Ultra-Fast Total Petroleum Hydrocarbons (TPH) Analysis with Agilent Low Thermal Mass (LTM) GC and Simultaneous Dual-Tower Injection

Significance of the Topic

Total petroleum hydrocarbons (TPH) analysis is critical for assessing environmental contamination in soil and water due to petroleum-derived pollutants. Rapid, high-throughput methods are essential to support laboratories facing growing sample volumes and tight reporting timelines.

Objectives and Overview of the Study

This work aims to develop an ultra-fast TPH analysis by integrating Agilent Low Thermal Mass (LTM) gas chromatography technology with simultaneous dual-tower injection. The primary goals are to dramatically reduce analysis and cycle times, maintain robust separation across C10–C44 hydrocarbons, and double overall sample throughput.

Methodology and Instrumentation

• Sample Preparation
  • Soil samples dried with sodium sulfate and sonicated with dichloromethane (3 × 60 mL).
  • Water samples extracted by liquid–liquid extraction with dichloromethane (3 × 100 mL) and concentrated to final volumes.
• Chromatographic Method Development
  • Translation of a conventional 30 m column method (40 min run) to a 15 m column (20 min), then to a 5 m LTM column (3.1 min run) using Agilent GC method translation software.
  • Ultra-fast oven programming with 200 °C/min ramp to 340 °C and rapid cooling from 340 to 40 °C in ≈2 min.
  • Simultaneous dual-channel injection on an Agilent 7890A GC with dual LTM modules to process two samples in parallel.
• Data Processing
  • Calibration using a custom n-alkane mix (C10–C44) at 1–100 µg/mL.
  • Peak grouping to derive average response factors and baseline-holding with peak summing across the full hydrocarbon range.

Used Instrumentation

• Agilent 7890A GC equipped with two G6579A LTM modules (5 m × 0.32 mm id, 1.0 µm DB-5).
• Dual split/splitless inlets and dual capillary flame ionization detectors with electronic pressure control.
• ChemStation software (32-bit version B.04.01) for acquisition and integration.

Main Results and Discussion

• Cycle time reduced from 45.4 min (conventional) to 5.1 min per two samples, representing an 18-fold productivity increase.
• Baseline separation of C10–C44 n-alkanes maintained under ultra-fast conditions.
• Calibration linearity (R² ≈ 0.9993) confirmed across the concentration range.
• Simultaneous dual-channel injection effectively doubled throughput with minimal additional cost versus two separate GCs.
• Quantitative TPH results for real samples agreed with conventional methods within acceptable variance.

Benefits and Practical Applications

• High-throughput environmental screening for petroleum hydrocarbons in soil and water.
• Reduced solvent consumption and energy use due to shorter runs and faster cooling.
• Cost-effective productivity gains by dual-tower injection instead of purchasing two instruments.
• Scalable approach for other hydrocarbon analyses or busy analytical laboratories.

Future Trends and Potential Uses

• Coupling LTM technology with mass spectrometry for enhanced selectivity and sensitivity.
• Integration into automated or online monitoring systems for continuous environmental surveillance.
• Extension of ultra-fast GC methods to other contaminant classes such as pesticides or PCBs.
• Development of field-deployable, miniaturized LTM-based GC modules for on-site testing.

Conclusion

The combination of Agilent LTM GC modules with simultaneous dual-tower injection delivers ultra-fast TPH analysis, achieving a 5.1-minute cycle for two samples while preserving analytical performance. This approach offers significant productivity improvements and cost savings for environmental laboratories requiring rapid, reliable hydrocarbon screening.

References

1. Agilent Low Thermal Mass (LTM) System for Gas Chromatography, Agilent Technologies publication 5989-8711EN, June 2008.
2. Wei Luan et al., Evaluation of Total Petroleum Hydrocarbon in Soil Using LC with Fraction Collector and GC/MS, Agilent Technologies publication 5989-6012EN, April 2007.