A holistic view of river water quality using passive sampling and GC×GC–TOF MS

Importance of the Topic

Passive sampling combined with comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry (GC×GC–TOF MS) delivers a time-integrated and high-resolution profile of river water contaminants. This integrated approach addresses limitations of grab sampling and enhances detection of both priority pollutants and emerging trace chemicals.

Study Objectives and Overview

This study aimed to evaluate the performance of semi-permeable membrane devices (SPMDs) for passive sampling of hydrophobic contaminants in a UK river and to characterize the extracts using GC×GC–TOF MS with a novel INSIGHT-Thermal modulator. Comparative analyses at two sites focused on priority organochlorines alongside emerging pharmaceuticals, personal care products, and industrial additives.

Methodology

Passive sampling devices were deployed at two river locations for four weeks. Extracts were desorbed with hexane, cleaned via size exclusion chromatography (SEC), and concentrated to 1 mL. Field blanks and surrogate spikes ensured quality control. Data acquisition targeted compounds with log Kₒw > 4, covering a broad volatility range (C₇–C₅₀+).

Instrumentation Used

• Passive sampler: Semi-permeable membrane device (SPMD)
• Gas chromatograph: Two-dimensional GC with INSIGHT-Thermal cryogen-free modulator (6 s modulation period, ramped cold jet flow)
• Mass spectrometer: BenchTOF2 operating m/z 30–600 at 100 Hz in Tandem Ionisation® mode (70 eV and 14 eV)
• Software: ChromSpace® for instrument control and data processing

Main Results and Discussion

The combined method detected a wide suite of analytes including siloxanes, PCBs (Cl₂–Cl₈ congeners), tris(2-chloropropyl) phosphate, chlorinated benzoates, and emerging contaminants such as pharmaceuticals and flame retardants. Site-to-site comparisons revealed distinct chemical fingerprints, underscoring spatial variability in contaminant profiles. The time-weighted SPMD approach captured episodic discharges missed by traditional grab sampling.

Benefits and Practical Applications

• Time-integrated sampling reduces the chance of overlooking transient pollution events
• Cryogen-free thermal modulation with variable cold jet flow enhances separation of high-boiling compounds
• Retrofittable modulator design facilitates deployment on existing GC platforms
• Comprehensive analyte coverage supports environmental monitoring, regulatory compliance, and risk assessment

Future Trends and Applications

Planned expansion to multiple sampling sites will enable broader spatial surveys. Integration of advanced data-processing workflows and machine learning could streamline screening of complex datasets and improve source apportionment. Continued modulator and detector innovations are expected to further lower detection limits and extend the analyte range.

Conclusion

The study demonstrates that passive sampling with SPMDs paired with GC×GC–TOF MS and a cryogen-free INSIGHT-Thermal modulator offers a robust framework for holistic river water quality assessment. The approach enhances sensitivity, resolution, and throughput, providing a versatile tool for environmental scientists and monitoring programs.