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 (Δ14 C) 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 Δ14 C values that were in strong agreement ( R2 = 0.998) with the original Δ14 C 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 Δ14 C values for accurate and precise CSRA and are widely applicable to future archeological and biogeochemical studies.