A Sample Prep-Free Analysis of Perfluorinated Carboxylic Acids with “SMCI+” using NCI - Environmental Monitoring -

Importance of the Topic

Perfluorinated carboxylic acids (PFCAs) are highly persistent environmental contaminants that accumulate in humans, wildlife, and ecosystems. Known as "forever chemicals," their resistance to natural degradation and prevalence in industrial processes have raised regulatory concerns worldwide. Reliable and sensitive analytical methods are essential for environmental monitoring, exposure assessment, and regulatory compliance.

Objectives and Study Overview

This study demonstrates a streamlined, sample preparation–free approach for qualitative GC/MS analysis of six PFCAs using a combination of a direct inlet probe and solvent‐mediated chemical ionization (SMCI+) under negative chemical ionization (NCI) mode. The goal is to replace conventional derivatization steps with a rapid, safe method that maintains or improves detection sensitivity.

Methodology and Instrumentation

Sample introduction and ionization were achieved using SMCI+ setup, comprising:

• A direct sample inlet (DI) probe fitted with miniature sample vials
• An SMCI unit enabling positive/negative chemical ionization using methanol as reagent gas
• A GCMS-TQ8050 NX triple-quadrupole GC/MS system

Standard solutions of PFHpA, PFOA, PFNA, PFDA, PFTriA, and PFTA (5,000 ppm in methanol) were deposited (1 µL) into DI vials and thermally desorbed using a temperature ramp (20 °C/min to 100 °C, then 40 °C/min to 450 °C, hold 7 min). Ion source temperature was 230 °C, scan range m/z 50–800 at 3,333 u/s.

Main Results and Discussion

NCI mass spectra featured prominent [M–H]– and [M–HF]– product ions for all PFCAs. The [M–HF]– signal consistently dominated, while [M–H]– intensities reached >20 % of the base peak (except PFTA). A recurring base peak at m/z 231 ([C5F9]+) was observed for PFOA and longer chain PFCAs, with successive losses of CF2 units appearing as 50 u intervals. Extracted ion thermograms of [M–H]– ions demonstrated clear elution of all analytes below 100 °C.

Benefits and Practical Applications

SMCI+ streamlines PFCA analysis by:

• Eliminating time-consuming derivatization
• Using methanol as a safe, nonflammable reagent gas
• Enhancing negative ionization sensitivity compared to PCI
• Facilitating rapid qualitative screening in environmental and industrial laboratories

Future Trends and Applications

Further development may include quantitative performance evaluation, extension to other perfluorinated analytes, and integration with high-throughput workflows. Adaptation to automated sampling systems could enable routine PFCA surveillance in water, soil, and biota.

Conclusion

The SMCI+ approach offers a convenient, safe, and sensitive alternative for GC/MS-based PFCA analysis without derivatization. Negative chemical ionization with methanol significantly improves detection, supporting rapid environmental monitoring.

Instrumentation Used

• Shimadzu GCMS-TQ8050 NX triple-quadrupole GC/MS
• Direct inlet (DI) probe
• Solvent-mediated chemical ionization (SMCI) unit with methanol reagent