Improved method for isotopic and quantitative analysis of dissolved inorganic carbon in natural water samples | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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  Improved method for isotopic and quantitative analysis of dissolved inorganic carbon in natural water samples

Type de publication:

Journal Article

Source:

Rapid Communications in Mass Spectrometry, Volume 20, Ticket 15, p.2243-2251 (2006)

ISBN:

0951-4198

URL:

http://www3.interscience.wiley.com/cgi-bin/jhome/110429751

Mots-clés:

Delta-c-13-analysis; surface-waters; ground-waters; dioxide-; fractionation-; lake-; evolution-; ratios-; system-; france-

Résumé:

<p>We present here an improved and reliable method for measuring the concentration of dissolved inorganic carbon (DIC) and its isotope composition (delta C-13(DIC) in natural water samples. Our apparatus, a gas chromatograph coupled to an isotope ratio mass spectrometer (GCIRMS), runs in a quasi-automated mode and is able to analyze about 50 water samples per day. The whole procedure (sample preparation, CO2(g)-CO2(aq) equilibration time and GCIRMS analysis) requires 2 days. It consists of injecting an aliquot of water into a H3PO4-loaded and He-flushed 12 mL glass tube. The H3PO4 reacts with the water and converts the DIC into aqueous and gaseous CO2. After a CO2(g)-CO2(aq) equilibration time of between 15 and 24 h, a portion of the headspace gas (mainly CO2+He) is introduced into the GCIRMS, to measure the carbon isotope ratio of the released CO2(g), from which the delta C-13(DIC) is determined via a calibration procedure. For standard solutions with DIC concentrations ranging from 1 to 25 mmol (.) L-1 and solution volume of 1 mL (high DIC concentration samples) or 5 mL (low DIC concentration samples), delta C-13(DIC) Values are determined with a precision (1 sigma) better than 0.1 parts per thousand. Compared with previously published headspace equilibration methods, the major improvement presented here is the development of a calibration procedure which takes the carbon isotope fractionation associated with the CO2(g)-CO2(aq) partition into account: the set of standard solutions and samples has to be prepared and analyzed with the same 'gas/liquid' and 'H3PO4/water' volume ratios. A set of natural water samples (lake, river and hydrothermal springs) was analyzed to demonstrate the utility of this new method. Copyright (c) 2006 John Wiley and Sons, Ltd.</p>

Notes:

Rapid commun. mass spectrom.Inst Phys Chim Fluides Geol, Inst Phys Globe Paris, F-75251 Paris 05, France; Univ Paris 07, CNRS, UMR 7154, F-75251 Paris, France; Inst Phys Globe, Ctr Rech Stockage Geol CO2, F-75252 Paris 05, France; Inst Phys Globe, Lab Geochim Eaux, F-75251 Paris 05, FranceArticleEnglish