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 (Delta C-14) 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 Delta C-14 values that were in strong agreement (R-2 = 0.998) with the original Delta C-14 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 mu gC, respectively, which are consistent with direct assessments of HPLC procedural blanks of 1.0 +/- 0.8 mu gC per sample. These contamination constraints allow correction of measured Delta C-14 values for accurate and precise CSRA and are widely applicable to future archeological and biogeochemical studies.