Determination of nitrogen compounds in catalytic diesel oil using gas chromatography

The method for the separation and determination of nitrogen compounds in catalytic diesel oil using gas chromatography-nitrogen chemiluminescence detection (GC-NCD) was established. The effects of the flow rate of the carrier gas and the oven temperature on resolution were discussed. More than 80 nitrogen compounds (such as aniline, alkyl anilines, quinoline, indole, alkyl indoles, carbazole, alkyl carbazoles) in catalytic diesel oil were enriched using an Al2O3 column and identified by the retention time of some pure nitrogen compounds, the retention index of nitrogen compounds and gas chromatography-mass spectrometry. Using indole as the reference nitrogen compound, it is found that the relative response factors of N,N-dimethyl aniline, tributylamine, quinoline, and carbazole are from 0.97 to 1.07, which means that the response factor is independent of the type of the nitrogen compounds. The relative standard deviations of the peak areas of the main nitrogen compounds in catalytic diesel oil were lower than 8%, and the detection limit (S/N = 3) for nitrogen of carbazole was 1.0 mg/L under the optimized conditions. The linear range of nitrogen was 1.0–600 mg/L for each nitrogen compound, and the correlation coefficient was more than 0.998. The recoveries of the four nitrogen compounds (aniline, quinoline, indole, carbazole) from catalytic diesel oil were in the range of 89.5%–99.8%. The method can be applied for the determination of each nitrogen compound in different catalytic diesel oils.