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Diffusion technique for 15N and inorganic N analysis of low‐N aqueous solutions and Kjeldahl digests

Diffusion technique for 15N and inorganic N analysis of low‐N aqueous solutions and Kjeldahl digests Diffusion of ammonia is a common sample preparation method for the stable isotope analysis of inorganic nitrogen in aqueous solution. Classical diffusion methods usually require 6–12 days of diffusion and often focus on 15N/14N analysis only. More recent studies have discussed whether complete N recovery was necessary for the precise analysis of stable N isotope ratios. In this paper we present a newly revised diffusion technique that allows correct and simultaneous determination of total N and 15N at% from aqueous solutions and Kjeldahl digests, with N concentrations down to sub‐0.5‐mg N L−1 levels, and it is tested under different conditions of 15N isotope labelling. With the modification described, the diffusion time was reduced to 72 h, while the ratios of measured and expected 15N at% were greater than 99% and the simultaneous recovery of total N was >95%. Analysis of soil microbial biomass N and its 15N/14N ratio is one of the most important applications of this diffusion technique. An experiment with soil extracts spiked with 15N‐labelled yeast showed that predigestion was necessary to prevent serious N loss during Kjeldahl digestion of aqueous samples (i.e. soil extracts). The whole method of soil microbial biomass N preparation for 15N/14N analysis included chloroform fumigation, predigestion, Kjeldahl digestion and diffusion. An experiment with soil spiked with 15N‐labelled yeast was carried out to evaluate the method. Results showed a highly significant correlation of recovered and added N, with the same recovery rate (0.21) of both total N and 15N. A kN value of 0.25 was obtained based on the data. In conclusion, the diffusion method works for soil extracts and microbial biomass N determination and hence could be useful in many types of soil/water studies. Copyright © 2008 John Wiley & Sons, Ltd. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Rapid Communications in Mass Spectrometry Wiley

Diffusion technique for 15N and inorganic N analysis of low‐N aqueous solutions and Kjeldahl digests

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References (35)

Publisher
Wiley
Copyright
Copyright © 2008 Wiley Subscription Services
ISSN
0951-4198
eISSN
1097-0231
DOI
10.1002/rcm.3525
pmid
18438764
Publisher site
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Abstract

Diffusion of ammonia is a common sample preparation method for the stable isotope analysis of inorganic nitrogen in aqueous solution. Classical diffusion methods usually require 6–12 days of diffusion and often focus on 15N/14N analysis only. More recent studies have discussed whether complete N recovery was necessary for the precise analysis of stable N isotope ratios. In this paper we present a newly revised diffusion technique that allows correct and simultaneous determination of total N and 15N at% from aqueous solutions and Kjeldahl digests, with N concentrations down to sub‐0.5‐mg N L−1 levels, and it is tested under different conditions of 15N isotope labelling. With the modification described, the diffusion time was reduced to 72 h, while the ratios of measured and expected 15N at% were greater than 99% and the simultaneous recovery of total N was >95%. Analysis of soil microbial biomass N and its 15N/14N ratio is one of the most important applications of this diffusion technique. An experiment with soil extracts spiked with 15N‐labelled yeast showed that predigestion was necessary to prevent serious N loss during Kjeldahl digestion of aqueous samples (i.e. soil extracts). The whole method of soil microbial biomass N preparation for 15N/14N analysis included chloroform fumigation, predigestion, Kjeldahl digestion and diffusion. An experiment with soil spiked with 15N‐labelled yeast was carried out to evaluate the method. Results showed a highly significant correlation of recovered and added N, with the same recovery rate (0.21) of both total N and 15N. A kN value of 0.25 was obtained based on the data. In conclusion, the diffusion method works for soil extracts and microbial biomass N determination and hence could be useful in many types of soil/water studies. Copyright © 2008 John Wiley & Sons, Ltd.

Journal

Rapid Communications in Mass Spectrometry – Wiley

Published: Jan 15, 2008

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