Running ASTM Methods D4815 and D5580 on a Single Agilent 6890N Gas Chromatograph with Nitrogen Carrier Gas

Importance of the Topic

Gasoline analysis requires precise measurement of oxygenates and aromatics, as these additives influence engine performance, emissions, and regulatory compliance.

Traditional implementation of ASTM methods D4815 and D5580 uses separate gas chromatographs and helium carrier gas, which increases laboratory costs, instrument footprint, and operational complexity.

This study addresses these challenges by combining both methods on a single Agilent 6890N GC and substituting nitrogen for helium, offering a cost-effective and efficient solution for fuel laboratories.

Objectives and Study Overview

The primary goal was to develop and validate a unified chromatographic system capable of:

• Running both D4815 (oxygenate analysis) and D5580 (aromatic analysis) sequentially on one instrument.
• Employing nitrogen as the carrier gas without sacrificing chromatographic performance.
• Maintaining analytical precision for retention time and detector response under changing method conditions.

Methodology

A two-column, ten-port switching valve setup was used:

• A polar TCEP micro-packed pre-column retains oxygenates, aromatics, and heavy hydrocarbons while light ends elute to a thermal conductivity detector (TCD).
• After light-end elution, the valve redirects retained compounds onto a 30 m×0.53 mm i.d. methyl silicone capillary column for boiling-point separation, detected by a flame ionization detector (FID).
• Post-analysis backflushing of heavy fractions to the FID is achieved by ramping the column pressure via electronic pneumatics control.
• Carrier gas: high-purity nitrogen throughout all method steps.

Used Instrumentation

• Agilent 6890N GC with capillary split/splitless inlet, FID and TCD (all with EPC control).
• PCM electronic pneumatics control module and temperature-controlled valve box housing a 10-port switching valve.
• 7683 autoinjector and Merlin Microseal autosampler syringe.
• TCEP pre-column (20% TCEP on Chromosorb PAW, 560 mm×0.38 mm) and HP-1 capillary column (5 µm film, 30 m×0.53 mm).

Main Results and Discussion

Backflush time optimization:

• D4815 oxygenates: optimal backflush at 0.22 min, fully venting light ends while retaining MtBE and ethanol.
• D5580 aromatics: two backflush intervals—0.58 min for benzene/toluene and 1.68 min for C8/C9 aromatics—followed by valve reset at 12.1 min and 22 min, respectively.

Sequential analysis precision:

• Retention time RSDs were below 0.2% for all analytes across five alternating runs of D4815, D5580A, and D5580B.
• FID response RSDs remained under 3.5% for oxygenates and under 1.0% for aromatics.

Chromatographic adjustments:
Variability in TCEP pre-column performance can accelerate elution and reduce resolution with nitrogen. A simple reduction of the initial oven temperature restored target retention and peak separation without altering flow settings.

Benefits and Practical Applications of the Method

• Single-instrument operation reduces capital expenditure and bench space.
• Nitrogen carrier gas lowers ongoing gas supply costs and simplifies logistics.
• Maintained high analytical precision supports regulatory testing and routine quality control in fuel production and distribution.

Future Trends and Applications

Emerging possibilities include:

• Automated method switching and data processing to increase throughput.
• Expansion to biofuel and renewable blend analysis with similar two-column strategies.
• Integration of multidimensional GC and advanced detectors for trace-level impurity profiling.
• Further carrier gas alternatives and miniaturization to reduce run times and sample requirements.

Conclusion

This work demonstrates that a single Agilent 6890N GC, equipped with column-switching and using nitrogen carrier gas, can reliably perform both ASTM D4815 and D5580 methods with precision comparable to traditional helium-based, dual-instrument setups. The approach enhances laboratory efficiency, reduces costs, and maintains robust analytical performance for gasoline oxygenate and aromatic measurement.

References

1. ASTM D4815, Standard Test Method for Analysis of Oxygenates in Gasoline by Gas Chromatography, ASTM International Vol. 05.02, 2023.
2. ASTM D5580, Standard Test Method for Measurement of Aromatic Hydrocarbons in Gasoline by Gas Chromatography, ASTM International Vol. 05.03, 2023.