Anasys Instruments reports on the study of cultural heritage painting cross-sections by researchers from UCSB and the Getty Conservation Institute using their breakthrough AFM-based nanoscale mass spectrometry technique. 

The analysis of cultural heritage materials presents a number of challenges such as: limited and extremely small samples, complexity of sample structure, the importance of maintaining spatial integrity and, most notably, the rarity of the samples. These limitations present specific challenges for 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 aspects of a painting’s history; and can assist in the painting’s 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. 

Mass spectrometry (MS) is one of the most widely used chemical characterization techniques with a worldwide market of over $3 billion/year. However it suffers from a major limitation in that its spatial resolution is currently restricted to 20 microns. A new AFM-MS technique developed by Oak Ridge National Laboratory researcher, Dr Gary Van Berkel uses a nanoscale thermal probe of an AFM to act as a nanoscopic shovel to thermally desorb material of interest into a mass spectrometer. A variation of this technique was recently developed by Professor Mattanjah de Vries of the University of California, Santa Barbara and Dr Catherine Schmidt Patterson of the Getty Conservation Institute where they decoupled 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 ionization coupled with mass spectrometry. 

Using this AFM-MS technique, they were able to acquire from a mock-up painting cross-section nanoscale chemical composition data for the red organic colorant alizarin crimson. With a spatial resolution of 750 nm, 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)¹. 

Reference

¹ Anal. Methods, 2014,6, 8940-8945 DOI: 10.1039/C4AY00919C

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