Environmental Engineering Reference
In-Depth Information
and it is usually selected for its main degradation product M1 [42, 44, 45,
48, 53]. For diuron, the DAD is set at 244 nm [44, 45, 53]. In the simultan-
eous determination of various biocide compounds (Diuron, TCMTB, Irgarol
1051 and Chlorothalonil), quantification is carried out with UV detection at
220 nm [19].
For further identification purposes by LC-MS analysis, different ionization
techniques—electrospray source ionization (ESI) and atmospheric pressure
chemical ionization (APCI)—ionization modes (negative ion NI and positive
ion PI) and monitoring modes, SIM and selected reaction monitoring (SRM),
have been employed. LC-MS techniques have been instrumental in detecting
mixtures of biocides and degradation products [46, 47]. One of the limitations
of LC-MS
MS is the susceptibility of interfaces to co-extract matrix compo-
nents from complex samples that can result in the suppression or less frequently
in the enhancement of the analyte signal. However, it is also demonstrated that
these effects can be minimized by good sample preparation, good chromato-
graphic separation and optimized MS
/
MS operating conditions. Analytical
methods using MS techniques are outlined for each compound in the following
sections. Special attention is paid to the compounds Irgarol 1051 and Diuron,
which have been of concern in several reports.
/
4.2
Irgarol 1051
For the determination of triazines, better sensitivity is often achieved using
APCI in PI mode. A higher response is observed as a result of the easy
protonation of the amine nitrogen atom. In this sense, most of the LC-MS
methods have been reported using the APCI interface for the determination
of Irgarol 1051 as well as its main degradation product M1 [19, 46-48, 51]
(Table 2). This degradation product has been observed in different degrada-
tion experiments such as photodegradation under controlled conditions or
biodegradation experiments by Phanerochaete chrysosporium [40, 41].
Although APCI techniques are soft-ionization modes, ions can be some-
times fragmented to produce structural information about a particular
molecule. Fragmentation can be performed with a single quadrupole by in-
creasing fragmentor or cone voltage. This voltage affects the transmission
and fragmentation of molecules, which are related. Thus, with a high frag-
mentor voltage, more fragmentation occurs; in the case where a compound
is not fragmented, better ion transmission can often succeed. The applica-
tion of a low fragmentor value (70-75 V) commonly provides a simple mass
spectrum characterized by the presence of the protonated molecule [M + H]
+
(Table 4). So this fragmentor value does not provide useful structural infor-
mation. At a high fragmentor voltage (120-125 V), mass spectra provide good
structural information and also enough sensitivity. Under these fragmenta-
tion conditions, in addition to the [M + H]
+
ion, the spectra shows a fragment
