Abstract

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.

Keywords: Comprehensive two-dimensional gas chromatography; Time of flight mass spectrometry; TOF-MS; Nitrogen chemiluminescence detector; NCD; Nitrogen-containing compounds; Middle distillates

Article Outline

1. Introduction

2. Experimental

2.1. GC × GC setup

2.2. GC × GC–TOF-MS setup

2.3. GC-NCD Set up

2.4. Total and basic nitrogen

2.5. Extraction of basic and neutral N-compounds

2.6. Materials and standard

2.7. Data processing and data handling

2.7.1. Data handling

2.7.2. Definition of two-dimensional resolution

2.7.3. Definition of peak asymmetry (As)

3. Results and discussion

3.1. Detectors performance evaluation

3.2. Separation of nitrogen compounds in diesel samples

3.2.1. Selection of the stationary phase of second dimension column

3.2.2. Influence of the length of the second dimension column

3.3. Identification of nitrogen compounds in diesel samples

3.4. Quantitative analysis

3.4.1. Comparison of GC-NCD and GC × GC-NCD

3.4.2. Comparison of GC × GC-NCD and ASTM methods

4. Conclusion

References