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ALTERNATIVE METHODS FOR CRUDE OIL DIGESTION AND SUBSEQUENT
ELEMENTAL DETERMINATION
Authors: A.O. Gomes1, R.C.L. Guimarães1, L.M.S.L. Oliveira1, E.I. Müller2, F.A.
Duarte2, P.A. Mello2, C.A. Bizzi2 and E.M.M. Flores2
Adscription: 1Centro de Pesquisas e Desenvolvimento Leopoldo Américo Miguez
de Mello, Petrobras S. A., 21941-945, Rio de Janeiro, Rio de Janeiro, Brazil.
2
Departamento de Química, Universidade Federal de Santa Maria, 97105-900,
Santa Maria, Rio Grande do Sul, Brazil
The development of methods for sample preparation of crude oil and subsequent
elemental determination requires that some aspects should be considered such as
simplicity, use of small amounts of reagents, sample mass and analytical throughput.
Among the methods commonly used for crude oil digestion it is possible to stand out
the dry ashing and microwave wet digestion. However, these methods are prone to
contamination and analyte losses during the digestion procedure. In this sense,
some alternative methods have been proposed for digestion of crude oil samples
such as microwave-induced combustion (MIC), microwave-assisted single reaction
chamber (MW-SRC) and microwave-assisted digestion combined to in situ ultraviolet
radiation (MWAD-UV). For MIC method, a sample mass of crude oil (up to 500 mg)
is combusted in a closed system under microwave heating. Analytes are absorbed
into a suitable absorbing solution and losses of elements (especially halogens) are
minimized. MIC allows digestion of light and heavy crude oils, as well as its fractions
allowing obtaining high digestion efficiency (>99%). The MW-SRC method allows the
digestion of crude oil with microwave heating using temperature and pressure up to
280 oC and 200 atm, respectively. The differential of this method is the possibility of
efficient digestion of relatively larger sample masses of crude oil and its heavier
fractions. The decomposition using MWAD-UV allows the combination of the
microwave and UV energy. The great advantage of this digestion method is the use
of diluted acids that minimizes interferences during elemental determination by
plasma-based techniques. By using of these alternative methods smaller quantities
of reagents are required, final digests with lower concentrations of residual carbon
content are obtained which minimize interferences in determination step and
contribute for improving detection limits.