Evaluation of Total Petroleum Hydrocarbon in Soil Using LC with Fraction Collectorand GC/MS

Significance of the Topic

A robust approach for quantifying total petroleum hydrocarbons (TPH) in soil is essential for environmental forensics, liability assessment, and remediation planning following oil spills. Weathering, biodegradation, and volatilization rapidly alter hydrocarbon composition in contaminated matrices. Accurate classification and quantification of paraffins and aromatic fractions help regulators and industry professionals to trace spill origins, monitor natural attenuation, and evaluate cleanup efficacy.

Aims and Overview of the Study

This study presents a streamlined workflow combining normal-phase liquid chromatography (NPLC) with a fraction collector and gas chromatography/mass spectrometry (GC/MS) to separate and identify key hydrocarbon classes in soil extracts. The objectives were to simplify the interface between HPLC and GC/MS, improve sample throughput, and deliver detailed compound-class information for TPH evaluation in crude-oil–contaminated soils.

Methodology and Instrumentation Used

• Sample Preparation
  – Artificially contaminated soil was aged for 48 h, extracted with hexanes in an ultrasonic bath, filtered, and concentrated under nitrogen to 1 mL prior to injection.
• Liquid Chromatography
  – Agilent 1200 Series NPLC system with vacuum degasser, binary pump, autosampler, diode-array detector, and fraction collector.
  – Agilent ZORBAX NH2 column (4.6 × 250 mm, 5 µm), hexanes mobile phase at 0.8 mL/min, 35 °C, isocratic mode.
  – Column-switching valve for backflush cleaning at 15 min.
  – Time-based fraction collection: first 3 min to waste, then 0.5 min slices up to 15 min.
• Gas Chromatography/Mass Spectrometry
  – Agilent 6890N GC coupled to 5975B inert MSD.
  – HP 5-ms capillary column (30 m × 0.25 mm, 0.25 µm), splitless injection, helium carrier.
  – Oven: 50 °C (1 min) to 300 °C at 30 °C/min, 2 min hold.
  – MS scan range 45–450 amu, source 230 °C, quadrupole 150 °C.

Main Results and Discussion

The combined NPLC/GC-MS approach fractionated the soil extract into four major classes based on polarity and boiling point: paraffins (RT 3.7–4.7 min), monoaromatics (4.7–6.2 min), biaromatics (6.2–11.2 min), and triaromatics (11.2–13.7 min). Total ion chromatograms of representative fractions confirmed characteristic mass fragments for n-alkanes (e.g., dodecane m/z 57, 71), alkylbenzenes (m/z 91, 105), and polycyclic aromatics (m/z 178, 192). No significant aromatic content eluted beyond 13.7 min, indicating efficient class separation.

Benefits and Practical Applications of the Method

• Class-specific quantification of TPH enables targeted environmental risk assessment and source identification.
• Fraction collector simplifies the LC–GC/MS interface, reducing system complexity and maintenance.
• Time-based collection improves sample throughput and reproducibility.
• Mass spectral identification provides unambiguous compound confirmation across hydrocarbon classes.

Future Trends and Potential Applications

Further enhancements may include coupling two-dimensional LC × GC platforms with high-resolution time-of-flight MS for deeper fingerprinting, integrating automated data-processing workflows for rapid field screening, and adopting portable GC/MS units for on-site contaminant profiling. Advances in stationary phases and miniaturized fraction collectors will continue to refine sensitivity and speed in environmental forensics.

Conclusion

The integration of NPLC with a fraction collector and GC/MS offers a practical, detailed method for evaluating TPH in soil. By separating paraffins and aromatic fractions according to polarity and boiling point, the workflow yields comprehensive compound-class data critical for environmental monitoring and remediation strategies.

References

1. Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung, Summarische Wirkungs- und Stoffkenngrößen, Bestimmung von Kohlenwasserstoffen (H18), DIN 38 409, Beuth Verlag, Berlin (1981).
2. Robert K. Nelson, Tracking the Weathering of an Oil Spill with Comprehensive Two-Dimensional Gas Chromatography, Environmental Forensics 7:33–44 (2006).
3. Sjaak de Koning, Group-type characterisation of mineral oil samples by two-dimensional comprehensive normal-phase liquid chromatography–gas chromatography with time-of-flight mass spectrometric detection, Journal of Chromatography A 1058:217–221 (2004).