Evaluating different methods for calculating the Carbon Preference Index (CPI): implications for palaeoecological and archaeological research

The Carbon Preference Index (CPI) is a molecular ratio often used to assign the biological source and maturity of organic matter. This parameter is frequently employed in paleoenvironmental studies and archaeological applications. In this paper, we have evaluated the different results for this index using peak areas or concentrations from calibration curves. For this purpose, plant reference samples (Celtis Australis L.) and sediments from two archaeological sites were analysed. The results show that the values obtained depend on the method employed and, thus, interpretations may differ significantly. Consequently, the method used must be clearly stated in each particular application and results can only be compared when using the same protocol.