Non-invasive characterisation of molecular diffusion of agent into turbid matrix using micro-SORS

Abstract This study proposes a non-invasive analytical method to study the molecular diffusion of a chemical agent into a turbid matrix with an emerging analytical technique, micro-Spatially Offset Raman Spectroscopy (micro-SORS). Here, the micro-SORS concept has been extended from the analysis of chemically distinct stratified layers to the studies and monitoring of the absorption and diffusion processes, addressing a key analytical need in a number of areas including polymer, pharmaceutical, forensic and biomedical sciences. In Cultural Heritage the knowledge of the penetration depth of a polymer used to consolidate or to protect an object or the absorption depth of solvents used during a cleaning procedure is crucial for the performance evaluation of restoration methods and their safety towards the work of art. To date the most common protocol for obtaining this type of information comprises the application of stratigraphical analysis on cross-sections prepared after taking a small amount of sample from the work of art. This approach is destructive and may lack of statistical meaning, since the analytical information is limited to the micro area of sampling. To overcome these drawbacks, in this study, micro-SORS was successfully used, for the first time, to non-invasively characterise the penetration of a polymer and of a viscous solvent into a gypsum substrate, permitting the reconstruction of the diffusion trends of the products into the matrix and the evaluation of their performances.