Selective extraction of traffic-related antimony compounds for speciation analysis by graphite furnace atomic absorption spectrometry

Most traffic-related antimony air pollutants are derived from brake dust. Brake dust contains Sb₂S₃, used as a friction material in brake pads, and its high-temperature oxidation products, Sb₂O₃ or Sb₂O₄. Systematic investigations were carried out to find the most selective leaching conditions for these substances. First, solubility experiments of the pure potential compounds mentioned above were carried out. Then, the leaching of these compounds from home-made artificial dusts previously spiked with these compounds at the trace level was investigated. A 0.5 mol L^?1 citric acid solution proved to leach the whole Sb₂O₃ content while extracting less than 10% Sb₂S₃ and no Sb₂O₄ at all. It was found that Sb₂O₃ and Sb₂S₃ traces were soluble in a 6 mol L^?1 HCl solution, quantitatively and selectively. Graphite furnace atomic absorption spectrometry and hydride generation graphite furnace atomic absorption spectrometry methods were developed to determine the Sb content of the extracts. The proposed method proved to be applicable to settled dust containing traffic-related Sb compounds. The detection limits were 1.2 and 0.3 μg g^?1 for leaching by citric acid and HCl solution, respectively, which were adequate for Sb content determination in the urban dust studied. The reproducibility of the method expressed as relative standard deviation was about 7%. The results showed that the concentration of leachable Sb was 40 μg g^?1 in the settled dust of Budapest, about half of which corresponded to Sb₂O₃. The Sb₂O₄ content calculated as the difference of total and leachable fraction was about 10% with high uncertainty.