Environmental Engineering Reference
In-Depth Information
for the sample treatment procedure that is based on imitating the neutral
bioaccumulation processes. This SPMD setup was indeed successful in accu-
mulating TBT and DBT from the water, but not MBT.
In respect of organotin analysis in seawater samples, it is worth stress-
ing that the development of sample preparation methods has mainly been
oriented to the reduction of time and to the use of solvent-free extraction
systems or those with reduced solvent need such as SPME or SPMD after
in situ derivatization. However, the complete validation of these methods is
far from being achieved, mainly because of reproducibility problems [12].
The summary of the most applied extractants, derivatizing reagents, pre-
concentration systems and instrumental techniques in the determination of
organotin species in seawater, derived from the literature published since
2000, is reported in Table 1.
2.2
Sample Preparation Methods
for the Determination of Organotin Compounds in Sediment Samples
Speciation from solid samples—restricted to sediments and biota in the case of
marine ecosystems—is obviously more challenging than from water. Although
the high salt content of seawater may cause difficulties in the determination step
(chromatographic separation and detection), the challenges of extraction, such
as the process of isolating the target analytes from complex cell structures and
biomolecules, and the number of possible errors are much higher.
Even if organotin compounds are not involved in mineralogical processes,
they strongly interact with particulate matter in association with a variety
of counterions, due to hydrophobic and
or ionic forces. The trisubstituted
(TBT, TPhT) compounds are mainly bound by hydrophobic forces, while the
monosubstituted ones (MBT, MPhT) by ionic forces. These forces influence
the efficiency of the different extraction methods.
In recent literature, leaching mixtures for organotin extraction have been
used in concert with various extraction devices, such as the Soxhlet, mechan-
ical shaker, sonication probe or ultrasonic bath, microwave and more recently
pressured liquid extraction (PLE). The most frequently adopted methods for
organotin extraction from sediments are leachings with acids or acid-polar
solvent mixtures. Acids with non-polar solvents and mixtures of different po-
larity grade solvents are seldom utilized.
The acidic conditions reduce the strength of mineral binding, break the
bonds between the matrix and the target organotin analytes and provide pos-
itively charged ionic species. The extraction of di-substituted (DBT, DPhT)
and, above all, mono-substituted organotin compounds (MBT, MPhT) from
the aqueous to organic phase is enhanced by the addition of a complex-
ing agent such as tropolone or diethyl dithiocarbamate. However, efficiency
should always be critically evaluated, especially under strong acidic condi-
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