Analysis of the ex-vivo transformation of semen, saliva and urine as they dry out using ATR-FTIR spectroscopy and chemometric approach

The ex-vivo biochemical changes of different body fluids also referred as aging of fluids are potential marker for the estimation of Time since deposition. Infrared spectroscopy has great potential to reveal the biochemical changes in these fluids as previously reported by several researchers. The present study is focused to analyze the spectral changes in the ATR-FTIR spectra of three body fluids, commonly encountered in violent crimes i.e., semen, saliva, and urine as they dry out. The whole analytical timeline is divided into relatively slow phase I due to the major contribution of water and faster Phase II due to significant evaporation of water. Two spectral regions i.e., 3200-3400 cm(-1) and 1600-1000 cm(-1) are the major contributors to the spectra of these fluids. Several peaks in the spectral region between 1600 and 1000 cm(-1) showed highly significant regression equation with a higher coefficient of determination values in Phase II in contrary to the slow passing Phase I. Principal component and Partial Least Square Regression analysis are the two chemometric tool used to estimate the time since deposition of the aforesaid fluids as they dry out. Additionally, this study potentially estimates the time since deposition of an offense from the aging of the body fluids at the early stages after its occurrence as well as works as the precursor for further studies on an extended timeframe.

Automated summary

The study focuses on analyzing the spectral changes in body fluids (semen, saliva, and urine) as they dry out using ATR-FTIR spectroscopy to estimate the time since deposition. Two phases are identified in the analytical timeline: a slow phase I with significant water contribution and a faster phase II with substantial water evaporation. Peaks in the spectral region between 1600 and 1000 cm(-1) showed highly significant regression equations in Phase II, compared to Phase I. Principal component analysis and Partial Least Square Regression were used as chemometric tools to estimate the time since deposition.