Raman spectroscopy looks inside Charles Darwin's jars

09 Mar 2026

Agilent and STFC use spatially offset Raman technique in museum setting for the first time.

UK researchers have successfully analyzed preservatives within some of Charles Darwin's historic specimen jars without opening the containers.

A team from life-science equipment vendor Agilent Technologies and the UK's Science and Technology Facilities Council Central Laser Facility employed a spatially offset Raman spectroscopy (SORS) approach.

"Until now understanding what preservation fluid is in each jar meant opening them, which risks evaporation, contamination and exposing specimens to environmental damage," said Sara Mosca from the Central Laser Facility. "A SORS approach can monitor and care for these invaluable specimens without compromising their integrity."

SORS, first developed at STFC's Rutherford Appleton Laboratory in 2006, is designed to counter conventional Raman's limited ability to penetrate beyond surfaces, and gather more data on a sample's subsurface composition.

Agilent acquired SORS and other Raman technology from STFC in 2017, as part of its efforts towards expanding applications for Raman spectroscopy in general.

Unlike a conventional Raman back-scattering setup, SORS uses a physical offset between the region of the sample being excited by the laser and the region from which a detector collects information, according to Agilent product data.

While direct Raman detection without this physical offset yields a spectrum rich in the top layer information, an offset geometry collects the detectable Raman signal stimulated in nearly areas, mostly from beneath the sample surface. The result is a spectrum derived from subsurface molecules.

"Selective probing is achieved by controlling the offset between the area of detection and area of excitation," noted Agilent. "The larger the offset, the further away from the surface the interrogated area is."

Raman spectroscopy for conservation and collection management

Long-term museum conservation of specimens depends on the chemical stability of the preservation fluids in which they are stored. The compositions of those fluids have historically varied widely, so identifying and monitoring them is essential for specimen conservation planning.

In a museum or archival context, the SORS technique offers a route to analyzing those materials while effectively reducing fluorescence and Raman signal interference from the container itself. Described in ACS Omega, the new study is the first in situ chemical characterization of historical fluids using SORS in a museum setting.

A set of 46 historic specimens in London's Natural History Museum, including some collected by Charles Darwin and stored in various combinations of ethanol, methanol and formaldehyde, were examined using Agilent's Resolve hand-held SORS device. The spectral data recorded were then compared with a variety of calibration solutions, and checked against the Museum's curatorial records for each jar.

"The method accurately identified the preservation fluids in 78.5 percent of cases and showed partial agreement in another 15 percent, often with visually similar or chemically complex solutions," noted the project in its paper.

"Only 3 samples (6.5 percent) were misclassified or unclassified. Additionally, the approach allowed distinguishing between different types of glass and/or plastic container, providing potential insights into fluid-container interactions and historical storage conditions."

This means that SORS may not just retrospectively identify historic chemicals but also help curators monitor chemical changes that have taken place over time, assisting their preservation efforts more broadly.

"This work is the next step in demonstrating the Museum's commitment to transforming the study of natural history," said Wren Montgomery from the Natural History Museum. "Analyzing the storage conditions of precious specimens, and understanding the fluid in which they are kept, could have huge implications for how we care for collections and preserve them for future research for years to come."