Environmental Engineering Reference
In-Depth Information
anid [19, 20, 27, 28, 34, 47, 51] or Sea-nine 211 [27, 28, 36] (from 45 to 53%)
using polymeric material (divinylbenzene-
N
-vinylpyrrolidone copolymer,
hydrophilic-lypophilic balance, HLB) as the sorbent. However, improvement
in recoveries (66-72%) are obtained when C18-bonded silica or polymeric
material (styrenedivinylbenzene copolymer) have been selected for both
compounds.
The goal of reducing the time needed and the quantities of organic solvents
has led also to the application of current extraction approaches including
SPME, HS-SPME or SME. Up to now and to our knowledge, few analyti-
cal methods have been reported using these techniques [21-24]. SPME is
carried out by direct dipping of the fibre into the aqueous sample [21, 22]
but also by exposing the fibre in the headspace of the sample contained in
a vial maintained at high temperature [23]. Compared with other sample
preparation techniques, the advantages of SPME can be the disposal costs
and the potential to improve detection limits. On the other hand, the ap-
plication of SPME-GC is limited to analytes and volatiles that are thermally
stable at the injection temperature. The coated fibres typically assayed are
polyacrylate (PA), polydimethylsiloxane (PDMS), carbowax-divinylbenzene
(CW-DVB) or polydimethylsiloxane-divinylbenzene (PDMS-DVB). The op-
timum extraction efficiency has been the aim of studies [21, 23] evaluating
various parameters: sample pH, addition of salt (NaCl) to the sample, tem-
perature in the absorption process and time in both the absorption and
desorption process. Extraction is usually enhanced with increasing salt con-
centration and increased polarity of the compound (the salting-out effect).
However, decreases in the extraction can be observed for high or even mod-
erate salt concentrations, which can lead to a reduction of the diffusion rate
of the analytes. Sample pH or time and temperature of absorption depend
on the compound studied, and in general, compromise solutions are consid-
ered for simultaneous extraction of various compounds [21, 23]. The relative
recoveries (instead of absolute recovery as used in exhaustive extraction pro-
cedures) of Irgarol 1051 [21, 22, 24] and Sea-nine 211 [21, 24] in seawater with
PDMS-DVB, is higher than 90%, indicating the effectiveness of extraction of
this technique.
SME is also an environmentally safe extraction technique (it generates lit-
tle waste and requires 1-2
L of organic solvents). Advantages offered by
this technique are simplicity, speed and potential for easy automation. In
addition, it does not suffer from carryout (exposure time of fibre in the
GC injector to completely desorb the compounds from the stationary phase)
between extractions that are observed in SPME procedures. SME has been
found to be effective for biocides such as Dichlofluanid, Chlorothalonil or
Sea-nine 211 [23] with high recoveries values in seawater (88-94%). In terms
of recovery, limits of detection and precision, SME also exhibits a favourable
performance and it is comparable to the SPME technique for the extraction of
biocides.
ยต
