Gas Diffusion Method: a Simple and Rapid Method for δ~(15)N - NH_4 Determination in Water Samples

摘要

Isotope tracer analysis is one of the most expected methods for studying the nitrogen cycle in aquatic environments in determining the sources and processes of nitrogen compounds. Previously, several researches proposed the analytical procedure for δ~(15)N - NH_4, those methods have been still insufficient for practical application in technical reasons. In this study, Gas diffusion method was developed for recovering ammonium followed by analysis of stable isotope ratios. This method was an enhancement of the liquid phase diffusion method, in which NH3 in base condition is trapped in acidic filter through gas phase instead of liquid phase as the original method suggested. The results demonstrated that, for environmental water samples having concentration more than 1 ppm, isotope ratios were determined with high precision, ± 0.41 ‰, after five days of sample diffusion. In summary, this method could shorten time threefold and need sample volume less than 80 times comparing to the liquid phase diffusion method.