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UV-Vis and ATR-FTIR spectroscopic investigations of postmortem interval based on the changes in rabbit plasma
Qi Wang1, Haijun He1, Bing Li1
1Department of Forensic Pathology, College of Forensic Medicine, Xi'an Jiaotong University, Xi'an, Shaanxi, China.
Abstract:
Estimating PMI is of great importance in forensic investigations. Although many methods are used to estimate the PMI, a few investigations focus on the postmortem redistribution. In this study, ultraviolet-visible (UV-Vis) measurement combined with visual inspection indicated a regular diffusion of hemoglobin into plasma after death showing the redistribution of postmortem components in blood. Thereafter, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy was used to confirm the variations caused by this phenomenon. First, full-spectrum partial least-squares (PLS) and genetic algorithm combined with PLS (GA-PLS) models were constructed to predict the PMI. The performance of GA-PLS model was better than that of full-spectrum PLS model based on its root mean square error (RMSE) of cross-validation of 3.46 h (R2 = 0.95) and the RMSE of prediction of 3.46 h (R2 = 0.94). The investigation on the similarity of spectra between blood plasma and formed elements also supported the role of redistribution of components in spectral changes in postmortem plasma. These results demonstrated that ATR-FTIR spectroscopy coupled with the advanced mathematical methods could serve as a convenient and reliable tool to study the redistribution of postmortem components and estimate the PMI.
Insights
This study reveals postmortem redistribution of blood components using spectroscopy. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy accurately estimates postmortem intervals (PMI) by analyzing these changes.
Area of Science:
- Forensic Science
- Biochemistry
- Analytical Chemistry
Background:
- Estimating postmortem intervals (PMI) is crucial in forensic investigations.
- Postmortem redistribution of components within the body is a significant factor influencing PMI estimation.
- Limited research has focused on understanding and quantifying postmortem redistribution in blood.
Purpose of the Study:
- To investigate the phenomenon of postmortem redistribution of blood components.
- To evaluate the utility of attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy for detecting these changes.
- To develop and validate spectroscopic models for accurate PMI estimation.
Main Methods:
- Utilized ultraviolet-visible (UV-Vis) spectroscopy and visual inspection to observe hemoglobin diffusion into plasma.
- Employed ATR-FTIR spectroscopy to analyze spectral variations due to postmortem redistribution.
- Constructed and compared full-spectrum partial least-squares (PLS) and genetic algorithm-PLS (GA-PLS) models for PMI prediction.
Main Results:
- UV-Vis measurements confirmed regular hemoglobin diffusion into plasma, indicating component redistribution.
- ATR-FTIR spectroscopy successfully identified spectral changes associated with postmortem redistribution.
- The GA-PLS model demonstrated superior performance for PMI estimation with a root mean square error (RMSE) of 3.46 h and R² values of 0.95 (cross-validation) and 0.94 (prediction).
Conclusions:
- Postmortem redistribution of blood components significantly impacts spectral characteristics of plasma.
- ATR-FTIR spectroscopy, combined with advanced mathematical modeling (GA-PLS), offers a reliable and convenient method for studying postmortem changes.
- This approach provides a promising tool for accurate postmortem interval estimation in forensic science.
