Quantification of nitrite and nitrate in seawater by triethyloxonium tetrafluoroborate derivatization-Headspace SPME GC-MS

Triethyloxonium tetrafluoroborate derivatization combined with direct headspace (HS) or SPME-gas chromatography-mass spectrometry (GC-MS) is proposed here for the simultaneous determination of nitrite and nitrate in seawater at micromolar level after conversion to their corresponding volatile ethyl-esters (EtO-NO and EtO-NO2). Isotopically enriched nitrite [N-15] land nitrate [N-15] are employed as internal standards and for quantification purposes. HS-GC-MS provided instrumental detection limits of 0.07 mu M NO2- and 2 mu M NO3-. Validation of the methodology was achieved by determination of nitrite and nitrate in MOOS-1 (Seawater Certified Reference Material for Nutrients. NRC Canada), yielding results in excellent agreement with certified values. All critical aspects connected with the potential inter-conversion between nitrite and nitrate (less than 10%) were evaluated and corrected for by the use of the isotopically enriched internal standard. (C) 2011 Elsevier B.V. All rights reserved.