Determination of OCPs and PCBs in Sediments Using SPE-GCxGC-TOFMS

Importance of the topic

Persistent organic pollutants (POPs) such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) remain critical targets of environmental monitoring because of their persistence, tendency to bioaccumulate, and enduring human and ecological health risks. Sediments act as long-term reservoirs and secondary sources of these contaminants; reliable, sensitive methods capable of resolving complex co-extracted matrix interferences at ultra-trace levels are therefore essential for environmental assessment, regulatory compliance, and risk management.

Objectives and study overview

This application note presents a validated analytical workflow combining solid-phase extraction (SPE) cleanup and enrichment with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOFMS) for simultaneous determination of 49 target organochlorine compounds (22 OCPs and 27 PCBs) in sediment matrices. The study aims to demonstrate the method's separation power, sensitivity, linearity, accuracy, and suitability for regulatory monitoring of legacy POPs in complex environmental samples.

Methods and workflow

Sample preparation and cleanup:

• Lyophilized sediment (5 g) subjected to sequential ultrasonic extraction (3 × 10 min) with acetone:hexane (1:1, v/v).
• Combined extracts concentrated under nitrogen to ~1 mL.
• Sulfur removal via tetrabutylammonium (TBA) sulfite treatment.
• Florisil SPE cleanup; analyte elution with acetone:hexane (10:90, v/v), concentration and reconstitution to 1.0 mL hexane.
• Internal standard spiking prior to analysis (decachlorobiphenyl, reported as 1000 µg mL−1 stock; final internal standard concentration noted in calibration protocol).

Calibration and quantification:

• External calibration using certified standard mixtures covering 0.10 to 1.96 ng kg−1 for each analyte (49 compounds total).
• Peak-area ratios normalized to the internal standard; calibration curves constructed and used for interpolation of sample concentrations.

Quality control and validation:

• Method performance assessed via linearity (r² > 0.99), limits of detection/quantification, accuracy and precision.
• Validation against a certified reference material (CNS391-50G) with most analytes within certified tolerance intervals.

Used Instrumentation

The instrumental platform and major consumables reported:

• GCxGC-TOFMS system: LECO Pegasus BTX 4D.
• Cryogenic modulation: QuadJet™ dual-stage cryogenic modulator for comprehensive two-dimensional separations.
• Data system: ChromaTOF® software for data acquisition and processing.
• SPE sorbent: Florisil cartridges for post-sulfur-cleanup purification.
• Extraction equipment: ultrasonic bath for accelerated solvent extraction; nitrogen blowdown for concentration.

Main results and discussion

Separation and detection:

• GCxGC-TOFMS achieved high-resolution two-dimensional chromatographic separation for the 49-target mix, enabling clear visualization of clusters and retention patterns in 2D total ion chromatograms.
• Examples reported show efficient separation of hexachlorobenzene from matrix interferences in the second dimension and resolution of PCB-52 from an isobaric interferent that would confound single‑dimension GC-MS analysis.

Analytical performance:

• Calibration linearity was excellent across the tested range (r² > 0.99).
• Very low limits of detection and quantification were reported (specific numerical LOD/LOQ values were stated as exceptionally low in the study; the workflow met international guideline requirements).
• Accuracy and precision were demonstrated by recovery and CRM analysis; most analytes in the CRM were quantified within certified tolerance ranges.

Application to environmental samples:

• Three real sediment samples (S1–S3) were analyzed. Target analytes including 4,4’-DDE and PCB-28 were detected at concentrations below the cited international guideline values; some analytes were not detected or were below LOQ.
• GCxGC improved confidence in identification and quantification by resolving co-eluting species and minimizing isobaric interferences, a common challenge in sediment analyses.

Benefits and practical applications of the method

Key advantages demonstrated by the workflow:

• Superior chromatographic resolving power relative to one-dimensional GC reduces false positives/negatives arising from coelution and isobaric interferences.
• Enhanced sensitivity through GCxGC-TOFMS and thorough sample cleanup supports ultra-trace quantification required by regulatory monitoring.
• Validated performance (linearity, LOD/LOQ, accuracy) and successful CRM analysis make the workflow suitable for routine laboratory use for legacy POP surveillance in sediments.

Practical use cases:

• Environmental monitoring programs for compliance with sediment quality guidelines.
• Baseline and trend studies to assess long-term pollutant reservoirs and re-mobilization risks.
• Forensic and source-apportionment studies where high-resolution separation aids congener-specific profiling.

Future trends and potential applications

Expected developments and opportunities to extend this work include:

• Integration with high-resolution accurate-mass (HRAM) instruments to combine GCxGC separation with exact-mass confirmation and non-target screening capabilities.
• Automation and miniaturization of sample-preparation workflows (e.g., online SPE, QuEChERS adaptations, accelerated solvent extraction) to increase throughput and reduce solvent consumption.
• Standardization of GCxGC-TOFMS methods and wider inter-laboratory validation to support regulatory adoption and comparability.
• Application of the workflow to other complex matrices (soils, biota) and expansion to include emerging halogenated contaminants and transformation products.

Conclusions

The combined SPE and GCxGC-TOFMS approach implemented on the LECO Pegasus BTX 4D delivers high chromatographic resolution, selectivity, and sensitivity for the simultaneous determination of 49 organochlorine pesticides and PCB congeners in sediment matrices. The method effectively resolves matrix interferences that commonly compromise single-dimension methods, demonstrates robust analytical performance against a certified reference material, and provides concentrations consistent with regulatory expectations for the examined samples. This workflow is a robust option for laboratories performing trace-level monitoring of legacy POPs in sediments.

References

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