Forensic Science Wolosin Fingerprints & inhydrin Information :
The reaction of amines with ninhydrin to form the colored reaction product known as Ruhemann's purple was discovered by Siegfried Ruhemann in 1910. An amine is an organic compound that contains a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia. The reaction of amines, amino acids, peptides and related compounds with ninhydrin has found extensive use in the qualitative and quantitative analysis of such compounds in chemistry and biochemistry. However, the value of ninhydrin for the development of latent fingerprints was not realized until 1954 when Odén and von Hofsten suggested its use in criminal investigations. Ninhydrin is now the most widely used method for developing latent fingerprints on paper surfaces.
Ninhydrin, as well as its analogues, reacts with the amino acid compound of the latent fingerprint deposit resulting from eccrine sweat gland secretions to give the dark purple product known as Ruhemann's purple (RP). Eccrine sweat glands are found all over the body but are most abundant on the palms of hands, soles of feet, and forehead. The ninhydrin method is very effective for the development of fingerprints on porous surface such as paper. However, some paper surfaces (certain bank notes, for example) react strongly with the reagent and its use is limited in such cases.
Amino acids are stable compounds that, due to an affinity for cellulose, do not tend to migrate through a dry paper substrate with time. The amino acid content of the eccrine secretion also appears to remain relatively constant. As a result, very old latent prints can be developed with ninhydrin on documents stored under favorable conditions. The development of 30-year -old prints has been recorded.
Figure 1 : The Chemical Composition of a Fingerprint Water (98.5%) Lactic Acid, Fatty Acids, Riboflavin, Pyridoxin, Glucose, Sugars, Organic Material (1%) Ammonia, Urea, Creatine, Fingerprint Residue Albumin, Peptides, Proteins, Isoagglutinogens Solid (1.5%)
Inorganic Material (0.5%) Na+, K+, Ca+2 - -3 Cl , PO4 CO -2, SO -2 3 4 Figure 2 : ame and Chemical Structure of Organic Compounds in a Fingerprint Compound ame Compound Structure Lactic Acid
Fatty Acid
Riboflavin
Pyridoxin
Figure 2 (continued): ame and Chemical Structure of Material in a Fingerprint Compound ame Compound Structure Glucose
Ammonia H 3
Urea
Creatine
Peptides (Polymers of amino acids) Glycine
Proteins Polymers of Amino Acids (Pictured Above) Figure 3: The inhydrin Reaction
The R-CHO notation in the products above is used to represent an aldehyde . An aldehyde has one alkyl group (indicated with R) and a hydrogen bonded to a carbonyl group (C = O ). The alkyl group indicated with the uppercase letter R is an alkane portion of a molecule, with one hydrogen removed to allow the carbon atom to bond to the functional carbonyl group . An alkane is a hydrocarbon (consist entirely of hydrogen and carbon) that only has single bonds .
Questions : 1. How many different types of organic materials are deposited on a surface when you touch it? 2. What is an organic compound? Explain. 3. What is an amine? Where are amines derived from? 4. How many of the organic compounds found in a latent fingerprint are considered amines? Explain why. 5. Where do all of the secretions that make up a latent fingerprint come from? Explain. 6. The structures above contain lines with angles forming a variety of shapes. What do the lines represent? What do the angles between the lines represent? 7. What are the products formed in the Ninhydrin reaction (list the names). 8. Describe what an aldehyde is. 9. Draw a line angle formula for a basic aldehyde.
10. When ninhydrin is applied to a latent fingerprint a chemical reaction occurs as illustrated in Figure 3. Using the information provided in Figure 3 and the structures of the organic compounds found in a latent fingerprint narrow down an eliminate all of the compounds that CAN NOT BE REACTING WITH NINHYDRIN (cross them off in Figure 2). 11. Draw structure(s) of the compound(s) that are left on the list. Based on their structure and the structure of the products in the ninhydrin reaction, is it possible to identify what component of a latent fingerprint is reacting with ninhydrin? Explain. 12. Ninhydrin is a chemical compound applied to a latent fingerprint so that it will become visible to the forensic scientist. Why does the fingerprint become visible? Explain your answer.