GC×GC-VUV and GC×GC-FID Analysis of Gasoline, Middle Distillates and Crude Oil Distillation Cuts using Zebron™ ZB-35HT and ZB-1plus GC Columns

Importance of the topic

Comprehensive two dimensional gas chromatography coupled with vacuum ultraviolet detection has emerged as a powerful tool for detailed analysis of complex fuel matrices such as gasoline, diesel, heating oil, and crude oil cuts. Accurate classification and quantification of paraffins, naphthenes, olefins, aromatics, and low level di-olefins are critical for regulatory compliance, fuel quality control, and addressing stability and gum formation issues.

Objectives and study overview

This study demonstrates the application of GC×GC coupled with VUV detection and compares it to a flow modulated GC×GC with FID for the analysis of heating oil, gasoline, and light crude oil distillation fractions. The goals were to assess chromatographic resolution, compound class identification, and the capability to detect trace conjugated and unconjugated di-olefins within standard test methods such as ASTM D8071.

Methodology and instrumentation

A reversed phase column setup was employed using Zebron ZB-35HT Inferno 20 meter in the first dimension and Zebron ZB-1plus 5 meter in the second dimension. Flow modulation was provided by an Insight flow modulator on an Agilent 7890A gas chromatograph.

• Carrier gas constant flow 0.5 mL per minute on column one and 20 mL per minute on column two
• Injection split ratio 1 to 100 at injector temperature 280 degrees Celsius
• Oven program first dimension 30 or 40 degrees hold then 2 degrees per minute to 200 or 300 degrees hold for one minute
• Detection by flame ionization detector at 350 degrees Celsius acquisition rate 100 Hertz and by VUV detector covering 125 to 240 nanometers

Key results and discussion

The GC×GC-FID method provided robust separation of heating oil components revealing saturates, aromatics, and minor diaromatics across a range of carbon numbers. Weight distributions were comparable to standard mixtures.

VUV detection enabled differentiation of n- and iso-alkanes, naphthenes, olefins, aromatics, and crucially conjugated di-olefins by their characteristic absorption wavelength ranges. Two dimensional wavelength plots highlighted that conjugated double bonds absorb strongly above 200 nanometers while unconjugated olefins primarily absorb between 170 and 200 nanometers.

Pure chromatographic resolution alone was insufficient to fully separate iso-alkanes, naphthenes, and olefins in the C4 to C9 range but the spectral selectivity of VUV detection allowed class assignments without complete baseline separation.

Benefits and practical applications

The hyphenation of flow modulated GC×GC with VUV detection offers:

• Enhanced sensitivity for trace di-olefins that can cause fuel instability
• Rapid compound class identification based on spectroscopic features
• Improved analytical reliability for fuel quality control and compliance
• Economic advantage of flow modulation compared to cryogenic systems

Future trends and possibilities

Further development of software libraries for two dimensional VUV spectra will facilitate automated compound classification and quantification. Exploring normal phase column combinations with higher polarity secondary columns may improve chromatographic resolution of challenging compound classes. Integration with mass spectrometry and advanced data processing workflows will expand applicability to emerging fuel formulations and environmental testing.

Conclusion

The combined GC×GC VUV approach represents a powerful method for comprehensive fuel analysis. It overcomes key limitations of existing techniques by providing both high separation efficiency and spectroscopic selectivity. This methodology shows promise for standard method development in gasoline, distillate, and crude oil cut analysis.

Instrumentation used

• Agilent 7890A gas chromatograph with Insight flow modulator
• Zebron ZB-35HT Inferno first dimension column 20 m x 0.18 mm x 0.18 µm
• Zebron ZB-1plus second dimension column 5 m x 0.25 mm x 0.1 µm
• Flame ionization detector
• Vacuum ultraviolet detector with 125–240 nm range