Agriculture Reference
In-Depth Information
v. High-throughput capabilities owing to these instruments requiring neither
optimizing the MS conditions to detect each analyte nor readjusting the
retention time windows such as in SRM-based methods.
vi. High-throughput capabilities considering that screening and identi
cation can
be carried out in one single injection.
city due to both high mass accuracy and
resolving power, and they permit the study of target, posttarget, and unknown
residues. These advantages, together with improved quanti
Consequently, they provide high speci
cation characteristics,
make the recent HRMS technologies adequate for both screening and con
rmation
methods.
In the following sections, a brief discussion of the chromatographic conditions as
well as HRMS analyzers used for the determination of VDs is given.
6.3.1 Chromatographic Separation
Chromatographic separation of VDs has currently relied on the use of LC, due to low
volatility and thermolabile characteristics of many of these compounds, although
some of them such as chloramphenicol,
florfenicol, and thiamphenicol have been
traditionally determined by GC [55]. The conventional LC systems coupled withMS
analyzers, in particular HPLC
-
QqQ
-
MS/MS, have become the techniques of choice
in the
field of analysis of VD residues in foodstuffs. However, new high-resolution
analyzers, based on full scan MS, require an adequate chromatographic separation,
since a faster elution with superior resolution and improved sensitivity is needed to
increase peak intensity and minimize interferences from coeluting peaks. Besides,
the high number of compounds to be separated may increase run times, which will
become relatively long by employing conventional LC systems. Therefore, advances
in conventional LC by utilization of ultrahigh performance liquid chromatography
(UHPLC) allowed low-dead-volume and high-pressure (1000 bar) LC equipment,
providing new strategies to improve resolution, maintaining or even shortening run
times. An essential aspect of the UHPLC concept is the use of sub-2
m particle for
the stationary phase, while maintaining other aspects of the column geometry. This
allows faster separation and/or increased peak capacity (i.e., the number of peaks that
can be separated in a given time window). Today, new high-resolution analytical
techniques for unambiguous identi
μ
cation of VDs in foodstuffs of animal origin are
mainly based on UHPLC
HRMS [56,57].
In this context, chromatographic separation of VDs with UHPLC analysis usually
involves reversed-phase LC (RPLC) using alkyl-bonded silica columns (C18 and C8),
although other columns such as phenyl [58,59] or C12-based stationary phases [60]
have also been used.
In relation to the mobile phase, it is usually selected as a compromise between
optimal chromatographic separation, adequate ionization ef
-
ciency, and overall MS
performance. The most suitable solvents for LC
HRMS
are water, methanol, and acetonitrile. Consequently, the mobile phases employed for
the separation of a single family or multiple families of VDs have been mixtures of
-
MS and speci
cally for LC
-
