Papliaka Zoi Eirini, Vaccari Lisa, Zanini Franco, Sotiropoulou Sophia
Elettra Sincrotrone Trieste S.C.p.A., AREA Science Park, 34149, Basovizza, Trieste, Italy,
Anal Bioanal Chem. 2015 Jul;407(18):5393-403. doi: 10.1007/s00216-015-8698-y. Epub 2015 Apr 30.
Fourier transform infrared (FTIR) imaging in transmission mode, employing a bidimensional focal plane array (FPA) detector, was applied for the detection and spatially resolved chemical characterisation of organic compounds or their degradation products within the stratigraphy of a critical group of fragments, originating from prehistoric and roman wall paintings, containing a very low concentration of subsisted organic matter or its alteration products. Past analyses using attenuated total reflection (ATR) or reflection FTIR on polished cross sections failed to provide any evidence of any organic material assignable as binding medium of the original painting. In order to improve the method's performance, in the present study, a new method of sample preparation in thin section was developed. The procedure is based on the use of cyclododecane C12H24 as embedding material and a subsequent double-side polishing of the specimen. Such procedure provides samples to be studied in FTIR transmission mode without losing the information on the spatial distribution of the detected materials in the paint stratigraphy. For comparison purposes, the same samples were also studied after opening their stratigraphy with a diamond anvil cell. Both preparation techniques offered high-quality chemical imaging of the decay products of an organic substance, giving clues to the painting technique. In addition, the thin sections resulting from the cyclododecane pre-treatment offered more layer-specific data, as the layer thickness and order remained unaffected, whereas the samples resulting from compression within the diamond cell were slightly deformed; however, since thinner and more homogenous, they provided higher spectral quality in terms of S/N ratio. In summary, the present study illustrates the appropriateness of FTIR imaging in transmission mode associated with a new thin section preparation strategy to detect and localise very low-concentrated organic matter subjected to deterioration processes, when the application of FTIR in reflection mode or FTIR-ATR fails to give any relevant information.
采用二维焦平面阵列（FPA）探测器的透射模式傅里叶变换红外（FTIR）成像技术，用于检测源自史前和罗马壁画的一组关键碎片地层中的有机化合物或其降解产物，并对其进行空间分辨化学表征，这些碎片中含有极低浓度的残留有机物或其变化产物。过去在抛光横截面上使用衰减全反射（ATR）或反射FTIR进行的分析未能提供任何可归为原始绘画粘结介质的有机材料的证据。为了提高该方法的性能，在本研究中，开发了一种新的薄片样品制备方法。该程序基于使用环十二烷C12H24作为包埋材料，并对样品进行后续双面抛光。这样的程序提供了可在FTIR透射模式下研究的样品，而不会丢失有关涂料地层中检测到的材料空间分布的信息。为了进行比较，还使用金刚石压腔打开地层后对相同样品进行了研究。两种制备技术都提供了有机物质衰变产物的高质量化学成像，为绘画技术提供了线索。此外，环十二烷预处理得到的薄片提供了更多的层特异性数据，因为层厚度和顺序未受影响，而在金刚石压腔中压缩得到的样品略有变形；然而，由于更薄且更均匀，它们在信噪比方面提供了更高的光谱质量。总之，本研究表明，当FTIR反射模式或FTIR-ATR应用未能提供任何相关信息时，与新的薄片制备策略相关的FTIR透射模式成像适用于检测和定位经历劣化过程的极低浓度有机物质。
