Agriculture Reference
In-Depth Information
9.
S
AMPLE
P
REPARATION
M
ETHODS
Sample preparation is the process of extracting chemical residues from a
sample and the subsequent purification of the extract to isolate the residues of
interest and remove any matrix interferents that may affect the detection
system. Even with the advance of separation and detection techniques, sample
preparation is a vital part of the analytical process and effective sample
preparation is vital for achieving reliable results and maintaining instrument
performance [88].
The EU Commission Decision 2002/657/EC and the Commission
Decision 93/256/EEC [87, 89]
lays down criteria for the identification and
quantification of veterinary drug residues in food of animal origin. Among the
general considerations it states that ―the sample should be obtained, handled
and processed in such a way that there is a maximum chance of detecting the
analyte, if present‖. Every analytical procedure should be developed, validated
and performed with this goal in mind [90].
There have been quite a number of changes in the approach to preparing
samples throughout recent years due to the widespread application of mass
spectrometry. While in the past, methods were only capable of analysing lower
numbers of residues (usually a single class of drug) [91-95], mass
spectrometry now offers the possibility to analyse vast numbers of residues in
a single run [96-99]. As a result, there is now a tendency to focus towards
more generic extraction and clean-up procedures to cover the wide range of
veterinary drugs that can be found in food of animal origin [99-101].
Although the use of mass spectrometry permits the use of simpler generic
clean-up methods, effective removal of matrix constituents is indispensable as
these may affect the performance of the mass spectrometer, particularly ion-
suppression and enhancement effects [102].
Besides classical liquid-liquid extraction, liquid-liquid partitioning and
the well-established solid-phase extraction, a number of new formats have
now found applications in residue analysis. QuEChERS (Quick, Easy, Cheap,
Effective, Rugged and Safe) approach [100-101], ultra-filtration [103], on-line
SPE [104]
and high throughput approaches such as 96-well plates are now
beginning to find purpose in the area. There is a constant need for new
techniques that are faster, cheaper, require less solvent and are amenable to
automation.
