Environmental Engineering Reference
In-Depth Information
solvents, which are used to leach
digest the biological matrices as much as
possible to remove the analytes from the binding sites.
The most-reported extraction methods for organotin compounds from
biota samples are also based on acidic digestion (mostly with HCl or acetic
acid) in the presence of a polar solvent which is mainly methanol [16, 17,
32, 33, 37, 51-53]. The preference of methanol is due to its osmotic activity
that induces rapid bursting of the cells and facilitates the homogenization of
biological materials.
The extensive comparative study of Pellegrino et al. [6] proved that the
use of a methanol
/
hydrochloric acid extraction mixture assisted
by ultrasound, out of 12 selected extraction methods (combination of organic
solvents of various polarity—methanol, dichloromethane, toluene, pentane,
hexane; the presence of a complexing agent (tropolone); the effect of different
acidic conditions—HCl, HBr, acetic acid; and different extraction devices—
ultrasonic bath, mechanical shaker, Soxhlet apparatus, microwave oven), pro-
vides the statistically most similar results to the certified butyl- and the
indicative phenyltin values of BCR 477 CRM.
As it has become popular for organotin extraction from sediments, pres-
surized liquid extraction has also been gaining popularity for the leaching of
marine biota samples. Wahlen and Catterick [51] utilized accelerated solvent
extraction in the determination of various organotin species in CRM samples
(BCR 477, candidate BCR 710) with the HPLC-ICP-MS technique achieving
accurate and precise results. A program of five static cycles of 5 min at 100
◦
C
and 1500 psi, with a solution of 0.5 Msodiumacetate
/
tropolone
/
/
1.0 Maceticacidin
methanol was applied.
Wasik and Ciesielski [17] reached excellent extraction efficiencies without
significant species degradation by applying ASE parameters as follows: four
static cycles with a solution of 90%v
/
v methanol with acetic acid:sodium
vtropolone,at800 psi and 125
◦
C. The most im-
portant factor affecting extraction efficiency turned out to be solvent compo-
sition and, in particular, the presence of the complexing agent. It considerably
improves DBT and above all, MBT recovery. The extraction efficiency of ionic
organotins with polar or medium polarity solvents is controlled by two op-
posite effects. On the one hand, the complexation of the ionic forms, MBT
in particular generates complexes that are less soluble in a medium polarity
solvent, and thus extraction decreases. On the other hand, the formation of
a tropolone-analyte complex that shields (owing to the steric effect) the ana-
lyte molecules from hydrogen bond forming functional groups of the protein
matrix, increases extraction efficiency. According to the authors, this latter
effect is prevalent and, consequently, the addition of tropolone does indeed
increase extraction efficiency.
Looser et al. [52] proposed the extraction of biological samples with
methanol
acetate containing 0.03%w
/
acetic acid by mechanical shaking at ambient temperature in the
dark followed by aqueous ethylation, LLE and GC-MS separation
/
/
determina-
