
-
MS (8,000 FWHM) and UHPLC coupled single-stage
Orbitrap
MS (50,000 FWHM) were developed and compared for the determination
of several classes of VDs in milk- and powdered milk-based formula samples. The
performance characteristics of these screening methods were compared in terms of the
uncertainty region and cutoff values. Better results were obtained using the Orbitrap-
based screening method, obtaining narrower uncertainty regions in all cases and lower
cutoff values (Figure 6.5). For the Orbitrap
-
-
MS screening method, cutoff values were
g/kg or higher,
although in all cases and using both analyzers, the obtained cutoff values were lower
than the MRLs established by the EU in the selected matrices. Therefore, the results
clearly suggested that the higher resolving power of the Orbitrap
5.0
μ
g/kg, while for QqTOF
-
MS, the values ranged from 5.0 to 7.5
μ
MS analyzer
ensured adequate high full scan selectivity, which enabled the detection of the
analytes at lower concentrations in these matrices. Additionally, the results
obtained with HRMS techniques were compared with two screening methods
developed with a LRMS analyzer, QqQ [42], one of them based on the selection of
neutral loss or product ions (method A), whereas the other one was based on the use
of a SRM transition for each compound (method B). HRMS analyzers provided
better results than LRMS analyzers. In terms of screening validation parameters,
such as cutoff and uncertainty region, it could be indicated that the single-stage
Orbitrap screening method provided better results than the QqTOF and QqQ
screening methods.
The applicability of UHPLC combined with full scan accurate mass TOF
-
-
MS and
LTQ
MS was also evaluated for the analysis of hormone and coccidio-
stats [102]. UHPLC
-
Orbitrap
-
MS analysis was performed at a resolving power
of 60,000 FWHM and it enabled the detection at accurate mass measurement (
-
LTQ
-
Orbitrap
-
3 ppm
error) of all 14 steroid esters at low ng/kg concentrations, despite the complex matrix
background. A 5 ppm mass tolerance window proved to be essential to generate
highly selective reconstructed ion chromatograms, having reduced background from
the hair matrix. UHPLC
<
-
LTQ
-
Orbitrap
-
MS at a lower resolving power of 7,500
