A Streamlined Turnkey Solution for Routine Total Petroleum Hydrocarbon Analysis with LECO Paradigm

Significance of the topic

The routine, reliable quantitation of total petroleum hydrocarbons (TPH) in environmental media (soils, sludges, groundwater) is critical for risk assessment, site remediation decision-making, and regulatory compliance. Petroleum contamination is chemically complex and spans a wide carbon-number range; robust analytical workflows that increase chemical resolution, reduce sample-prep variability and cost, and support high sample throughput are therefore highly valuable to environmental and commercial testing laboratories.

Objectives and study overview

This application note presents a turnkey GCxGC-FID solution (LECO Paradigm with reverse fill‑flush modulator) for routine TPH analysis covering equivalent carbon ranges >C8 to C40. The workflow aims to: streamline sample preparation by eliminating SPE fractionation, provide class-based separation (aliphatic vs aromatic) during acquisition, enable rapid automated data processing and reporting, maintain low detection limits and broad dynamic range, and demonstrate robust long-sequence performance with no carryover.

Methodology and workflow

The approach uses comprehensive two-dimensional gas chromatography with an orthogonal column set to separate aliphatic and aromatic hydrocarbon classes during acquisition. A single solvent extraction and one injection are used (no SPE fractionation). Automated carbon-band classification is applied using an n-alkane equivalent-carbon standard to define regular reporting bands (>C8–C9, >C9–C10, … up to C40). Processing and quantitation are automated via ChromaTOF software with typical processing times of ~5 seconds per sample, enabling high throughput.

Used instrumentation

- Instrument: LECO Paradigm GCxGC-FID equipped with the Paradigm reverse fill-flush (RFF) modulator and ChromaTOF processing software.
- Injection: Pulsed splitless.
- Carrier gas: Hydrogen.
- Columns: Orthogonal 1D (TPH 1st-dimension) and 2D (TPH 2nd-dimension) columns specific for TPH separation; short guard column used upstream of the primary column for matrix protection.
- Modulation: 2.6 s second-dimension separation time (flush factor 1.75).
- Temperature program: 40 °C hold 1.5 min; ramp 25 °C/min to 350 °C; hold 2.5 min.
- Detector and acquisition: Flame ionization detector (FID) at 200 Hz data collection rate.
- Automated features: Modulator flow balancing and verification (inject n-C8–n-C30 in GC and GCxGC within a single acquisition to confirm full analyte transfer), simple swaging and column access design for maintenance.

Main results and discussion

- Performance and linearity: Calibration demonstrated a broad dynamic range suitable for trace to highly impacted samples. Typical calibration range reported was 2 µg/mL to 5,000 µg/mL total equivalent petroleum hydrocarbons (EPH/TPH); higher ranges (e.g., up to 20,000 µg/mL) are achievable when needed.
- Repeatability and sequence stability: Ten injections each of a mid-range standard (1,000 µg/mL) and a low-level standard (5 µg/mL) were analyzed repeatedly over a sequence of 80 environmental extracts, followed by surrogate standards. Results indicated excellent precision and analytical stability across extended sequences.
- Carryover: A stress test using a 10% crude oil in hexane matrix (100,000 µg/mL) followed by a solvent blank showed no detectable carryover, indicating effective system cleanliness and analyte transfer control.
- High-molecular-weight aromatics and wraparound: The selected modulation and 2D space prevent wraparound of high-ring-number PAHs (six or more fused rings), enabling correct capture and quantitation of high-molecular-weight aromatics from source matrices like coal tar.
- Non-petroleum co-extractives: Eliminating SPE can introduce biogenic or polar matrix components (e.g., plant waxes, fatty acids). GCxGC class separation and equivalent-carbon mapping allow these non-petroleum compounds to be visually identified and excluded from TPH quantitation.

Key advantages and practical applications

- Simplified sample prep: Eliminates SPE fractionation, reducing analyst labor, consumable cost, solvent volume, and single-use plastic waste while lowering method variability.
- Improved chemical detail: Two-dimensional separation resolves unresolved complex mixtures (UCMs) into structured class-resolved chromatographic space, improving source assessment and weathering interpretation.
- High throughput and automation: Fast automated processing (~5 s per file), automated modulator balancing and one-injection workflow speed throughput for routine labs.
- Robustness and maintenance: Guard column strategy protects the primary column, easy modulator and column access reduce downtime and leak risk, and automated balancing ensures quantitative transfer.
- Use cases: Routine environmental monitoring, contaminated site investigation and delineation, remediation monitoring, regulatory reporting (multiple reporting band formats from a single dataset), and high-throughput commercial testing.

Future trends and potential uses

• Regulatory adoption and standardization: Wider acceptance of GCxGC workflows for regulatory TPH/EPH methods and harmonized carbon-band definitions across jurisdictions.
• Hybrid detection and confirmatory methods: Integration of GCxGC with MS (time-of-flight or high-resolution MS) for compound-level identification alongside FID quantitation in targeted or forensic applications.
• Enhanced automation and data analytics: Machine-learning tools for automated class recognition, source apportionment, anomaly detection, and retrospective data mining of archived GCxGC datasets.
• Expanded dynamic range and miniaturization: Adapting injection strategies and detector options to measure both ultra-trace and heavily contaminated samples in the same run with minimal manual intervention.
• Green sample-prep workflows: Further reduction in solvent use and single-use plastics through single-extract approaches and inline cleanup or trapping when necessary.

Conclusion

The LECO Paradigm GCxGC-FID turnkey solution provides a streamlined, robust, and high-throughput workflow for routine TPH analysis spanning >C8–C40. By performing aliphatic versus aromatic separation during acquisition, the method eliminates SPE fractionation, reduces costs and waste, and improves chromatographic detail for better interpretation. Automated modulator balancing, fast processing, good linearity and repeatability, negligible carryover, and the ability to isolate non-petroleum co-extractives make this approach well suited for modern environmental testing laboratories seeking consistent routine performance.

References

1. Agency for Toxic Substances and Disease Registry (ATSDR). Total Petroleum Hydrocarbons (TPHs) Toxicological Profile, Section 2: Overview of TPH.
2. McLaughlan RG, Merrick NP, Davis GB. Natural attenuation: a scoping review. CRCCARE Technical Report no.3; CRC for Contamination Assessment and Remediation of the Environment; 2006.
3. Misselwitz M. Research Hype to Practical Analysis: Benefits of Comprehensive Two-Dimensional Gas Chromatography (GCxGC) for a Routine Laboratory.
4. Massachusetts Department of Environmental Protection (MassDEP). Method for the Determination of Extractable Petroleum Hydrocarbons (EPH), Revision 2.1; December 2019.