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.
Highlights
Determining the postmortem interval (PMI) is a task of great importance in daily forensic casework
ATR-FTIR spectroscopy achieved the purpose of estimating PMI and monitoring the postmortem molecular changes using the postmortem arterial blood plasma
By establishing partial least-squares (PLS) models for PMI estimation, the results showed a satisfactory predictive ability on the whole with the best RMSECV of 3.46 h (R2 = 0.95) and RMSE of prediction (RMSEP) of 3.46 h (R2 = 0.94)
Summary
Determining the postmortem interval (PMI) is a task of great importance in daily forensic casework. Progress has been made in exploring new methods focused on the changes in biomolecules or other regular morphometric, physical, and chemical indices[1,2,3,4,5,6,7], excluding some traditional methods to estimate PMI, such as the evaluation of cooling of the body, rigor mortis, stomach contents, livor mortis, and insect growth after death [8, 9] Most of these exploratory methods either require sophisticated procedures or are destructive to the limited forensic sample. Implementing a quick nondestructive and samplesaving method would be highly advantageous for determining the PMI at a crime scene.
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