Differentiation of body fluid stains on fabrics using external reflection Fourier transform infrared spectroscopy (FTIR) and chemometrics

Abstract

Body fluids are evidence of great forensic interest due to the DNA extracted from them, which allows genetic identification of people. This study focuses on the discrimination among semen, vaginal fluid and urine stains (main fluids in sexual crimes) placed on different coloured cotton fabrics by external reflection FTIR spectroscopy combined with chemometrics. Semen-vaginal fluid mixtures and potential false positive substances commonly found in daily life such as soaps, milk, juices and lotions were also studied. Results demonstrated that the IR spectral signature obtained for each body fluid allowed its identification and the correct classification of unknown stains by means of Principal Components Analysis (PCA) and Soft Independent Modelling of Class Analogy (SIMCA). Interestingly, results proved that these IR spectra did not show any bands due to the colour of the fabric and no substance of those present in daily life which were analysed, provided a false positive.