Determination of As and Se in crude oil diluted in xylene by inductively coupled plasma mass spectrometry using a dynamic reaction cell for interference correction on 80Se

Abstract

Arsenic and selenium can be found in crude oils and represent an important source of pollution when released to the environment during any stage of extraction or refinery. These elements present low sensitivity in the direct determination by inductively coupled plasma mass spectrometry (ICP-MS), due to their high ionization potential, and are also prone to spectral interferences. Hydride generation (HG) can be alternatively employed for the separation of these analytes from the sample matrix and introduction into the instrument. However, the required sample preparation usually increases the analysis time. In this work, a method was developed for the determination of As and Se in crude oil by ICP-MS, after sample dilution in xylene. The use of a dynamic reaction cell (DRC) allowed for the overcoming of Ar2+ interference on 80Se, but was not necessary for As, since interference on m/z 75 was not observed. The optimized operational conditions for 75As and 80Se were: 1350W of RF power, 0.4Lmin−1 of Ar nebulizer and 0.7Lmin−1 of Ar auxiliary flow rates. The DRC conditions for 80Se were 0.5Lmin−1 of methane and rejection parameter q (Rpq) of 0.2. The analyses were carried out by analyte addition and the limits of detection (LOD) were 0.04μgkg−1 for As and 0.1μgkg−1 for Se. The accuracy was verified by the analysis of residual fuel oil certified material, with agreement at a 95% confidence level. Nine Brazilian crude oil samples were analyzed and the results compared to those obtained by hydride generation ICP-MS. In this case, samples were decomposed with nitric acid in a digester block, the analytes pre-reduced with HCl 6molL−1 and the determination carried out by external calibration. Although better instrumental LODs were obtained by HG (0.002μgkg−1 of As and 0.04μgkg−1 of Se), the direct determination of As and Se in crude oil diluted in xylene by DRC-ICP-MS showed to be an adequate and a faster method.