Determination of Ca, Mg, Sr and Ba in crude oil samples by atomic absorption spectrometry

Abstract

The presence of Ca, Mg, Sr and Ba in crude oil samples should be controlled, since they can lead to incrustations on steel pipes, valves, pumps and other equipment used in crude oil drilling. This paper proposes procedures for the determination of these metals in crude oil by atomic absorption spectrometry, using the formation of O/W emulsions for sample preparation. Emulsions were prepared in 0.2% v/v HNO₃ using Triton X-100 as a surfactant and showed good stability for the four studied analytes of at least 5 days after preparation. Flame atomic absorption spectrometry (FAAS) was used for the determination of Ca, Mg and Sr and graphite furnace atomic absorption spectrometry (GFAAS) was used for the determination of Ba. External calibration could be performed for the determination of Ca, Mg and Sr with inorganic standard solutions in the form of emulsions; for Ba, calibration was possible in aqueous medium. The limits of detection obtained were 0.54, 0.09, 0.10 and 0.04 μg g⁻¹ for Ca, Mg, Sr and Ba respectively in the crude oil samples. Recoveries ranging from 96 to 104% and the good agreement among the found and certified values in the analysis of a certified reference material (NIST 1085b) warranted the accuracy of the procedures.