High-throughput mineral oil determination in water samples by automated in-vial extraction, clean-up, and on-line GC-FID analysis

Significance of the Topic

Mineral oil hydrocarbons, spanning from C10 to C40, are pervasive pollutants introduced during extraction, processing and use of crude oil and its derivatives. Monitoring their levels in water is vital to protect ecosystems and public health. Automated workflows ensure reliable, high-throughput analysis to meet stringent environmental regulations.

Objectives and Study Overview

This study demonstrates a fully automated in-vial liquid-liquid extraction (LLE) and Florisil clean-up protocol coupled to on-line GC-FID, according to EN ISO 9377-2. Goals:

• Validate precision, accuracy and sensitivity for mineral oil quantification in surface and wastewater.
• Reduce solvent use and manual handling time through automated sample preparation.
• Implement intelligent sequencing and decision logic to streamline workflows in a public testing laboratory.

Methodology and Applied Instrumentation

Sample preparation involves:

• Manual addition of 10 mL water sample to a 20 mL vial.
• In-vial addition of C10/C40 internal standard, saturated salt solution and 2 mL n-hexane.
• Vortex mixing, phase separation, and transfer of 600 µL supernatant to a Florisil vial for clean-up.
• Automated syringe mixing and large-volume (40 µL) injection into a GC-FID system.

Applied Instrumentation

• TriPlus RSH autosampler with automated tool changer, 100 µL and 1 mL syringes, vortex mixer and integrated washing stations.
• Thermo Scientific TRACE 1310 GC with iConnect Programmable Temperature Vaporizer and FID detector.
• Chromeleon CDS with Intelligent Sequence and eWorkflow for automated decision-making, QC control and LIMS integration.

Main Results and Discussion

The automated method delivered:

• Blank chromatograms free of carry-over, ensuring reliable integration.
• Linearity (0.1–10 mg/L) with r2 ≥ 0.999 for both external and internal calibration.
• Retention time repeatability of internal standards C10 (RSD 1.6 %) and C40 (RSD 0.2 %).
• Accuracy with recoveries of 96–104 % across spiking levels.
• LOQ of 0.036 mg/L and LOD of 0.018 mg/L after miniaturized extraction.
• Automated QC checks that halt sequences on out-of-spec results, reducing waste.

Benefits and Practical Applications

The workflow yields:

• Up to six-fold increase in sample throughput (40–75 samples/day vs. 10 manually).
• 97 % reduction in solvent cost (from 300 L to 9 L per year).
• Significant labor savings through unattended 24/7 operation.
• Enhanced data quality and traceability via automated QC and LIMS reporting.

Future Trends and Applications

Emerging directions include:

• Extension to other hydrocarbon fractions and complex matrices.
• Integration with advanced data analytics and machine learning for pattern recognition.
• Further miniaturization and green solvent alternatives to lower environmental footprint.
• Remote monitoring and IoT connectivity for real-time environmental assessment.

Conclusion

The automated in-vial extraction, Florisil clean-up and on-line GC-FID method offers a robust, high-throughput solution for mineral oil analysis in water. It delivers excellent precision, sensitivity and cost-efficiency, supporting regulatory compliance and environmental protection.

References

1. ISO 16703:2004 Soil quality — Determination of hydrocarbon content (C10–C40) by GC.
2. EN ISO 14039:2004 Characterization of waste — Determination of hydrocarbon content (C10–C40) by GC.
3. ISO 9377-2:2000 Water quality — Determination of hydrocarbon oil index by solvent extraction and GC.
4. ASTM D7678-11 Standard Test Method for Total Petroleum Hydrocarbons in Water and Wastewater by Solvent Extraction and Mid-IR Laser Spectroscopy.
5. Thermo Fisher Scientific Application Note 001289: High-throughput mineral oil determination in water by automated in-vial extraction and on-line GC-FID.