food hygiene & safety 21
Fig. 4. The
importance of
resolution for
the molecular ion
AND its isotopes.
At high resolution
the complete
molecular
ion cluster
is correctly
detected.
molecular ion cluster and therefore allows automated chromatograms for all 116 compounds (3 ppm window)
assignment of an elemental formula with a high degree at 50 ppb (in matrix). The number of recovered
of confidence. pesticides in different concentrations is shown in Fig. 5.
Analysing highly complex samples such as extracts The data illustrates a greater number of detected
from food or animal feeds, and the screening of compounds (higher sensitivity) with an extraction
☞
regulated substances including pesticides, mycotoxins
and veterinary drugs is a major analytical challenge for
mass spectrometry.
On one hand, the methodology must have a
high intra scan dynamic range in order to detect low
concentrated compounds in presence of high abundant
matrix ions, on the other hand high selectivity and high
sensitivity is needed to avoid false positive, or even worse,
false negative results.
In this procedure an extract from horse feed was
analysed as an example of an extremely complex matrix,
spiked with a mixture of 116 pesticides and mycotoxins.
A dilution series ranging from 2 to 250 ppb (for each
compound) was measured in duplicates at two different
resolution settings. In addition a 100 ppb sample of the
same mixture was analyzed at a resolution of 50 000 in
order to determine the maximum number of detectable Fig. 5. Overlaid extracted ion chromatograms from a mixture of 116
substances for this method. pesticides and mycotoxins at a 100 ppb level. Extraction was done with
LC-MS analysis of the extracted spiked samples 3 ppm mass window. The inset chart shows the number of detected
showed the presence of 95 out of 116 compounds compounds at different concentrations (in matrix) at two different
at 100 ppb in matrix. Fig. 5 shows the overlaid ion resolution settings.
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