Portable ER-FTIR as a non-destructive method to pre-screen collagen for ZooMS analysis in archaeology

In the last decades, archaeology has witnessed a significant increase in the use of biomolecular analyses to study a variety of materials, including skeletal elements, as they are frequently preserved in archaeological deposits and directly linked to cultural and economic dynamics of ancient human populations. Radiocarbon dating, isotopic studies, and proteomic analyses are particularly useful to explore these questions, while their success is highly dependent on the state of preservation of collagen, the most abundant component of the organic fraction of skeletal elements. Over time collagen degrades, and its preservation is often compromised in very ancient archaeological contexts or when taphonomic processes are particularly severe, which can significantly limit the feasibility of subsequent biomolecular analyses. The aim of this study is to test whether external reflectance Fourier Transform Infrared Spectroscopy (ER-FTIR) can serve as a rapid, non-destructive pre-screening tool for assessing collagen preservation prior to ZooMS analysis. To evaluate the method's effectiveness, various faunal bone fragments were selected from different archaeological contexts (e.g., rock shelters, pits in dune fields, etc.) located in the Central Sahara (SW Libya), dating to the Middle and Late Holocene (8300–3400 cal BP). The bone fragments were first subjected to ER-FTIR analysis and then to ZooMS (Zooarchaeology by Mass Spectrometry) to compare the results and assess the presence of collagen in the samples. Our results indicate that collagen was detected in about one-third of the samples, consistently associated with specific spectral features and further validated by ZooMS analyses. The method effectively distinguished well-preserved from poorly preserved samples while avoiding destructive sampling. This pre-screening approach reduces time and financial costs and safeguards the integrity of archaeological bones. Beyond its practical application, it also contributes to bioarchaeology and conservation science by providing a reproducible, non-destructive framework for evaluating biomolecular preservation across different sites and periods.