Brazilian Journal of Analytical Chemistry - BRJAC - Brazilian Journal ...

Eberlin et al.
of new and stable coatings has been produced [14]
[15]. The advantages of these sol-gel coatings, such as
better chemical and mechanical resistances (including
thermal resistance), when compared with the commercial
fibers, result from the chemical anchoring of
the sorbent phase onto the fused silica fiber. Briefly,
sol-gel reactions are based on the hydrolysis and condensation
of (generally) silicon alcoxides, leading to
a three-dimensional glassy network. Organic compounds
containing reactive functionalities (hydroxyl,
for example) may take part of the reaction, giving rise
to an organically modified silica (ormosil). The surface
of the ormosil possesses hydroxyl groups, hence they
are able to bind to the surface of the fused silica fiber,
which has also superficial hydroxyl groups. The characteristics
of an ormosil may be tailored according to
the condensable organic compounds added. A sol-gel
fiber based on aminopropyltrimethoxysilane (APTMS)
and PDMS [16] has been described.
Chromatographic analysis of CP often requires a derivatization
step, since their acidic hydrogens give rise
to peak tailing with poor detection limits and poor
quantitation. The derivatizating agents usually employed
are acetic anhydride [17] and reactive silicon
compounds such as hexamethyldisilazane [18] and
bis(trimethylsilyl)trifluoroacetamide [19], but their use
introduces a new step into the analytical process.
We have reported on the coupling of SPME with MS
and its direct use with no pre-separation and derivatization
steps and termed this new technique as fiber
introduction mass spectrometry (FIMS) [20]. In FIMS
(Figure 1), the SPME fiber is directly inserted into the
mass spectrometer source (between the EI filaments)
by means of a proper fiber holder, allowing efficient
analyte desorption by filament heating and ionization
by the action of the 70 eV electrons. This direct fiber exposure
is aimed to eliminate the need of derivatization
and pre-separations, thus reducing analysis time, manipulation
and separation biases and has been shown
to be efficient for multiresidual determination, with the
target analytes being monitored by molecular ions or diagnostic
fragment ions. Using this technique, we have
analyzed phtalates in mineral water samples, achieving
limits of detection of 3.6 ng mL -1 with a polydimethylsiloxane/divinylbenzene
(PDMS/DVB) fiber [21]. Pesticide
determination from P. edulis herbs was also performed,
and limits of detection of a few ng mL -1 were achieved
with a sol-gel PDMS/PVA fiber. This fiber displayed
good chemical and mechanical resistance to the severe
EI desorption conditions, being used for more than 400
extraction/desorption cycles [22].
Herein we describe the use of a new sol-gel fiber
based on aminopropyltrimethoxysilane (APTMS) and
PDMS [16] for the direct, fast and efficient FIMS analysis
of CP in aqueous solutions.
fi g u rE 1. ovErviEw o f thE m a i n stEPs i n v o l vE d in fims analysis.
2. ExPErimEntal
2.1. Ch E m i C a l s a n d m a t E r i a l s
Optical fibers (ABC-Xtal, Campinas, SP, Brazil) with a
128 μm core were used as support. The sol-gel materials
were 3-aminopropyltrimethoxysilane (APTMS
- Acros Organics, Geel, Belgium), hydroxyl-terminated
polydimethylsiloxane (PDMS-OH - Aldrich, Milwankee,
WI, USA), trimethylmethoxylsilane (TMMS - Fluka, Buchs,
Switzerland), methyltrimethoxysilane (MTMS -
Fluka) and trifluoroacetic acid (TFA - Acros Organics).
The CP selected for this work, 4-chloro-3-methylphenol
(43CP), 2-chlorophenol (2CP), 2,4,6-trichlorophenol
(246CP) and pentachlorophenol (PCP), were obtained
from Merck (Schuchardt, Germany). Stock solutions
containing 1000 mg L -1 of each CP were prepared in
HPLC-grade methanol (Merck) and stored in a refrigerator.
The extractions were performed in Teflon/silicone
septa-capped 15 mL glass vials (Supelco, Bellefont, PA,
USA). Analytical grade NaCl and HCl (Aldrich) were also
used. Deionized water was generated with a Direct-Q
UV water purification system (Millipore, Molsheim,
France).
2.2. sa m P l E s
Water from Anhumas Creek, a highly polluted water
course in the city of Campinas (95 km NW from São
Paulo, Brazil), was collected for analysis. This sample
was filtered to eliminate suspended solids and stored in
sealed glass vials under refrigeration until use. Samples
from three wooden railway sleepers, stored in open
air near a deactivated railway station in the same city,
were also collected. Chunks of the wood samples were
brought to the laboratory, broken into small (~ 1 – 2
170 Br J Anal Chem