title: Microwave-induced combustion of crude oil for further rare earth elements determination by USN-ICP-MS.
abstract: A procedure for light and heavy crude oils digestion by microwave-induced combustion (MIC) is proposed for the first time for further rare earth elements (REE) determination by inductively coupled plasma mass spectrometry (ICP-MS) equipped with an ultrasonic nebulizer (USN). Samples of crude oil (API density of 10.8-23.5, up to 250 mg) were inserted in polycarbonate capsules and combusted using 20 bar of oxygen and 50 μL of 6 mol L(-1) ammonium nitrate as igniter. Nitric acid solutions (1-14.4 mol L(-1)) were evaluated for analyte absorption and a reflux step was applied after combustion (5 min of microwave irradiation at 1400 W) in order to achieve better analyte recoveries. Accuracy was evaluated using a spiked sample and also by comparison of results obtained by microwave-assisted digestion combined to ultraviolet radiation (MW-UV) and by neutron activation analysis (NAA). Using 3 mol L(-1) HNO3, quantitative recoveries (better than 97%) were obtained for all analytes. Blank values were always negligible. Agreement was higher than 96% for La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y by comparison of results with those obtained by MW-UV and by NAA (only for La, Ce, Nd, Sm, and Yb). Residual carbon content in digests using MIC was always below 1%. As an advantage over conventional procedures for crude oil digestion, using MIC, it was possible to use diluted acid as absorbing solution, obtaining better limits of detection and avoiding interferences in REE determination by USN-ICP-MS.
authors.affiliation: Departamento de Química Inorgânica, Universidade Federal do Rio Grande do Sul, 97105-900 Porto Alegre, RS, Brazil.
authors.forename: J S F
authors.initials: JS
authors.lastname: Pereira
authors.affiliation: Departamento de Química, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil.
authors.forename: L S F
authors.initials: LS
authors.lastname: Pereira
authors.affiliation: Departamento de Química, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil.
authors.forename: P A
authors.initials: PA
authors.lastname: Mello
authors.affiliation: CENPES/PETROBRAS, 21941-945 Rio de Janeiro, RJ, Brazil.
authors.forename: R C L
authors.initials: RC
authors.lastname: Guimarães
authors.affiliation: CENPES/PETROBRAS, 21941-945 Rio de Janeiro, RJ, Brazil.
authors.forename: R A
authors.initials: RA
authors.lastname: Guarnieri
authors.affiliation: CENPES/PETROBRAS, 21941-945 Rio de Janeiro, RJ, Brazil.
authors.forename: T C O
authors.initials: TC
authors.lastname: Fonseca
authors.affiliation: Departamento de Química, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil. Electronic address: ericommf@gmail.com.
authors.forename: E M M
authors.initials: EM
authors.lastname: Flores
keywords: Crude oil; ICP-MS; Microwave-induced combustion; Rare earth elements; Ultrasonic nebulizer