RESUMEN
The identification of organic dyes is a challenging task in all the fields such as the forensic and conservation sciences, especially in cases where the amount of sample is extremely small. In this paper we propose a new enhanced FTIR method (MU-ATR metal underlayer ATR spectroscopy), which we believe is the first of its kind, for the analysis of a few ng of dyes. With this method, dyed fiber micro-extracts can be analyzed using a commercial FTIR microscope with a fixed incident angle, obtaining the same separation between the different classes of dyes investigated as we obtained analyzing pure dyes in transmission mode. Moreover, the new enhancement method has been validated on a real sample dated back to the 1893, showing how it can be promising for the analysis of trace amounts of organic substances in artistic samples such as dyes in paintings or textiles, varnishes and organic residues on archaeological objects.
RESUMEN
We present an overview of recent advances in the application of Fourier Transform Infrared (FTIR) microscopy for analysis of complex, multicomponent, and multilayer samples such as those typically encountered in the field of heritage materials. This technique is particularly useful since it allows identification and localization of both organic and inorganic (if IR active) compounds. New improvements have been possible thanks to the introduction of ad hoc sample preparation methods to obtain either thin or cross sections that allow both avoidance of contamination from organic embedding resin and improvement of the quality of the acquired spectra. Moreover, integrated use of spectra registered in the near-infrared (NIR) and mid-infrared (MIR) regions allows better comprehension of cross section composition. Data interpretation has been improved thanks to the development of chemometric methods for elaboration of hyperspectral data. A new and very promising field is the development of enhanced FTIR methods for detection of trace components in microextracts. These systems, allowing detection of extractable organic compounds from about 0.1 mg of sample, will be extremely useful in the future for analysis of natural and synthetic colorants, varnishes extracted, for instance, from cotton swabs used during cleaning of paintings, and organic residues on archeological remains.