| Abstract [eng] |
One of the types of fraud is document falsification, like money, pieces of art, diplomas insurance, documents. Such forgery causes massive damages to individuals, organizations, and even economies of whole countries. Forensic scientists are looking for a way to determine if the questioned document is faked. The usual analysis methods require a sample taken from the document, which damages it. Optical methods like Surface-enhanced Raman spectroscopy (SERS) and Attenuated total reflectance infrared spectroscopy (ATR-FTIR) allow the analysis of the samples without damaging them and without any special preparations required for them. The objective of this work was to use SERS and ATR-FTIR spectroscopies to determine the differences and chemical composition of different companies' pen inks. To achieve the objective, a few goals were established: 1. To register SERS spectra of different companies' inks, analyze them, and determine their chemical composition. 2. To register and specify the chemical composition of inks using ATR-FTIR spectroscopy. 3. To determine if used methods allow differentiation of inks of the same color. 4. To practically apply the SERS method for analysis of written texts. In this work, four different companies' blue inks and three black inks were examined using SERS and ATR-FTIR spectroscopies. The spectra showed that blue inks mainly consisted of Crytal violet and Victoria blue R dye, which are common in many blue pen inks. Two samples had additional peaks that matched the spectral lines of Copper phthalocyanine dye. The differences between the blue inks were visible in the SERS spectra. However, the spectra of three black inks did not have any differences and the only component determined was crystal violet. To specify the compounds for black inks, ATR-FTIR spectra of dried-out ink drops were registered. In the spectra, differences were seen and additional compounds were found. Black inks mainly consisted of Crystal violet and sodium salts like Acid black and Acid blue. The analysis of ink lines on paper didn‘t show any differences and were overshadowed by the spectral lines of paper. A few written texts were analyzed as well using SERS. Differences between four pens inks were seen in the first document and two pens inks in the second document. This showed that SERS spectroscopy is a useful and practical method to analyze the text without significant damage. |
