NCJ Number
222155
Journal
Journal of Forensic Sciences Volume: 53 Issue: 1 Dated: January 2008 Pages: 100-106
Date Published
January 2008
Length
7 pages
Annotation
Because the tools commonly used to analyze dye-based inks on questioned documents cannot be used for the analysis of the insoluble pigment inks that are rapidly replacing dye-based inks for pens and printers, the use of laser desorption mass spectrometry (LDMS) for the analysis of pigment-based inks was tested.
Abstract
The testing found that LDMS is a useful and sensitive tool for the chemical identification of both dye-based and pigment-based inks. Since laser desorption can be performed directly from a paper substrate, there is no solubility requirement. Because pigments cannot be analyzed by the commonly used method of TLC, LDMS is an attractive alternative. Although the degradation of simple pen ink dyes over time may be useful for estimating the age of a written sample, pigments apparently do not change over time; however, the detection of the polyethylene glycol is an encouraging result. In addition to the additional feature of being able to detect nonabsorbing components in the presence of an absorbing pigment, preliminary work suggests that the intensities of the polyethylene glycol peaks decrease with time. Perhaps such measurements may allow estimation of the age of a document written with pigmented ink. The Uni-ball 207 pens use pigmented ink available in eight colors (blue, light blue, green, orange, red, pink, purple, and black). Uni-ball pens with each of these colors were used in this analysis. Using each of the pens, a stroke was made on paper. The pen stroke was sampled using a forensic document punch. This was introduced into the instrument and subjected to laser irradiation. A pulsed nitrogen laser was used to focus on each pen stroke, and positive and negative ions representative of the pigment were generated for subsequent mass spectrometric analysis. 8 figures and 23 references