Determination of total dissolved nitrogen in seawater by isotope dilution gas chromatography mass spectrometry following digestion with persulfate and derivatization with aqueous triethyloxonium.

•High-precision ID GC–MS method for total dissolved nitrogen in seawater.•Procedural detection limit of 0.5 μmol/kg.•Recovery of typical nitrogen containing compounds better than 90%.•High throughput primary ratio method.