Environmental Engineering Reference
In-Depth Information
relative abundance (10%) is also reported to be present in the mass spec-
tra, with a fragmentor voltage of 75 V [51]. A higher contribution (34%) is
shown by this ion, when the fragmentor voltage value is 120 V. Under these
fragmentation conditions, useful structural information is obtained without
loss of sensitivity. A predominant ion at m
z 91, which corresponds to the
[M - SCCl
2
FSO
2
N(CH
3
)
2
]
-
ion together with another two ions at m
/
/
z 199 and
z 155, the ion [M - SCCl
2
FNCH
3
]
-
155, are shown in the spectra. For the m
/
has been assigned [51].
4.6
Sea-nine 211
For optimal conditions to determine Sea-nine 211 by LC-MS using APCI, the
PI mode is often chosen. This compound easily accepts a proton in the chem-
ical structure, so that, it exhibits a higher sensitivity under PI mode [46,
47, 52] (Table 4). However, under different fragmentation conditions (70, 110
and 120 V), no fragmentation is often observed for Sea nine 211 and only
the molecular ion [M + H]
+
z 282. In
spite of the poor structural information provided by the mass spectra, this
compound has been generally identified and quantified in seawater sam-
ples by monitoring of the protonated molecular ion [M + H]
+
[46, 47, 52].
With this methodology, levels of ng L
-1
can be detected (with a detection
limit of 1 ppt) in seawater. For sediments, the sensitivity is at the ng g
-1
level
(Table 3).
is present in the mass spectra at m
/
4.7
TCMTB
For the selection of the mode of ionization using the APCI interface—the
usual procedure—PI and NI modes have been studied for TCMTB [31]
(Table 3). The NI mode is much more sensitive than the PI mode that pro-
duces a protonated molecule at m
z 239. However, the NI mode does not
yield a deprotonated molecule [M - H]
-
. Under the application of different
fragmentor voltage values (70-110 V), TCMTB has a similar behaviour show-
ing total fragmentation that can yield an intense characteristic ion at m
/
z
166. It is suggested that this fragment is formed due to the loss of the thio-
cyanomethylthio substituent [31] that corresponds to the [M - CH
2
SCN]
-
ion
(Table 4). Higher fragmentor voltages have also been applied (120 V), but no
further structural information is obtained. Similar to compounds with a low
fragmentation rate, such as Sea-nine 211, the SIM mode for m
/
z 166 and the
retention time, are the identification criteria used for their determination in
environmental samples. Comparable sensitivity is also obtained with the de-
veloped analytical method for the determination of TCMTB, usually at the
ng L
-1
level (1-20 ppt) [19, 31, 47].
/
