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A simple method for the removal of dissolved organic matter and δ 15 N analysis of NO 3 – from freshwater
Author(s) -
Huber Benjamin,
Bernasconi Stefano M.,
Pannatier Elisabeth Graf,
Luster Jörg
Publication year - 2012
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.6243
Subject(s) - chemistry , nitrate , dissolved organic carbon , nitrogen , sodium nitrate , sodium hydroxide , isotopic signature , environmental chemistry , acetone , hydroxide , isotopes of nitrogen , organic matter , stable isotope ratio , analytical chemistry (journal) , inorganic chemistry , physics , organic chemistry , quantum mechanics
RATIONALE Stable isotopes of nitrogen in nitrate (NO 3 – ) are frequently used to identify nitrate sources and to study nitrogen (N) transformation processes, but the measurement methods available are generally rather labor intensive and/or costly, and dissolved organic matter (DOM) can interfere with the δ 15 N signature of nitrate. We therefore have developed a simple cleanup procedure for freshwater samples with low nitrate and high DOM concentrations. METHODS Nitrate and DOM are extracted from a freeze‐dried water sample by using a concentrated sodium hydroxide solution. By the subsequent addition of acetone, two liquid layers are formed, and nitrate migrates into the acetone while DOM remains in the concentrated NaOH solution, thus separating the nitrate from the DOM. For nitrogen isotope analysis, purified nitrate salts are combusted at 1030 °C to produce N 2 gas in an elemental analyzer (EA) coupled to an isotope ratio mass spectrometer (IRMS). RESULTS With this novel technique up to 99% of DOM could be removed from river water and soil solutions. The method has been tested for sample amounts as small as 4 µmol NO 3 – with a precision of <0.1‰ (1SD). Nitrate standards are reproduced accurately without any blank correction. CONCLUSIONS The benefits of this method are the lack of interferences derived from DOM on the δ 15 N signature and the ease of sample preparation. Copyright © 2012 John Wiley & Sons, Ltd.