COMPOUND-SPECIFIC RADIOCARBON DATING OF ESSENTIAL AND NON-ESSENTIAL AMINO ACIDS: TOWARDS DETERMINATION OF DIETARY RESERVOIR EFFECTS IN HUMANS

When humans consume foods from different radiocarbon reservoirs offset in age to the atmosphere, inaccuracies in the C-14 date of bone collagen can occur. Mesolithic human skeletons from the Iron Gates section of the Lower Danube Valley have yielded reservoir offsets of up to similar to 500 yr. This has been demonstrated through direct dating of bulk collagen from human bones and the remains of ungulate bone projectile points that were found embedded in them (Cook et al. 2001). We present improvements to a novel HPLC method for the detection and separation of underivatized amino acids using a water-only mobile phase free of organic or inorganic modifiers, ensuring very low carbon backgrounds. Our hypothesis is that direct C-14 dating of single essential and non-essential amino acids might allow an improvement in the dating accuracy for reservoir-affected human bones. The method facilitates separation of less polar amino acids (mostly essential), currently not possible in the recently published protocol. We discuss methodological developments, demonstrate carbon backgrounds, and present analytical approaches to minimize their effects. We validate the precision and accuracy of the method by accelerator mass spectrometry (AMS) dating relatively modern and C-14-dead, known-age bone standards. Finally, we apply the method to the dating of single amino acids from bone samples with a proven similar to 500-yr carbon reservoir effect from Mesolithic burials at the Iron Gates sites. We investigate whether differences can be found in AMS dates for essential and non-essential amino acids since, although contemporaneous, these are expected to derive from dietary sources with differing C-14 reservoirs.