Examination of Two-Dimensional Gas Chromatography with a Nitrogen Chemiluminescence Detector to Facilitate Quantitation and Characterization of Nitrogen-Containing Compounds in Petroleum-Derived Fuels

Abstract

A semiqualitative and quantitative method was developed to classify and quantify nitrogen-containing compounds (NCCs) in aviation and diesel fuels and marine gas oils by using two-dimensional gas chromatography with a nitrogen chemiluminescence detector (GCxGC NCD) without the need for lengthy extractions. Homoscedasticity was evaluated for different forms of linear regression. The weighted (1/x) trend line was more accurate than the nonweighted and weighted (1/x2) trend lines when quantitating six mixtures composed of several NCCs ranging from 50 ppb to 50 ppm. The lower limits of detection and quantitation of nitrogen were 6 and 20 ppb, respectively, by using the weighted (1/x) trend line. Relative response factors (RRF) of nitrogen were measured for several compounds, which showed that several aromatic (aniline, quinoline, benzothiazole, o-anisidine, and carbazole) and nonaromatic (N,N-dimethyldecylamine and N,N-dimethyldodecylamine) compounds have similar responses. Conversely, pyridine and pyrrole have smaller RRF. Further, alkylated pyridine and pyrrole were shown to have greater RRF than pyridine and pyrrole. Hence, equimolar responses for different NCCs were not observed in this study. Small RRF were likely not the result of thermally-induced degradation of analytes upon entry into the GC inlet. The elution times of known compounds were repeatable, which enabled the production of a template composed of chromatographic bins that facilitated characterization and quantitation of unknown NCCs in fuel samples. The template advances the classification of unknown NCCs in fuels compared to simplified classifications as basic, nonbasic, and neutral. Clear differences were observed in the chemical composition and concentrations of NCCs when the disparate fuel types were compared and between the same type of fuels (i.e., aviation fuels). Interday quality control measurements demonstrated high repeatability. Overall, the GCxGC NCD method was shown to be robust, repeatable, facilitated high throughput chemical analysis without the need for extractions, and provided detailed compositional and quantifiable data. This information may aid in linking correlations between NCCs and fuel properties such as stability.