Agriculture Reference
In-Depth Information
derivatization [45]. However, GC
-
MS-based assays are favored and used for speci
c
applications.
In this context, the combination of LC and MS appears to be a suitable approach
that ful
rmation
for rapid and reliable determination of analytes at low concentrations in complex
matrices. Tandem MS (MS/MS) or multidimensional MS (MS
n
) has presented
remarkable advantages in the
lls key requirements in terms of sensitivity, selectivity, and con
field of residue analysis at trace concentrations in
food samples. QqQ analyzers operating in selected reaction monitoring (SRM)
mode [9,46] or ion trap (IT) analyzers [47,48] operating in product ion scan (PIS)
mode have evolved from single analyte to multianalyte monitoring. However, the
reported methods based on LC
-
QqQ
-
MS/MS or LC
-
IT
-
MS/MS have been limited
to one class or similar classes of VD compounds [49
51]. In addition, the number of
analytes that could be monitored during one chromatographic run is necessarily
limited (e.g., 100 in 10
-
20min analysis time) because of sensitivity and/or limited
number of MS/MS data acquisition time windows that
-
tinonechromatogram.
This limitation is also more remarkable in IT instruments due to their lower scan
speed in comparison with QqQ systems and the type of acquisition mode. On the
other hand, by de
nition, SRM in QqQ and PIS in IT methods are focused on target
compounds, but in certain circumstances, retrospective analyses are demanded.
Therefore, there is an inherent limitation when these analyzers are used: their
inability to detect new/additional residues for which no MS/MS conditions are
programmed in the method. For this aim, it is always necessary to have standards to
optimize MS/MS conditions. Furthermore, the lack of commercial availability of
some reference substances (e.g., active compounds, degradation products, and
metabolites) requires instrumentation that does not need previous individual com-
pound-speci
c instrument tuning.
Due to these new needs, other LC systems coupled with full scan technologies
are being successfully implemented in the area of VD residue analysis, such as
linear ion traps (LITs) [52], TOF, or more recent technologies such as Orbital trap
(Orbitrap
TM
) [53] and a new generation of hybrid instruments such as QqTOF [54],
quadrupole-linear ion trap (QqLIT), or linear-orbital trap (LTQ-Orbitrap). These
HRMS technologies offer several advantages, which can be summarized as
follows:
i. Mass accuracy, which is one of the most important characteristics of HRMS
coupled with LC because it is necessary for an adequate con
rmation and peak
assignment.
ii. Resolving power, which allows the reconstruction of highly selective accurate
mass chromatograms.
iii. Ability to analyze a theoretically unlimited number of compounds in a sample
because these instruments operate basically in the full scan mode.
iv. Possibility of performing retrospective analyses, which means that they let a
careful examination of old raw data sets to search for additional residues
without reinjecting the samples.
