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METHODS FOR FIXING CONSTITUENTS OF HUMAN SWEAT FOR DEVELOPING LATENT FINGERPRINTS

GS Sodhi*, Jasjeet Kaur**

*Department of Chemistry, SGTB Khalsa College, University of Delhi, Delhi 110007. **College of Applied Sciences for Women (University of Delhi), Delhi 110095.

Two formulations based, respectively, on eosin-blue dye and erythrosin-B dye, have been prepared for detecting latent fingerprints. The formulations are non-toxic and cost-effective. They can develop fingerprints on a wide range of surfaces by fixing the inorganic ions and proteins of the human sweat deposit.

INTRODUCTION

A latent fingerprint is formed when the sweat pores of the papillary ridges leave a deposit of prespiration on a surface with which the finger has been brought into contact. [1] Human body possesses the following three types of glands - viz. eccrine, apocrine and sebaceous, the secretions of which contribute to a fingerprint deposit. [2]

Eccrine glands are widely distributed throughout the body and are particularly numerous on the palms of hands and the soles of feet. Chemicals secreted by these glands result from material in the blood stream crossing the gland barrier. Besides water content, eccrine sweat contains upto 1% of the other substances of which inorganic salts constitute about one-half. [3] Amongst these, sodium and chloride are the most abundant ions, representing nearly 90 mM proportion. Potassium (5 mM), magnesium (0.4 mM), calcium (0.5 mM), sulphate (0.4 mM) and phosphate are also present, together with traces of iron, copper, manganese, iodide, bromide and fluoride. The other half is constituted by organic derivatives like, amino acids, urea, creatinine, choline, lactic acid, sugars, uric acid and fatty acids. [4] The constituents of the sweat may be selectively fixed by different chemical reagents so as to make the latent finger prints visible. [5]

Various chemical reagents, such as, silver nitrate, iodine and ninhydrin are available for rendering visibility to latent prints. These reagents react with sodium chloride, fatty acid and amino acid contents, respectively, present in the sweat. The powder technique of developing latent prints is the most common and most widely used. [6]

Ninhydrin reagent may be used for developing prints as old as 15 years. However, the disadvantage of this technique is that ninhydrin has to be dissolved in an organic medium. Since nowadays oil based inks are more often used, spraying an organic solvent on a document may despoil the calligraphic script. Further, ninhydrin gives a background reaction with melamine coated currency notes and its use is therefore precluded. [7] The prints obtained by iodine fuming are not permanent and tend to fade out with time, unless fixed. The toxicity of iodine also limits the use of this method. Silver nitrate has been used to reveal fingerprints on non-porous material and paper. The effectiveness of silver nitrate results from its reaction with chlorides present in sweat by forming silver chloride which rapidly turns black on exposure to light.

In an earlier communication, [8] we devised a technique wherein calcium content of sweat was fixed with the help of a phase transfer catalyst. Thesuccessful development of fingermarks prompted us to try out the technique using a similar catalyst and eosin-blue dye. In addition, powder formulations based on erythrosin-B dye has been prepared. The formulations use cheap, insoluble, salts as adhesive materials in place of costly, resinous polymers, which most conventional powders incorporate.

The structures of eosin-blue and erythrosin-B are depicted in Figs. 1 and 2, respectively.

Experimental

The disodium salts of eosin-blue and erythrosin-B and t-tetrabutylammonium iodide were purchased from Aldrich Chemical Co., USA and used without further purification.

Fig 1: Structure of eosin-blue.
Fig 2: Structure of erythrosin-B.
Fig 1
Fig 2
Structure of eosin-blue.
Structure of erythrosin-B.

 

Preparation of eosin-blue based spray formulation

An aqueous solution containing 0.38-0.40% disodium eosin-blue and 0.25-0.30% t-tetrabutylammonium iodide in distilled water was placed in a petridish. Small pieces (about 2" x 2") of paper, lamination sheet, polythene or plastic surface bearing sample latent prints, were immersed in the test solution for 2-3 minutes. The surface was then dipped in distilled water and allowed to dry. For larger objects such as polythene bottles, bakelite switches, glassware and stainless steel utensils, the test solution was sprayed onto the surface containing the fingerprint impression. After 2-3 minutes, the surface was washed under a gentle stream of distilled water and dried.

Preparation of erythrosin-B based powder formulation

The fingerprint powder contained 62-65% by weight of erythrosin-B dye and 35-38% by weight of an adhesive material like calcium fluoride, calcium carbonate, barium sulphate or zinc carbonate. Weighed quantity of disodium erythrosin-B was dissolved in a minimum quantity of water. It was poured over weighed amount of the adhesive material. The mixture was stirred vigorously and then allowed to dry at room temperature for 4-7 days. For every 1 g of the material, 0.02 g talc was added. The dried mass was ground with a mortar and pestle and the fine powder was stored in a tightly stoppered vessel.

The powder was applied to the surface impinged with the latent fingermark with a camel hair brush. The excess powder was dusted off. The prints were then photographed.

RESULTS

Two reagents were used for detecting latent fingerprints on various surfaces.

1. Eosin-blue in spray form

2. Erythrosin-B in powder form

These reagents offered many advantages. They are absolutely non-toxic and are being used in cosmetics and as dyes. [9,10] They are fluorescent in nature and, therefore, can detect weak prints under ultraviolet light. Moreover, they are known to form coloured complexes with inorganic ions and proteins present in human sweat.

Latent fingerprints developed by using the aforementioned two formulations are sharp, clear and visible to the naked eye. They persist over prolonged periods of time.

