This work presents a new analytical technique designed with the goal of identifying organic components in cultural heritage objects. The approach uses atomic force microscopy (AFM) to image, sample, and collect material by proximal probe thermal desorption (TD) at sub-micron resolution. Sample material is transferred to a specialized substrate and analyzed by high resolution laser spectroscopy and mass spectrometry (L2MS) to provide detailed information in three dimensions: spatial mapping, high resolution spectroscopy and mass spectrometry. The method is applicable to samples typically used in conservation science, with the spatial resolution necessary to isolate small quantities of organic material in discrete, cross sectional layers, and the sensitivity to provide molecular identification of constituents in very low concentrations.<br/><br/>Thin films of caffeine, the red organic colorants alizarin and purpurin, and the synthetic pigments PV19 and PO43 have been desorbed, ionized and detected using the present technique. Currently, we are undertaking studies on real-world samples supplied by the Getty Conservation Institute. Topographic images can be taken throughout each experiment to investigate the AFM-TD depression sizes as well as any other changes to the morphology of the sample. Depression diameters ranged from 300 to 1500 nm with depths of 20 to 1000 nm. This method retains the bulk of the sample, which may be retained and/or used for analysis by other complementary techniques. We employ L2MS as the second step, which combines resonant multiphoton ionization with mass spectrometry. This approach collects simultaneously both vibronically resolved optical spectra and fragment-free mass spectra for molecules of interest. The wavelength selectivity in our ionization step (a) allows for detection of a specific analyte in a mixture, eliminating the need for sample preparation, (b) provides the necessary high sensitivity, and (c) provides unique selectivity in the identification of the compound.

AFM-sampling-L2MS on painting cross-sections

251st National Meeting (2016)

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