Published:Journal of Chromatographic Science,
ISSN 0021-9665 Volume
45, Number 10, November/December 2007, pp. 690-693
Determination of Total Biodiesel Fatty Acid Methyl,
Ethyl Esters, and Hydrocarbon Types in Diesel Fuels by Supercritical
Fluid Chromatography–Flame Ionization Detection
John W. Diehl and Frank P. DiSanzo
Analytical Sciences Laboratory, ExxonMobil Research and Engineering,
Paulsboro Technical Center, Paulsboro, NJ 08066
A method for determining total biodiesel methyl
and ethyl ester content in diesel fuels by supercritical fluid
chromatography–flame ionization detection (SFC–FID)
is developed. A silica column typically used for determining
aromatics in conventional diesel fuels by ASTM D5186 is back-flushed
after separation of the hydrocarbons to allow elution of the
various esters as a single “total biodiesel” distinct
peak. The modification concurrently allows the determination
of total aromatic hydrocarbons and their distribution as mono-
and polynuclear compounds, as described in the current version
of D5186. The instrument response is linear from 1.0% to 50%
biodiesel esters with a signal-to-noise ratio of 25 at the 0.1%
level. The short-term relative standard is 0.8%. Normalized percent
quantitation using a hydrocarbon response factor of 1.00 and
an ester response factor of 1.19 provide an average percentage
error of 1.8% when measuring actual biodiesel/hydrocarbon fuel
blends. The ester response factor is the average of the response
factors of 10 pure ester compounds. These responses are calculated
from respective solutions of each ester and the four compounds,
hexadecane, toluene, tetralin, and naphthalene, as used for the
D5186 response factor mixture.
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