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The following paper was submitted for publication by its author, Dr. O. P. Jasuja. Any comments on the article by readers may be made directly to the author.
JASUJA, O.P.* and UKPERE, M.I. Department of Forensic Science, Punjabi University, Patiala –147 002 India Atul K. Singla Forensic Science Consultant Gurbax Colony, Patiala Corresponding author:
Ninhydrin is one of the simplest and a very commonly used reagent for development of latent fingerprints on documents and porous surfaces of similar nature. Various methods like spraying, dipping and swabbing etc. are used to apply ninhydrin to the surface but the background coloration, ink bleeding and flammability of solvents used are reported as measure drawbacks of this method. In the present study, the sandwich method, mentioned in Scott's fingerprint mechanics (1), deals with the development of latent fingerprints on paper. Various conditions affecting the development of prints as temperature, concentration of reagent, type of paper etc. have are discussed. INTRODUCTION: There are a large number of methods to visualize latent fingerprints. These methods vary from the very simple powder method and the iodine method to the most modern and expensive methods using the argon ion laser. Each method has its own advantages and limitations. None of these methods can be used for all and every type of surfaces bearing the latent fingerprints. One of the methods, a very simple and commonly used one, is the ninhydrin method. This method involves the reaction of ninhydrin with amino acids present in the sweat making latent fingerprints. The ninhydrin solution is applied directly on the porous surface of the paper by spraying, by swabbing the solution on the surface, or by dipping the paper in a ninhydrin solution, followed by optionally heating it at around 100 C temperature. The ridges appear in purple color and remain unfaded on the document for a considerably long period. But, this method has certain drawbacks as the background coloration of the paper may cause a low contrast of ridges with background. If ink writings are present on the surface of the paper, the ink may dissolve due the solvent used causing ink bleeding. As these solvents are also flammable, they may prove hazardous (2,3). To avoid some of these limitations, the reagent has been available in different forms as NFN (nonflammable ninhydrin)preparations (2,4-5), but these preparations are comparatively very costly and also hazardous to the environment. With spraying and dipping, the vapours of the solvent and crystals of ninhydrin may enter the human body causing ill health. Olsen(1) in his book titled Scott's Fingerprint Mechanics described dry ninhydrin methods. One of these methods involves sandwiching of the document having latent fingerprints between papers saturated with the reagent. But he has not recommended this method for general use, nor has he mentioned the reasons for this. Moreover, his method has not been described in detail. It is for that reason that the authors have initiated work on this method so as to study it in detail and to standardize the method so that it can be used more widely as a general method for visualizing latent fingerprints. Latent fingerprints were obtained from volunteers, including the authors, at various intervals by requesting them to impress a palmprint on paper with such pressure as one might expect when an object is handled in ordinary routine. The latent fingerprints thus obtained were dated and other details like name, age, sex and address were recorded for further reference. These latent fingerprints were obtained on different type of the paper viz., cyclostyling paper, bond paper, newspaper, glossed paper. Some of the samples were obtained on these papers where the writings written in Ball point pen and roller pen inks were already present. The paper used for impregnating with ninhydrin was cycloctyling paper and bond paper. The reagent was placed in a dish; the paper to be impregnated was dipped in the reagent for about 30 seconds so that the whole paper became saturated without becoming torn while removing it from the dish. The paper was then allowed to dry in the open. In this way, a number of sheets was prepared as and when the inquiry required it. On every use, the reagent was prepared afresh. After drying, these sheets became the "Sandwiching" sheets. The document bearing latent prints was then sandwiched between two sheets for reaction at different temperatures such as, at room temperature, and at 50, 80 and 100 C in a hot air oven. Another method used for heating the document was passing a hot iron over the sandwich papers.
In the left photograph, the latent fingerprints were developed by conventional as well as the suggested method.
RESULTS AND DISCUSSION: In using the sandwich method of applying ninhydrin, latent fingerprints were visualized under different conditions as age of the latent prints, concentration of reagent, type of paper, temperature for treatment and time taken to complete the reaction. Results are presented as following: The latent prints were impressed on various type of the papers and treated with the reagent by sandwich method, first on same day, then on the 10th day, the 30th day, and after three months of storage in an envelop. All the samples could by visualized with this method without any significant difference. The concentration of the reagent was found to be important in this method. Reagents of three concentrations – that is 0.5, 1.0 and 1.5% – of ninhydrin were prepared. With the 0.5% reagent, three month-old prints could not be visualized while reagents with other two concentrations were able to make the prints visible. When using the 1% reagent, prints were lighter than those as compared to 1.5% reagent when the fingerprints were treated for the same length of time. It was also observed that prints could be made visible in less time with 1.5% reagent when treated at room temperature. All the experiments were conducted during summer season when the room temperature was around 38 C in this part of the globe (India). It was observed that, at room temperature, the prints were made visible in about 12 hours when using 1.0 and 1.5% reagents. When the sandwiched document was heated at 80 and 100 C temperature in a hot air oven, prints were developed in 30 minutes. When the document was kept sandwiched for two hours at room temperature before having a hot iron passed over the sandwich, the fingerprints became visible almost immediately. The same immediate result was obtained when the document was sandwiched and then immediately covered with the hot iron. It was interesting to note that there was no ink bleeding when the document treated had ink writings on it; no background coloration was developed on the document either. Various solvents for dissolving the ninhydrin to prepare the reagent has been suggested by various workers (2,7-10), namely, Acetone, methanol,ethanol, ethyl acetate, ethyl ether. The pH of the reagent was adjusted to 4 by adding few drops of the glacial acetic acid. It was found that all these reagents were able to develop the latent fingerprints on the paper without any ink bleeding and background coloration. But the reagent prepared with Acetone and glacial acetic acid was observed to be the most suitable one insofar as the time required to develop the prints and temperature required. Though some variation may also be due to the variable amount of the amino acids present in the latent fingerprints, it was not possible to control for this factor. The prints were also developed successfully on all types of paper used in the present study, though it was observed that the type of paper used for making the sandwich sheets affected the results. When comparatively more fibrous paper, less filled with fillers, such as bond paper was used, development of prints took less time. This may be due to the reason that more reagent was being soaked into the paper and thus more reagent would be available to produce a reaction with the amino acids of the latent prints. It was also observed that the sandwich sheets could be reused for developing latent prints if the reaction was carried out without heating in an oven or without the use of a hot iron. Though the time taken in this process was quite high in comparison to using a heating method, the operating costs were significantly reduced. If quick results are required, the application of heat by a hot iron should be considered. CONCLUSION: The sandwich method described in the present study was found to be very simple, non destructive, inexpensive and harmless. It is suggested that sandwich sheets of various sizes can be prepared commercially and supplied to latent fingerprint laboratories for its use on the spot. Further observations will be made in a follow-up study with regard to the usable shelf life of sandwich sheets. Results of that study will be reported upon its completion. REFERENCES:
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