FORENSIC CHEMISTRY LABORATORY MANUAL

by R.Q. Thompson; Oberlin College

SPECTROSCOPIC AND CHROMATOGRAPHIC ANALYSIS OF PEN INK

Objective

To determine the color and composition of pen inks and inked writing found on documents pertinent to the case.

 

Sample

Collect a variety of ballpoint and felt tip pens and prepare documents with those pens. Assign pens and documents to the suspects and to the crime scene.

 

Reagents

Extraction fluid and mobile phase: aqueous 0.005 M heptanesulfonic acid and acetonitrile mixed in 45:55 ratio.

 

Standard Reference Material

 

None

 

Methods

Visible spectrophotometry ; liquid chromatography

 

Special equipment

UV-Vis spectrophotometer; pair of small-volume, 1-cm cuvettes; liquid chromatograph with C18 column and diode array detector ; 2-mL chromatography vials with screw caps

 

Procedure

For instructor (detailed); For student (brief)

 

Typical results

Visible spectra of felt tip and ballpoint inks ; representative chromatograms of two (A and B) pen inks: 20-µL injection of liquid sample; C18 column; isocratic elution with 45:55 aqueous 0.005 M heptanesulfonic acid (pH = 4.7): acetonitrile, flowing at 0.3 mL/min.