Analysis of Currency with SPME and GCxGC-TOFMS—Advanced Data Processing with Classifications

Significance of the Topic

Understanding volatile and semivolatile compounds present on paper currency has broad implications for forensic science, anti-counterfeiting efforts, and security screening applications.

Objectives and Overview

This study aimed to capture and identify the complex mixture of headspace volatiles from a single US one-dollar bill using solid-phase microextraction (SPME) and comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOFMS). Advanced data processing through chemical classification was employed to streamline compound identification.

Methodology and Instrumentation

The experimental workflow included sampling, chromatographic separation, mass spectrometric detection, and classification-based data processing.

• Sample preparation: A $1 bill placed in a 20 mL vial, equilibrated at 30 °C; headspace extracted for 60 minutes using a 75 µm Carboxen-PDMS SPME fiber; desorbed at 225 °C for 15 s.
• Chromatography: Two-dimensional GC with a 30 m × 0.25 mm × 0.25 µm Rtx-1 primary column and a 1 m × 0.10 mm × 0.20 µm Rtx-Wax secondary column; primary oven ramp from 30 °C to 220 °C; secondary oven from 40 °C to 230 °C; quad-jet dual-stage modulation at 5 s intervals.
• Mass spectrometry: Time-of-flight MS with electron ionization at 70 eV; source temperature 200 °C; acquisition rate 100 spectra/s over m/z 35–400.
• Data processing: LECO ChromaTOF software utilizing user-defined classification regions to group alkanes, aldehydes, and alcohols for efficient review.

Results and Discussion

The rapid 27-minute analysis revealed over 300 distinct compounds.

• n-Alkanes spanning hexane through heptadecane.
• Aldehydes including butanal, pentanal, hexanal, heptanal, nonanal, and decanal.
• Alcohols such as 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, linalool, and menthol.

Classification filtering enabled focused review of the alcohol region, highlighting major contributors like benzaldehyde (22.9 % of the alcohol class) and 1-hexanol, 2-ethyl- (29.5 %). The two-dimensional contour plot demonstrated clear separation of homologous series across retention planes.

Benefits and Practical Applications

This integrated approach delivers:

• High chromatographic resolution to resolve coeluting species.
• Rapid throughput under 30 minutes per sample.
• Automated classification regions for targeted compound grouping.
• Versatility for forensic investigations, counterfeiting detection, and security screening.

Future Trends and Possibilities

Advancements may include:

• Automated script-based classification to refine identification accuracy.
• Application of GCxGC-TOFMS to a wider range of substrates beyond currency.
• Integration with chemometric tools and machine learning for pattern recognition.
• Development of portable two-dimensional systems for on-site screening.

Conclusion

SPME combined with GCxGC-TOFMS and classification-based data processing provides a powerful, rapid, and detailed method for headspace analysis of complex samples such as currency. The workflow enables identification of hundreds of volatile and semivolatile compounds with high confidence and efficiency.

References

No external literature references were provided.