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Direct determination of arsenic and antimony in naphtha by electrothermal atomic absorption spectrometry with microemulsion sample introduction and iridium permanent modifier

Cassella, Ricardo J., Barbosa, Bruno Alberto R. S., Santelli, Ricardo E., Rangel, Alessandra T.
Analytical and bioanalytical chemistry 2004 v.379 no.1 pp. 66-71
antimony, arsenic, atomic absorption spectrometry, detection limit, emulsifying, iridium, octoxynol, pyrolysis, surfactants, temperature
This paper reports the determination of arsenic and antimony in naphtha by employing electrothermal atomic absorption spectrometry (ETAAS) as the analytical technique. In order to promote the direct determination of the analytes in the very volatile naphtha, the formation of a microemulsion with different surfactants (Triton X-100 and Brij-35) and different chemical modification strategies were tested. The results indicated that Triton X-100 is the best emulsification agent for naphtha in both As and Sb determination when it is employed at a concentration of 1% w/v in the microemulsion. Under these conditions, the microemulsion was stabile for at least 2 h. By using Brij-35 it was possible to achieve good stability only in the first 15 min. Among all chemical modification approaches investigated (Ir permanent modifier, W-Ir permanent modifier, and Pd modifier), the Ir permanent modifier provided better sensitivity for both analytes and allowed a higher pyrolysis temperature, which decreased the background signals at lower levels. Under the best conditions established in this work, an RSD of 4.6% (20 μg L⁻¹) and a detection limit of 2.7 μg L⁻¹ were observed for arsenic. For antimony, an RSD of 4.0% (20 μg L⁻¹) and a detection limit of 2.5 μg L⁻¹ were obtained. The accuracy of the procedure was assessed by analyzing spiked samples of naphtha from different origins.