1. Introduction
There is a need to quantify trace metal concentrations in source
rocks because of their importance in the geochemical characterization
of source rocks and basins. Trace metals have been used
as geochemical tools to understand the depositional environments
of sediments and source rocks [1–3]. Trace metals are useful to
understand the source and thermal maturity of kerogen [4]. Trace
metal concentrations and ratios have been found to be invaluable
tools in oil–oil correlation and oil–source rock correlation
studies [5–7]. A few studies on the integration of trace metal and
biomarker data of source rocks are also available [1,3,8]. Refining
and environmental considerations are other important reasons for
the determination of metals in the petroleum industry. Some trace
elements especially vanadium and nickel behave as catalyst poisons
during catalytic cracking process in refining of crude oil.Metals
are released into the environment during petroleum exploration
and production and also during the refining of crude oil. To make
a meaningful impact assessment, it is necessary to know the composition
of the oils and also the source rocks from which the oils
were generated.
In most of these studies, the trace metals were determined
by either atomic absorption spectrometric method or inductively
coupled plasma-mass spectrometricmethod. These analytical tech-niques require acid digestion prior to analysis. Apart from the fact
that acids are corrosive and hazardous, the acid digestion method
procedure is time consuming and severely limits the rate of sample
throughput. Trace metal contamination from the acid reagents,
digestion vessels, and airborne particulates can jeopardize the
accuracy of the analytical results. Also, quantitative recovery of elements
such asmercury, boron, and selenium could be compromised
during hot acid digestion.
Therefore, an alternative method that is non-hazardous, environmentally
friendly and that will not compromise the qualitative
and quantitative recovery of the metals from the sample matrix is
required and superheated water extraction (SHWE) is a potential
alternative method. The method has been applied successfully for
the extraction of organic compounds from different solid matrices
[9–14]. Since metals are more soluble in water, even the organically
bound metals in sediments should be amenable to the superheated
water extraction. In previous work selected toxic metals have been
successfully extracted from coal and sludge samples using superheated
water at 180 ◦C and 250 ◦C [15–17] and Morales-Munoz et
al. [18] used acidified pressurized hot water at 250 ◦C for the continuous
extraction of cadmium and lead from plants. In this study,
the extraction of some trace metals from petroleum source rocks
by superheated water was carried out. The study was undertaken
in order to determine the effects of temperature and time on the
extraction yields of the metals and to establish the conditions for
maximum yields of the metals from the superheated water extraction
of petroleum source rocks in order to use the information for
geochemical characterization. A previous study in this laboratory