[Isotope analysis of ammonium and nitrate: A review on measured methods and their application].

In the past several decades, a variety of methods have been developed for measuring the isotopic composition of ammonium (δN) and nitrate (δN and δO). This review summarized the advantages and disadvantages of these methods. Nowadays, the most popular method for measu-ring δN of ammonium is the combined hypobromite (BrO) and hydroxylamine (NHOH) me-thod, while for δN and δO of nitrate is the denitrifier method and the sodium azide (NaN) me-thod. These methods convert NH or NO into nitrous oxide (NO) and measure its isotopic compositions, with higher analytical precision because of the lower background concentration of atmospheric NO. Accordingly, these methods are suitable for the samples with lower N concentration, and normally require 10-60 nmol N. The development of new methods for measuring N isotopic composition has greatly stimulated the studies in nitrogen cycling worldwide.