Identification and characterization of nitrogen compounds in Brazilian diesel oil by particle beam l.c.-m.s.

A simple procedure has been developed to isolate the basic and neutral nitrogen compounds from a Brazilian diesel distillate through acid partition and open column chromatography using alumina. With minimum sample preparation and clean-up, isolated fractions were analysed by particle beam liquid chromatography-mass spectrometry (l.c.-m.s.) using both reversed phase and normal phase chromatography. The basic fraction was found to contain mostly alkyl benzoquinolines (C₂C₄). The neutral fraction contained mostly alkyl carbazoles (C₁C₅). The identification was based upon electron impact mass spectra of each class of nitrogen compounds, and confirmed by ultraviolet (u.v.) spectral characteristics obtained using online photodiode array detection. Reversed phase chromatography was found to be more appropriate for resolving each class of carbazoles and benzoquinolines, while normal phase chromatography was superior for separating individual isomers. The quantitation of each class of carbazoles and benzoquinolines was obtained by high performance liquid chromatography-ultraviolet (h.p.l.c.-u.v.) analysis at 254 nm using carbazole and benzo[h]quinoline as calibration standards. Comparison of the Brazilian diesel distillate to diesels having other origins indicated that they were nearly identical in terms of the nitrogen compounds present.