doi:10.1016/j.chroma.2006.04.069 
Copyright © 2006 Elsevier B.V. All rights reserved.
Procedure for and results of simultaneous determination of aromatic hydrocarbons and fatty acid methyl esters in diesel fuels by high performance liquid chromatography
aDepartment of Analytical Chemistry, Chemical Faculty, Gdańsk University of Technology, 11/12 G. Narutowicza St., 80-952 Gdańsk, Poland
bLOTOS S.A., LOTOS Lab. Ltd., 135 Elbląska St., 80-718 Gdańsk, Poland
cScience & Mathematics Department, Kettering University, 1700 West Third Avenue, Flint, MI 48504, USA
Received 19 December 2005;
revised 11 April 2006;
accepted 21 April 2006.
Available online 15 May 2006.
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Abstract
The content of aromatic hydrocarbons in diesel fuels is regulated by appropriate standards, and a further reduction in the allowed concentration of these hazardous substances in these fuels is expected. The content of aromatic hydrocarbons in diesel fuels is most often determined using standard methods EN-12916 or ASTM D-6591. The content of polycyclic aromatic hydrocarbons (PAHs) is determined from a single peak obtained using normal phase high-performance liquid chromatography (NP-HPLC), a column of the NH2 type, n-heptane as the eluent, refractive index detector (RID) and backflushing of the eluent. However, the methods mentioned above cannot be applied when the fuel contains fatty acid methyl esters (FAME), which lately has become more common. The content of FAME in diesel oils is determined using mid-IR spectrophotometry based on the absorption of carbonyl group. However, no standard procedure for the determination of classes of aromatic hydrocarbons in diesel fuels containing FAME is yet available. The present work describes such a modification of methods EN-12916/ASTM D-6591 that provides a simultaneous determination of individual groups of aromatic hydrocarbons, total content of polycyclic aromatic hydrocarbons and the FAME content in diesel fuels. The refractive index detector (RID) and n-heptane as the mobile phase are still used, but backflushing of the eluent is applied after the elution of all polycyclic aromatic hydrocarbons. Additionally, ultraviolet diode array detection is used for the exact determination of low contents of polycyclic aromatic hydrocarbons and to confirm the presence of FAME in the analyzed fuel.
Keywords: Diesel fuels; Simultaneous determination of aromatic hydrocarbons and FAME; Normal phase-high-performance liquid chromatography (NP-HPLC); Refractive index and spectrophotometric detection and determination (RID/UV-DAD)
Fig. 1. Schematic diagram of the HPLC apparatus with backflush used for the determination of class composition of diesel fuel: paraffins/olefines/mono-/di-/tri- and above aromatics hydrocarbons/fatty acids methyl esters.
Fig. 2. Typical chromatograms obtained with RID to determine the class composition of diesel fuel (Eurodiesel), containing about 7% (m/m) FAME. Chromatogram shown in insert A has sensitivity lowered by a factor of eight. Column: LiChrospher NH2 5 μm, 250 × 4 mm i.d.; mobile phase flow rate 0.8 mL/min; temperature 20 °C; volume injected 20 μL; sample concentration 0.05 g/mL; backflush point 14 min. Peaks: (1) paraffins + naphthenes + olefins (PNO); (2) monoaromatic hydrocarbons; (3) diaromatic hydrocarbons; (4) polyaromatic hydrocarbons; (5) fatty acid methyl esters (FAME); BF, backflush; lines (a and b) are the baselines for peak integration, leading to different contents of groups of aromatic hydrocarbons: line a, drawn according to the procedure described in method EN 12916 (underestimated content of MA, and particularly of DA); line b, drawn in order to determine the content of PA (at the same time, it allows correct determination of MA and DA; see text for further details).
Fig. 3. Separation of diesel fuel EuroDiesel containing about 7% FAME. For chromatographic conditions, see Fig. 2. (A) UV-DAD chromatogram with programmed wavelength (210, 260 and 210 nm), marked with dotted line in (B); (B) three-dimensional UV-DAD chromatogram; (C) spectrum of the group of pyrene derivatives with the retention time of about 12 min, characteristic of diesel fuels obtained by catalytic hydrocracking. For peak labels, see Fig. 2.
Fig. 4. UV-DAD chromatogram for diesel fuel produced by catalytic hydrorefining, free of FAME, but containing chrysene and its derivatives and also a substantial concentration of resins. (A) Three-dimensional UV-DAD chromatogram; (B) UV spectrum of chrysene and its alkyl derivatives; (C) so-called best chromatogram, obtained using the wavelength program as in Fig. 3, but at a 10 times higher sensitivity; (D) chromatogram as in (C), but at about 50 times lower sensitivity. Chromatographic conditions and peak labels as in Fig. 2 and Fig. 3, except for peak 4—chrysene and its alkyl derivatives.
Fig. 5. RID and three-dimensional UV-DAD (insert) chromatograms of reference diesel fuel, stored for 2 years at room temperature. (a) Diesel fuel containing ca. 7% FAME; (b) diesel fuel free of FAME, but containing a substantial content of polar compounds. Separation conditions, integration baselines and labels of chromatographic peaks as in Fig. 2, except for peak 5—polar substances, so-called resins (R).
Fig. 6. UV spectra corresponding to the peak maximum of compounds eluted using backflush. (1a and 1b) FAME spectra; (2a and 2b) resin spectra; (6a) normalized spectra (see text for explanation) and (6b) raw spectra.
Table 1.
Calibration data for the simultaneous determination of aromatic hydrocarbons and FAME in diesel oils
a Response factor determined at 260 nm.
b Response factor determined at 210 nm.
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