Good quality prints have been lifted from lamination sheets. Thus, the present method may be extended for obtaining fingerprints from laminated documents, such as archeological scripts, certificates, driving licences and identity cards. Prints may also be developed on polythene bags - commonly used for carrying household items, and polythene bottles - commonly used for storing household items. Though neutron activation analysis has been employed to render visibility to extinct palm prints on polythene, [2] but this technique has a host of limitations, including long processing time, high cost and non-availability in many laboratories. However, the present method takes just 2-3 minutes to render visibility to extinct prints on polythene surface and can be used in all forensic science laboratories.

Other surfaces on which an unscrupulous element is likely to leave his fingerprint impressions include glassware, steel handles and knobs, bakelite switches and switchboards and plastic table mats. The present technique of fingerprint detection gives good results on all these surfaces.

Some sample prints developed by eosin-blue spray and erythrosin-B powders are shown in Figs. 3 and 4, respectively.

Fig 3 : Sample prints developed by using eosin-blue spray formulation.(Paper)
Fig 3: Sample prints developed by using eosin-blue spray formulation. (Porcelain)
Fig 3: Sample prints developed by using eosin-blue spray formulation. (Plastic)
Fig 3
Sample prints developed by using eosin-blue spray formulation.

 

Fig 4: Sample prints developed by using erythrosin-B powder formulations.(Bakelite)
Fig 4: Sample prints developed by using erythrosin-B powder formulations(Glass)
Fig 4: Sample prints developed by using erythrosin-B powder formulations (Polythene)
Fig 4
Sample prints developed by using erythrosin-B powder formulations.

 

DISCUSSION

Eosin-blue spray

Although mental ions present in human sweat form a number of coloured complexes with xanthen dyes, but attempts to fix these ions for developing fingermarks have been largely unsuccessful. The reason being that metal ions, after being deposited along the ridges, are converted into insoluble salts. Further reactions of these insoluble salts - if at all they occur - would be extremely slow to have a practical utility. On spraying with an acid buffer, the ions are, no doubt, resolubilized, but they spread out of the ridges, giving a diffused impression.

To overcome this problem we used a phase transfer catalyst which accelerates the reaction between insoluble cations and an aqueous solution of a complexing agent. A phase transfer catalyst is concerned with the conversions of chemical species present in different phases. [11] We used t-tetrabutylammonium iodide as the phase transfer catalyst and a solution of disodium salt of eosin-blue as a complexing agent. t-Tetrabutylammonium iodide acts not only as a catalyst, but also as a precipitating reagent. A red coloured complex becomes deposited along the ridges within 2-3 minutes, making the latent prints visible. In the absence of the catalyst the reaction is so slow that by the time the complex begins to deposit, the ridges get mingled-up.

Erythrosin-B powders

The application of finely divided materials and the subsequent removal of the excess powder by brushing, blowing or tapping has been the universal method of intensifying fingerprints on non-absorbent surfaces since the early days of fingerprint technology. [2] The technique relies on the mechanical adherence of fingerprint powder to the moisture and oily components of skin ridge deposits. Regular fingerprint powders consist of a resinous polymer for adhesion and a colorant for contrast. Over the years it became evident that powders containing toxic, inorganic salts posed a health hazard. [12] As a result, the organic based fingerprint powders became more popular. [13]

The powder formulations based on erythrosin-B dye are non-toxic and fluorescent in nature. Most of the conventional dusting powders use costly polymeric adhesives like silica gel, starch or rosin. We have used the following insoluble salts for this purpose: calcium fluoride, calcium carbonate, barium carbonate and zinc carbonate. These salts are quite cheap and, therefore, the dusting formulations being reported in this communication, are cost-effective.

ACKNOWLEDGEMENT

The authors are grateful to ‘RD Birla Smarak Kosh’, Medical Research Centre, Bombay Hospital Trust, Mumbai, India, for financial assistance.

REFERENCES

    1. Thomas GL. The physics of fingerprints and their detection. Journal of Physics E 1978; 11 : 722-31.
    2. Knowles AM. Aspects of physicochemical methods for the detection of latent fingerprints. Journal of Physics E 1978; 11 : 712-21.
    3. Kuno Y. Human Perspiration, Thomas, Springfield. 1956.
    4. Scruton B, Robins BW, Blott BH. The deposition of fingerprint films. Journal of Physics D 1975; 8 : 714-23.
    5. Nath S. Fingerprint Identification, Spectra of Anthropological Progress, Delhi. 1984; 75-96.
    6. Chatterjee SK. Finger, palm and sole prints, 2nd Edn., Kosa Publishers, Calcutta. 1967; 88-103.
    7. Lennard CJ, Margot PA, Stoilovic M, Warrener RN. Synthesis of ninhydrin analogues and their application to fingerprint development : Preliminary results. Journal of Forensic Science Society 1986; 26 : 323-28.
    8. Kaur J, Sodhi GS, Nath S. The application of phase transfer catalysis to fingerprint detection. Science and Justice 1996; 36 : 267-69.
    9. Merck Index No. 3554, Merck and Co., Inc., New Jerse, 11th edition. 1989; 564.
    10. Dictionary of Analytical Reagents No. E-21, Chapman and Hall, London. 1993; 474.
    11. Dehmlow EW, Dehmlow SS. Phase Transfer Catalysis, 3rd Edn., VCH publishers, Inc. New   York. 1983; 1-27.
    12. Lee HC, Gaensslen RE. In : Advances in Fingerprint Technology, Lee HC and Gaensslen   RE (Eds.), Elsevier, New York. 1991; 59-101.
    13. Kerr FM, Haque F, Westland AD. Organic based powders for fingerprint detection on   smooth surfaces. Can Soc Forens Sci 1983; 16 : 140-42.

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