Fully Automated, Trace-Level Determination of Parent and Alkylated PAHs in Environmental Waters by Online SPE-LC-APPI-MS/MS

Significance of the topic

Polycyclic aromatic hydrocarbons (PAHs) and their alkylated homologues are persistent organic pollutants with toxic, mutagenic, and carcinogenic properties. Monitoring trace levels of these compounds in environmental waters is essential for source identification, regulatory compliance, and protection of public health and ecosystems.

Objectives and Overview of the Study

This study aimed to develop and validate a rapid, fully automated method for trace‐level determination of 28 parent and alkylated PAHs in environmental waters using online solid‐phase extraction (SPE) coupled with liquid chromatography and tandem mass spectrometry (LC‐MS/MS) with atmospheric pressure photoionization (APPI). The method was compared with conventional liquid–liquid extraction (LLE) followed by GC‐MS.

Methodology and Instrumentation

Environmental water samples (seawater, reclaimed water, rainwater runoff) were collected in pre-cleaned amber glassware, fortified with isotopically labeled internal standards, and directly injected (10 mL) into an automated online SPE system. Optimized chromatographic gradients combined methanol/water and acetonitrile/methanol to resolve isobaric and alkylated PAHs on a Hypersil Green PAH column. Dopant‐assisted APPI (chlorobenzene) enhanced ionization, enabling sensitive SRM detection on a TSQ Quantum Access triple quadrupole MS.

Used Instrumentation

• Thermo Scientific EQuan online SPE system with HTC‐PAL autosampler
• Accela 1000 and Accela 600 liquid chromatography pumps
• Thermo Scientific Hypersil GOLD aQ SPE column (20×2.1 mm, 12 µm)
• Hypersil Green PAH analytical column (150×2.1 mm, 3 µm) with guard column
• Thermo Scientific TSQ Quantum Access triple-quadrupole MS with IonMax APPI source
• Chlorobenzene dopant delivery via programmable syringe pumps

Main Results and Discussion

The method achieved linear calibration (5–500 ng/L, R²>0.99) and method detection limits of 7.9–34 ng/L for priority PAHs, approximately one order of magnitude lower than LLE‐GC‐MS. Alkylated isomers (e.g., C1‐naphthalenes, C1‐phenanthrenes) were partially resolved using the dual‐gradient flow strategy. Automated SPE prevented salt carryover and minimized sample preparation time. Application to field samples detected naphthalenes and alkylated PAHs in boating areas, parent and alkylated PAHs in rainwater runoff from a partially flooded parking lot, and trace C2‐PAHs in reclaimed water.

Benefits and Practical Applications

• High sample throughput (28 min/run) with minimal manual preparation
• Improved sensitivity per volume (1 ng on column) and lower solvent use
• Reduced toxic waste generation and environmental impact
• Capability to screen for localized contamination events
• Robust quantitation in diverse matrices without filtration or cleanup

Future Trends and Applications

Further integration with high‐resolution mass spectrometry and expanded compound libraries could enable comprehensive fingerprinting of complex PAH mixtures. Real‐time monitoring platforms and miniaturized extraction modules may facilitate continuous surveillance of industrial effluents, runoff, and drinking water. Advancements in column chemistry may improve separation of closely related isomers and alkyl homologues.

Conclusion

The fully automated online SPE‐LC‐APPI‐MS/MS method offers a rapid, sensitive, and environmentally friendly alternative to traditional LLE‐GC‐MS for routine monitoring of parent and alkylated PAHs in environmental waters. Its high throughput and low solvent consumption make it well suited for regulatory laboratories, environmental research, and quality assurance in water analysis.

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