New procedure for extraction of ammonium from natural waters for N isotopic ratio determinations.

A new method for extracting ammonium from natural waters for N isotopic ratio determination is described. The method employs the conversion of the ammonium nitrogen into indophenol, which is then concentrated onto an octadecylsilane column. The method shows accuracy and precision comparable to those of other methods described in the literature. Some results from field experiments on the Swedish west coast are presented.