Analysis of human bodily fluids on superabsorbent pads by ATR-FTIR

Superabsorbent pads are composed of different layers with different grades of absorbent capacity, being the lower one the most absorbent layer. Due to their complexity, the analysis of bodily fluids on superabsorbent pads is certainly difficult. In this study, semen, vaginal fluid and urine stains placed on superabsorbent pads including sanitary napkins, panty-liners and diapers were non-destructively detected by Attenuated Total Reflectance (ATR) Fourier Transform Infrared spectroscopy (FTIR). In spite of the higher absorbent capacity of the lower layers, this technique was able to detect the three fluids on the upper layer of all pads, showing that bodily fluids are distributed within all layers. Additionally, mixtures of these bodily fluids prepared on superabsorbent pads and cotton were studied, since real forensic investigations involving sexual abuse cases usually deal with mixtures of these fluids. Due to their IR marked protein region (1800-1480cm^-1), semen and vaginal fluid were easily distinguished from urine. However, since semen and vaginal fluid have both a high protein composition, that region of their IR signatures were quite similar, except for slight visual differences, that should be further analysed. Therefore, we propose ATR-FTIR as a suitable, presumptive, non-destructive and rapid approach to detect stains of human bodily fluids on the upper layer of superabsorbent pads from sexual crimes.