Sus utilidades en el marco de la Medicina Forense serán dignas de estudio en los años venideros.En vez de la clásica estampa de mojar las yemas de los dedos en la tinta china, me veo recogiendo con la torunda de algodón la grasilla de los dedos y pasándola por un Cromatógrafo de Gases...
A fingermark feast
For instance, it is now generally accepted that traces of explosives and gunshot residue can be detected in latent prints by chemical and spectroscopic techniques. Smokers can be pinpointed by the presence of nicotine and its metabolite cotinine in the prints. Drugs and their metabolites can also travel through the body to emerge in fingermarks to point the finger at people who have taken illicit or prescription drugs.
Researchers at Sheffield Hallam University, UK, have shown that the gender of a person can be predicted with promising accuracy from the presence of peptides and proteins in the fingermarks. They expect that their mass spectrometric technique will be able to "provide information on traits such as nutritional habits, drug use or hormonal status."
Now, a team of researchers in the USA has used a different approach which examines the fatty acids in latent fingermarks. Preliminary results appear to show that ratios of particular fatty acids can discriminate between race and gender. Frank Dorman, Seth Michalski and Robert Shaler from the Forensic Science Program at Pennsylvania State University published details of their findings in the Journal of Forensic Sciences.
There are three glands in the human body which contribute to fingermarks. The eccrine glands, which are found all over the body but are abundant on the palms and soles, secrete a complex mixture of organic and inorganic components as well as a high proportion of water. The apocrine glands in the pubic, anal and mammary regions secrete a mixture of iron, proteins and carbohydrates.
It was the third type of gland that interested the research team. The sebaceous glands secrete an oily mixture known as sebum which consists of triglycerides, wax esters, fatty acids and the hydrocarbon squalene. Although they are absent from the palms and soles, they are prolific on the face and scalp, so it is very easy for sebum to be transferred to the fingers by touch. It is already known that the composition of sebum is affected by diet and gender, so would it be possible to use it to discriminate between male and female suspects?
The team collected fingermarks from a total of 37 people aged 18-21, comprising 16 Caucasian males, 13 Caucasian females, 3 African American and 3 Asian males and 1 African American and 1 Asian female. Since this was a proof-of-principal study, the effects of various factors like diet, washing and the use of personal care products were discounted at this stage for later consideration.
The fingermarks were removed from the glass slides with wipes that were treated with a solvent mixture to remove the organic components. This extract was used for GC/MS analysis, with two added fatty acids as recovery standard and internal standard. The fatty acids present were resolved on a low polarity silarylene phase GC that is similar to 5% phenyl-95% dimethylpolysiloxane.
The fatty acids were identified by reference to a mixture of 37 fatty acid methyl esters and they were measured from the peak areas in the chromatograms. The amounts of each acid present could easily vary from person to person, so their measured ratios against hexadecanoic acid (HDA) were considered rather than their singular concentrations to give a degree of normalisation. This acid was chosen as a reference because it was prominent in every chromatogram.
Gender and race definedHuman sebum is known to secrete the so-called Delta6-fatty acids, which have a double bond in the 6-position, but (Z)-6-octadecenoic acid (ODA) was the only one detected. The absence of others might be due to their low concentrations in the fingermarks or possibly extraction losses or coelution from the GC column.
Other fatty acids were found and the ratios of a number of fatty acids were found to differ between race and gender. For instance, the ratios of ODA to HDA and of octadecenoic acid to HDA differentiated between Caucasian males and females, African American males and Asian males. An unidentified fatty acid which was tentatively identified as a C21-C22 isomer also differentiated between Caucasian males and females, Caucasian males and African American males, as well as Asian males.
Other ratios involving an unidentified C16-C17 fatty acid isomer made the same distinctions. The difficult identifications involved the African American females and Asian females. For some of the aforementioned acids, the ratios for these two groups fell within the range of other groups or the acids were not detected.
So, it might be possible to use fingermarks to gain more information on gender or race. This will provide support to data gleaned from the nuclear or mitochondrial DNA of fingermarks, which can be inconclusive due to low concentrations. However, the fatty acid data must be treated with caution at this stage. A far larger data set must be used along with a comprehensive statistical evaluation of the data. Factors like diet, cosmetic use and individual behaviour could also influence the results.