Targeted and Non-Targeted Screening of Persistent Organic Pollutants (POPs) in Groundwater and Trade Effluent Wastewater Using the Xevo™ G3 QTof Mass Spectrometer

Significance of the topic

Persistent organic pollutants (POPs), and in particular per- and polyfluoroalkyl substances (PFAS), are a growing global concern because of their persistence, mobility and bioaccumulation. Routine monitoring limited to compounds with available standards underestimates environmental exposure. Combining targeted screening with unbiased, data-independent acquisition (DIA) and pattern-based non-targeted workflows enables more comprehensive surveillance of drinking-water sources, groundwater and trade effluents, supporting both regulatory compliance and early detection of emerging contaminants.

Objectives and study overview

The application study aimed to demonstrate a combined targeted and untargeted workflow for PFAS/POP screening in environmental waters using the Xevo G3 QTof mass spectrometer with DIA (MSE) acquisition. Two trade wastewater samples (WW1, WW2) and one groundwater sample (GW) from the UK were analyzed by direct injection UPLC-QTof. Targeted screening used a PFAS library to identify and quantify known analytes, while a pattern analysis-based untargeted workflow was applied to search for PFAS-like features not covered by the library.

Methodology and used instrumentation

Sample preparation and standards:

• Calibration: 10-point curve (0.001–50 ng/mL) prepared from a 30-PFAS standard mix (PFAC30PAR) in MeOH:water:acetonitrile (50:25:25) with 0.1% formic acid.
• Samples: two trade wastewater samples and one groundwater sample. Aliquots centrifuged (5 min, 10,000 rpm), supernatant diluted 1:1 with 50:50 MeOH:water + 0.1% formic acid. Injection volume 50 µL (direct injection).

Chromatography and mass spectrometry:

• UPLC: Waters ACQUITY Premier UPLC I-Class System with PFAS kit; column ACQUITY Premier CSH C18, 1.7 µm, 2.1 x 100 mm; column 35 °C, autosampler 10 °C; flow 0.3 mL/min.
• Mobile phases: ammonium acetate-containing aqueous/methanolic compositions optimized for PFAS retention; gradient described in the original note.
• Mass spectrometry: Waters Xevo G3 QTof in negative ion mode, sensitivity tuning; mass range 50–1200 m/z; MSE acquisition with low-energy fixed 4 V and high-energy ramp 20–70 V; scan time 0.25 s; source/desolvation temperatures 100 °C/250 °C; cone 30 V; capillary 0.5 kV; StepWave optics employed.

Data processing and discovery criteria:

• Software: waters_connect platform with UNIFI and the Pattern Analysis application.
• Targeted screening used a 149-analyte PFAS library (retention time, accurate mass, fragments) and quantified identified analytes against the calibration curve (n = 3).
• Untargeted filters (applied to WW2): mass defect between 0.9 and 0.1 (Kendrick normalization to CF2), [m/z]/C_n > 30, response > 500, and presence of characteristic neutral losses and fragments (e.g., HF, CF2, SO3, FSO3, C2F4SO3).

Main results and discussion

Targeted findings:

• From the 149-library panel, identified and quantified compounds: 9 in WW1, 12 in WW2 and 10 in GW. Quantitation was performed in triplicate against the PFAS standard curve. Branched isomers were accounted for and compared to their linear counterparts.
• Direct injection simplified sample handling and reduced biases introduced by extraction workflows while retaining sufficient sensitivity for quantitation down to the low ng/mL and sub-ng/mL range.

Untargeted discovery (WW2):

• Initial feature finding returned 298 components above the chosen response threshold. Pattern analysis reduced candidates to five PFAS-like features based on mass-defect and homologous-series behavior.
• Kendrick mass defect plots (normalized to CF2) were effective in grouping homologous PFAS series and distinguishing them from natural organic matter. Closely eluting feature pairs were interpreted as branched and linear isomers; branched isomers exhibited earlier elution consistent with reduced retention on reversed-phase columns.
• Putative assignments: formula searches and PubChem querying suggested a homologous series of unsaturated difluoroacetate PFAS (nominally C6–C9 chains with multiple fluorinated ether motifs), with both linear and branched forms among the five features. Mass errors for these putative IDs ranged from about −1.0 to −2.5 ppm; larger errors correlated to low-intensity peaks and expected poorer ion statistics.
• No confirmatory standards were available for these putative compounds, so definitive identification (RT, fragmentation match vs standard) remains pending.

Benefits and practical applications

• Combining DIA (MSE) acquisition and targeted libraries allows simultaneous collection of precursor and fragment information in a single run, increasing confidence in identifications and enabling retrospective data mining.
• Pattern analysis and Kendrick mass defect-based filtering enable detection of homologous PFAS series and low-abundance isomers not present in libraries, addressing the limitation posed by scarce analytical standards.
• Direct injection workflows reduce sample manipulation and accelerate throughput for routine surveillance of groundwater and wastewater.
• Sub-2 ppm mass accuracy on the Xevo G3 QTof strengthens putative assignments and supports regulatory reporting and risk assessment when standards are available.

Future trends and opportunities

• Expanded and curated reference standard availability remains critical; coordinated efforts between producers, regulators and researchers are needed to provide quantitative standards for emerging PFAS.
• Integration of orthogonal techniques (ion mobility, higher resolving power instruments, tandem MS libraries) will improve isomer separation and structural confidence for non-target identifications.
• Automated suspect-list workflows, community-shared spectral libraries and machine-learning approaches to pattern recognition will accelerate discovery and reduce false positives.
• Use of DIA datasets as permanent digital archives will facilitate retrospective surveillance for transformation products, industrial by-products, and regulatory compounds added in the future.
• Application of these workflows to large monitoring networks can inform remediation priorities, source-tracing and public-health risk assessments.

Conclusion

The combined targeted DIA and pattern-analysis untargeted approach demonstrated on the Xevo G3 QTof provides a robust, flexible workflow for PFAS/POP surveillance in groundwater and wastewater. Targeted library screening delivered quantitative results for known PFAS, while pattern analysis uncovered additional PFAS-like homologues including branched isomers. The approach addresses limitations caused by the scarcity of standards and supports comprehensive environmental monitoring, retrospective data interrogation and discovery of emerging contaminants. Definitive confirmation of putative findings requires matching authentic standards (retention time and MS/MS), but the presented workflow reliably prioritizes candidates for follow-up.

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