Automated Clean-up of PCB extracts from Waste Oil using the Agilent 7696A Sample Prep WorkBench

Significance of the topic

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that accumulate in waste oils and pose serious environmental and health risks. Reliable detection and quantification of PCBs in transformer and waste mineral oils is essential for regulatory compliance, environmental monitoring and preventing contamination of analytical systems.

Study objectives and overview

This application note demonstrates an automated, miniaturized dispersive solid phase extraction (d-SPE) workflow on the Agilent 7696A Sample Prep WorkBench for efficient clean-up of PCB extracts from waste oils. The aim is to simplify sample preparation, improve reproducibility and integrate seamlessly with GC-ECD, GC-MS or GC-MS/MS analysis with back-flushing to protect the system from apolar matrix buildup.

Methodology and used instrumentation

The two-step d-SPE method involves:

1. Add 50 µL of 10% waste oil in hexane plus 1 350 µL hexane and 150 µL internal standard to a vial containing 100 mg H₂SO₄-coated silica and 100 mg SAX adsorbent.
2. Vortex at 4 000 RPM for 5 min, then pause 2 min for binding of polar interferences.
3. Transfer 1 000 µL supernatant to a second vial with 100 mg washed silica; vortex and wait as before.
4. Transfer 200 µL of the final cleaned extract to an analysis vial and flag as result.

Used instrumentation:

• Agilent 7696A Sample Prep WorkBench for automated d-SPE.
• Agilent 7000 Triple Quad GC/MS with MMI inlet.
• DB-5MS column (0.25 mm × 30 m, 0.25 µm) with Quick-Swap connector and back-flush capability.
• Helium carrier gas, MRM acquisition for targeted PCB congeners and octachloronaphthalene internal standard.

Main results and discussion

The dark brown oil extract becomes clear after the first d-SPE step and remains clean after the second silica purification. GC-MS/MS MRM chromatograms of five replicates from BCR-449 reference oil show well-resolved PCB peaks and an internal standard at 22.8 min. Repeatability of relative peak areas for six PCB congeners yielded RSD values around 4–10 %, demonstrating robust performance. Back-flushing is recommended to prevent accumulation of residual apolar matrix components in the inlet and column.

Advantages and practical applications

This workflow offers:

• Automated, hands-off operation for higher throughput and reduced manual variability.
• Miniaturized adsorbent volumes and solvents, lowering cost and waste.
• Compatibility with GC-ECD, GC-MS and GC-MS/MS for selective, sensitive detection.
• Enhanced system protection via integrated back-flush, extending column and detector lifetime.

Future trends and opportunities

Potential developments include:

• Extension of automated d-SPE to other persistent organic pollutants such as dioxins and brominated flame retardants.
• Integration with fully robotic sample tracking and online data evaluation.
• Adoption of green solvents and sustainable sorbent materials.
• High-throughput environmental screening using multiplexed WorkBench configurations.

Conclusion

An automated, two-step dispersive SPE method on the Agilent 7696A WorkBench enables accurate, reproducible and efficient clean-up of PCBs from waste mineral oils. Combined with GC-MS/MS and back-flushing, this approach delivers robust quantitation and system protection, meeting environmental laboratory requirements.

References

1. DIN EN 12766 and DIN EN 61619: Standard methods for PCB analysis in waste oils.
2. Sandra P. and David F., “The 1999 Belgian Dioxin Crisis: the Need to Apply State-of-the-Art Analytical Methods,” in A Century of Separation Science, H.J. Issaq, Ed., Marcel Dekker, 2002.
3. QuEChERS information portal, CVUA-Stuttgart.
4. David F. and Klee M.S., “GC/MS Analysis of PCBs in Waste Oil Using the Backflush Capability of the Agilent QuickSwap Accessory,” Agilent application note 5989-7601 EN, 2007.