Environmental Engineering Reference
In-Depth Information
tions [25], and it has to be kept in mind that high complexing agent concen-
trations might adversely affect chromatographic separation.
The choice of acid for organotin extraction mainly falls on acetic or hy-
drochloric acid whereas the polar solvent mostly chosen is methanol [14, 15,
26-36]. The extraction is mostly assisted by mechanical shaking, microwave
energy or sonication [15, 18, 26, 29, 31-41]. Several authors have reported on
the influence of, for example, sonication time, extraction temperature, ex-
tractant concentration and volume on the efficiency of organotin extractions
from sediments [41]. The leached compounds are then derivatized in the
aqueous medium, for example, buffered with AcOH
AcONa in the presence
of a polar solvent and analyzed by GC separation. Results indicate that one
of the most important factors within the extraction conditions is the acid
concentration, too strong acid conditions leading to significant organotin
degradation, mainly in the case of TPhT [42].
The influence of MW energy has been tested in several variations. From
the closed-vessel microwave system to open focused microwave systems, in-
tegrating several steps of the sample preparation procedure or following the
traditional step-by-step method. Yang and Lam [43] recently investigated the
extraction of organotins from sediment in a closed-vessel microwave system
with glacial acetic acid without a complexing agent. 6 min at 100
◦
Censured
quantitative recovery in the HPLC-ICP-MS determination of all the three
butyltin species.
In extensive studies Ruiz Encinar et al. [14, 26] and Rodriguez-Gonzalez
et al. [15] compared and evaluated the efficiency of all together four different
solid-liquid extraction techniques—mechanical shaking, ultrasonic shaking,
microwave, ASE—on sediment reference materials (PACS-2 and BCR 646),
the extraction solution being a 3 : 1 (or 9 : 1 with ASE) mixture of methanol
and acetic acid. The extraction time was higher than 4 h for mechanical shak-
ing and in the order of minutes for the other three techniques. The best results
in terms of butyltin recovery— quantitative for TBT and DBT—were pro-
vided by ultrasonication with a relatively short treatment time. Microwave
extraction provided adequate data for DBT and TBT but only in a narrow
range of MW conditions, while MBT seemed to be less prone to degradation.
Ambient temperature leaching with mechanical shaking also provided data in
agreement with certified values for all the three species, including MBT that
until then seemed to require harsher extraction conditions and even longer
extraction times (several hours) for quantitative recovery. A spike solution of
118
Sn and
119
Sn isotopes and the GC-ICP-MS technique, based on the deter-
mination of isotope ratios 120
/
119 for TBT, were used to check
for transbutylation, and no evidence of the phenomenon was found under
any of the tested extraction conditions.
In the last years, the application of ASE is becoming more and more
popular for organotin speciation. With carefully optimized extraction condi-
tions, it has been proven to give comparable results to ultrasonication and
/
119 and 118
/
