Environmental Engineering Reference
In-Depth Information
techniques applied to support the extraction such as Soxhlet, ultrasound,
microwave, supercritical fluid and pressurized solvent systems. The most
commonly applied method is ultrasonication, even if microwave energy and
pressurized solvent extraction have begun to be widely applied as well. Ultra-
sonication presents the advantages of being simple and relatively inexpensive,
but on the other hand, requires long treatment times as ultrasonic extraction
is generally performed with acid(s) and
or polar solvents, successively di-
luted with water and followed by LLE. The use of microwaves and particularly
of focused microwaves allows a significant reduction of treatment time in the
release of the organotin compounds from solid matrices, but the following
steps are the same as in the case of ultrasonication (LLE of the extract diluted
with water). The main advantages of the recently popularly used accelerated
solvent extraction (ASE) are the high sample throughput, significantly lower
solvent consumption and consequently, lower cost, and the high potential of
being used routinely.
In all the cases, however, the presence of a complexing agent has proved
to be mandatory for enhancing the extraction efficiency of the mono- and
disubstituted tin compounds.
/
Derivatization
The derivatization of organotins is achieved by hydridization and
or alky-
lation with tetraalkylborates (mainly tetraethyl- and, to a lesser extent,
tetrapropylborate) and
/
or a variety of Grignard reagents (from methyl- to
hexylmagnesium bromide). Hydridization is strongly influenced by the type
and concentrations of acid used and the sample matrix. Particularly, the
presence of high metal concentration of the matrix, which leads to boride for-
mation; humic substances and fat content leading to foam formation, strongly
affect the efficiency and reproducibility of the derivatization.
The yield of derivatization in the case of alkylation with borates is influ-
enced also by the reagent concentration, derivatization pH and reaction time
as well as by the substitution degree of the organotin compounds. The main
disadvantage of alkylation is the lack of stability of the alkylating reagents.
Both hydridization and alkylation with borates are particularly suitable for
water samples, where, exploiting the reagents' compatibility with water, they
can be used for in situ derivatization showing, particularly in the case of alky-
lation, high yields of derivatization. On the contrary, both techniques are less
suitable in the case of solid samples.
Grignard derivatization is widely applied. The reaction yields are influ-
enced by the concentration and type of reagent, however, regardless of the
type, all Grignard reagents provide very high yields of derivatization. Penty-
lation and hexylation are preferable, as their derivatives are less prone to
volatilization losses during the successive preconcentration steps. The main
disadvantages of Grignard derivatization are the “violent” nature of the Grig-
/
