In recent years Cu, Mo and Sb were identified as traffic-related
elements (TRE), as up to 4% of Cu, 1% of MoS2 and 7% of Sb2S3 are
used in brake linings (or pads) [1]. Kukutschová et al. [2] estimated
that approximately 30,000 tonnes of break wear debris is being
released in the USA yearly and investigated the mutagenic potency
and pulmonary toxicity of wear debris. Several studies were carried
out recently to assess the influence of traffic on atmospheric
pollution in urban areas and to determine TRE in urban aerosols
[1,3]. Several investigations were carried out on the determination
of Sb as a new global pollutant in APM [4–6]. In a comprehensive
study, Weckwerth [7] analyzed APM by neutron activation analysis
in samples collected at 12 sites in Cologne (Germany); he compared
the measured levels with specific element patterns from relevant
emission sources such as coal, soot, tires, brake linings, and rails. On
the basis of the agreement between the Cu and Sb ratio (∼5) in brake
linings and measured levels in APM, it was suggested that both elements
might be taken as quantitative tracers for the brake-lining
component in APM. In 67 samples of APM collected in Buenos Aires
(Argentina) Sb concentrations varied between 0.9 and 15.3 ng m−3
with a mean value of 4.7 ng m−3 [4]. The Cu:Sb ratio was calculated
to further support the view that brake linings contribute significantly
to the aerosol fraction <10 m (PM-10), and values between
5.6 and 8.0 were determined [8].
APM is often collected on glass-fiber filters using high-volume
samplers with a PM-10 filter, and a typical sampling flow rate
of 1000 L min−1. However, the determination of trace elements in
APM collected on glass fiber filters is difficult because of the refractory
nature of the matrix. The total analyte concentration can only
be determined after acid digestion in the presence of hydrofluoric
acid, a procedure that is relatively time-consuming and certainly
not without problems. Digestions in hydrofluoric acid are dangerous,
and next to silicon, which should be removed in this manner, a
number of elements, including Sb, form volatile fluorides which
might be lost during sample preparation. Owing to these problems,
instead of a total digestion, it is common in environmental
analysis to use leaching with aqua regia [4,8–10]. This method,
however, should be considered an acid leaching rather than a digestion,
which cannot replace a determination of the total content of
an analyte in all situations. In addition, the resulting acid matrix
can cause serious interferences in most spectrometric techniques,
such as ICP-MS or GF AAS. This means that the solutions need to
be strongly diluted, which is often not possible in trace element
determinations, or the analyte has to be extracted, which is another
time-consuming procedure. The determination of Cu, Mo, Sb and
other trace elements in APM with direct solid sampling (SS) GF
AAS appears as an attractive alternative [11–14]. Even though, it
still presents problems when conventional line-source GF AAS is
used because complex matrices may cause spectral interference
due to molecular absorption with rotational fine structure, such
as that caused by SiO [15]. High-resolution continuum source AAS
(HR-CS AAS), in contrast, offers much more sophisticated and efficient
background correction [15,16]; background that is continuous
within the spectral range covered by the array detector is corrected
automatically and simultaneously using correction pixels on both
sides of the analytical line, whereas structured background can be
corrected using reference spectra and a least-squares algorithm
[14–17].
The aim of this study has been to develop a fast, reliable and
sensitive alternative to conventional methods for Cu, Mo and Sb
determination in APM, collected on glass fiber filters, using direct
solid sampling HR-CS GF AAS, and hence avoiding the dissolution
of the sample. The proposed procedure will be compared with conventional
techniques with respect to accuracy (agreement) of the
results, precision, limits of detection and quantification, and the
time necessary to carry out a complete analysis, a facto
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