Analysis of Trace 2-Ethylhexyl Nitrate in Diesel Using ChemiluminescenceDetector (NCD)

Importance of the Topic

Diesel engines benefit from cetane number enhancers such as 2-ethylhexyl nitrate for improved cold start behavior, reduced emissions and smoother combustion. Accurate quantification of trace 2-ethylhexyl nitrate in diesel and biodiesel blends is essential for fuel specification compliance and quality control.

Objectives and Study Overview

This study evaluates a gas chromatograph with a chemiluminescence detector as an alternative to spectrophotometric methods defined in ASTM D4046. It aims to demonstrate enhanced sensitivity, selectivity and calibration simplicity in quantifying trace 2-ethylhexyl nitrate in diesel matrices.

Methodology and Instrumentation

A GC system equipped with an HP-5MS column (15 m x 0.32 mm, 0.32 µm) and an Agilent 255 nitrogen chemiluminescence detector was used. Key conditions included inlet temperature 250 °C with 10:1 split, oven program from 60 °C (2 min) to 280 °C at 20 °C/min, NCD temperature 200 °C, detector pressure 7.7 Torr, burner at 905 °C, hydrogen flow 5 sccm and oxygen flow 10 sccm.

Main Results and Discussion

The method achieved a signal-to-noise ratio suitable for detecting 1.87 ppm nitrogen as 2-ethylhexyl nitrate without hydrocarbon interference. Calibration showed a linear response from 1.87 to 186.9 ppm nitrogen with an equimolar response for different nitrogen compounds. Precision in pump diesel yielded an RSD of 1.15%. Chromatograms revealed 2-ethylhexyl nitrate at 1.18 ppm in pump diesel and 18.7 ppm in B20 biodiesel, along with other nitrogen species at higher boiling points.

Benefits and Practical Applications

• High sensitivity allows low ppm level detection of nitrogen additives.
• Excellent selectivity prevents hydrocarbon interference in complex fuel matrices.
• Linear equimolar response simplifies calibration and eliminates separate response factors.
• Applicable to conventional diesel, biodiesel blends and quality control workflows.

Future Trends and Applications

Advances may include extension to other nitrogen-based fuel additives, coupling with high-throughput or hyphenated techniques for structural identification and integration into online process monitoring systems for real-time quality assurance.

Conclusion

Gas chromatography with chemiluminescence detection provides a robust, sensitive and selective approach for trace analysis of 2-ethylhexyl nitrate in diesel fuels, offering a reliable alternative to traditional spectrophotometric methods.

References

• ASTM D4046-91(2005) – Standard Test Method for Alkyl Nitrate in Diesel Fuels by Spectrophotometry, ASTM Annual Book of Standards Volume 05.04, West Conshohocken PA USA
• Agilent Technical Overview 5989-6774EN – Analysis of Trace Nitrogen Species in Benzene, Agilent Technologies publication