Isolation of Underivatized Amino Acids for Radiocarbon Analysis Using a Porous Graphite Column

We developed a method for isolation and purification of individual underivatized amino acids for compound-specific radiocarbon analysis. Our method employs a semipreparative porous graphitic carbon column that allows for separation and isolation of all proteinogenic amino acids in a single step. To minimize contamination, we utilized a mixed-mode ion-exchange column to further purify the isolated amino acid fractions. Radiocarbon measurements of standard amino acids processed with this method resulted in F¹⁴C values closely aligned with their original F¹⁴C values. From these measurements, we calculated the blank contribution to 1.0 ± 0.3 μg C with F¹⁴C = 0.6 ± 0.12, rendering this approach suitable for ultrasmall samples with enhanced measurement reliability.