Forensics Journal - Stevenson University 2011 | Página 17

FORENSICS JOURNAL

Determining the Effects of Ranging Reagent
Grade Solvents on Thin-layer Chromatography
Ink Analysis Using Solvent System I
(Ethyl Acetate: Ethanol: Water)
Julia Wikoff
ink formula can be identified, if two separate writings have a common
origin, and to date the ink. Dr. Neumann and Dr. Margot published
Consideration on the ASTM Standards 1789-04 and 1422-05 on the
Forensic Examination of Ink. They noted that the ASTM standards
stated that appropriate materials need to be chosen to minimize
variability, but did not provide details regarding these materials [3].
The guidelines do not specify the solvent grades needed for Solvent
System I: (ethyl acetate: ethanol: water) (70:35:30).

INTRODUCTION
A field of significant importance within Forensic Science is questioned documents. A document with any doubt as to the author, date
written, or age is a questioned document, and may include printed
materials such as letters, drivers’ licenses, contracts, passports, lottery
tickets, and checks. Writings or markings found on larger objects such
as walls or doors are also included in this field. A document examiner must be skilled in non-destructive techniques such as non-flash
photography and microscopy as well as destructive techniques such
as thin-layer chromatography [4]. Examinations of questioned documents can involve determining the type of paper and/or ink used to
write the document as well as determining the author of the document.

Two main types of inks are currently on the market today. Two-thirds
of the available inks are non-ballpoint inks. These water-based inks
are visualized as glossy and fluid on a paper; they commonly bleed
through a thin piece of paper. Since the inks are water-based, the dyes
are dissolved in ethanol: water for analysis. One-third of available inks
are ballpoint inks. These glycol-based inks leave metallic appearing
striations on paper and commonly leave a well when writing because
pressure must be exerted to release the ink. The glycol-based inks are
dissolved in pyridine.

Crimes involving questioned documents include larceny, forged
wills, identity theft, ransom notes, traced signatures, altered medical
records, watermarks, signatures on legal documents, pre- and postnuptial agreements, and death threats. Questioned documents could
be typed or written in ink, pencil, marker, blood, or other bodily
fluids. Most altered documents are written with “white-collar criminal intent” [2], but some are written with darker purposes including
kidnapping and murder. A document examiner must consider all the
characteristics of a document including “the writing medium used
and the surface it is written upon, the age of the paper or ink, and
watermarks” [2].

This study was conducted to determine if different grades of solvents
in Solvent System I produce inconsistent chromatography plates. The
separation and clarity of the ink components and the reproducibility
of the Rf values were both studied to determine the solvent system
combination that produced the best results.

MATERIALS AND METHODS

Questioned documents are commonly encountered in the forensics
field. If ink from a writing instrument, printer, or typewriter is used
to create the document, then thin-layer chromatography can be used
to determine the manufacturer of the ink. The separation of the ink
components is viable on a chromatography plate by the appearance
of individual colored bands. The retention factor, Rf, can be used to
identify a specific ink by using a library of previously run Thin-layer
Chromatography (TLC) plates. The United States Secret Service
Forensic Science Division currently has the largest library of ink types
with a collection of over 10,800 ink samples.

Sample and Solvent System Preparation:
A total of fifty black and blue inks were chosen for analysis. Twentyfive of the chosen inks were ballpoint and twenty-five were nonballpoint. The brand, color, and classification of each ink can be seen
in Tables 1 and 2. Five Kimble glass Ink Opticlear® 12 X 35 mm
vials were labeled according to the classification of each ink. The inks
chosen were available on scribble sheets, labeled in binders and written on using the matching ink. A micro-punch was used to collect
between four and eight 1 µm micro-punches of each ink for each of
the five glass labeled vials.

The American Society of Testing and Materials (ASTM) created a
“Standard Guide for Test Methods for Forensic Writing Ink Comparison” in 2008 [1]. These guidelines are followed to determine if the

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