Methods of sampling and visualisation fingerprints Identification of blood stains

Transcription

1 Methods of sampling and visualisation fingerprints Identification of blood stains The collection and analysis of fingerprints is engaged in the sector forensic technique called fingerprinting. This field of forensic science examines fingerprints papillary lines. In addition to providing investigative stop and search is the main objektive of fingerprints investigation to determine the identity of the person who left an imprint. Given that the course of papillary lines are unique for each person (like DNA), we can say that most likely that there are not two people who have all identical fingerprints. Each ridge is a raised skin layer, which leads to a passageway leading into the sweat glands. Touch of papillary lines transferred dust particles and other impurities with sweat, creating a forensic trail - fingerprints. Visualisation of the fingerprint There are several basic methods, which are commonly used in forensic practice. The most common procedure for visualisation (finding) is the use of the fingerprint. Fingerprint powders. Professional products vary considerably and depends primarily on environmental conditions (temperature, humidity, physical substrate fingerprint etc.) And the age of the fingerprint. For the purposes of this exercise, we will use two types of fingerprint powders - magnetic iron powder and carbonized carbon (graphite powder). For latent fingerprints or fingerprints on objects and locations for which the powder methods we use inappropriate methods of chemical visualisation, based on the chemical reaction between the components fingerprint (especially perspiration and its components) and chemical agent. 1.1 Powder methods These methods are particularly suitable for fingerprints left on matte surfaces such as glass, plastic and other synthetic materials or ceramic. The principle of this method is the adsorption on the powder material constituents fingerprint. Fingerprinting powders can be roughly divided into magnetic (e.g. modified or pure iron powder), or non-magnetic (e.g., aluminum powder, copper powder and said graphite (or fine activated charcoal). The advantage of magnetic powders is that they can be applied either directly via a permanent magnet or magnet excess powder can capture and remove. The acquired fingerprint traces are then either photographed (depending on the surface on which they are) or is transmitted so. dactyloscopic foil and then further processing (photographing, scanning, etc.). dactyloscopic foil there is also a range and depends, and their choice depends on the particular case of application. Generally, the use of black or white film on the basis of gelatin, which is the fingerprint after visualization transferred. for our purposes as film for transmitting fingerprint white adhesive tape or adhesive film.

2 1.2 Chemical methods A sweat transferred from the ridge, leaving a fingerprint contains many chemicals that can interact with reagents. Among the chemicals that are used to improve the visibility of fingerprints include in particular ninhydrin, iodine, silver nitrate or cyanoacrylic acid esters (ie. Cyanoacrylates). Iodine as such it falls on the boundary of physical and chemical methods, since the detection principle is based on the iodine sublimation and capture of the particles on the fingerprint. Other methods are then used in chemical reactions that lead to visible changes (highlight color), but can often cause damage or destruction of the material or article, on which the imprint is located. Ninhydrin reagent works by reaction of ninhydrin with amino acids contained in the sweat (Fig. 1) which adheres when touching the object. Fig. 1: Ninhydrin reaction with an aminoacid Ninhydrin is commonly used as a reagent to detect the amino acid acts as an oxidizing agent and the reaction first occurs decarboxylation of the corresponding amino acid (e.g. alanine, which in Fig. 1, R = CH 3 ) and the resulting amine then undergoes oxidative deamination. Ninhydrin during the reaction is converted to a colored product. The reaction can take place in neutral (Fig. 1.1) and an acidic environment (Fig. 1.2) and the two products then have a slightly different color. Iodine is used as a powder or fine crystals and is usually either a heat release on the spot (special heating tube hands), or in the steam container in the laboratory. Silver nitrate is used as a reagent for the detection of halide ions and as such, may react with chloride ions present in perspiration. A white precipitate which is the effect of

3 radiation (conventional polychromatic light or UV radiation) is converted to elemental silver and thereby highlights fingerprint coloring (blackening). Cyanoacrylic esters, which are used as instant adhesives, have also found applications in forensic chemistry, especially when detecting so. Latent fingerprints. By heating cyanoacrylates will develop vapors to fingerprint deposited as polycyanoacrylates (Fig. 2). It is visible to the naked eye, but you can use an encore fluorescent or non-fluorescent dye, which fingerprint accentuated and visible. Thus, the detected fingerprints can also be easily transferred and further processed. Fig. 2: A general scheme of methyl cyanoacrylate polymerization (Nu - is a nucleofil, e.g. OH - in the case of fingerprints) Finding and the visualisation of the fingerprint Task: Make a series of practices leading to the visibility of fingerprints on submitted articles. Tools: a set of fine brushes, plastic or glass petri dishes, sealable transparent plastic container (developer chamber for cyanoacrylate or iodine reaction), dispenser, beakers, graduated cylinder, plastic containers, glass slides, scales and weighing boating or paper, drying, white paper. Chemicals: ninhydrin, ethanol, methanol, acetic acid, iodine, cyanoacrylate (e.g. glue), silver nitrate, iron powder, activated carbon or graphite powder, water. Reagent Preparation: 1) Ninhydrin - 50 mg ninhydrin was weighed and transferred to a plastic container and 25 ml of ethanol and 75 ml acetic acid (99%) was added. The reconstituted solution is transferred to the aerosol. 2.) The Silver nitrate - prepare a methanolic solution of silver nitrate by dissolving 500 mg of AgNO 3 in 25 ml of methanol. Store the solution in brown bottles protected from direct light. 3.) Iodine and cyanoacrylate - use iodine powder or fine crystals, which is placed directly into the developing chamber. If we cyanoacrylate small amount (a few drops) glue eg. A piece of aluminum foil and place in the developing chamber. In preparing these agents and the

