Anal. Chem. 1998, 70, 1228-1230
Decomposition of Acenaphthylene by Ultrasonic
Irradiation
E. Leonhardt and R. Stahl*
Institut fu¨r Chemische Technik, Forschungszentrum Karlsruhe GmbH, Postfach 3640, D-76021 Karlsruhe, Germany
P olycyclic aromatic hydrocarbons were extracted from a
soil sample using ultrasound and dichloromethane-,
cyclohexane-, and toluene-water mixtures. It was found
that when dichloromethane is used as an extractant,
acenaphthylene reacts with the solvent. Several chlori-
nated and oxygenated derivatives were identified. The
results show that chlorinated solvents should be avoided
because of their sonolytic decomposition. P articularly
unsaturated nonaromatic compounds might react with
intermediate decomposition radicals of the solvent.
Polycyclic aromatic hydrocarbons (PAH) are environmental
pollutants often resulting from incomplete combustion or high-
temperature pyrolytic processes. They represent a risk to the
environment because PAH have been found to be mutagenic or
Figure 1. Schematic diagram of setup for ultrasound extraction
(a - b ≈ 10 mm).
carcinogenic and resistant to degradation.1 As nonpolar, lipophilic
compounds, PAH are adsorbed on solid particles such as soil, fly
ash, or river sediments.2,3 The U.S. Environmental protection
Agency (U.S. EPA) has included 16 PAH in its pollutant list and
has promulgated regulations for their monitoring in wastewater.4,5
The absolute concentrations of selected PAH serve as indicators
for environmental contamination.6 Thus, the identification and
quantification of these compounds are an important task. The
sample preparation is a time-consuming extraction step which has
to be done very carefully. For the extraction of PAH from solid
samples, Soxhlet extraction,7-9 supercritical fluid extraction,10-13
accelerated solvent extraction,14 and sonication processes15,16 have
been used. Some authors document the reproducibility and
efficiency of ultrasonic extraction.17-18 On the other hand it is
well-known that imploding cavitation bubbles inside a liquid
concentrate the acoustic energy in a small volume, resulting in
high pressures and temperatures for a very short time.19,20 Solvent
radicals formed during the cavitation might react with some of
the PAH. The sonolytical decomposition of PAH may be useful
as a means for their destruction.21 These facts indicate that the
application of ultrasound for sample preparation is affecting the
quantification of these compounds. The intention of this paper
was to investigate the decomposition of PAH during their
ultrasonic extraction from solid samples.
(1) Manahan, E. S. Fundamentals of Environmental Chemistry; Lewis Publishers:
London, 1993.
(2) Hoffman, E. J.; Mills, G. L.; Latimer, J. S.; Quinn, J. G. Environ. Sci. Technol.
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EXPERIMENTAL SECTION
Chemicals. All solvents used were analytical-grade chemicals
obtained from Merck (Darmstadt, Germany). Water was prepared
using a Millipore Q unit. Acenaphthylene and standards were
purchased from Supelco GmbH.
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Technol. 1 9 8 8 , 22, 1219-1228.
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386.
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Analysenschemas fu¨ r organische Chemikalien im Boden; Wilhelm Dostall
KG: Esschweiler, Germany, 1990.
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Anal. Chem. 1 9 9 2 , 49, 221-230.
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208.
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Vol. 3, pp 17-83.
B. Anal. Chem. 1 9 9 6 , 68, 3892-3898.
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Greenwich, CT, 1990; Vol. 1, pp 197-230.
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Aromat. Compd. 1 9 9 0 , 1, 125-135.
1228 Analytical Chemistry, Vol. 70, No. 6, March 15, 1998
S0003-2700(97)01008-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/10/1998