Determination of the Concentration of Carbonic Species in Natural Waters: Results from a World‐Wide Proficiency Test |
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| Authors: | Mahendra P Verma Enrique Portugal Sophie Gangloff María Aurora Armienta Dornadula Chandrasekharam Mayela Sanchez Roberto E Renderos Miguel Juanco Robert van Geldern |
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| Affiliation: | 1. Geotermia, Instituto de Investigaciones Eléctricas, Cuernavaca, Morelos, México;2. Laboratoire d'Hydrologie et de Géochimie de Strasbourg, Université de Strasbourg/EOST, CNRS, Strasbourg Cedex, France;3. Laboratorio de Química Analítica, Instituto de Geofísica, Universidad Nacional Autónoma de México, Circuito Exterior, C.U., Mexico D.F, Mexico;4. Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai, India;5. Dirección Planta Geotérmica, ENEL Central. Intersección de Pista Juan Pablo II y Prolongación de Avenida Bolívar, Managua, Nicaragua;6. Laboratorio Geoquímico, Gerencia de Estudios y Evaluación, La Libertad, Centro America, El Salvador;7. Instituto de Ciencias Agrarias CSIC, Madrid, Spain;8. Department of Geography and Geosciences, GeoZentrum Nordbayern, University of Erlangen‐Nuremberg (FAU), Erlangen, Germany |
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| Abstract: | The results of an international interlaboratory proficiency test for the determination of carbonic species are presented. Eight laboratories analysed twelve water samples (four synthetic waters, one lake water, four geothermal waters, one seawater and two petroleum waters) by two methods: (a) individual laboratory analytical procedure and (b) acid–base titration curves in tabular form following a standardised protocol. In case (b), the concentrations of carbonic species were calculated by the organiser using the (1) Hydrologists' method, (2) Geochemists' method and/or (3) initial pH and total alkalinity method. For synthetic waters, the averaged % trueness and precision of measurement of the two methods were (trueness = 7.6, precision = 9.4) and (9.0, 3.4) for total alkalinity, and (6.6, 31.0) and (7.8, 6.1) for carbonic alkalinity, respectively. This indicates that the total alkalinity calculation procedure is in general correct in the individual laboratory method, but the carbonic alkalinity calculation procedure has serious problems. The measurements of total alkalinity for lake and seawaters were in agreement in both the methods; however, the individual laboratory measurement method for geothermal and petroleum waters was conceptually incorrect. Thus, the analytical procedures for the determination of carbonic species were reviewed. To apply the Hydrologists' and/or Geochemists' methods, the location of NaHCO3EP and H2CO3EP is necessary, even for samples with pH lower than that of NaHCO3EP, and a backward titration curve after complete removal of CO2 must be performed. The initial pH and total alkalinity method is appropriate where a complete analysis of species that contribute to the alkalinity is known. |
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| Keywords: | acid– base titration analytical method CO2 chemistry interlaboratory comparison natural waters titrage acide‐base mé thode analytique chimie du CO2 comparaison inter‐laboratoires eaux naturelles |
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