Agriculture Reference
In-Depth Information
OH
NH
2
N
N
N
N
H
N
H
H
2
N
N
2
Cyanuric acid 32.6% Nitrogen
Melamine 66.7% Nitrogen
H
3
C
CH
3
NH
2
H
3
C
CH
3
H
H
2
N
NH
OH
OH
H
2
N
H
O
O
Valine 12.0% Nitrogen
Arginine 32.2% Nitrogen
Figure 4.7.
Chemical structures of melamine and cyanuric acid compared with two common amino acids,
one of which has the highest nitrogen content available for an amino acid.
milk [64]. In response to the recent issue, methods have been developed again using
ESI, but the need for screening for unknown contaminants outside the scope of
regulations is becoming a more pressing requirement for authorities. To this end,
screening techniques are starting to be used by research organizations and government
laboratories to look for new contaminants. When the structures of compounds are
totally unknown, multiple analytical techniques are required and these include GC
-
MS, NMR, IR, and LC
-
MS/MS. Again, with no prior knowledge of structure, it is
dif
cult to identify compounds. However, accurate mass measurements are important
to provide molecular weight information, which together with the structural infor-
mation of MS/MS spectra and statistical approaches (where control groups are
compared with suspect samples) can enable the detection of unknown contaminants.
Although this area is relatively new, it has been applied already to pesticide screening
and it is starting to be applied to other classes of contaminants in food. Recent
publications [65
68] have shown how this approach can help authorities maintain
food safety in the future.
In summary, food testing over the last 10
-
-
15 years has seen the emergence of
LC
MS as a routine technique. Although its use started in the detection of veterinary
drug residues and pesticide residues, it is rapidly moving into the
-
field of other
chemical contamination detection. The increase in sensitivity of the newer LC
-
MS
instruments means that sample preparations can be simpli
ed, speeding up analyses.
The ability to detect compounds that are thermally unstable means that LC
-
MS is
replacing GC
MS in some areas due to speed improvements as a result of removing
the need for a derivatization required previously for GC
-
-
MS.
Although LC
-
MS will not replace all GC
-
MS methods, as some compounds are
not detectable by LC
MS at present, the use of accurate mass systems in the future
will mean that more contaminants will be grouped together and analyzed simulta-
neously. An increasing amount of screening for unknown compounds is envisaged to
-
