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.