The Use of the 'Ammonium Diffusion' Method for delta N-15-NH4+ and delta N-15-NO3- Measurements: Comparison with Other Techniques

Several methods have been developed for nitrogen isotope measurements on ammonium (NH4+) and nitrate (NO3-) in solid or aqueous samples. We have tested the accuracy and reproducibility of the ammonium diffusion method for delta N-15 measurements on NH4+ and NO3- and compared this technique to other established methods. Our results show that the ammonium diffusion technique is capable of generating accurate and reproducible delta N-15 values for minute quantities of NH4+-N and NO3--N in aqueous samples, if sufficient care is taken to minimize nitrogen blanks and to optimize the extraction procedure. Hence, the ammonium diffusion method offers an attractive alternative to more labour-intensive and costly methods for determining nitrogen isotope ratios of NH4+ and NO3- in aqueous samples.