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Citric acid traps to replace sulphuric acid in the ammonia diffusion of dilute water samples for 15 N analysis
Author(s) -
Schleppi Patrick,
BucherWallin Inga,
Saurer Matthias,
Jäggi Maya,
Landolt Werner
Publication year - 2006
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.2351
Subject(s) - chemistry , citric acid , ammonia , diffusion , inorganic chemistry , nuclear chemistry , radiochemistry , analytical chemistry (journal) , chromatography , organic chemistry , thermodynamics , physics
The analysis of 15 N in aqueous samples requires the concentration of dissolved nitrogen (N) into a small volume that can be analysed by mass spectrometry. This is conveniently achieved by the NH 3 diffusion technique, where NH 4 +is captured on small acidified filters enclosed in PTFE. NO 3 −can be analysed the same way by reducing it to NH 4 +with Devarda's alloy. H 2 SO 4 is commonly used for the acidification of the filters. During combustion, however, this acid leads to the production of SO 2 and elemental sulphur, which both have detrimental effects on the mass spectrometer. We propose here to replace H 2 SO 4 with citric acid because it is combusted completely to CO 2 and H 2 O in the elemental analyser before entering the mass spectrometer. Citric acid was found to give comparable results in terms of N recovery and 15 N values, both for NH 4 +and for NO 3 −samples. Blank samples revealed that N contamination was slightly lower using citric instead of sulphuric acid as acidifier of the glass filters. NH 4 +samples first concentrated over cation‐exchange columns were strongly acidic and several methods were tested to raise the pH for the subsequent diffusion. These samples gave incomplete N recoveries, but this problem was independent of the acid used on the filters and of the final pH of the sample. Complete recovery was achieved only by increasing the volume of the eluate from the columns. Citric acid can thus generally be recommended instead of H 2 SO 4 for ammonia diffusion. Copyright © 2006 John Wiley & Sons, Ltd.