Environmental Engineering Reference
In-Depth Information
mode was used. Low ng L
-1
levels are obtained as detection limits (1.5-3 ppt)
considering the pre-concentration step of the marine water samples (Table 1).
The EI spectrum does not provide as the base peak the M
-
ion, which has
an abundance of 25%. Most of the fragment ions obtained under these con-
ditions, have a low abundance, between 20-30%forthem
/
z. The base peak
z 180, which is the [M - SCN]
-
ion. The m
is at m
/
/
z 136 can be attributed to
[M - SHCH
2
SHCN]
-
.WhenMS
MS conditions have been applied, improve-
ment in the selectivity and sensitivity are obtained achieving detection limits
of 0.05 ppt, also after SPE treatment. However, with NCI-MS
/
MS conditions
and using methane, low fragmentation is observed from the precursor ion at
m
/
z 166 [M - CH
2
SCN]
-
,givingonlyonefragmentionatm
/
/
z 134 that is the
[M - SCH
2
SCN]
-
ion [27, 28] (Table 3).
4
Liquid Chromatography-Mass Spectrometry
4.1
General Remarks
As has been previously noted, GC is common technique, but the amenability
of some booster biocides to be sperated by LC, has also led to the application
of LC analysis, as alternative of GC with a derivatization process. To avoid the
need for derivatization, several applications utilizing LC analysis have been
reported [19, 51] (Table 2). Reversed-phase LC (RPLC) with an octadecylsi-
lane stationary phase (C18) has been used for the separation of these com-
pounds in most of the studies in the literature [19, 30, 42, 45, 47, 48]. The mo-
bile phase generally consists of acetonitrile or methanol together with water.
However, modification of the mobile phase has been performed to improve
the sensitivity of MS detection. Acid acetic or ammonium acetate is added to
enhance the ionization, in particular of Irgarol 1051 and Diuron [32, 44, 51].
Gradient elution is performed starting from a low percentage of organic sol-
vent, generally 20-30% and increasing linearly to 100%. With this gradient,
atimeof10-25 min is suitable to separate mixtures of compounds and degra-
dation products. The column and pre-column are maintained at 30-50
◦
C
with a block heater. To improve the detectability of the target analytes, the
volume of injection is typically increased from 20 to 50
L.
The coupling of LC to DAD and mainly MS detectors is frequently used for
the analysis of phenylureas or triazines [1, 19, 45]. The identification by LC-
DAD is accomplished on the basis of the retention time, through comparison
of the UV spectrum of the target compounds in a standard solution with the
UV spectrum of the detected peak in the sample. Therefore, a limited identifi-
cation capability can be achieved by UV detectors. The working wavelengths
are 224-230 nm that correspond to the maximum absorbance of Irgarol 1051
µ
