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O
CH 3
N
O
N
CH
3
N
N
N
N
N
OH
OH
OH
Sudan I
Sudan II
para -Red
N
N
N
N
CH
3
N
N
CH 3
N
N
OH
OH
Sudan III
Sudan IV
Figure 4.6.
Structures for some common Sudan dyes found in food as contaminants.
manufacturing and could illegally be used to improve a food product
s appearance, so
methods have been expanded to include an increasing number of azo dyes. Either
APCI ionization or ESI is used. Table 4.4 shows the LC-MS conditions used for a
screen for 13 different dyes by a reversed-phase gradient separation on a C8 column
with positive ESI [59].
As previously discussed, melamine became an issue in 2007 due to its illicit use for
arti
'
cially increasing the nitrogen content in food and feed. The structures of
melamine and cyanuric acid are shown in Figure 4.7. Melamine
s nitrogen content
is higher than that of a typical amino acid, valine, and even higher than one of the
nitrogen-rich amino acids, asparagine. Due to this high nitrogen content and wide
industrial use, it was ideally suited for this fraudulent activity. Methods for its
detection are mainly based around LC
'
MS methods have been
developed for the analysis of melamine in wheat, rice, and other gluten products.
These GC
-
MS/MS, although GC
-
MS methods require extensive sample cleanup with hazardous solvents
and derivatization is needed to give limits of detection typically in the mg/kg
-
 
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