Analysis of PIONA composition in finished motor gasoline by GC-VUV

Significance of the Topic

The detailed breakdown of paraffins, isoparaffins, olefins, naphthenes and aromatics (PIONA) in finished motor gasoline is critical for optimizing refining operations, ensuring product quality and meeting regulatory standards. Accurate hydrocarbon profiling supports fuel formulation, process control and compliance with industry specifications.

Study Objectives and Overview

This work aimed to develop a rapid and reliable analytical procedure for quantifying all PIONA components in finished motor gasoline using gas chromatography with vacuum ultraviolet spectroscopy (GC-VUV). The method was benchmarked against ASTM D8071 and addressed challenges of coelution and lengthy run times associated with conventional approaches.

Used Instrumentation

• Gas chromatograph: Shimadzu Nexis GC-2030
• Detector: Vacuum ultraviolet detector VGA-101
• Column: SH-Rtx-1, 30 m×0.25 mm×0.25 µm
• Injector temperature: 250 °C; transfer line and flow cell: 275 °C
• Carrier gas pressure: 78.8 kPa; flow: 1 mL/min; split ratio: 300:1
• Spectral acquisition: 125–430 nm at 4 Hz

Methodology

The procedure follows ASTM D8071 with modifications to shorten analysis time to 33 minutes. Temperature programming begins at 35 °C (10 min) with a 7 °C/min ramp to 200 °C. VUVision software identifies groups by characteristic absorption spectra, while VUVAnalyze applies time interval deconvolution (TID) to resolve coeluting species based on spectral and retention time differences.

Main Results and Discussion

Analysis of a commercial 95-octane gasoline sample yielded complete PIONA separation within 33 minutes. Key features include:

• Effective deconvolution of benzene/1-methylcyclopentene and toluene/2,3,3-trimethylpentane pairs.
• Group concentration ranges: 6–17% normal alkanes, 24–70% branched alkanes, 0.1–16% olefins, 1–14% naphthenes, and 16–58% aromatics.
• Repeatability: five injections showed relative standard deviations below 1% for both mass and volume fractions.

Benefits and Practical Applications

This GC-VUV method combines spectral specificity with TID to eliminate the need for pre-columns or traps, significantly reducing analysis time and hardware requirements. It delivers high confidence in qualitative and quantitative results and is well suited for routine quality control, fuel blending assessments and process monitoring in refinery laboratories.

Future Trends and Possibilities

Emerging developments may include expanded spectral libraries, automated deconvolution algorithms and integration with online sampling systems for real-time monitoring. Advances in detector sensitivity and miniaturized GC-VUV platforms could further enhance throughput and applicability to other complex hydrocarbon matrices.

Conclusion

A streamlined GC-VUV technique based on ASTM D8071 has been established for rapid PIONA analysis in finished motor gasoline. The approach offers complete group separation, reliable deconvolution of coelutions and excellent precision within a 33-minute run. It provides an effective tool for fuel analysis in both research and industrial settings.

References

• ASTM D8071: Standard Test Method for Determination of Hydrocarbon Group Types and Select Hydrocarbon and Oxygenate Compounds in Spark-Ignition Engine Fuel Using GC-VUV
• Shimadzu Corporation: GC-2030 and VGA-101 VUV Detector Documentation