Discrimination and analytical profiling of colored printed documents using ATR-FTIR spectroscopy coupled with...

Area of Science:

• Forensic Science
• Analytical Chemistry
• Spectroscopy

Background:

• Printed documents are crucial evidence in forensic investigations.
• Spectroscopy and chemometrics enhance the analysis of printing inks.
• Previous studies have not comprehensively examined both black and colored printed documents using advanced chemometric methods.

Purpose of the Study:

• To explore the discriminatory potential of Principal Component Analysis (PCA), Soft Independent Modelling of Class Analogy (SIMCA), and Partial Least Square-Discriminant Analysis (PLS-DA) for forensic document examination.
• To determine the source of origin for unknown printed documents using a non-destructive approach.
• To analyze and compare ink-based and toner-based printed samples.

Main Methods:

• Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) spectroscopy was employed for non-destructive analysis.
• Seventy-four printed document samples (40 ink-based, 34 toner-based) were analyzed.
• Chemometric techniques including PCA, SIMCA, and PLS-DA were utilized for data analysis and classification.

Main Results:

• ATR-FTIR identified common binder polymers (polystyrene, bisphenol A, acrylates) and specific pigments (e.g., Carbon black, PB 15, PY 74).
• PCA revealed that Cyan contributed most to classification accuracy, explaining 97% of the variance.
• PLS-DA achieved 98.6% discrimination accuracy between sample classes, with 100% accuracy on blind test samples; SIMCA showed limitations with ink-based samples.

Conclusions:

• PLS-DA is a highly effective supervised method for discriminating between ink-based and toner-based printed documents.
• The combined use of ATR-FTIR spectroscopy and PLS-DA offers a robust, non-destructive method for forensic document source determination.
• This study provides a significant advancement in the analytical interpretation of printed evidence in forensic science.