Geology Reference
In-Depth Information
Composition of the Cuticle and Lipid Compounds
Matured Without Chemical Treatment
The pyrolysate of matured commercial chitin, analysed after thermodesorption at
300 °C (Fig.
8.2a
), contained pyridine and its alkyl derivatives, and phenol and its mono,
di, tri and tetra alkyl derivatives. The phenol derivatives are amongst the most abundant
in the pyrolysate. Other important compounds tentatively identifi ed include indene and
its alkyl derivatives. Furans, pyrones, pyridones, pyrroles and oxazoline structures,
which are the most important pyrolysis products of unmatured chitin, were not detected
thereby confi rming that the chitin has undergone chemical change. No
n-
alkane/alk-1-
ene homologues were detected. Benzene derivatives also were not detected but, along
with alkylated phenols, were the primary thermally desorbed components.
The chitin-derived compounds are clearly evident in the pyrolysates of artifi -
cially matured scorpion, cockroach and shrimp cuticle (the latter two shown in
Fig.
8.2b, c
). The fatty acids
n
-C
16
and
n
-C
18
are abundant, as they were in the fresh
cuticles. The relative abundance of fatty acids in the artifi cially matured shrimp
cuticle (Fig.
8.2c
) is less than in the cockroach (Fig.
8.2b
) and scorpion (not shown),
and
n
-C
18
fatty acid was released only in trace abundances. The thermally desorbed
products of all the matured cuticles consisted primarily of alkylated phenols, ben-
zene derivatives and
n
-alkanes (primarily C
9
to C
20
).
The matured cuticles also yielded a range of compounds upon Py-GC/MS that were
not detected in either the matured commercial chitin (Fig.
8.2a
) or the non-matured
cuticles (Fig.
8.1b
). These include
n
-alkyl amides, with C
16
and C
18
homologues being
the most abundant (Fig.
8.2b, c
). Although not readily apparent in the partial ion current
chromatogram, the
m/z
83 + 85 mass chromatogram reveals the presence of
n-
alkane/
alk-1-ene homologues ranging at least from C
9
to C
19
with the C
14
to C
17
components
being dominant. Such
n-
alkane/alk-1-ene homologues (
n
-C
8
to
n
-C
19
; Fig.
8.3a
) were
also generated during pyrolysis of matured pure C
16
and C
18
fatty acid mixture.
However, base hydrolysis of the matured cuticle yielded no recoverable residue.
Shrimp cuticle matured in the presence of clay and calcium carbonate (Fig.
8.3b
)
yielded pyrolysates similar to those of shrimp cuticle matured in the absence of any
minerals.
Composition of Cuticle Matured After Chemical Treatment
Cockroach cuticle matured following lipid extraction and base hydrolysis (Fig.
8.4
)
yielded pyrolysis products related to chitin and protein similar to those observed in
the cuticle matured without chemical treatment. However,
n
-alkyl components,
including
n
-alkanoic acids,
n
-alkyl amides and
n
-alkanes/alkenes, were not detected
in the pyrolysate (inset, Fig.
8.4
). Thermodesorbed products were similar to those
released from matured chitin; in particular, no alkanes were detected.
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