New ink sampling techniques

Researchers at the Midwest Forensics Resource Centre at Iowa State University are building a library of ink profiles to help forensic scientists identify inks on fraudulent documents and other evidence.

Scientists at the centre are pairing mass spectrometry with a new sampling technique called Direct Analysis in Real Time (DART) to reveal the chemical makeup of ink faster and in greater detail than ever before.

DART mass spectrometry analyses ink by creating a stream of warm gas containing excited-state helium atoms or nitrogen molecules in the DART source. The gas stream is pointed at an ink sample, and the gas and excited-state species evaporate and ionize molecules from the sample. A mass spectrometer measures the production of ions to create mass spectrum data for each ink sample tested.

In contrast to other types of ink analysis, DART mass spectrometry is able to test documents without physically or visually altering them.

The questioned document is open to the environment, and all sizes of materials may be tested in their original form.

“The great thing about the DART system is that it can sample the ink straight off the paper,” said Roger Jones, associate chemist at the US Department of Energy’s Ames Laboratory.

“You don`t have to extract a sample first. Before DART, we had to cut a little bit of sample out and dissolve it in solvent for analysis. So, now we can look at the document without visibly altering it, which is good for forensic science. We don`t destroy the evidence.”

Mr Jones said that eliminating the sampling extraction process saves busy forensic scientists time.

“We would have been satisfied with the mass spectra looking basically like the spectra obtained by the old extraction mass spectrometry methods, because the DART system still gets around damaging the sample and reduces the work involved in analysis,” he added.

“Constraints are the major complaint of every forensic scientist. Their caseloads are so large that they just don`t have the time to do traditional ink analysis.”

The DART method also yields richer data about ink samples than previous sampling methods. Mr Jones said initial tests of the DART system indicate that the mass spectra reveal more components of the ink than conventional mass spectra.

“Using DART, forensic scientists may be able to differentiate between inks like never before,” he said.

The DART initiative is a three-stage project. Currently in the first phase, the scientists are experimenting to determine the best way to analyse inks and build the library. The library of ink mass spectra will be produced in the second phase of the project.

Researchers will use samples from the US Secret Service International Ink Library to create a comprehensive, vetted, and computer searchable library of mass spectra of the more than 8,000 inks the Secret Service has compiled.

The third phase of the project will focus on creating computer software used to store and access the mass spectra library.

“Commercial mass spectrometry software available today is all based on the old style of mass spectrometry. We get a different type of data from DART. So, the assumptions used in existing software for searching and matching mass spectra do not work the best for DART,” said Mr Jones.