Florida Beach Tarball 5 on Rxi®-5HT (15 m x 0.25 mm x 0.10 μm)

Importance of the Topic

This application addresses the chemical characterization of weathered oil residues (tarballs) collected from Florida Gulf beaches. Hydrocarbon profiling of tarballs is crucial for environmental monitoring, source identification of oil spills, and assessment of natural attenuation processes along coastlines.

Objectives and Study Overview

The main goal of this study was to separate and quantify high molecular weight n-alkanes (C20, C30, C40, C50) in a tarball sample using gas chromatography with flame ionization detection. The work demonstrates the performance of a short, high-temperature capillary column in resolving heavy hydrocarbon fractions for environmental forensics.

Methodology and Instrumentation

The analysis employed temperature programming from 40 °C to 400 °C at 19.6 °C/min on an Rxi-5HT column (15 m × 0.25 mm × 0.10 μm). A 1 μL split injection (10:1) of carbon disulfide-diluted sample was introduced at 275 °C. Hydrogen was used as the carrier gas at 1.75 mL/min, with nitrogen makeup, and an FID operated at 420 °C.

Instrumentation

• GC system: Agilent/HP 6890
• Column: Rxi-5HT, 15 m × 0.25 mm ID × 0.10 μm film
• Injection liner: 4 mm precision liner with wool
• Carrier gas: H₂ constant flow 1.75 mL/min
• Detector: FID at 420 °C with N₂ makeup (50 mL/min)
• Oven program: 40 °C (0.1 min) to 400 °C at 19.6 °C/min (1.53 min hold)

Main Results and Discussion

The chromatogram resolved four prominent n-alkane peaks: C20 (468.9 s), C30 (694.3 s), C40 (856.7 s), and C50 (982.8 s). Peak resolution remained high despite the compact column length, demonstrating efficient separation of heavy hydrocarbons. Retention times correlate well with expected carbon chain lengths, supporting method reliability.

Benefits and Practical Applications

• Rapid profiling of tarball composition for spill forensics and environmental assessment
• High-temperature column robustness for heavy hydrocarbon analysis
• Efficient sample throughput with split injection and fast temperature ramp

Future Trends and Possibilities

Continued development of ultra-thin film, short-length columns coupled with faster ramp rates could further reduce analysis times. Hybrid detectors or two‐dimensional GC could enhance compound identification in complex weathered oil matrices. Integration with mass spectrometry would improve source apportionment capabilities.

Conclusion

The study validates the use of a 15 m Rxi-5HT column for robust separation of high-molecular-weight n-alkanes in weathered oil samples. The method offers a fast, reliable tool for environmental monitoring and oil spill forensics on coastal beaches.