Post-mortem interval estimation in rat liver tissues using attenuated total reflection Fourier transform infrared spectroscopy combined with chemometrics

Post-mortem interval (PMI) estimation is one of the most challenging tasks in forensic practice. Therefore, for PMI estimation, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy coupled with chemometrics was utilized to monitor the biochemical changes in rat liver tissues with increasing PMI at 4 degrees C, 20 degrees C and 30 degrees C. First, principal component analysis (PCA) revealed that the spectral points were distributed from right to left with increasing PMI along PC-1, and this trend was more obvious at the higher temperature (20 degrees C and 30 degrees C) groups. Second, a partial least squares (PLS) regression model was successfully constructed with the 30 degrees C group, with a root mean square error of cross-validation (RMSECV) of 6.9 h (R-2 = 0.92) and a root mean square error of prediction (RMSEP) of 4.6 h (R-2 = 0.96). Lastly, a partial least squares-discriminant analysis (PLS-DA) classification model was established in the 20 degrees C group and demonstrated a complete separation of the spectra among the three classes (0-24 h, 48-96 h and 120-168 h) with 90% accuracy (not-assigned rate: 11%). In conclusion, these results demonstrated that ATR-FTIR spectroscopy combined with chemometrics could serve as a convenient and reliable tool for studying PMI estimation.