FTIR Spectroscopy of Vitreous Humor for Postmortem Interval Estimation: A Multivariate Regression Approach

Area of Science:

• Forensic Science
• Biochemistry
• Analytical Chemistry

Background:

• Accurate postmortem interval (PMI) estimation is vital in forensic investigations.
• Current methods for PMI determination face limitations, necessitating novel approaches.
• Vitreous humor offers a valuable biological matrix for postmortem changes analysis.

Purpose of the Study:

• To develop and validate a novel method for PMI estimation using ATR-FTIR spectroscopy and chemometrics.
• To analyze spectral changes in vitreous humor related to PMI.
• To identify key biochemical markers indicative of PMI.

Main Methods:

• Utilized attenuated total reflection-Fourier-transform infrared (ATR-FTIR) spectroscopy on human vitreous humor samples.
• Employed chemometric techniques, including Principal Component Analysis (PCA) and Partial Least Squares Regression (PLSR).
• Analyzed spectral data from 20 forensic cases with known PMI (24.8–97.6 hours) and 10 with unknown PMI.

Main Results:

• Significant correlations were observed between specific vibrational band intensities and PMI, particularly in the carbohydrate/phosphate region.
• PCA revealed distinct spectral evolution over time, linked to carbohydrate/phosphate and protein changes.
• PLSR model achieved a cross-validated RMSE of 15.8 h (R² = 0.53), identifying glycoprotein and phospholipid degradation as key predictors.

Conclusions:

• ATR-FTIR spectroscopy combined with chemometrics provides a promising approach for postmortem interval estimation.
• The model demonstrated good performance on unknown samples, with five out of ten falling within the prediction interval.
• Future research should focus on larger datasets to further refine and validate this methodology.