Mass Spec Imaging Goes to Court

Challenges Determining the Correct Deposition Order of Different Intersecting Black Inks by Time-of-Flight Secondary Ion Mass Spectrometry

“…Such correct results are as described in prior literature, − and similar ambiguous results have been reported due to mixing from inadequate drying times . However, this is the first time that clearly incorrect results have been reported for the ToF-SIMS determination of deposition order, where the first line (in this case, the vertical line) that is below, appears continuous, and the second line (in this case, the horizontal line) that is above, appears interrupted (e.g., Pvert1–Bhoriz2 and Svert1–Bhoriz2 intersections in Figure b).…”

“…He et al used imaging ToF-SIMS to study intersections of different ink colors (e.g., red and black inks), concluding that ink deposition order could be correctly determined if sufficient drying time (1.5 h in this study) was provided between the first and second inks . Preliminary results also reported the correct determination of the deposition order by ToF-SIMS between two overlapping black inks used on a signature line, which struck popular interest for its potential use in the court setting . Additional intersections have been reported to produce apparently correct deposition orders via ToF-SIMS analysis of black gel and black ballpoint pens and between red ballpoint and red fiber tip pens .…”

“…Given the dominance of correct writing sequence results in previously reported ToF-SIMS literature, − it is alarming to find so many incorrect determinations of deposition order via all three methods of analysis (all-ROI, single-ROI, and MCR of images).…”

“…Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been investigated as a technique for the chemical imaging of inks on paper for forensic purposes for many years. − Like other mass spectrometry techniques, ToF-SIMS provides more specific chemical information, including both inorganic and organic ions, than do Raman and IR spectroscopies. The excellent surface sensitivity of ToF-SIMS also allows for good exclusion of paper signals and provides the possibility that the upper ink in an intersection would be dominantly detected within the typical 1–2 monolayer sampling depth.…”

Determination of the Deposition Order of Overlapping Latent Fingerprints and Inks Using Secondary Ion Mass Spectrometry

“…The aim of this research is to investigate whether it is possible to identify if a fingerprint is below or on top of ink on a document using time-of-flight secondary ion mass spectrometry (ToF-SIMS). He et al 9 and Arnaud et al 10 have both used ToF-SIMS to establish the deposition order of overlapping writing inks on paper but have not investigated overlapping fingerprints and inks. Previous work by Bailey et al 11 used a high energy variant of ToF-SIMS (an experimental technique which is currently in the early stages of development and not widely available to the scientific community) to show that determining the deposition order of fingerprints and inks is potentially possible.…”