Determination of TPH in Water using SPE-DEX® and LVI-GC-FID

Significance of the Topic

Determining total petroleum hydrocarbons (TPH) in water is critical for assessing environmental contamination and safeguarding public health. Rapid, reliable analysis supports regulatory compliance and reduces risks associated with solvent use in laboratory workflows.

Study Objectives and Overview

This study introduces a combined workflow leveraging automated solid-phase extraction (SPE-DEX® 4790), hydrophobic membrane drying (DryDisk™), and large-volume injection GC-FID (LVI-GC-FID) to quantify TPH (C10–C40) in aqueous samples at 0.05–25 mg/L. The method aims to enhance throughput, reproducibility, and safety compared to traditional liquid–liquid extraction.

Instrumentation Used

• Horizon Technology SPE-DEX® 4790 automated SPE system
• BAKERBOND™ Speedisk® C18 50 mm extraction disks
• Horizon Technology SDS-100 solvent drying system with DryDisk™ membrane
• ATAS Optic 3 high-performance large-volume injector
• Agilent 6890N gas chromatograph with FID and HP-5 column

Methodology

Samples (1 L tap water) were spiked with a TPH standard mix (diesel/mineral oil in n-hexane). The SPE-DEX® 4790 unit sequentially preconditions C18 disks with dichloromethane and methanol, draws the sample through the sorbent, and elutes analytes with acetone followed by n-hexane. Biphasic extracts receive 15 mL water to promote phase separation. The hexane layer is dried via DryDisk™ and made up to 25 mL before injecting 50 µL into GC-FID under near-ambient start conditions.

Main Results and Discussion

Calibration was linear up to 25 mg/L (R²>0.999) and validated at low levels (0–1.25 mg/L) without weighting biases. Spike recoveries at 1 mg/L averaged 91.8% (RSD 7.9%). The method reporting limit for C10–C40 is estimated at 0.05 mg/L, with minimal chromatographic carryover above 2.5 mg/L. Automated SPE improved reproducibility and reduced solvent handling compared to manual methods. DryDisk™ drying eliminated the need for chemical desiccants.

Benefits and Practical Applications

• Increases sample throughput and reduces turnaround time
• Minimizes operator exposure to hazardous solvents
• Enhances reproducibility through automation
• Reduces bench space and labor requirements
• Eliminates chemical drying agents and associated contamination

Future Trends and Potential Applications

Emerging directions include integration of internal/surrogate standards for continuous quality control, miniaturized and portable SPE-GC systems, coupling with mass spectrometry for enhanced specificity, and further adoption of green chemistry principles to reduce solvent consumption and laboratory footprint.

Conclusion

The combined SPE-DEX®/DryDisk™/LVI-GC-FID workflow offers a robust, efficient, and safer alternative to traditional TPH analysis in water. Automation delivers consistent recoveries, high throughput, and low detection limits while reducing solvent use and labor demands.

Reference

• VAM Bulletin No. 18, Spring 1998, “Regression & Calibration,” pp. 18–21
• Anatune Ltd. Application Note No. 099, Horizon Technology