doi:10.1016/j.chroma.2006.02.096 
Copyright © 2006 Elsevier B.V. All rights reserved.
Determination of polycyclic aromatic sulfur heterocycles in diesel particulate matter and diesel fuel by gas chromatography with atomic emission detection
Fuyan Lianga, Mingming Lua, 
, 
, M. Eileen Birchb, Tim C. Keenera and Zifei Liua
aDepartment of Civil and Environmental Engineering, University of Cincinnati, P.O. Box 210071, Cincinnati, OH 45221, USA
bUS Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Division of Applied Research and Technology, 4676 Columbia Parkway, Cincinnati, OH 45226, USA
Received 28 November 2005;
revised 7 February 2006;
accepted 13 February 2006.
Available online 30 March 2006.
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Abstract
The sulfur content of diesel fuel is of environmental concern because sulfur can facilitate the formation of diesel particulate matter (DPM) and sulfur dioxide (SO2) in the exhaust can poison catalytic converters. The US Environmental Protection Agency (EPA) has established more stringent regulations to reduce the sulfur content of diesel fuels in the near future. In this study, various types of organosulfur compounds in DPM extracts and the corresponding fuels have been determined by gas chromatography with atomic emission detection. The diesel fuels used have sulfur contents of 2284 and 433 ppm, respectively, and are labeled as high-sulfur and low-sulfur diesel fuels. The compounds identified are mainly polycyclic aromatic sulfur heterocycles (PASHs). In the fuels tested, trimethylbenzothiophenes (TMBTs), dibenzothiophenes (DBTs), and 4-methyldibenzothiophene (4-MDBT) were the most abundant sulfur compounds, while larger PASH compounds were more abundant in DPM extracts. The high-sulfur diesel fuel contained a larger proportion of PASHs with one or two rings (lighter PASHs). In DPM, the concentrations of total organic sulfur and individual PASHs are higher for the high-sulfur diesel fuel, and the relative percentage of one or two-ring PASHs is higher as well. The influence of engine load on the DPM composition was also examined. With increasing load, the PASH concentration in DPM decreased for lighter PASHs, increased for heavier PASHs, and had a bell-shaped distribution for PASHs in between.
Keywords: PASH; Diesel particulate matter; Diesel fuel; GC/AED; Engine load
Fig. 1. Schematic of high-volume dilution sampler.
Fig. 2. Structures of PASH standard compounds.
Fig. 3. Carbon (179 nm) and sulfur (181 nm) AED chromatograms for low-sulfur (433 ppm) diesel fuel.
Fig. 4. Sulfur (181 nm) AED chromatogram for high-sulfur (2284 ppm) diesel fuel.
Fig. 5. Possible alkylated PASH groups in low- and high-sulfur diesel fuels (LSDF and HSDF, respectively).
Fig. 6. PASH distribution in low- and high-sulfur diesel fuels (LSDF and HSDF, respectively).
Fig. 7. Sulfur (181 nm) AED chromatogram of DPM generated at 0 kW with low-sulfur (433 ppm) diesel fuel.
Fig. 8. Sulfur (181 nm) AED chromatogram of DPM generated at 75 kW with low-sulfur (433 ppm) diesel fuel.
Fig. 9. Total organic sulfur in DPM generated under various loads.
Fig. 10. Organosulfur distribution in DPM under 25 and 75 kW for LSDF (L) and HSDF (H).
Fig. 11. PASH distribution in DPM generated with LSDF and HSDF under different engine loads: (a) decreasing with load, (b) bell-shaped distribution, (c) increasing with load.
Table 1.
GC/AED operating parameters
Table 2.
List of thiophene standards and related information
a Molecular weight.
b b.p., boiling point; m.p., melting point.
c b.p. 738 is the boiling point at the pressure of 738 mmHg.
d Not available.
Table 3.
Sulfur response factors for three sulfur compounds
Results are based on five injections.
a Molecular weight.
b Area count per nanogram sulfur.
c Relative standard deviation.
Table 4.
PASHs in low- and high-sulfur diesel fuels (LSDF and HSDF) and DPM extracts (L0 through H75)
a L or H indicates low- or high-sulfur diesel fuel was used; 0 through 75 is the engine load (kW). For both fuels (LSDF and HSDF) and DPM at LSDF, three sets of samples were collected and injected, but for DPM at HSDF only one set of samples was collected.
b The unit for concentration is μg S/g diesel fuel or μg S/g DPM.
c Total sulfur was calculated by integrating the entire sulfur response as one peak. Integration began where the sulfur emission line increased from baseline or at the beginning of the first peak (7 min for both diesel fuel and DPM). The final integration point was designated after the sulfur emission returned to baseline and remained stable (25 min for diesel fuel and 32 min for DPM). The standard temperature program indicated in
Table 1 was used.
d ND (not detected) indicates result below the minimum detectable level (MDL). MDLs are based on results for a test mixture (Agilent part 8500-5067). The specification for sulfur 181 is 2 pg/s. The MDL for our laboratory was typically about 0.5 pg/s, or 1 pg S for a peak having a 2-s width (at half height).
e The coelution between 3- and 4-MBT may occur.
f The coelution between 5- and 6-MBT may occur.
g This peak is assigned as Ph45T based on the retention time of a standard compound. It is possible that this peak also contains a C
3-DBT because C
3-DBTs can also elute in this region. Currently, we do not have a C
3-DBT standard to examine this possibility.
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