THE EIGHT(Y) MILLION POUND QUESTION: USING DESI AMBIENT MS IMAGING FOR THE FORENSIC ANALYSIS OF CHEQUE FRAUD

Importance of the topic

The rising sophistication of cheque forgery causes substantial financial losses and challenges traditional handwriting analysis, which is time-consuming and often fails to detect small-scale alterations.

• Fraudulent modifications can inflate payout amounts or change payee names.
• Handwriting experts struggle with subtle single-character forgeries.
• There is a clear need for objective, molecular-level detection techniques that preserve evidence integrity.

Objectives and study overview

This study evaluates desorption electrospray ionization (DESI) ambient mass spectrometry imaging (MSI) for detecting cheque fraud. A simulated case involved altering a bank cheque originally written for £80,000,000 and changing the recipient’s name. The goal was to map distinct ink chemical signatures to reveal unauthorized changes with minimal or no sample preparation.

Methodology and instrumentation

DESI-MSI was used to perform surface chemical analysis under ambient conditions without extraction or derivatization.

• Three different pens (A, B, C) created the original text and subsequent forgeries.
• A blackout marker concealed the cheque number for recovery tests.

Used instrumentation

• DESI source mounted on a Waters SYNAPT G2-Si QTof mass spectrometer.
• Solvent: 100% methanol at 1.5 µL/min; nebulizing gas: nitrogen at 0.5 MPa; sprayer voltage: 4.5 kV; positive ion mode; m/z range: 50–1200.
• Imaging pixel sizes: 100 µm for broad scans and 50 µm for high-resolution areas.
• Data acquisition in MassLynx 4.2, visualization in HDI 1.4, principal component analysis in EZ Info 2.0.

Key results and discussion

• Unique m/z markers distinguished pen A (original writing), pen B and C (forgery strokes), and blackout marker ink.
• Spatial distribution maps revealed alterations to the numeric amount, written words, and payee name with single-character precision.
• Overlay MS images and PCA of regions of interest segregated the three pen signatures into distinct clusters.
• MS imaging of the blackout pen recovered the obscured cheque number as 100135.

This ambient approach provided unambiguous molecular evidence of forgery while preserving the physical specimen for follow-up analyses.

Benefits and practical applications

• Rapid, objective detection of minute ink alterations undetectable by visual inspection.
• Minimal specimen damage allows subsequent forensic or analytical testing.
• High spatial resolution enables attribution of individual pen strokes.
• Seamless integration into forensic workflows and quality-control processes.

Future trends and applications

• Expansion to negative ion mode for additional molecular markers.
• Higher spatial resolution imaging and 3D surface profiling.
• Integration with complementary techniques such as Raman spectroscopy and DNA analysis.
• Development of automated spectral libraries for rapid ink identification and authentication.

Conclusion

DESI ambient MS imaging demonstrates a powerful capability for forensic cheque analysis, offering precise, non-destructive chemical mapping of inks. This method enhances objectivity, sensitivity, and preserves evidence integrity, with significant potential for broader forensic and industrial quality-control applications.