The Use of LD/MALDI MS
in the Analysis of Ink in
Questioned Documents
Mike Rusak & Laura Fairburn
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
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.
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
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
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)
Degradation Products After
Demethylation
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
Uncontrolled Aging Study
UV Aging Study
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
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”
Aging within the Ink Cartridge
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
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
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