Improved Method for Isolation and Purification of Underivatized Amino Acids for Radiocarbon Analysis

We have improved a method for isolation and purification of individual amino acids for compound-specific radiocarbon analysis (CSRA). To remove high-performance liquid chromatography (HPLC) eluent blanks from isolated amino acid fractions prior to the radiocarbon (Δ14C) measurement, each fraction was filtered through a membrane filter and then washed with diethyl ether twice. Radiocarbon measurements on standard amino acids processed and purified with the above method using elemental analyzer–accelerator mass spectrometry resulted in Δ14C values that were in strong agreement (R2 = 0.998) with the original Δ14C value of each amino acid standard. From these measurements, we calculate dead and modern carbon contamination contributions as 1.2 ± 0.2 and 0.3 ± 0.1 μgC, respectively, which are consistent with direct assessments of HPLC procedural blanks of 1.0 ± 0.8 μgC per sample. These contamination constraints allow correction of measured Δ14C values for accurate and precise CSRA and are widely applicable to future archeological and biogeochemical studies.