GC×GC–TOF-MS Detects Persistent Organic Pollutants in Sediment

Researchers at the University of Ferrara have developed a method combining solid-phase extraction with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC–TOF-MS) to simultaneously quantify organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in sediment from the northern Adriatic Sea.¹ Because these legacy contaminants continue to accumulate in aquatic environments decades after their use was restricted, environmental monitoring programs need workflows precise enough to resolve them from a chemically complex sediment background. The method enables simultaneous determination of OCPs and PCBs in a single analytical run, reducing the need for separate workflows across contaminant classes. LCGC International spoke with study authors Flavio A. Franchina and Allan Polidoro about how the method was developed and where it could be applied next.

How does comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC–TOF-MS) compare in terms of cost and complexity to traditional one-dimensional GC methods for detecting persistent organic pollutants (POPs)?

Flavio A. Franchina: Answering this comprehensively and fairly requires decoupling the separation technique (GC vs. GC×GC) from the detection technology (TOF-MS vs. alternative MS or non-MS detectors). In short, adopting GC×GC–TOF-MS elevates initial capital costs and method complexity compared with 1D GC coupled with low-resolution single-analyzer MS, or non-MS detectors. However, for POPs analysis, GC×GC–TOF-MS offers unmatched versatility, sensitivity (with cryomodulation), and sample information. Furthermore, the operational costs of GC×GC can be substantially reduced by adopting cryogen-free thermal modulation alternatives, making the technique even more economically attractive and practical for routine POPs analysis.

Ultimately, it remains the optimal platform for laboratories needing to consolidate multiple target methods while simultaneously expanding their screening capabilities for emerging or suspected contaminants.

What challenges did you encounter when developing and validating the SPE-GC×GC–TOF-MS method, particularly regarding matrix interference or analyte stability?

Allan Polidoro: One of the main challenges was the complexity of sediment as an analytical matrix, as it is highly heterogeneous and may contain natural organic matter, sulfur compounds, and other substances that can interfere with extraction efficiency and compromise quantification, which was one of the main reasons for combining ultrasonic extraction with sulfur cleanup and SPE cleanup before GC×GC–TOF-MS analysis. Another challenge was ensuring selectivity for trace-level analytes in the presence of a very crowded background, and this is where GC×GC–TOF-MS was important for confidence in identification and quantification. The paper results show that sediment extracts contained several additional compounds that could interfere with the target analytes if chromatographic selectivity were insufficient.¹Regarding analyte stability, this issue was addressed by proper handling during sample preparation and cleanup. For example, to avoid losses of semi-volatile compounds during extract concentration, the extract was gently concentrated under nitrogen at controlled temperature without being taken to dryness, thereby minimizing volatilization losses.

Given the ultra-trace detection limits achieved, how feasible is this method for routine large-scale environmental monitoring programs?

AP: The proposed method is promising for routine large-scale environmental monitoring, but its feasibility depends on the analytical context and the goals of the monitoring program. From a performance perspective, the method is highly feasible, as the achieved detection limits were below sediment guideline values, indicating that the workflow is sensitive not only to detect contamination when regulatory thresholds are exceeded but also to identify trace background contamination, which is an important advantage for environmental programs that aim to detect contamination early, assess long-term trends, or monitor areas historically impacted by contamination.

Another point is that the method enables simultaneous determination of OCPs and PCBs in a single analytical run. That multi-residue capability is highly useful for monitoring programs because it reduces the need for separate analytical workflows for different classes of persistent halogenated contaminants. In that sense, the approach is operationally attractive, since a single validated workflow can provide broad analytical coverage with high selectivity.

Did you observe any significant interference from coeluting compounds in sediment matrices during your analysis, and how does GC×GC improve resolution in such cases?

AP: Indeed, as aforementioned, a chemically complex background was observed in the sediment samples containing many other compounds, mainly phenolic compounds and aliphatic and aromatic hydrocarbons, which could potentially interfere with the determination of OCPs and PCBs if sufficient selectivity were not achieved. In this context, GC×GC becomes particularly valuable because it distributes compounds across a 2D separation space using columns with different selectivity mechanisms. In the presented method, this was achieved by combining a non-polar first-dimension column with a mid-polar second-dimension column, enabling the separation of compounds that might otherwise partially or fully coelute in 1D GC.

