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3
Results and Discussion
Structural Identification and Confirmation
Figure 2 shows extracted ion chromatograms and MS/MS
spectra obtained from full-scan LC-MS/MS analysis of a
mixture containing MC-RR, MC-YR and MC-LR at
concentrations of 0.5 µg/L. MC-RR, MC-YR and MC-LR
eluted at 5.62, 6.85, and 6.93 minutes, respectively. The
MS/MS spectrum of MC-RR was generated by collision-
induced dissociation (CID) of the [M+2H]
2+
ion and is
characterized by major fragment ions at
m/z
505, 452 and
887, which correspond to [M+2H-CO]
2+
, [M+2H-C
9
H
10
O]
2+
and [M+H-C
9
H
10
O-NH
3
]
+
, respectively (C
9
H
10
O is a
fragment of the Adda residue). The closely eluting compounds
MC-YR and MC-LR are easily distinguished by their
MS/MS spectra. The MS/MS spectrum of MC-YR,
generated by CID of the [M+H]
+
ion, contains major
fragment ions at
m/z
1017, 599, and 916, which
correspond to [M+H-CO]
+
, [Arg+Adda+Glu + H]
+
, and
[Arg+Adda+Glu+Mdha+Ala+Tyr + H]
+
, respectively. The
CID MS/MS spectrum of the [M+H]
+
ion of MC-LR is
characterized by major fragment ions at
m/z
967,
corresponding to [M+H-CO]
+
;
m/z
599, corresponding to
[Arg+Adda+(Glu or MeAsp) + H]
+
;
m/z
866, corresponding
to [Ala+Adda+Arg+(Glu or MeAsp) +Leu+Mdha + H]
+
;
and
m/z
553, corresponding to [Ala+Arg+(Glu or MeAsp)
+Leu+Mdha+ H]
+
.
Figure 2. Extracted ion chromatograms and MS/MS spectra for MC-RR, MC-YR and MC-LR at concentrations of 0.5 µg/L
MC-RR
MC-LR
MC-YR