A new sample preparation approach based on microwave-induced combustion in disposable vessels for Ni and V determination by ICP-MS in crude oil

The presence of Ni and V in crude oil is associated with pollutant emissions, corrosive processes and low-quality products. Nevertheless, the knowledge of the concentration of these elements, helps to predict geochemical characteristics and to bring information about the crude oil source. Moreover, Ni and V can cause problems during the crude oil refining process. Therefore, the development of alternative, low-cost and rapid approaches for Ni and V determination in crude oil is still welcomed and was the aim of this work. The proposed microwave-induced combustion in disposable vessels (MIC-DV) system allows the use cheap and/or reusable materials, combined to the possibility of sample combustion under atmospheric pressure and using a domestic microwave. The parameters evaluated during MIC-DV optimization were, sample mass (5-20 mg), and volume (1-10 mL) and concentration (0.5-7 mol L^-1 HNO₃) of absorbing solution. MIC-DV was applied for the digestion of ten crude oil and the results were compared with those obtained after microwave-assisted digestion (MAD) and Ni and V determination by inductively couple plasma mass spectrometry (ICP-MS). The agreement values achieved ranged from 92 to 103 % for Ni and from 93 to 106 % for V. The limits of quantification after MIC-DV/ICP-MS were 0.28 and 0.15 μg g^-1 for Ni and V, respectively. The developed MIC-DV method, can be considered environmentally friendly since it uses low-cost materials and instrumentation, requires reduced handling (based on the single vessel principle), avoids the use of additional dilution steps and minimizes the digest contamination.