Agriculture Reference
In-Depth Information
method, the average signal suppression for all compounds improved. In conclusion,
the authors attributed all these improvements to the higher resolution (50,000 versus
15,000 FWHM) and the superior mass stability of the Orbitrap over the previously
used TOF instrument.
Single-stage Orbitrap
MS was also used for the determination of some anthel-
mintic drugs and phenylbutazone residues in milk and muscles [105], obtaining good
performance characteristics compared with the QqQ
-
MS/MS method (Table 6.2).
Another example of the successful application of Orbitrap
-
-
MS, using HPLC
-
LTQ
g/kg concentrations of chlorampheni-
col in meat products [114]. Because of the higher mass accuracy of the extracted ion
obtained with LTQ
-
Orbitrap was the determination of sub-
μ
MS, which minimizes matrix interferences, this method
consisted of a simpler sample preparation compared to that required by a traditional
analysis of chloramphenicol. Selectivity is achieved here by the MS instrument and
not by the application of tedious extraction methods. The high resolution and high
accurate mass used to detect chloramphenicol greatly reduced matrix interferences
and increased the signal to noise ratio, achieving LOQ of 0.1
-
Orbitrap
-
μ
g/kg when isotope
internal standard calibration was used (Table 6.2). The application of HRMS detected
the presence of false positives of chloramphenicol in some of the samples analyzed
by QqQ. In spite of the fact that the diagnostic ion found in the suspected samples
by LC
MS/MS was outside the range of maximum permitted tolerances, the
inexistence of chloramphenicol was unambiguously demonstrated by HRMS.
The application of HRMS technologies as con
-
QqQ
-
rmation tools was shown by
Marchesini et al. [115,116], who applied TOF
-
MS technology for unambiguous
identi
fluoroquinolones in chicken. These works showed the feasibility of
coupling the simultaneous screening of
cation of
fluoroquinolones using a dual surface plasmon
resonance biosensor immunoassay in parallel with LC
-
TOF
-
MS for their con
rmation.
Six
fluoroquinolones were simultaneously screened at or below their MRLs in chicken
muscles [115] and the noncompliant samples were further concentrated and fractionated
with gradient LC. The ef
uent was split toward two 96-well fraction collectors resulting
in two identical 96-well plates. One fraction was rescreened with the dual biosensor to
identify the immunoactive fractions and the second one was analyzed with high-
resolution LC
-
TOF
-
MS [115] and with nano-LC
-
TOF
-
MS [116]. Both studies
demonstrated the possibility to screen and identify known
fluoroquinolones and the
potential for discovering and identifying unknown compounds.
Even though published screening methods employing IT technology to analyze
VDs in food samples can be easily found, in general, this analyzer has been more
frequently used for quanti
cation and con
rmation. LC
-
IT
-
MS has been demon-
strated to be an adequate con
rmatory tool within the group of LRMS analyzers, due
to the different scanning modes. Two of these modes have been compared by
Fagerquist et al. [49]. A con
β
rmatory method of 11
-lactam antibiotics in kidney
MS/MS with SRM and MS n scanning modes was developed. They
compared the advantages of SRM
using HPLC
-
IT
-
MS n ( n =
2 or 3) and full scan MS n ( n =
-
2 or 3) for
MS n mode provided
analysis of unknown incurred tissue. They found that the SRM
-
rapid and unambiguous identi
cation of analytes in the unknown incurred tissues,
whereas full scan MS n mode required manual mass
'
'filtering'
'
for each analyte to
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