Direct elemental analysis of petroleum heavy fractions by means of ICP-OES equipped with a high temperature torch integrated sample introduction system

Abstract

The present work describes and discusses the use of a high temperature sample introduction system, hTISIS, for the analysis of crude oil and heavy petroleum fractions by means of inductively coupled plasma optical emission spectrometry, ICP-OES. A commercially available sample introduction system based on a conventional cyclonic spray chamber operated at room temperature has been used for comparison purposes. The method has been based on gentle heating of the sample while stirring, dilution and introduction into the spectrometer. A 5 μL solution volume has been injected into an air carrier stream and introduced to the sample introduction system. Therefore, a transient signal has been obtained. Meanwhile, the quantification strategy has consisted in an external calibration using a single set of multielemental standards prepared in xylene. The achieved results indicate that, for crude oil and its heavy cuts, the hTISIS operated at 400 °C provides signal enhancements in terms of peak height of about 4 to 15 times with respect to the cyclonic spray chamber. Furthermore, the repeatability is improved and the limits of quantitation lowered when working with the high temperature device. The measured LODs for real samples have also been determined and it has been observed that the cyclonic spray chamber affords figures 2.5 to 50 times higher than the hTISIS at 400 °C. Moreover, for the latter design, matrix effects have been compensated for and it has been possible to apply the concept of universal calibration in which a single set of xylene multielemental standards has been applied to the simultaneous accurate quantification of silicon, vanadium, iron, aluminum and nickel in crude oil, atmospheric residue, fuel, vacuum residue and vacuum distillates.