![]() ![]() Between them, non-destructive and destructive methods of analysis can identify more than 90% of ballpoint pen inks. Hplc involves injecting the ink sample onto a long thin metal column that is then washed over with a mixture of solvents, carrying the ink components one at a time to an electronic detector. Treasury has a database of ink thin layer chromatograms which can be very informative.Īnother technique called high performance liquid chromatography (hplc), which can be used as an alternative to tlc. The United States Secret Service has a reference ink database and the U.S. If the sample ink has the same chromatogram as one of the reference inks, it suggests they are the same, and so identification can be made. Different inks will have different chromatograms. The end result with TLC is a pattern of colored spots, known as a chromatogram, for each ink. ![]() Chromatography means "writing with colors" and the chemical components of the ink, which are, of course, colored, travel with the solvent at a speed that depends upon their composition. The solvent is drawn up the paper through capillary action and the sample spots move up with it. It is positioned so that the paper dips into the solvent but the spots of sample remain dry. The paper is placed in a beaker containing a small amount of another solvent. Next, a tiny spot of the sample solution is placed onto a strip of paper, alongside spots from various reference ink samples. The sample is placed in a test tube with a solvent that dissolves the ink. This avoids any interference with subsequent handwriting analysis. The investigator avoids places where the pen has changed direction or where ink lines meet. A tiny sample of the inked paper is punched out using a thin, hollow needle a hypodermic syringe is ideal. However, a photographic record of the original document is taken before the procedure is started. In reality, it is not very destructive to the document if done with care. The main method of destructive testing of ink is known as thin layer chromatography (TLC). Light because, at high frequencies, ink is invisible but pencil marks which may lie underneath will show up. It can be very informative to scan the document with infrared Other non-destructive or minimally destructive methods, such as Raman spectroscopy, can be used to supplement micro-spectrophotometry. The spectrum of the ink on the document can therefore be compared with the spectra of standard inks. Put simply, this is a way of discovering the true "color" of the ink. Each ink should give a distinct pattern or spectrum on exposure to ultraviolet or visible light. Some inks fluoresce, or emit light, on exposure to ultraviolet, while others disappear. This involves scanning the ink with ultraviolet or infrared light to record its spectrum, that is, the wavelengths of light it absorbs. The main method of non-destructive ink analysis is micro-spectrophotometry. It is preferable to try the non-destructive approach first, so that the document is left intact. The ink itself may be analyzed by non-destructive or destructive testing, depending on whether a sample needs to be taken from the document, a process that would alter it. The investigator may be able to see slight changes in ink color, not visible to the naked eye, that could be indicative of alterations, or there may be suggestions of obliteration and overwriting. These can be revealed by laboratory analysis and the results can help assess whether there have been any additions or alterations to a document.Īnalysis of documents under a microscope can be informative as a first step. Although all blue or black inks may look the same, there can be some important differences in their chemical composition. Ink analysis may be an important part of the investigation of questioned documents, including forged checks, wills, or altered records. ![]()
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