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

cm) pieces, mixed with dry ice to avoid loss of volatile
species and pulverized in a stainless steel blender
(Cole Parmer, Vernon Hills, IL, USA). The samples were
ground, sieved (particle size ranging from 75 µm to 100
µm) and stored in closed flasks under refrigeration prior
to use.
2.3. fims
All FIMS analysis were performed in an Extrel Mass
Spectrometer (Pittsburgh, PA, USA) fitted with a hightransmission
¾” quadrupole and an EI ion source. The
ion source of the MS was modified as previously described
[20] to allow a SPME fiber to be placed directly
between the two parallel MS filaments for uniform
heating and efficient desorption of the analytes (Figure
1), being ionized by 70 eV EI. The desorption time was
60 s for all experiments and no carryover between runs
was observed with this time. The MS gain and electron
multiplier voltages were 1 x 10 10 and 1100 V, respectively.
Detection and quantification of the CP were performed
by selective ion monitoring (SIM) of diagnostic
fragment ions of m/z 107 for 4-chloro-3-methylphenol,
m/z 128 for 2-chlorophenol, m/z 196 for 2,4,6-trichlorophenol
and m/z 266 for pentachlorophenol.
2.4. PrE P a ra t i o n o f t h E s o l-g E l aPtms / Pdms fiBEr
Two centimeter pieces of the optical fiber were dipped
in concentrated sulfuric acid for 3 h for removal of the
protective polyimide layer. In sequence, the uncoated
fibers were exposed for 1 h to 1 mol L -1 NaOH solution,
to activate its surface. The activated fibers were
subsequently washed with 0.1 mol L -1 HCl for removing
the excess base, rinsed with distilled water, dried
at 70°C and stored in a desiccator. The sol-gel reaction
was carried out in a 3 mL disposable polyethylene vial:
300 mg of APTMS, 75 mg of MTMS, 150 mg of PDMS-
OH and 125 μL of TFA (with 5 % of water) were mixed.
The mixture was vortexed for 2 min; the dry activated
fused silica fibers were exposed to the resulting sol for
1 h at lab temperature (22 °C – 27 °C), removed from
the sol and stored overnight in a desiccator. This procedure
was repeated five times with fresh sol, in order to
obtain thicker coatings. The fibers were then exposed
to a solution of 20 % methanolic solution of MTMS
for 5 minutes, to end-cap residual superficial hydroxyls.
Finally, the fibers were mounted on used, discarded
commercial (Supelco) SPME assemblies, after careful
removal of the original (deteriorated) fiber. Prior to use,
the fibers were conditioned at 100°C for 1 h and then
at 260°C for 6 h in the injection port of a gas chromatograph
under flow of nitrogen (1 mL min -1 ).
2.5. sPmE
Water Samples. The extraction profiles for the CP using
the APTMS / PDMS fiber were determined using
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determination o f C h l o ro p h e n o l s in e n v i ro n m e n t a l samples by fiber i n t ro d uC t i o n m a s s
speCtrometry u s i n g a n o v e l s o l-g e l fiber
aqueous solutions containing 100 µg L -1 of each analyte
as sample. Due to the acidity of the analytes (pK a
ranging from 4.8 to 7.8), and to maintain the CP in
their protonated forms so as to maximize their sorption
by the fiber coating, the pH of the aqueous samples
were adjusted to 1.0 prior to all extractions by dropwise
adding of conc. HCl (10 µL to 15 µL). For the extractions,
the APTMS / PDMS fiber was immersed in 10 mL
of test sample in septum-sealed glass sample vials under
magnetic stirring of 1000 rpm, for periods ranging
from 1.0 to 20 min. After extraction, the analytes were
immediately desorbed inside the MS. Analytical curves
were obtained for the concentration range between 25
and 400 µg L -1 and the optimized extraction time of 7.5
min allowed assessment of quantitative figures of merit
of the method. The LOD and the limits of quantitation
(LOQ) were calculated from signal-to-noise ratios (S/N)
of 3 and 10, respectively, estimated from data collected
from extractions of 25 µg L -1 of the CP. The recovery
was estimated with creek water samples spiked with
100 µg L -1 of each analyte.
Samples of sleeper wood. A suspension of 1.000 g of
powdered wood sample in 6 mL of a water / methanol
mixture (5:1 v/v) was stirred for 1 h at room temperature.
This suspension was filtered, acidified and quantitatively
transferred to vials for SPME analysis, which
were carried out using the same parameters as above.
Quantitation was then performed via analytical curves
obtained by extractions of standard solutions of the
analytes in water / methanol mixtures.
fi g u rE 2. El E C t ro n s C a n n i n g m iC ro g ra P h y o f a) thE u n C o a t E d fiBEr w i t h
800× m a g n i f iC a t i o n a n d thE aPtms/Pdms s o l-g E l fiBEr w i t h B) 600×
a n d C) 10,000× m a g n i f iC a t i o n. ad P a t E d f ro m rEfErEnCE [16].
3. rEsults a n d disCussion
APTMS / PDMS SPME Fiber. Figure 2 shows the morphology
of the sorbent coating of the APTMS / PDMS
fiber. With magnification of 600×, it is seen that the
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