Analysis of Alcohols and Aromatics in Gasoline and Fuel Ethanol by a Two-Dimensional GC Method

Importance of the Topic

Oxygenated additives such as alcohols and ethers are critical in modern gasoline formulations to enhance octane ratings, reduce smog-forming emissions and comply with environmental regulations. Analysis of these compounds is also essential in fuel ethanol production and petrochemical feedstocks to ensure purity, accurate blending ratios and prevention of process interferences.

Objectives and Study Overview

The study aims to establish a robust two-dimensional gas chromatography (2D GC) method using a Deans Switch fluidic device and capillary heart-cutting to separate and quantify target oxygenates (methanol, ethanol, 2-butanol, dimethoxyethane, 2-hexanone) alongside aromatics (benzene, toluene) in gasoline and fuel ethanol samples. Calibration standards and gasoline blanks were employed to optimize retention times, heart-cut windows and assess matrix interferences.

Methodology and Instrumentation

An Agilent 7890A GC system was configured with a Deans Switch heart-cutting device, two capillary columns (HP-1 nonpolar and INNOWax polar, each 30 m×0.25 mm, 0.25 µm) and dual flame ionization detectors. The oven program ramped from 40 °C to 250 °C, injection volume was 0.1 µL splitless at 250 °C with a 400:1 split ratio. Primary column flow was 3 mL/min with a 2.36 min backflush; secondary column flow was 4 mL/min. Heart-cut timings were predefined for each analyte and controlled via OpenLab chromatography data system. Automated sample preparation utilized the Agilent 7696A WorkBench.

Main Results and Discussion

Chromatograms of oxygenate standards demonstrated well-resolved retention times. Gasoline blanks confirmed minimal coelutions from hydrocarbon matrix. Application to commercial gasoline and ethanol blends yielded stable baselines and sharp, quantifiable peaks. Automated sample preparation achieved weighing precision (RSD <0.4 %) and compound quantitation precision that exceeded ASTM D4815 single-lab reproducibility requirements.

Benefits and Practical Applications

• Complete chromatographic separation of polar oxygenates from complex hydrocarbon matrices.
• High sensitivity and dynamic range (from 1 ppm trace levels to >12 % m/m ethanol).
• Rapid analysis within a 7 min runtime per sample.
• Reliable compliance with ASTM fuel quality and safety standards.

Future Trends and Opportunities

Future developments may include coupling 2D GC heart-cutting with mass spectrometry for enhanced compound identification, use of microfluidic switching for reduced dead volume, adoption of alternative eco-friendly carrier gases, and miniaturized systems for field deployment, further accelerating turnaround and reducing environmental impact.

Conclusion

The described two-dimensional GC heart-cutting method on the Agilent 7890 platform offers a rapid, sensitive and precise approach for simultaneous analysis of oxygenates and aromatics in gasoline and fuel ethanol. Its robust performance, ease of setup and compliance with industry standards make it ideal for routine QA/QC and regulatory applications.

Reference

Shannon Coleman. Analysis of Alcohols and Aromatics in Gasoline and Fuel Ethanol by a Two-Dimensional GC Method. Agilent Technologies Applications Note 5991-4129EN, February 27, 2014.