Noninvasive Characterizationof Preservation Fluidsthrough Glass Container Using Spatially Offset Raman Spectroscopy:Potential in Heritage Science

The conservation and characterization of preservation fluids are crucial for maintaining specimen integrity in natural history fluid collections. However, characterizing these fluids analytically poses significant challenges, especially as noninvasive methods are preferred to avoid opening jars and reduce the risk of compromising specimens. This proof-of-concept study investigates the feasibility of using a hand-held spatially offset Raman spectroscopy (SORS) instrument to determine the chemical composition of preservation fluids through their original glass containers. Results demonstrate that SORS can noninvasively verify the chemical identity of dominant excipients in these fluids measured through a historic glass jar. Additionally, multivariate analysis combined with SORS measurements successfully differentiated several types of typical preservation fluids prepared as mixtures of different alcohols in water, such as glycerol, ethanol, methanol, and formaldehyde. The proposed noninvasive approach was also able to differentiate between different concentration points of components in water within the same type of preservation fluid.