CHAPTER-V SUMMARY AND CONCLUSIONS

CHAPTER-V SUMMARY AND CONCLUSIONS

SUMMARY AND CONCLUSIONS The present work has been devoted to the differentiation and characterization of inkjet printed documents. All the four primary inks used in printers are the matrix of interest for analysis in this study. The coloured sample printouts were printed in Cyan, Magenta, Yellow and Black colour ink from inkjet printers of the four leading manufacturers viz HP, Brother, Canon and Epson. The entire work carried out is organized in four chapters excluding this conclusion chapter which comprises the brief summary of the work carried out and use of the applications of the techniques investigated described below briefly (VSC, FT-IR, SEM-EDX, HPTLC, UV-Vis, ICP-MS) in printed document examination. The whole work was carried out by keeping in consideration availability of instruments in the common forensic laboratory. Video Spectral Comparator-5000 (VSC-5000), the core instrument used in forensic document examination was employed for the non destructive examinations of the printed ink. The spectral analysis was carried out by scanning all the samples in the visible and partial NIR range (400-1000nm). The proposed methodology was found suitable to differentiate between the Black coloured cartridges of different and even same manufacturers through their characteristic spectral patterns. It was observed that the inter manufacturer difference were more in the magenta colour and maximum in black colour. The samples were examined using Fourier Transform- Infrared (FT-IR) Spectrometer in the IR beam ranging from 3500-400 wavenumber cm- 1. The samples were scanned in the path of IR beam under microscope without extracting ink from the document and by preparing KBr pellet of ink extract of samples. It was concluded that the IR spectrum of questioned document can be compared with IR spectrum of specimen and also can be differentiated based on the functional groups present in the ink of printed document. The characteristics spectra were generated to allow for conclusive differentiation of printers. Different brands of ink exhibit characteristic IR spectra whereas common ingredients in different brands gave similar IR peak. Both the techniques can be ideally used for comparing questioned prints with admitted prints in a successful manner. Summary and Conclusion Page 135

The inorganic trace elemental profile (in weight percentage) of printer inks was obtained by using Scanning Electron Microscope-Energy Dispersive X-ray Spectrometry (SEM-EDX). The presence and absence of elements as well as different weight percentage indicates the respective samples have a similar/different elemental composition. The presence of potassium in few samples differentiates those samples from others. A simple and inexpensive High-Performance Thin-Layer Chromatography (HPTLC) technique employed for the analysis of Magenta colour printed ink extracted from 32 printed sample documents. Chromatography was performed on silica-gel 60 F254 plates with N-butanol: Acetone: Distilled water: Ammonia as mobile phases. The chromatogram obtained was then scanned in the densitometer and the spectrum was obtained. The HPTLC profile (no. of spots, Rf values, colour and fluorescence) of printed material could be used as a reliable comparison technique. The absorbance profile of inkjet ink for the differentiation and comparative analysis was obtained by scanning the ink extracts under the wavelength range of 200-700 nm using the UV- Visible Spectrophotometer. The various parameters of absorption studies of different components of printer ink formulation in the visible and UV region, after the extraction process enables us to differentiate and distinguish different document sample of distinct composition by their characteristic absorbance spectra and pattern profile. A very effective technique of Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) was utilized to obtain elemental profiling of coloured ink (in ppb levels) extracted from printed document. After the analysis zinc, iron, chromium, barium, lead, copper, strontium, arsenic, manganese, cobalt, nickel, gallium, selenium, rubidium, silver, caesium, uranium and others were detected in the ink samples. The elemental profile shows different identification limits for different brands which allow identification of brands of printing ink. All the techniques used though expensive are simple, reproducible, sensitive and having good applicability to the routine analysis of printed ink samples. Even though many of the techniques are destructive one, under special circumstances, with permission of the court the proposed methods can be used successfully, as all the techniques involves a very small sample. All of the Summary and Conclusion Page 136

proposed methods were found most suitable when the admitted specimen was provided along with the questioned document. Both the document can be processed and prepared in the same manner as described in the studies carried out by us and can be compared with each other. In case when specimen is not available then the profile of the questioned document can be compared to the respective profile of printed inks of different instruments as given in chapter 4 for the inclusion and exclusion of the printing ink analyzed in the present study. If time is provided by the court for giving opinion then all of the techniques or more than one technique could be employed and the decision could be taken on the involvement of suspected printer. This would be helpful for forensic document examiners in giving opinion and it would be a cross check also regarding the source of document etc. Summary and Conclusion Page 137

RECOMMENDATIONS The recommendations are given below to allow for better discrimination of samples as well as different inkjet ink brands with more certainty 1. It is recommended to make addition of taggants/markers in ink product. The taggant should be select such that its addition in small amount will not change the properties of ink product. The taggant should be specific to particular ink brand of printing ink. This can provide the useful information of the year of ink production along with the brand of printing ink. 2. Although the experimentation in this research work has been carried out by preparing the sample in a convenient manner, it is recommended that in the actual routine case work the sample should be collected by taking the micro punches/plugs of samples. 3. The ink database should be created and the ink standards should be stored. This can be done by smearing the ink onto the paper using a cotton swab and store the ink standard in a file or notebook after drying. The exposure of light should be avoided to minimize the fading of ink. 4. TLC of every ink (using different concentrations on the same plate) manufactured by all the manufactures should be stored and kept for further reference (away from sunlight) to compare with questioned ink. Timely update is necessary. 5. Further work can be carried out on the analysis of ageing of printing inks at different intervals of time. Recommendations Page 138