High Resolution Detailed Hydrocarbon Analyses by Capillary Column Gas Chromatography

Importance of the topic

Accurate separation and quantification of hundreds of hydrocarbons in complex petrochemical samples is critical for process control, product quality and regulatory compliance. High resolution capillary gas chromatography enables detailed analysis of naphthas, gasolines, reformates, fuel additives and light hydrocarbons by resolving individual paraffins, isoparaffins, aromatics, naphthenes and olefins.

Objectives and study overview

This work presents the development and evaluation of both polar and nonpolar fused silica capillary columns tailored for detailed hydrocarbon analyses. Key goals include achieving baseline resolution of challenging isomer pairs, optimizing analysis speed, and extending capability from light gases through C30+ fractions in a single analytical platform.

Methodology and instrumentation used

Gas chromatographs equipped with flame ionization detectors or thermal conductivity detectors were used with helium or nitrogen carrier gas. A series of capillary columns was tested:

• Polar SUPELCOWAX 10 (polyethylene glycol phase, 30 m x 0.20 mm I.D., 0.20 µm film)
• Nonpolar SPB-1 and SPB-Octyl phases (60 m x 0.75 mm and 60 m x 0.25 mm I.D.)
• Petrocol DH series columns: 50 m x 0.20 mm I.D. (0.50 µm film), 100 m x 0.25 mm I.D. (0.50 µm film) and 150 m x 0.25 mm I.D. (1.0 µm film)

Temperature programs ranged from subambient isothermal holds (–50 °C to 35 °C) to gradients up to 320 °C.

Main results and discussion

Key findings include:

• SUPELCOWAX 10 resolved benzene, toluene and all xylene isomers to baseline in under ten minutes and allowed faster analysis by modestly raising the isothermal temperature.
• SPB-Octyl provided enhanced separation of aromatic/alkylcyclopentene and toluene/trimethylpentane pairs that coelute on standard dimethylsilicone phases.
• Petrocol DH 50.2 columns delivered efficient PNA, PONA and PIANO class separations with a 30-minute hold at 35 °C followed by a slow ramp, or accelerated analysis with reduced hold time.
• Petrocol DH 100 m columns enabled detailed gasoline profiling (C3–C12), separation of cyclopentane/2,3-dimethylbutane, ENB/VNB isomers, MTBE impurities and olefin isomerization products.
• Petrocol DH 150 m columns achieved maximum resolution of light C1–C5 gases, oxygenates in C4 streams, natural gas versus liquid hydrocarbons and polynuclear aromatics in reformates.

Benefits and practical applications

These tailored capillary columns offer:

• High theoretical plate counts for complex mixture fingerprinting
• Flexible trade-off between analysis speed and resolution
• Single-column solutions for multi-class hydrocarbon assays
• Robust quantification of trace isomers and oxygenates
• Applicability across petrochemical QA/QC, environmental gas streams and specialty products

Future trends and possibilities of use

Emerging directions include novel stationary phases for ultra-fast separations, tighter bore columns, integration with mass spectrometry and automated data processing. On-line process monitoring and supercritical fluid chromatography may further extend capability for challenging hydrocarbon matrices.

Conclusion

The combination of polar SUPELCOWAX 10 and nonpolar Petrocol DH series columns provides a versatile toolkit for high resolution, quantitative hydrocarbon analysis over a broad boiling range. These optimized capillary GC methods meet the demanding needs of modern petrochemical and fuel laboratories.

Reference

• ASTM D5441 Standard Test Method for Analysis of Fuel Grade Ethanol by Capillary Gas Chromatography
• US Patent No. 4,293,415 Fused Silica Capillary Columns