A low‐blank photochemical extraction system for concentration and isotopic analyses of marine dissolved organic carbon

We report the development of a modified, low blank, ultraviolet oxidation and vacuum line system to convert marine dissolved organic carbon into carbon dioxide for concentration, Δ14C, and δ13C analyses. The system performs quantitatively and precisely with preservation of isotopic signatures (± 3‰) based on additions of pure International Atomic Energy Agency standards. Analytical blank reduction from < 1.5 µM to 0.2 µM enabled a decreased detection limit from a sample size of ~650 mL to 30 mL using a simple dilution technique. Combined with advances in analyses of ultra‐small (2 µgC) samples using accelerator mass spectrometry, the technique provides a means for measuring Δ14C values in samples that were previously not analyzable.