Spectrochemical fingerprinting and chemometric discrimination of 19th-Dynasty mummified entrails from a tomb in Saqqara.

Laser-Induced Breakdown Spectroscopy (LIBS) is well established for elemental analysis of inorganic cultural heritage materials such as stone, ceramics, and metals. Still, its application to degraded, organic-rich funerary residues, a matrix type that is both compositionally complex and often too fragile for conventional destructive analysis, remains comparatively unexplored. Here, LIBS was applied to four residues recovered from jars in the newly excavated (2020/2021) tomb of Ptahemwia near Djoser's Step Pyramid at Saqqara, dated to the 19th Dynasty of Ramesses II (1279-1213 BC). The main elemental constituents identified were Si, Ca, Mg, Fe, Al, Na, and C. Beyond qualitative fingerprinting, we combined unsupervised (PCA) and supervised (PLSR, ROC/AUC) multivariate analysis of the LIBS spectra to build and statistically validate a classification model (PC1 + PC2 = 92.7% of variance; PLSR R2 = 0.97-1; ROC AUC = 0.92-0.99) capable of objectively discriminating samples that are macroscopically very similar. EDX and FTIR analyses corroborated the LIBS-based classification. They provided complementary molecular context, revealing that sample calcium is hosted within a silicate rather than a carbonate matrix, and that a consistent CN molecular band across all four samples indicates shared nitrogen-bearing organic content consistent with degraded biological/embalming material. This combined LIBS-chemometric workflow offers a reproducible, minimally destructive approach for discriminating and characterizing complex organic-inorganic funerary residues at the point of excavation, with direct implications for artifact triage, provenance assessment, and conservation planning.