Environmental Engineering Reference
In-Depth Information
increased selectivity. This is based on its two stages of mass analysis—one to
pre-select an ion and the second to analyze fragments induced. The setting
of the MRM transitions channel for the monitoring of target analytes is gen-
erally selected considering the signal intensities and structure-specificities of
the product ions. Figure 3 shows a chromatogram corresponding to the mon-
itored MRM transitions for Irgarol 1051. In the analysis of Irgarol 1051 by
LC-QqQ-MS two main ions characterize the mass spectrum and one tran-
sition, which corresponds to the [M + H]
+
[MH - C
4
H
8
]
+
ions, can be
monitored [32] (Table 4). Although the confirmation criteria of Irgarol 1051
can be based on the monitoring of one MRM transition and the retention time
(in environmental analysis), two transitions provide greater capacity for con-
firmation of target analytes. Typically, the first is used for quantification and
the second for confirmation.
Regarding the sensitivity achieved with enrichment through the SPE step,
ESI-MRM analysis was found to afford detection limits for Irgarol 1051 one
order of magnitude higher than those achieved with APCI-MS in the SIM
mode. In the ESI-MRM mode the limits of detection are at the sub-low ng L
-1
level (0.5 ppt), while in APCI and SIM mode, the limits of detection are at the
low ng L
-1
level (4-5 ppt) [32, 47, 51].
→
4.3
Diuron
Diuron is a phenyl-substituted urea herbicide whose analysis has been de-
scribed in several publications using LC-DAD or LC-MS. However, it is known
that some urea herbicides generally do not have extremely strong UV or
visible light absorption that would allow selective and high-sensitivity de-
tection. The application of GC to phenyl-ureas is difficult because these
compounds are thermally unstable and rapidly degrade to isocyanates and
amines. Derivatization to compounds more thermally stable will make
them amenable to GC analysis. For confirmatory and quantitative trace
analysis of Diuron, the use of LC-MS is appropriate and several applica-
tions have been reported. Phenylurea derivatives can be determined eas-
ily by LC as well as the degradation products that are usually more po-
lar than its parent compound. LC-MS has been developed for the main
degradation products of Diuron resulting from transformation processes
in sediments and water: DCPMU [1-(3,4-dichlorophenyl)-3-dimethylurea],
DCPU [1-(3,4-dichlorophenyl) urea], DCA [3,4-dichloroaniline], CPDU
[1-(3-chlorophenyl)-3,1-dimethylurea] [45, 46, 53]. Other degradation prod-
ucts, such as demethyldiuron, 1-(3,4-dichlorophenyl)urea, have also been
determined in sediments [47, 52].
Structural information is obtained by LC-MS with APCI and ESI inter-
faces that allow the soft ionization of the analytes in both positive (PI) or
negative (NI) modes (Table 4). Using single quadrupole MS detection, APCI
