TECHNICAL NOTE Direct determination of nickel in petroleum by solid sampling–graphite furnace atomic absorption spectrometry Geisamanda Pedrini Brandão & Reinaldo Calixto de Campos & Eustáquio Vinicius Ribeiro de Castro & Honério Coutinho de Jesus Received: 4 June 2006 / Revised: 4 September 2006 / Accepted: 21 September 2006 / Published online: 24 October 2006 # Springer-Verlag 2006 Abstract A procedure for the direct GFAAS determination of Ni in petroleum samples using a solid sampling strategy is proposed. Palladium was used as conventional modifier. Central composite design multivariate optimization defined the optimum temperature program and the Pd mass, allowing calibration using aqueous analytical solution. The limit of detection (LOD) at the optimized conditions was 0.23 ng of Ni, for typical sample masses between of 0.10 and 0.60 mg. Linearity at least up to 11 ng of Ni and a characteristic mass of 45 pg were observed, defining a dynamic range between 0.52 and 110 μgg -1 . Typical coefficients of variation (n =10) in the analysis of oil reference materials were 7%. Method validation was performed both by the analysis of oil certified reference materials and by comparison with an independent method (ASTM 5863-B). No statistically significant difference was observed between obtained and expected values. The total determination cycle lasted 5 min, equivalent to a sample throughput of 6 h -1 for duplicate determinations. Keywords Nickel . Petroleum . SS-GFAAS Introduction The determination of metallic trace elements in petroleum is of importance to the oil industry, since it provides information about crude oil origins, migration, and types. Nickel naturally occurs in petroleum at the μgg -1 range associated to the formation process, mostly as metal- loporphyrins and metallonon-porphyrins [1–3]. Ni inter- feres with the refining of crude oils: it may cause corrosion of refinery equipment and affects catalyst activity, leading to undesirable side reactions and decreasing cracking yields [3, 4]. Hazardous Ni compounds might also be generated during combustion of petroleum and its derivatives, leading to environmental and health concerns. Consequently, Ni emissions control under national and international regula- tions have been established. The evaluation of the Ni concentration may also be utilized to identify sources of unregulated releases of petroleum [4, 5]. A number of analytical methods for the determination of Ni in petroleum and their viscous heavy products have been proposed including X-ray fluorescence spectroscopy [6–8], high- performance liquid chromatographic (HPLC) with UV [9] or atomic absorption spectrometry (AAS) [1] detection, inductively coupled plasma optical emission (ICPOES) [4, 10–12] and mass spectrometry (ICPMS) [13–16], flame atomic absorption spectrometry (FAAS) [2, 5, 17–19], and graphite furnace atomic absorption spectrometry (GFAAS) [20–23]. In ICP techniques desolvatation under cryogenic cooling and the removal of carbon by feeding oxygen into the plasma [16] have been proposed in order to avoid plasma extinction or carbon deposition on the sampler and skimmer cones. FAAS allows the direct analysis of hydrocarbon matrices after just a dilution with an adequate organic solvent. However, aside from its low sensitivity, both the solvent and the compounds used for calibration Anal Bioanal Chem (2006) 386:2249–2253 DOI 10.1007/s00216-006-0875-6 G. P. Brandão : R. C. de Campos (*) Department of Chemistry, Pontifical Catholic University, Rua Marquês de S. Vicente 225, Gávea 22453-900 RJ, Brazil e-mail: rccampos@rdc.puc-rio.br E. V. R. de Castro : H. C. de Jesus Department of Chemistry, Espírito Santo Federal University, Avenida Fernando Ferrari s/n, Campus de Goiabeira, Vitória 29000-000 ES, Brazil