4 subsequent work with them Always wear gloves and a hood! Particular attention to the glue, because even a small amount dries quickly and will bond most materials. 4.) The materials such as iron powder or graphite powder used directly from storage bottles and hood (gloves and preferably with a cloak and hood, because inhaling dust is harmful and irritating). Procedure: The submitted materials that were applied fingerprints (or yourself fingerprints apply - according to the tutor), through a detailed investigation using these reagents. Glass, ceramic or plastic materials are suitable as methods of chemical and pulverized, while fingerprints e.g. on paper can be made more visible by means of chemical agents - silver nitrate and ninhydrin. The general process is as follows: Using the gloves (to avoid damage or the formation of additional fingerprints) examine subjects, divide it into plastic, metal, glass or ceramic (group 1) and paper (or other absorbent materials, group 2). Always prepared from each material more samples to be tested, all techniques. Fingerprints on the materials from the group and underwent first daktyloskopickému exploration Powder and record any changes. We work very carefully and powder rather "sprinkle" than we paint brush. At too rapid deposition will wipe fingerprints or to detect only parts thereof. The same materials then put into the developing chamber, so that their surfaces do not touch the walls of the vessel. Put the reagent and leave minutes to develop. If the replaced developing too slowly and there is no visualisation of fingerprints, pan may be slightly warm (about C), e.g. a water bath. Visualisation of fingerprint appears as a white coating in the case of cyanoacrylate or brownish imprints in the case of iodine). Materials from group B (mainly paper) is placed on a hard surface (eg. Plastic or glass) in the hood and uniformly applied agents using a nebuliser. Allow to dry reagents or carefully transfer the examined sample in the oven and dry (at about C). Unless the tint, it is necessary to repeat drying. In the case of silver nitrate applied to the white base is needed to sample a few minutes to let the light or the UV lamp used in place to avoid elemental silver and darkening fingerprint. Evaluation: Try to find the most suitable reagent for the material presented. The revealed fingerprints record (eg. Photographically or scanning through the transparent film).

5 Screening test for the presence of blood Screening test is an essential part of the previous own analysis. It is necessary to confirm or refute whether this is indeed a suspect sample, because the analysis is often costly. Usually, when possible, this qualitative analysis performed directly on the spot, to avoid confusion of samples. It is not always possible, however, e.g. due to the quantity of the sample, its localization (hard surface fabric or other material capable of sorption agents) and the like. Of the many types of qualitative analysis of blood traces are given two most common and simplest. 1. The reagent based on luminol Luminol (or 5-amino-2,3-dihydro-phthalazine-1,4-dione) is a luminophore, while the oxidation in basic medium catalyzed chemiluminescence occurs, which is characterized by a light blue color. Catalysis of the oxidation-reduction reaction is ensured precisely blood stain - hemoglobin, which is present in blood and blood test traces Reference assisted luminol has its limitations. Addition of hemoglobin may also catalyze said reaction, some transition metal ions, particularly Cu2 + and the Co2 + or hypochlorite anions are often present in disinfectants (e.g. SAVO). The basic environment can be arranged in various ways, the optimum ph is in the range 9 to 10 Selection and use of buffer depends on many factors, in particular, neither of buffer components did not interact with the sample or its parts. Luminol is a substance, however, very poorly soluble in aqueous media and the their influence plays not only the ph but also the ionic strength of the solution. 2.) Reagent based on 3,3 ', 5,5'-tertramethylbenzidine (TMB) Benzidine derivatives with hydrogen peroxide or another oxidizing agent to oxidize the products of a blue color, called. Benzidine blue. The reaction is catalyzed by either enzymatically using peroxidase (POD) or substances which contain in their molecule porphyrin heme central iron atom, eg. Blood pigment hemoglobin. For the purpose of qualitative orientation analysis using 3,3 ', 5,5'-tertramethylbenzidine (TMB) in acetic acid or an acidic buffer.

6 Task: Demonstrate the presence of blood stains on the submitted sample Materials: plastic containers, beakers, dispenser, test tubes, pumps, scales, micropipettes. Chemicals: hydrogen peroxide (30%, v / v) acetic acid, 3,3 ', 5,5'-tertramethylbenzidin (TMB), luminol, sodium carbonate, sodium perborate, water, dimethylsulfoxide (DMSO). Preparation of reagents and procedure: 1) Luminol Weigh 100 mg of luminol in 50 ml beaker and add 9 ml of deionized water. To the resulting suspension, add 0.5 g of anhydrous sodium carbonate (Na2CO3) and mix until dissolved (in the event that all of luminol dissolved again add smaller amounts of carbonate). In microtube Weigh 0.5 g of sodium perborate and bring the volume to 1 ml with deionized water and thoroughly ropzusťte using an ultrasonic bath. Before using reagents for the analysis of both the solution was decanted and apply either to the solution of which presuppose that contains blood or blood-contaminated Spray on surface (clothing, paper, etc.). Positive test shows visible blue fluorescence, which must be seen in the dark. 2) TMB Weigh 5 mg of tetramethylbenzidine (TMB) and dissolve in 5 ml of dimethylsulfoxide (DMSO). Prepare 50 ml of the basic solution of glacial acetic acid and 0.1 mol.dm -3. After mixing 1 ml of TMB-dissolved in DMSO with 9 ml of acetic acid solution and mix well. Before analyzing the prepared mixture, add 5 µl of 30% hydrogen peroxide and mix thoroughly. Births reagent apply similarly luminol (see above), a positive test is reflected clearly in blue (green) staining.