New benchmark for basic and neutral nitrogen compounds speciation in middle distillates using comprehensive two-dimensional gas chromatography

This paper reports an analytical method for the comprehensive two-dimensional gas chromatography (GC × GC) separation and identification of nitrogen compounds (N-compounds) in middle distillates according to their types (basicity). For the evaluation of the best chromatographic conditions, a non-polar × polar approach was chosen. The impact of the second dimension (stationary phase and column length) on the separation of basic and neutral N-compounds was evaluated by mean of two-dimensional resolution. This study revealed that the implementation of polar secondary column having free electron pairs improves drastically the separation of N-compounds. Indeed, the presence of permanent dipole-permanent dipole interactions between neutral N-compounds and the stationary phase was enlightened. The comparison of two different nitrogen chemiluminescence detectors (NCD) was also evaluated for GC × GC selective monitoring of N-compounds. Owing to higher resolution power and enhanced sensitivity achieved using developed chromatographic and detection conditions, it was possible to identify univocally and to quantitate N-compounds (i) by class of compounds and (ii), within a class, by carbon number. Finally, quantitative comparison of GC × GC-NCD with conventional gas chromatography illustrates the benefits of GC × GC leading to an excellent correlation with results obtained by American Society for Testing Materials (ASTM) methods for the determination of basic/neutral nitrogen ratio in diesel samples.