The instrument that we used in our initial proof-of-principle study was a modified commercially available LC IsoLink™ interface (Thermo Fisher Scientific Inc., Bremen, Germany) (see Figure ). In a preliminary step (i), nitrate was chromatographically separated from the injection peak and potential matrix interferences on a porous graphitic carbon (PGC)-HPLC column. In a second step, nitrate was reduced by a V(III)Cl3 solution to NxOy with nitric oxide (NO) being the main product formed. Nitrogen oxides were separated from the eluent by membrane pervaporation (iii). After Nafion™ drying (iv), NxOy and NO were reduced to N2 gas by a copper-filled ceramic reduction tube in a furnace (v). Furthermore, oxygen was scavenged during this step, which enhances the precision and longevity of the filament in the IRMS ion source. Following reduction to N2, carbon dioxide was removed by a cryo trap with a slurry of acetone / dry ice (vi) before the N2 entered the IRMS via an open split.