Main content area

Measuring the water content in freshly-deposited fingermarks

Keisar, Or, Cohen, Yair, Finkelstein, Yacov, Kostirya, Natalie, Ben-David, Roey, Danon, Albert, Porat, Ze’ev, Almog, Joseph
Forensic science international 2019 v.294 pp. 204-210
evaporation, quartz crystal microbalance, sebum, spectroscopy, water content
The literature view regarding the composition of deposited fingermarks has long been that the average water content is in the range of 98–99wt.%. This value has recently been challenged by Kent, claiming that it should be 20wt.% at most. Herein we have measured the weight percentage of water content in freshly-deposited fingermarks, with and without hand pre-washing. Two complementary techniques were utilized for the measurements, namely quartz crystal microbalance (QCM) for determining the relative mass-loss and its rate at ca. 37°C, and temperature-programmed desorption-mass spectrometry (TPD-MS) for establishing that the mass loss arises solely from the complete evaporation of all the water content in the fingermarks (done with hand pre-washing only). Unlike the traditional narrow-range values of 98–99% and the limiting value of 20wt.% suggested by Kent, our measurements indicate the occurrence of a broad 20–70% water content. Higher contents of water in fingermarks were found post hand pre-washing, most probably due to removal of the sebum from the fingertips, but none of the results exceeded 90%.