Agriculture Reference
In-Depth Information
screening methods are normally followed up using another method that provides
unequivocal con
rmation of identity and may also be used for quanti
cation
purposes. Such follow-up methods are referred to as
“
con
rmatory methods.
”
Validation of con
dence in
detection, at and above a satisfactory reporting limit (RL) for each analyte that is
to be sought. This RL, or screening detection limit (SDL), is likely to correspond to a
threshold or action limit. Such action limits may correspond to regulatory limits or
levels, such as maximum residue levels (MRLs) for pesticides, mycotoxins, and
authorized veterinary drugs. For unauthorized analytes, such as certain veterinary
drugs, the action limit would be the minimum required performance limit (MRPL) as
speci
rmatory methods must establish a degree of con
ed in the particular EU regulation. Any residues that are detected using a
qualitative screening multiresidue method should trigger further analysis using a fully
validated quantitative method.
In this context, we are using the term
“
con
rmatory
method
”
to describe a method
that is used to provide
“
con
rmation of identity
”
of the target analyte(s). In other
publications,
ned as the analysis of a second
subsample in order to check that this second result agrees with the original result (in
terms of both identity and concentration). Selectivity/speci
“
con
rmatory
analysis
”
is correctly de
city is a key component of
con
rmatory methods. The methods must be capable of providing unequivocal
identi
cation of a target analyte from an exclusive signal response. Thus, such
methods should have been developed through a suitable combination of analytical
procedures such as cleanup, chromatographic separation, and spectrometric detection.
Con
rmatory methods are generally not considered to be high throughput and
therefore validation and ongoing AQC requirements of con
rmatory methods are
not covered in this chapter.
3.2.3 Validation of Qualitative Screening Multiresidue Methods for
Pesticide Residues in Foods
Within the con
nes of a topic chapter, it is not feasible to produce validation
procedures for QSMRMs for all the chemical contaminants that are covered in
this topic.
In this section, the focus will be on the use of these methods for analyzing pesticide
residues in foods and veterinary drug residues in products of animal/
sh origins.
However, the same approaches to method validation and analytical quality control
could also be applied to many other food contaminants. Indeed, some workers have
already published QSMRMs that analyze pesticides, veterinary drugs, plant toxins,
and mycotoxins in the same sample extract [6]. MRMs can be considered to be
“
high
because large numbers of analytes can be detected at the same time. They
are therefore normally used to improve ef
throughput
”
ciency by increasing analytical scope
rather than improving the speed of analysis. The main challenge with validating
multiresidue methods is to include a large number of target analytes, probably with
differing physicochemical properties, and cover a wide range of food matrices. In
addition to this, action levels, as speci
ed by regulations/legislation, may be set at
very low concentrations. A number of published methods based on GC
-
MS and LC
