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

High Cu content in King George Island soils has already
been detected in past studies, and is related to
chalcopyrite (a Cu mineral) mineralization in volcanic
rocks of the area [39].
Vanadium is associated with petroleum contamination
[40], although high V contents were observed in
soils obtained at a great distance from the station. This
behavior can be explained by the geochemical affinity
of this element for Fe oxides [41], especially because
samples distant from Ferraz have high Fe content (see
Fig. 2b).
Although Zn is commonly associated with atmospheric
deposition coming from burning diesel [42], in
this study no clear evidence of high Zn content in the
soils around the station was observed (see fig. 2d).
Claridge et al.. [43] studied polluted soils for anthropogenic
activity in the vicinity of the American Antarctic
Station (McMurdo) and found evidence of contamination
by heavy metals, such as Cu, Pb and Zn, although
the observed levels did not present a threat to the Antarctic
environment.
Chromium has been associated with petroleum contamination
[44], and soils collected in the vicinity of oil
tanks can be seriously polluted by fuel. Chromium can
also be associated with paints used to protect the station’s
oil tanks [9].
Chromium species can be adsorbed onto soil components,
preventing leaching of Cr into the groundwater
or uptake into plants, thus reducing bioavailability.
These soil components can be macromolecular clay
compounds or humic acids recognized to form stable
Cr (III) compounds [45]. It is important to highlight that
Antarctic soils usually have low clay (generally ranging
to 1 – 5%) and organic matter contents [43]. Santos
et al.. [46] studied soil chemical characteristics of marine
terraces around the Ferraz Station and found low
organic matter levels, with an average of 2.60 % m/m.
3.2. re c o v e r y o f studIed elements
In order to verify the accuracy of the extraction and
quantification of metals, a certified reference material,
BCR 146 R (sewage sludge from industrial origin) was
used. The accuracy of the proposed methods falls in the
range of 89 – 102 %.
In spite of the recognized irreproducibility inherent
to SEPs [47], the sum of element concentration in the
fractions were in good agreement with the pseudototal
concentration, with recoveries of 96 ± 6; 97 ± 11 and
87 ± 16 % for Cu, Mn and Zn, respectively.
3.3. use o f a t o m t r a p t e c h n Iq u e s a n d fa s t-se q u e n t Ia l
fl a m e at o m Ic absorptIon spectrometry (fsfaas)
f o r s o Il e x t r a c t a n a l y s Is
Thermospray Flame AAS was employed for determination
of Cd and Pb in the DTPA soil extracts, achieving
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adequate detectivity in quantifying these elements. In
this particular case, the use of a carrier composed of
0.5 % w/v EDTA and 0.1 %v/v Triton X-100 to prevent
capillary clogging during sample introduction was
important. Unfortunately, it was not possible to use
the fast sequential mode for Cd and Pb determination
because this approach requires sample introduction
without an aqueous carrier and capillary clogging was
systematically observed.
Moreover, the aqua regia soil extracts could not be
determined by TS-FF-AAS even in monoelement mode,
because high background signals were observed. This
behavior was due to the high concentration of chloride
salts inside the atomizer and the undissociated matrix
species derived from them can generate molecular species
at a much higher degree than commonly observed
in FAAS [48]. Then, in order to achieve both high analytical
throughput and detectivity over the conventional
mono-element flame AAS, Slotted Tube Atom Trap
(STAT) was combined with FS-FAAS for the sequential
determination of Cd and Pb in the aqua regia soil extracts.
In table II, the figures of merit of the spectrometric
methods employed in this work are shown.
ElEmEnts
taBlE ii. fi g u rE s o f m E r i t f o r thE
EmPloyEd sPECtromEtriC m E t h o d s
tyPE o f
fl a m E
mE t h o d
ma x i m u m
aC h i E v a B l E
an a l y t i C a l
th ro u g h P u t
(d E t E r m i n a t i o n s PEr h o u r)
Cd and Pb Air-Acetylene FS-FAAS 386
Cd and Pb Air-Acetylene STAT-FAAS 386
Cd and Pb Air-Acetylene TS-FF-AAS 109
Cu and Ni Air-Acetylene FS-FAAS 363
Mn and Zn Air-Acetylene FS-FAAS 379
Guerra et al.
LOD
(μg
L-1)
3.6 and
86
0.7 and
31
0.3 and
8.8
8.5 and
27
9.9 and
2.6
Cr Acetylene-N 2 O FAAS 257 60
Two groups of elements were formed for determinations
by FAAS in the fast-sequential mode: 1) Mn and
Zn and 2) Cu and Ni; based in the same dilution factor
required by both groups of elements in the AAS determinations.
In table II, a comparison between FAAS,
STAT-FAAS and TS-FF-AAS in the fast-sequential mode
can be seen. For the calculation of maximum achievable
analytical throughput, the following conditions
were used: 1 second of pre-read delay; 3s of integration
time per each element and 33 nm s -1 as wavelength
scan speed of the equipment, and, for routine analysis,
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