Study On The Identification Of Writing Age By Application Of Modern Instrument Analysis Technology

Identification of documents forming for the court has been always a hot issue of international forensic science. The earliest time of writing age identification can be traced back to 1904, studied on the fountain pen and ink. The existence of ball-point pen in 1937, the forensic scientists study on the large amount of ink type and formation. The written media flows through the ball rolling, such writing tools collectively known as the ballpoint pen. According to the viscosity, written media can be divided into ball pens, gel and water-based pen, two pens afterwards which is also known as the roller pen, is a new type of pop writing tools in social community. Nearly a century, scientists at home and abroad has been unremitting exploration and use all kinds of techniques and methods, the analysis of ball-point pen ink carried out a lot of research, because of interference factors are too more, identification of writing age has been a major problem, plagued forensic science workers. In the various economic cases, the perpetrators or parties are often subsequently through forged or falsified documents time to reach the criminal purposes, accurate identification of writing age, has become the key to determine the basis of such cases.In this paper, the composition of solvent and dye or pigment in ball-point pen ink and roller pen ink was analyzed mainly through modern equipment analysis methods, thus changing rules of ink entries'writing age stored in common and the changes of heat, light and other factors on the impact to writing age were studied.Analyticl method of differential pen ink's were established by Gas Chromatography (GC), the relative content of solvent in ink such as benzyl alcohol or phenoxy ethanol to triarylmethane dyes in the ball-point pen ink with natural changes of aging was studied. After pen writing on paper, solvent content in ink speedy decline in 20 days, with the ink resin film, solvent content changes gradually slows, after 100 days the slope of the aging curve near zero, it is very difficult to volatile solvent composition out of the ink. By gas chromatography and mass spectrometry techniques it was determined the solvent composition of roller pen ink is main glycol, diethylene glycol and glycerin, and other polyols, on the use of two solvent extractions, analysis by GC from the extraction drawing curve rate of extract vs writing age. At the same time the aging of same solvent composition in different roller pen ink were statistical study. By analyzing relative content of solvent in ball-point pen ink and solvent extraction rate of roller pen ink changes of threshold of heated before and after can be abtained, to infer the formation of handwriting without the comparable samples.High performance liquid chromatography (HPLC) on the identification of the ball-point pen ink handwriting analysis method to determine the blue ball-point pen ink dyes include crystal violet 5 BN, alkaline Brilliant Blue B, and their homologue, and in accordance with the types and relative content of dyes blue ball-point pen were classified. Ball-point pen ink changes in the composition of the dye relatively slow, when writing age in six months to one year, demethylase reaction of the dye will happen so the relative content will change.The analytical method of water-based pen inks was established by capillary electrophoresis (CE). After optimizing conditions, 20mmol/l borate buffer pH 8.5, 100μm×40cm fused silica capillary column, separation voltage 15kV, photo diode array (PDA) detector and scanning range 190-600nm was adopted in experiment. Electropherogram of different roller pen inks'extracts were obtained. The problem of relative writing age was investigated from relative changes between different dyes in inks detected by PDA in visible wavelength. Better change that law can be analyzed at least 600 days within formation time of the black water-based pen inks. Light can accelerate the change of dye decomposition in water-based ink water. Gel ink pen is a new popular pen. Its coloring matter is usually pigment which is could not be extracted by water or organic solvents, so method of GC and HPLC to analyze ink of ballpoint pen and water-based pen cannot be used. There are no performance methods to identify gel ink pen in forensic science now. Pyrolysis gas chromatography (Py-GC) was used to analyze 60 different blue gel ink pen entry on paper. The Pyrolysis of entry was performed with a CZ-100 pyroprobe system using a coil filament with a quartz sample tube, temperature setting is 770℃with 10 seconds. Angilent-6890N gas chromatography was used with NPD detector; column is Dikma Technology DM-5 (30m×0.32mm i.d.×0.25μm). Based upon the number and retention time of peaks in the pyrograms, the gel ink pens were separated into 3 classes. Most of the gel ink pen fell into 2nd group: those containing the peaks of copper phthalocyanine pigment. The results showed that the retention time and ratio of the peak areas were stable and reproducible. Writing age of blue gel ink pen was primarily investigated by the relative change rule of main components in ink, and curve of writing age was obtained.