Estimation of Postmortem Interval in Rat Liver and Spleen Using Fourier Transform Infrared Spectroscopy

The aim of this study was to investigate the changes of Fourier transform infrared (FT-IR) spectra of rat liver and spleen tissues from time zero to 144h postmortem. The absorbance (Ax represents the infrared absorbance at wavenumber xcm-1) ratios of major absorbance bands were examined. A3303/A2925, A1647/A1541 (liver), A1238/A1338, A1153/A1338 (liver), A1080/A1338, and A1030-1050/A1338 (liver) showed a decrease postmortem, whereas the A1396/A1456 ratio (spleen) showed an increase. Furthermore, these absorbance ratios showed a strong linear relationship with increasing time postmortem, and the A1238/A1338 ratio of spleen offered a stronger correlation (R2=0.88) than did the others. A new absorbance band appeared at 1120cm-1 for the liver and spleen at 120h postmortem and another new band appeared at 1170cm-1 for the liver, but the existing absorbance band at 1170cm-1 disappeared in the spleen. Our initial results demonstrate that the quantitative analysis of FT-IR spectrum related to postmortem interval (PMI) shows a strong linear correlation between absorbance ratios and increasing time after death. The FT-IR changes of spectra and absorbance ratios can support further study for estimating short-term and long-term PMI. Upon future validation, FT-IR can offer advantages in combination with established methods to improve PMI estimation.