N and O isotope (δ15 Nα , δ15 Nβ , δ18 O, δ17 O) analyses of dissolved NO3- and NO2- by the Cd-azide reduction method and N2 O laser spectrometry.

The Cd-azide method yielded excellent results for routine determination of δ15 N, δ18 O and δ17 O values (and the 17 O excess) of nitrate or nitrite by laser spectrometry. Disadvantages are the toxicity of Cd-azide chemicals and the lack of automated sampling devices for N2 O laser spectrometers. The 15 N-enriched tracer test revealed potential for position-specific experimentation of aqueous nutrient dynamics at high 15 N enrichments by laser spectrometry, but exposed the need for memory corrections and improved spectral deconvolution of 17 O.