Determinação de Ca, K, Mg e Na em petróleo utilizando amostragem direta e espectrometria de absorção atômica com forno de grafite

Abstract

Crude oil is a complex matrix and with variable chemical composition, and the determination of trace elements in this sample is not an easy task. The presence of some metals can result in problems during transportation and refining process of petroleum such as reduction of heating efficiency and clogging or corrosion of pipes. In this work, the determination alkaline and alkaline earth elements by direct sampling graphite furnace atomic absorption spectrometry (DS-GF AAS) was proposed. This technique was applied for the determination of Ca, K, Mg and Na in crude oil using Zeeman effect background correction system. The heating program for Ca, K, Mg and Na was established based on pyrolysis and atomization curves. After optimizations, DS-GF AAS was applied for analytes determination in eleven crude oil samples. Results obtained using DS-GF AAS were compared with those obtained by inductively coupled plasma optical emission spectrometry after conventional microwave-assisted digestion and microwave-assisted digestion and ultraviolet radiation. In addition, accuracy of DS-GF AAS was evaluated by using recovery tests and quantitative recoveries were obtained for all analytes. The use of DS-GF AAS allows to obtain low limits of detection and quantification, a suitable linear range (by changing wavelength or magnetic field) and a good precision (below 14% for all analytes). The limits of quantification for Ca, K, Mg e Na were 103, 14, 1.2 e 24 ng g-1, respectively. The determination of Ca, K, Mg and Na in crude oil samples by DS-GF AAS provides some advantages, such as no sample preparation, possibility of calibration using aqueous reference solutions and low contamination risk.