Agriculture Reference
In-Depth Information
10.
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NALYTICAL
A
PPROACH
Selecting a suitable method of residue analysis will, in many instances,
depend on the problem at hand as well as on the final goal. To quote two
widely different situations, when large sample series have to be monitored for
a group of antibiotics, sample throughput will be an important criterion since
speed is of the essence. In this situation a screening method is selected because
high sample throughput and speed characterize such a method.
When, on the
other hand, samples are suspected to contain an illegal growth-promotor,
method selectivity will undoubtedly be the main criterion because avoiding
false non-compliant results now is of overriding importance. In this situation a
confirmatory method is of interest because provides full or complementary
information enabling to confirm the identity of the substance [105].
10.1 Screening Methods
The full procedure and the methodologies for confirmatory analysis are
costly in time, equipments and chemicals. In addition, they require trained
personnel with high expertise. Control laboratories must face a large number
of samples, with a variety of analytes, to be screened in relatively short periods
of time. Thus, there is a need for screening methods that allow the analysis of
such a large number of samples in short periods of time [121]. This means that
high through-put methods with low cost must be available. These methods
must be able to detect an analyte or class of analytes at the level of interest
[122]. Some false positives (false compliant) are acceptable, as they will be
further submitted for confirmatory analysis. But the method must avoid or
reduce to a minimum the number of false negative results (non-compliant)
because samples considered negative for screening methods will not be further
analysed by more specific procedures.
There are different techniques available for the screening of residues in
animal foods. Antigen and antibody reaction has been used for many years to
detect a wide variety of food constituents including substances responsible for
adulterations and contaminations. The interaction antigen-antibody is very
specific and useful for the detection of residues of chemical and veterinary
drugs in animal foods. The most usual technique consists in the enzyme-
linked-immunosorbent assay (ELISA) and the detection system is usually
based on enzyme-labelled reagents [123].
