THE STUDY of cross-sections of heritage paintings has benefitted from a ‘breakthrough’ in atomic force microscopy (AFM)-based nanoscale mass spectrometry, reports Anasys Instruments.
Researchers at the University of California Santa Barbara (UCSB) and the Getty Conservation Institute developed a variation of the Berkel technique, decouplingd the AFM step from the MS step.
They collected sub-micron size samples through AFM based thermal desorption, followed by separate analysis with resonant two photon ionisation coupled with mass spectrometry.
The new AFM-MS technique was originally developed by Oak Ridge National Laboratory researcher Dr Gary Van Berkel, using the the thermal AFM probe to act as a nanoscopic ‘shovel’ to thermally desorb material of interest into a mass spectrometer.
This is said to overcome the 20 micron limit of spatial resolution encountered with conventional mass spectrometry.
The analysis of cultural heritage materials presents a number of challenges, because of the extremely small and complex samples, the importance of maintaining spatial integrity and, most notably, the rarity of the samples.
These complicate the identification of many traditional organic dyes, particularly in paintings that may have multiple original paint layers (depending on the artist’s technique) as well as subsequently applied restoration or conservation layers.
Elucidating the nature of these organic compounds with high spatial resolution may help clarify a painting’s history, and can assist in conservation since these molecules are often prone to degradation from light or other environmental agents.
Therefore, there is a need for analytical techniques that can provide spatially resolved, molecularly-specific, and unambiguous identification of organic compounds such as dyes in cultural heritage materials.
The researchers, Professor Mattanjah de Vries of the University of California, Santa Barbara and Dr Catherine Schmidt Patterson of the Getty Conservation Institute, were able to acquire nanoscale chemical composition data for the red organic colorant alizarin crimson from a mock-up painting cross-section.
With a spatial resolution of 750nm, they could extract several samples within thin paint layers while maintaining the bulk of the cross-sections for further analytical work.
Professor de Vries said: “We are very excited about this new AFM-MS technique that enables us to study the chemistry of cultural heritage materials at sub-micron spatial resolution for the first time using Mass Spectrometry.
“We expect it to have wide applicability in cultural heritage and other applications”.
The research results were published in the September 2014 issue of the Journal Analytical Methods. (Anal.Methods, 2014, 6, 8940)