Compound-Specific Radiocarbon Analysis by Elemental Analyzer–Accelerator Mass Spectrometry: Precision and Limitations

Abstract

[EN]We examine instrumental and methodological capabilities for microscale (10−50μg of C) radiocarbon analysisof individual compounds in the context of paleoclimate and paleoceanography applications, for which relatively high-precisionmeasurements are required. An extensive suite of data for14C-free and modern reference materials processed using differentmethods and acquired using an elemental-analyzer−accelerator-mass-spectrometry (EA-AMS) instrumental setup at ETHZurich was compiled to assess the reproducibility of specific isolation procedures. In order to determine the precision, accuracy,and reproducibility of measurements on processed compounds, we explore the results of both reference materials and threeclasses of compounds (fatty acids, alkenones, and amino acids) extracted from sediment samples. We utilize a MATLAB codedeveloped to systematically evaluate constant-contamination-model parameters, which in turn can be applied to measurementsof unknown process samples. This approach is computationally reliable and can be used for any blank assessment of small-sizeradiocarbon samples. Our results show that a conservative lower estimate of the sample sizes required to produce relativelyhigh-precision14C data (i.e., with acceptable errors of <5% onfinal14C ages) and high reproducibility in old samples (i.e., F14C≈0.1) using current isolation methods are 50 and 30μg of C for alkenones and fatty acids, respectively. Moreover, when theF14C is >0.5, a precision of 2% can be achieved for alkenone and fatty acid samples containing≥15 and 10μg of C, respectively