3.5 min Total Petroleum Hydrocarbons (TPH) Analysis Using the Nexis GC-2030 and H2 Carrier

Importance of the topic

Petroleum hydrocarbons in soil and water (reported as Total Petroleum Hydrocarbons, TPH, or Total Recoverable Hydrocarbons, TRH) represent a widespread environmental and human-health concern because many fractions are persistent and potentially toxic. Rapid, reliable chromatographic banding by carbon-number ranges (e.g., C10–C14, C15–C28, C29–C36, etc.) improves risk assessment compared with a single bulk TPH value. Laboratories require methods that combine broad boiling-point coverage (typically up to C40), low discrimination on sample introduction, high analytical precision, and high throughput to support environmental monitoring, remediation verification and regulatory programs.

Study objective and overview

The application note demonstrates an ultra-fast GC method for routine TPH/TRH analysis using the Shimadzu Nexis GC-2030 with hydrogen carrier gas and a short, non-conventional Rxi-1ms column. The aims were to: shorten injection-to-injection cycle times, maintain chromatographic resolution across C10–C40 (and with modification C6–C40), preserve quantitative linearity across typical TPH concentrations, and increase daily sample throughput (single and dual-line configurations). The method was validated by calibration series, representative matrix testing (water and soil extracts), and demonstration of minimal injection discrimination for high-boiling analytes.

Methodology and instrumentation

Key experimental elements and instrumental settings are summarized below.

• Gas chromatograph: Shimadzu Nexis GC-2030 (Nexis GC-2030NX high-performance oven referenced).
• Injector: SPL-2030 split/splitless inlet operated at 320 °C; shown to deliver negligible discrimination (C40/C20 area ratio >0.96).
• Detectors: Flame ionization detector (FID-2030) at 350 °C; single or dual FID configuration available for throughput scaling.
• Column: Restek Rxi-1ms, non-conventional short dimension 12 m × 0.2 mm × 0.33 µm film thickness. A reduced oven-volume “pillow” was used to accelerate heating/cooling.
• Carrier gas: Hydrogen, programmed flow 7 mL/min ramped to 10 mL/min to permit faster separations while maintaining resolution.
• Oven program: Start 100 °C hold 0.3 min, then maximum ramp rate to 340 °C; full run programmed to 3.5 min to allow elution of components through >C40 (observed RT ≈ 2.9 min).
• Autosamplers: Dual AOC-30 liquid autosamplers used in dual-injector mode for parallel analysis.
• Software: LabSolutions GC for flexible integration, automatic banding and baseline handling to translate chromatograms into carbon-number bands.

Sample introduction and scope

Volatile hydrocarbons below C10 were noted to be better analysed by headspace or purge-and-trap to avoid solvent interference and improve quantitative reliability. The presented method focuses on liquid injection for higher molecular weight fractions up to C40, which covers most regulatory TPH/TRH determinations. The split/splitless inlet was demonstrated to be an acceptable alternative to on-column injection for broad-range liquid-introduced TPH work when optimized.

Main results and discussion

The ultra-fast method produced linear calibration across six standards spanning nominal total hydrocarbon concentrations from 32 ppm to 3200 ppm. Calibration was performed for common bands (C10–C14, C15–C28, C29–C36) and aggregated bands (>C10–C16, >C16–C34, >C34–C40); all band regressions returned R2 > 0.998, indicating excellent linearity.

Chromatographic performance: the Rxi-1ms short-column configuration permitted raising the oven start temperature to reduce solvent/analyte overlap for low-boilers while still eluting high-boilers (up to C40) within the 3.5-min program. Use of hydrogen carrier gas plus reduced oven volume accelerated separations without compromising resolution across the carbon-number bands. The SPL-2030 inlet showed minimal discrimination against high-boilers (area ratio C40/C20 > 0.96), supporting accurate quantitation across the target range.

Throughput: With a single line (single injector) the method delivered injection-to-injection times of approximately 7 minutes (3.5 min run + overhead), allowing analysis of over 200 samples per 24-hour period. Employing dual-injector mode with two autosamplers and dual FIDs reduced effective per-sample time to 3.5 minutes and enabled processing of over 400 samples per 24 hours. Representative chromatograms included matrix samples (water and soil extracts) and a mixed petroleum sample (1% w/v diesel + 1% w/v motor oil) illustrating banded TPH resolution.

Benefits and practical applications

• High throughput: Suited to high-volume environmental testing labs requiring hundreds of TPH determinations daily.
• Broad coverage: Resolves carbon-number bands up to C40, supporting regulatory reporting and risk-based assessment.
• Speed without sacrifice: Hydrogen carrier and short-column approach yield sub-4-min run times while preserving band resolution and quantitation linearity.
• Operational flexibility: Split/splitless inlet acceptable for liquid injections, avoiding the need for on-column injectors in many routine workflows.
• Software support: LabSolutions GC automates band integration and eases migration from other chromatography data systems.

Future trends and potential applications

Several developments and applications are anticipated based on this approach:

• Wider adoption of hydrogen carrier gas for environmental GC methods as helium availability and cost drive labs to alternatives.
• Further optimization of short-column, high-heating-rate strategies for other broad-boiling environmental analyte classes to maximize throughput.
• Integration of automated sample preparation (online extraction, robotic systems) with dual-injector GC setups to further increase unattended daily throughput.
• Extension of rapid banding methods to standardized methods and regulatory acceptance for faster turn-around in contamination assessments.
• Development of robust headspace or purge-and-trap complementary workflows for the volatile (<C10) fraction enabling end-to-end coverage from C6–C40.

Conclusion

The application demonstrates that a Nexis GC-2030 configured with a short Rxi-1ms column, hydrogen carrier gas, SPL-2030 inlet and FID detection provides a rapid, reliable, and high-throughput solution for TPH/TRH banded analysis up to C40. The method achieves excellent linearity across relevant concentration ranges, minimal injection discrimination for high-boilers, and throughput scaling to >400 samples/day using dual-injector/dual-FID configurations. This combination of speed, resolution and automation supports routine environmental monitoring and remediation verification workflows while offering a commercially viable alternative to helium-based methods.

References

• Shimadzu Oceania Pty Ltd. Application note: 3.5 min Total Petroleum Hydrocarbons (TPH) Analysis using the Nexis GC-2030 and H2 carrier. First Edition Oct. 2026.
• Restek Corporation. Rxi-1ms column specifications and reduced oven-volume accessory (manufacturer product documentation).