Running ASTM Method D4815 for Determining Oxygenates in Gasoline on the Agilent 6820 GC

Importance of the Topic

The addition of oxygenates such as ethers and alcohols to unleaded gasoline improves octane rating and lowers carbon monoxide emissions. Regulatory limits on the types and levels of these compounds demand reliable analytical methods. Adherence to ASTM D4815 ensures consistent quality control and environmental compliance in gasoline production and distribution.

Objectives and Study Overview

This application demonstrates the implementation of ASTM Method D4815 on the Agilent 6820 gas chromatograph. The goal is to achieve accurate quantification of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), diisopropyl ether (DIPE), and C1–C4 alcohols in gasoline samples. The study evaluates chromatographic separation, method linearity, and repeatability under realistic operating conditions.

Methodology and Used Instrumentation

Sample preparation employs 1,2-dimethoxyethane (DME) as an internal standard. Analytical separation is performed in three valve positions: initial venting of light hydrocarbons on a polar TCEP prefractionation column; timed backflush transfer of target oxygenates onto a nonpolar HP-1 column; final purge of heavy residues. Key instrumentation and configuration:

• Agilent 6820 GC with split/splitless inlet (200 °C, split 15:1) and FID (250 °C)
• 10-port manual switch valve coupled to independent heater
• Micropacked TCEP prefractionation column (56 cm × 1/16″)
• HP-1 capillary analytical column (30 m × 0.53 mm, 5 µm)
• Auxiliary 2-channel gas pressure regulator for stable N₂ carrier flow
• Cerity NDS software for valve timing control and data processing

Backflush timing was optimized between 0.18 and 0.34 min. A 0.22 min switch unloads light hydrocarbons while retaining MTBE and DIPE; a 0.28 min switch is used when DIPE analysis is omitted.

Main Results and Discussion

Chromatograms show baseline separation of all target analytes including methanol, ethanol, isopropanol, tert-butanol, n-propanol, sec-butanol, isobutanol, tert-pentanol, MTBE, DIPE, and TAME. Calibration over 0.1–20 mass % yields linear responses with R² > 0.99 and minimal intercept bias (wi < 0.1 mass %). Repeatability data from five replicate injections meet or exceed ASTM D4815 specifications for each compound.

Benefits and Practical Applications of the Method

The described GC configuration offers rapid, robust analysis for routine QA/QC in fuel blending, distribution, and regulatory compliance laboratories. Automated valve switching and comprehensive software control minimize operator intervention and improve throughput.

Future Trends and Opportunities

Advances may include integration of mass spectrometric detection for compound confirmation, development of shorter columns or high-temperature rapid ramps for faster cycle times, and expansion to emerging bio-oxygenates. Automated data review and cloud-based trending could further streamline regulatory reporting.

Conclusion

The Agilent 6820 GC system, configured with a heated valve and dual-column setup, reliably meets ASTM D4815 requirements for gasoline oxygenate analysis. The method delivers excellent linearity, repeatability, and ease of use, supporting high–quality fuel manufacturing and environmental protection.

References

1. ASTM D4815, Standard Test Method for Determination of MTBE, TAME, DIPE, Tertiary-Amyl Alcohol, and C1 to C4 Alcohols in Gasoline by Gas Chromatography.
2. James D. McCurry, Running ASTM Methods D4815 and D5580 on a Single Agilent 6890N Gas Chromatograph With Nitrogen Carrier Gas, Agilent Technologies Publication 5988-9153EN.