Pyrolysis Compound-Specific Isotope Analysis (Py-CSIA): a novel analytical approach for archaeological studies

Abstract

The measurement of stable isotopes has become an important tool within the field of archaeology. The isotopic trace of human and animal tissues and components (bone, collage, keratin, muscle, fat etc.) allowed insight into the diet of our ancestors in a specific period of time, as well as its relationship with various human pathologies. Furthermore, this technique informs about food origin and possibly also their commercial routes, as well as population migrations. Pyrolysis-compound specific isotope analysis (Py-CSIA) is a cutting-edge analytical approach able to provide, not only a precise identification of organic compounds in different complex matrices, but also additional valuable information about nature and origin of the materials based on their isotope composition. This technique is based on the coupling of a micro-furnace pyrolysis unit to a gas chromatograph equipped with an isotope ratio mass spectrometer (IRMS) as detector. The individual volatile pyrolysis products separated by gas chromatography are directed to a combustion or pyrolysis micro-reactor (GC-Isolink system) and finally the isotope composition of the gases produced measured in a continuous flow IRMS via an interface unit. With this technique it is possible to make direct determinations of stable isotope ratios (i.e. δ13C, δ15N, and δ2H) of specific compounds with minimum sample handling and pre-treatment, thus minimizing the chance of contamination and artefacts productions. In this communication, we introduce the Py-CSIA technique into the field of archaeology by studying the direct determination of the isotopic composition of human skeletons buried in medieval necropolises from Center and South of Portugal.