Evaluation of reagents for the chemical enhancement of fingermarks on porous surfaces : optimisation and characterisation of the 1,2-indanedione technique
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There is a continual search for new and improved reagents to detect fingermarks on a variety of surfaces. With increased technology and resources the possibilities are continually expanding. 1,2-Indanedione is a relatively new reagent for the development of fingermarks on porous surfaces. Its boundaries have not been completely explored nor has the method of reaction with fingermarks been determined. The initial aim of this project was to investigate the fingermark reagent 1,2-indanedione and determine if it was a viable reagent for routine use in Australia. The secondary aim was to study the reaction that occurs between 1,2-indanedione and amino acids and the subsequent reaction with metal salts to gain further insight into the reaction than has been previously published. Additionally the fingermark reagent 5-methylthioninhydrin, which although had shown good results in detecting fingermarks in the early 1990’s, did not seem to be widely used or studied since its commercial manufacture began. A new reagent for the problematic and increasingly encountered thermal paper, ThermaNin, was also evaluated and compared to other proposed methods for the development of fin germ arks on thermal paper. The investigation of 1,2-indanedione as a fingermark reagent for use in Australia was performed by comparing a number of formulations and development procedures, encompassing all published recommendations as well as some novel approaches. 1,2-indanedione formulations were compared with respect to initial colour, fluorescence, concentration of the reagent, acetic acid concentration and the effect of different carrier solvents. Numerous development conditions were also investigated, including a conventional oven, a heat press and humidity. Further enhancement using metal salts and liquid nitrogen was also evaluated. The heat press set at 165°C for 10 s proved to give the best initial colour and most intense luminescence. Secondary metal salt treatment improved initial colour and luminescence and was found to provide consistent results despite different environmental conditions. It is for this reason that it is recommended that metal salt treatment consistently be performed after treatment with 1,2-indanedione or included in the formulation of 1,2-indanedione. The Polilight, the VSC 2000, and the Condor Chemical Imaging macroscope have been used to detect fingermarks developed with 1,2-indanedione on a variety of high- and low- quality porous and semi-porous surfaces with impressive results overall. Laboratory and field tests were conducted to compare 1,2-indanedione with DFO and ninhydrin as well as to investigate the position of 1,2-indanedione in the sequence of reagents for fingermark detection on porous surfaces. Overall 1,2-indanedione proved to be a viable alternative to tradition methods for the detection of fingermarks on porous surfaces, with more fingermarks being developed using this reagent on real samples than both DFO and ninhydrin and a combination of the two reagents. The isolation of a single pure product from the reaction of 1,2-indanedione with several different amino acids was not achieved. The study was able to establish that 1,2-indanedione reacts differently with different amino acids with some reactions, such as those with alanine and cysteine, following a similar pathway. A study performed by nuclear magnetic resonance spectroscopy and colour reactions showed that increasing the content of water in the reaction retarded the kinetics of the reaction and thus it is possible that the concentration of water in the reaction may influence the path the reaction takes. Solid state nuclear magnetic resonance spectroscopy indicated that the product of the reaction is ionic, which may help explain the problems encountered on separation and isolation of the product. Thermal and elemental analysis provided some information on the by-products released by the reaction, whilst mass spectroscopy provided information on the possible pathway of the reaction. The results of this study support the proposal made by Petrovskaia (1999) that the main reaction product of 1,2-indanedione and amino acids is a Ruhemann’s purple type product with a molecular mass of 275. A study of the reaction between metal salts and the 1,2-indanedione/amino acid product was also performed on a crude reaction mixture. This was due to the inability to provide a pure starting materials as well as the unsuccessful separation of the complex by thin layer chromatography. The information gained; however, from a study via nuclear magnetic resonance spectroscopy, mass spectroscopy, UV-visible spectroscopy and infrared spectroscopy indicates that two 1,2-indanedione molecules react with the nitrogen atom in the amino acid forming a tridentate ligand which then complexes with the metal ion. The evaluation of 5-methylthioninhydrin found that the reagent is superior to ninhydrin; however, 1,2-indanedione exhibits much stronger luminescence when used to treat latent fingermarks. The high cost of the reagent accompanied by the fact that 1,2-indanedione was found to be a superior reagent and is already in use in many laboratories precludes a recommendation for its routine use. ThermaNin was evaluated against other recommended reagents for the development of fingermarks on thermal paper. ThermaNin itself was found to be extremely sensitive to water and humidity and must be made fresh before its use due to poor stability. Once again a 1,2-indanedione formulation, albeit without acetic acid, was found to be the optimal method to detect fingermarks on this particular surface.
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