The Use of LD/MALDI MS in the Analysis of Ink in Questioned Documents

1. The Use of LD/MALDI MS in the Analysis of Ink in Questioned Documents Mike Rusak & Laura Fairburn

2. Introduction • The study looks at the changes in ink pigments over time. • LD/MALDI Mass Spectrometry is used to analyze the ink. • Relatively gentle on the analyte; little decomposition of the molecular ion takes place, resulting in an uncomplicated spectrum. • GC-MS is the earliest method used in ink analysis  produced complicated spectra due to harsh conditions of electron impact MS

3. What is Ink? • Inks, as mentioned in this article and the many articles read concerning this topic, are defined as chemical mixtures that exist in a liquid, gel or solid form. • Now, most people who counterfeit documents use computers with advanced printing equipment, instead of handwritten inks.

4. Inks Studied in the Article • Blue Ballpoint Pen Ink • Generally made up of: • Crystal violet - Uniformly decomposes over time leading to… • Methyl violet – derived from crystal violet • Red Ballpoint Pen Inks • Rodamine B or Rhodamine 6G • All of these inks contain multiple methyl and/ or ethyl groups

6. LD/MALDI Mass Spectrometry • In LD, a UV laser heats the analyte, causing desorption into the air and into the machine • Useful in pigment and dye analysis because only the compounds that absorb at the wavelength of the laser are desorbed. Highly conjugated compounds such as dyes are in the range of the laser • Relatively non-destructive and doesn’t visually alter the documents in question • In MALDI, the process is the same except the analyte is impregnated in a crystal matrix that absorbs the energy and transfers it to the analyte • Needed to successfully desorb some of the inks • The m/z ratio is then determined by time of flight MS • Larger m/z ratio ions will travel slower than smaller m/z ions when accelerated with an electric field

7. Oxidative Demethylation/ethylation • The basis of the argument is that during aging, oxidative demethylation/ethylation where methyl or ethyl groups are lost and more degradation products are formed, of which the mass spectrometer can detect • TiO2, a common white pigment used in paper manufacturing, catalyzes the above reaction. • The reaction can also be photocatalyzed using UV rays  basis behind UV and incandescent accelerated aging. • Two inks were examined in the study, black/blue (containing methyl violet) and red inks (rhodamine B and 6G)

8. Degradation Products After Demethylation

9. Aging studies • Two studies were carried out: • 1) Controlled UV aging study • Writing samples were subjected to UV light for a period of 24 hours • 2) Non-controlled study • Numerous writing samples that have been stored in the basement of the University of Michigan Chemistry Department were used • All samples had indications of when they were written

10. Uncontrolled Aging Study

11. UV Aging Study

12. Aging in Red Ink • Study completed by Dunn et al. • Incandescent light was used for photodegradation • Inexpensive compared to UV-based studies • Through this study, it was determined that Rhoadmine 6G and B are isomers • Though when aging occurs, it results in different products from each isomer • The rhodamine dyes contain alkylated amino groups • When it undergoes aging, the alkyl groups are replaced with hydrogens

13. Aging within the Ink Cartridge • One may worry about the degradation of the ink occurring within the pen, before it’s used on document in question • Studies were completed, using a variety of pen types, to discredit this concern • It was concluded that, for the most part, the ink remains stable while still in the cartridge • There were some cases in which degradation did occur within the cartridge, most likely caused by the solvent use • “The possibility that a dye can degrade in a pen need not negate the use of methods, such as laser desorption MS for the analysis of inks to determine the age of a written line, since other methods are commonly used that evaluate solvent content”

14. Aging within the Ink Cartridge

15. Other Uses of LD-MS for the Analysis of Ink • The chemical make up of ink can be used to determine where the documents in question came from. • For example, looking at counterfeit money, one can now determine from which type of printer it came from. Most well know counterfeits have a ink/ printer type they use. • Counterfeiting has become more and more advance with the development of new technologies • Making it very hard to distinguish the real from the fake • This technique makes identifying these documents a very easy process

16. Real Case Example • To test the real world applicability of using Laser Desorption/ Ionization Mass Spectrometry for the identification of fake money, • They tested 50 representative samples from the Brazilian police evidence to classify whether the banknotes were authentic or counterfeit. • Had far fewer false positives versus the people trained to visually determine if the money is counterfeit

17. Citations • Eberlin, Livia S. et. al., Instantaneous chemical profiles of banknotes by ambient mass spectrometry Analyst. 2010 vol 135, pp. 2533-2539 • Grim, Donna M. et. al., Does Ink Age Inside of a Pen Cartridge? J Forensic Sci. 2002 vol 47:6, pp. 1-4 • Siegel, Jay et. al., The use of laser desorption/ ionization mass spectrometry in the analysis of inks in questioned documents Talanta. 2005 vol 67, pp. 425-429