Biomedical Engineering Reference
In-Depth Information
Fig. 7
Fragmentation pattern, registered in ESI, of Cocaine, BEG, and NCOC. Fragments at
m
/
z
150 for BEG and 136 for NCOC are characteristic and permit to resolve these two metabolites
of all the molecules which have in their structure a benzene ring to which a methylene
group is attached.
The MDA, MDMA, and MDEA only differ in the type of amino substitution on
nitrogen: for these three molecules the most abundant fragment in the CID spectra
has the same ratio
m
/
z
163. For both spectra in addition to protonated adduct, it can
be observed the mass peak of the fragment originated from the cleavage in a (Fig.
6
)
and the mass peak due to the formation of tropylium ion.
Cocaine and its metabolites
, i.e., BEG and NCOC, follow a common pattern of
fragmentation [
77
]. The ionization of cocaine, working in the ESI ion source in
positive mode, leads mainly to the formation of charged species [M+H]
+
mass of
304 amu, while for BEG and NCOC [M+H]
+
mass of 209 amu. The metabolites of
cocaine, here considered, have the same molecular weight as both are different from
cocaine for fourteen mass units, corresponding at the replacement of a methyl with a
hydrogen (cf. Sect.
4.1
). This replacement occurs on the aminic nitrogen for the
NCOC, while BEG originates by cocaine from the hydrolysis of the methyl ester. The
use of different MRM transitions allows to discriminate these isobaric substances, and
patterns of fragmentation of cocaine and metabolites are shown in Fig.
7
. When this
is not possible isobar masses must be resolved chromatographically.
