Brazilian Journal of Analytical Chemistry - BRJAC - Brazilian Journal ...

Br J Anal Chem 2011, 03, 131–135
ClosEd-vEssEl m iC r o w a v E-assistEd d i gE s t i o n u s i n g
a d i l u tE d o x i d a n t m i x t u rE f o r traCE ElEmEnt
d E t E r m i n a t i o n in PEtroChEmiCal samPlEs By axiallyviEwEd
iCP oEs
an g E r s o n n. nasCimEnto a , Ju l i a n a na o z u k a B , PE d ro v. olivEira a *
A) Instituto de Química, Universidade de São Paulo, 05508-000 - São Paulo, SP, Brazil
B) Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-170 - Santo André, SP, Brazil
*Corresponding author:
PV Oliveira/Phone: + 55
11 3091 8516 / e-mail:
pvolivei@iq.usp.br
www.brjac.com.br
ab s t r a c t
A simple, robust and reliable analytical method for the determination of metals (Ag, Al,
Ba, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Mo, Na, Ni, Pb, V and Zn) and nonmetals (P and S) in
petrochemical samples (petroleum, diesel oil, biodiesel, and oil sludge waste) by axiallyviewed
inductively coupled plasma optical emission spectrometry (ICP OES) is proposed.
A diluted oxidant mixture (4 mL HNO 3 + 2 mL H 2 O 2 + 2 mL H 2 O) was used to achieve
almost complete oxidation of the organic matrix in a closed-vessel microwave oven. The
residual carbon (3-9 % w/w) supported the effectiveness of the sample digestion with
the diluted oxidant mixture. The accuracy of the analytical method was confirmed by
analysis of a standard reference material (residual oil - NIST SRM 1634c) and another
reference material (hydrocarbon oil - Alfa Aesar JM-21). The reference values showed
good agreement at a 95% confidence limit (Student’s t-test).
Ke y w o r d s : petroleum, diesel oil, biodiesel, sludge waste, ICP OES, diluted oxidant
mixture, microwave
In t r o d u c t Io n
The development of analytical methods for elemental
determination in petrochemical products has been
arousing interest, mainly due to their prominence, in
terms of quality control, economics and environmental
factors [1-3]. Crude oil contains several metals as organometallic
complexes and information on these trace
elements is important for geological (crude oil origin)
[4,5] and environmental studies (anthropogenic emission
of petroleum-based fuels) [6,7]. The poisoning of
catalysts in the petroleum cracking process and corrosion
of equipment, owing to the presence of these
trace metals in oils, has also been widely reported [8,9].
Therefore, with the exception of certain additives, it is
desirable that petrochemical products have low metal
concentrations, aiming at a highly sensitive and precise
method for quality control and for emission controls of
these elements to the atmosphere.
Elemental determination in petrochemical products
by spectroscopic techniques is not easy, mainly because
of the high complexity and organic nature of their matrix
[1,10]. Despite this, inductively coupled plasma optical
emission spectrometry (ICP OES) is the technique
recommended by the American Society of Testing Materials
(ASTM D 4951) [11] and the European Commit-
tee for Standardization (CEN-EN 14 107) [12]. This analytical
technique is a well-established multielementar
one and presents a wide linear dynamic range, good
analytical detectivity and high sample throughput [13].
However, ICP OES usually requires the conversion of organic
samples into a clear solution with low residual
carbon content [14].
In general, digestion procedures are useful for petrochemical
samples as a pre-treatment before elemental
determination by ICP OES [1]. Microwave-assisted
sample preparation has been used for a wide range of
applications [15]. Sample preparation procedures using
digestion with diluted oxidant mixtures are still little
explored for petrochemical samples. Some favorable
characteristics of the digestion with diluted reagents
are low blank values, low standard deviations and less
contamination. Particularly for ICP OES, it is important
to point out the minimization of interferences caused
by concentrated acids, mainly during sample nebulization,
and the reduction of chemical attack on equipment
parts, such as the nebulizer, nebulization chamber
and torch [14]. Finally, this procedure promoted the application
of clean analytical methods with low residue
generation, and is economically viable due to its low
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