Trace Metal Analysis in Petroleum Products: Sample Introduction Evaluation in ICP-OES and Comparison with an ICP-MS Approach

The needs of the petroleum industry in studies dedicated to trace metals determination are highly related to exploration, but also to exploitation activities for corrective actions during oil production and refining. Two techniques provide a very large concentration range of metal compounds to be determined on a routine basis, ICP-OES being preferred for major element analysis whereas ICP-MS is particularly convenient for ultra trace metals analysis. Direct introduction of petroleum product in the plasma require a methodical approach in order to minimise matrix effect. Here, three different sample introduction modes have been investigated depending on the elements of interest and the matrix analysed. A classical pneumatic nebulizer and an ultrasonic nebulizer (USN) were compared for ICP-OES. These introduction modes were compared with a microflow pneumatic concentric nebulizer associated with a chilled spray chamber used with ICP-MS. Classical pneumatic nebulisation with ICP-OES leads to ppm range limit of quantification in the petroleum product and five times higher with gasoline due to important dilution factor. The use of an USN coupled with ICP-OES reduce limit of quantification in gasoline to the 50 ppb range, but further study of matrix effects with such an introduction must be done. The PFA-100 associated with a cooled Scott chamber used with ICP-MS reduce also limit of quantification in the petroleum product to the 10 ppb range for most elements. The initial important dilution factor allows the introduction of light matrices without further dilution, but require anyhow the use of a standard addition method, which is time-consuming. Then, the choice of a technique is definitively dependant on the needs required by the laboratory between high throughput analyses and very low limit of quantification. Les besoins de l'industrie pétrolière en analyse de métaux traces sont étroitement corrélés aux besoins de l'exploration géochimique, mais aussi en raffinage et pétrochimie pour les problèmes de pollution. L'ICP-OES et l'ICP-MS sont deux techniques pouvant répondre dans une large gamme de concentration aux besoins exprimés en analyse de routine. La première est préférée pour l'analyse des éléments majeurs et la seconde est particulièrement adaptée pour la détermination de métaux en ultra-traces. L'introduction directe de produits pétroliers dans le plasma nécessite une approche méthodique pour limiter les effets de matrice. Dans cet article, trois modes d