A Chemistry Whodunit Forensic Examination of Pen Inks Michael N. Quigleyl and Hongyan Qi Chevron Science Center, University of Pittsburgh, Pittsburgh, PA 15260
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Forensic chemistw has lone been recoenized in this Journal as a source of interesting experiments for undergraduate analytical chemistry students. Papers have included those covering: a comprehensive symposium collection (I),general introductions (2-7). narcotics (8,9),arson (10). alcohol breath testing (11,12), blood detection (13, 14) and typing (151, analgesic analysis (16), and sampling (17). Surprisingly, the area of questioned document analysis and the role of pen ink analysis has only recently been specifically addressed in the Journal (18). Considering that relevant techniques are simple and inexpensive to implement (19), a 16sum6 is now presented of the many different aspects of ink analysis together with a suggestion for an interesting laboratory class experiment. Many physical and chemical techniques are used in the forensic analvsis of written documents auite anart from graphologicai(handwriting)examination. ~ e f o r the e advent of classical and modern-dav instrumental methods of analvsis, graphology was the mainstay of questioned document examination. Today, graphology still has a major role to play in the authentication of questioned documents but is used mostly in combination with scientific methods of analysis. The comparison of pen inks is a notable chemical method of identification and may be usedin certain circumstancesto date documents as well. Such techniaues are eenerallv used when, for example, fraud or tax evasion is sispected. The Bureau of Alcohol, Tobacco and Firearms a t their National Laboratory Center in Rockville, MD, has collected thousands of ink samples manufactured in the United States since the late 1950's. Unfortunately, the collection is incomplete and inks of foreign manufacture are largely ignored. Even so, the library has proved useful in many authentication cases of questioned documents. In the last decade or so, major advances have also been made in the dating of ink writing by instrumental methods (20-24).
58), but results obtained are often visually dramatic (59) and easily demonstrable in a classroom environment (19). Qualitative analvsis mav be simnlvnerformed bv com~arisonofRI values and quanktation -b;-either phot"oden&tometry o; manual mot removal with subseauent solvation of senarated cornpone& and spectrophotom&ic examination. ' Most chromatoara~hictecbniaues are based on the minute sampling of asingle written character representative of the questioned text. For example, a syringe needle may be used to punch through the paper and the paper microplug or microdot either extracted with a suitable solvent and this solution spotted onto paper or a TLC plate (60) or applied directly to a TLC plate (61). One recent modification to the basic TLC technique apparently solves the problem of separating components with similar R, values (62). For student type experiments, removal of a section of handwritten text (i.e., a word or sentence) with subsequent extraction, results in afaster and less finicky procedure. Although the following description involves identification of ball-point pen inks, earlier papers in this Journal haveprovided details on the analysis of fountain pen (18,63) and felt-tip pen inks (18).
Methods of Ink Analysls Manv different nondestructive techniaues are available including those based upon: reflected ultrkoletlvisible radiation (25,26)-the approach of which may be modified to take account of the disappearing or erasable inks that are available (27.28).reflected infrared radiation (29-31). transmission a i d ieflectance microspectrophotome& (3zj,infrared luminescence (29, 30, 33-35), dichroic filters (29, 30), lasers (36-39), scanning electron microscopy (40,41),and Xray fluorescence (40-42). Unfortunately, the reflectance methods are often subject to interference effects from "bronzing" or "sheening" of the ink ( 4 3 4 ) . Semidestructive chromatoera~bv ., . . mav involve whollv instrumental techniques such as high-performance liquid or electronhoresis (50-52).Student chromatomanhv - - (46-49) . appreciation can be readily engendered a t all leveis, however, by using either paper (53,54) or thin-layer chromatography (55, 56). Applications of both techniques to criminal investigation predate both electrophoresis and HPLC (57,
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Journal of Chemical Education
Figure 1. A sample documem containing several repeated signatures at the bottom.
