Determination of nitrogen-containing polycyclic aromatic compounds in diesel and gas oil by reverse-phase high performance liquid chromatography using introduction of sample as detergentless microemulsion

• Microemulsified diesel and gasoil were introduced into HPLC system.
• Basic and neutral NPACS were determined altogether.
• Minimum sample preparation required for screening complex samples.
• Effective detectable concentration of NPACs in fuels in the mg L−1 level.

Carbazoles, quinolines, indoles, pyrroles, anilines and acridines are nitrogen-containing polycyclic aromatic compounds (NPAC) that contribute to deteriorate fuels affecting storage stability, causing problems to motor engines and poisoning automotive catalysts. Carbazole, 3-ethylcarbazole, 9-ethylcarbazole, 9-methylcarbazole, quinoline, benzo[h]quinoline, indole, 3-methylindole, acridine and N,N-dimethylaniline were separated and quantified in diesel and gas oil by reverse-phase high performance liquid chromatography with fluorimetric detection and molecular absorption photometric detection using introduction of fuel samples as detergentless microemulsion (DME). The DME is composed by ethanol, propan-2-ol, water and iso-octane in specific proportions to stabilize the organic samples. The introduction of sample in the DME simplifies the procedure since it avoids extraction of the analytes and enables the determination of basic and neutral NPAC altogether. The limits of quantification for the analytes in the DME were in μg L−1 order (ng range for 10 μL of injected volume). Satisfactory analyte recoveries were achieved (between 89.5% and 108.7%). Results were found to be comparable using or not using 7-methylindole and N-methylpyrrole as internal standards (since these were not found in the analyzed samples). Studies showed homogeneity of the analytes in the DME after mechanical stirring (at 7200 rpm for 5 min). Stability studies indicated results with coefficients of variation below 3%. The method is adequate for a rapid screening of NPACs in petroleum samples.

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