Comparing ASTM D8071 (GC VUV) ASTM D6730 (DHA) for Hydrocarbon Analysis

Importance of the Topic

Analysis of hydrocarbons in spark ignition fuels is critical for meeting modern fuel quality regulations and ensuring optimal engine performance. Precise characterization of paraffins, isoparaffins, olefins, naphthenes and aromatics (PIONA), along with oxygenates and aromatics, supports octane rating control and impurity monitoring at increasingly lower detection limits.

Objectives and Study Overview

This application note compares two standardized methods for hydrocarbon analysis in spark ignition fuels:

• ASTM D8071 using gas chromatography with vacuum ultraviolet detection (GC–VUV)
• ASTM D6730 detailed hydrocarbon analysis (DHA) using GC–flame ionization detection (GC–FID)

Three sample types (gasoline, alkylate and racing fuel) were analyzed on the same SCION 436 GC system equipped respectively with VUV and FID detectors to evaluate accuracy, selectivity and processing efficiency.

Methods and Instrumentation

Both methods use retention indices and relative response factors for compound identification and quantification. Key parameters:

• GC model: SCION 436 with 8400 autosampler and S/SL injector
• GC–VUV: VUV detector (125–240 nm), 30 m×0.25 mm×0.25 µm column, 35 °C (10 min) rising at 7 °C/min to 200 °C, helium at 1 mL/min
• GC–FID: FID at 250 °C, 100 m×0.25 mm×0.50 µm column, 5 °C (10 min) to 48 °C at 5 °C/min, then to 200 °C

Key Results and Discussion

Both methods yielded highly comparable PIONA and oxygenate mass percentages across all samples. Specific findings:

• Gasoline sample: total hydrocarbon groups varied by less than 1 % between methods; isoparaffins and naphthenes showed minor 2–3 % differences attributed to manual peak assignment in DHA.
• Alkylate sample: both methods correctly identified a predominance of isoparaffins with negligible olefins and aromatics.
• Racing fuel sample: no MTBE, TAME, t-BuOH or butane detected by either method; slight naphthene differences under 3 %.

GC–VUV analysis benefits from automated spectral deconvolution and built-in UV library, reducing reliance on precise retention times and manual processing compared to DHA.

Benefits and Practical Applications

GC–VUV under ASTM D8071 offers:

• Shorter analysis cycles and reduced post-processing time
• Automated peak deconvolution leveraging unique VUV absorbance spectra
• Robust identification unaffected by minor retention shifts

These advantages make it an efficient alternative for quality control in refining, fuel blending and regulatory laboratories.

Future Trends and Applications

Advancements may include expanded spectral libraries for novel fuel additives, integration with machine learning for pattern recognition, real-time online monitoring in blending operations and further lowering of detection limits for emerging contaminants.

Conclusion

GC–VUV (ASTM D8071) and GC–FID DHA (ASTM D6730) produce equivalent hydrocarbon profiles in diverse fuel samples. The GC–VUV approach streamlines analysis through automated spectral processing and enhanced selectivity, presenting a compelling alternative to time-intensive detailed hydrocarbon analysis.

References

• ASTM D8071: Standard Test Method for Determination of Hydrocarbon Group Types in Spark Ignition Fuels Using Vacuum Ultraviolet Spectroscopy
• ASTM D6730: Standard Test Method for Detailed Hydrocarbon Analysis of Spark Ignition Fuels by Gas Chromatography