How might this method be adapted or extended to detect emerging contaminants or other classes of pollutants in environmental samples?

FAF: An extension of this method would be to shift from a targeted workflow to a broader, non-targeted strategy. Since GC×GC–TOF-MS provides highly complex, structured chromatographic data, it can reveal many additional compounds beyond the target OCPs and PCBs. Indeed, in the published paper we highlight that the comprehensive data output can support non-targeted analysis and the identification of additional contaminants that conventional targeted approaches would likely miss.¹

The strategy is conceptually ready for emerging contaminants, but the method would need to be more class-flexible, with the workflow revalidated for new analytes. From an analytical standpoint, the first adaptation would likely be in sample preparation, since the current workflow was optimized for semi-volatile halogenated contaminants in sediments, which is well-suited to OCPs and PCBs. Other pollutant classes would require a new optimization of extraction solvent composition and sorbents. A second extension would be at the data-processing workflow, expanding the analyte scope by building larger spectral and retention databases and incorporating suspect lists for other semi-volatile contaminants, such as per- and polyfluoroalkyl substances (PFAS), brominated flame retardants, and polycyclic aromatic hydrocarbons (PAHs). For non-volatile or more polar emerging contaminants, the extension might require derivatization or working in parallel with complementary liquid chromatography (LC)–MS methods.

Could you comment on the potential for this technique to be used in non-laboratory field settings or in portable applications?

FAF: Currently, the main value of this technique is in laboratory settings rather than in field-portable applications. The workflow described in our study includes several preparative and instrumental steps, including ultrasonic extraction, cleanup, solvent concentration, and GC×GC–TOF-MS analysis on a benchtop platform equipped with a cryogenic modulator and a time-of-flight mass spectrometer. Furthermore, the analytical architecture itself is a limitation for portable use, since the GC×GC technique requires precise thermal and flow control, modulation, fast acquisition, and advanced data processing, including the handling of large data sets. These features make the technique powerful, but they also make miniaturization and field implementation difficult at present.

That said, the broader analytical concept could still indirectly support field-oriented monitoring. For instance, this gain in separation power and sensitivity of GC×GC–TOF-MS can simplify field sampling and on-site sample preparation, while the final analysis would still be carried out in the laboratory.

What future research directions do you foresee stemming from this work, especially regarding the monitoring of POPs in different environmental compartments or regions?

FAF: A promising research direction is to extend this approach beyond sediments to other environmental compartments, including water, soils, particulate matter, and biota. Although sediments are relevant because they act as reservoirs of POPs, a more comprehensive understanding of their environmental fate and transport requires integrating across multiple matrices. Since the published study demonstrated that the method is sensitive and selective for trace-level determination in a complex solid matrix, it provides a good analytical base for broader monitoring frameworks.

Another path is to expand the geographical scope, since the proposed method was successfully applied to sediment samples from the northern Adriatic Sea, suggesting that the workflow could be useful for monitoring across coastal, estuarine, riverine, and industrially impacted regions. Besides, there is potential for longitudinal monitoring, which is important for legacy POPs that may persist for decades and can be redistributed by dredging, flooding, sediment disturbance, or changes in environmental conditions.

A further research possibility is to leverage GC×GC–TOF-MS’s highly informative data output to combine targeted quantification with broader non-targeted strategies, integrating legacy POP monitoring with suspect screening for other persistent or semi-volatile emergent pollutants, thereby making environmental assessment more comprehensive without abandoning robust targeted quantification.

Reference

1. Polidoro, A.; Costa, V.; Romagnoli, M.; et al. Multitargeted Analysis for the Simultaneous Determination of Organochlorine Pesticides and Polychlorinated Biphenyls in Sediments Exploiting Comprehensive Two-Dimensional Gas Chromatography Coupled to Mass Spectrometry. J Chrom Open 2025, 8 100245. DOI: 10.1016/j.jcoa.2025.100245