1. Harmonization of VFAs measurement by GC: Something more than R2 to evaluate the calibration function
- Author
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Raposo Bejines, Francisco, Borja Padilla, Rafael, Cacho, Jesús A., Noguerol, J., Mühlemberg, J., Schuit, A. D., Rehde, G., Frigon, J.C., Peñuela, G. A., Aymerich, E., Battimelli, Audrey, Bolzonella, David, Instituto de la Grasa, Veolia Environnement, Institute of Agrifood Research and Technology (IRTA), Deutsches Biomasseforschungszentrum (DBFZ), Delft University of Technology (TU Delft), Leibniz Institute for Agricultural Engineering and Bioeconomy, Bioengineering Group (GEBI), Université Catholique de Louvain = Catholic University of Louvain (UCL), University of Antioquia, Universidad de Navarra [Pamplona] (UNAV), Laboratoire de Biotechnologie de l'Environnement [Narbonne] (LBE), Institut National de la Recherche Agronomique (INRA)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Department of Biotechnology, University of Verona (UNIVR), and International Water Association (IWA). INT.
- Subjects
chromatographie ,[SDV]Life Sciences [q-bio] ,méthode analytique ,[SDE]Environmental Sciences ,digestion anaérobie ,étude interlaboratoire ,acide gras volatil - Abstract
Anaerobic digestion is sensitive to many environmental factors requiring a robust control of this process. One of the analytical measurements considered as key parameter is the volatile fatty acids (VFAs) content. Total amount of volatile acids (TVFA) to control the relative changes over time has been suggested as a useful tool. However, TVFA does not provide sufficient information to reveal the overall reactor performance, and individual components have been considered of particular interest. Although some attempts have been described as on-line measurements for individual VFAs, normally they are determined by off-line chromatographic techniques (GC and HPLC). A previous interlaboratory study showed the lack of harmonization in the analytical methodologies dealing to individual VFAs, and giving an overall analytical performance rather poor. One of the reasons to justify these results was the inappropriate calibration procedures. It is widely used to check the linearity of the calibration curves based on the correlation and determination coefficients. However, these statistical parameters are erroneously interpreted. The objective of this interlaboratory study was to achieve the harmonization of results. By this way, the use of internal standard methodology (ISTD) should be useful to obtain accurate calibration functions. In addition, five different statistical parameters such as lack of fit test, residual standard deviation, relative standard deviation of the slope, relative standard deviation of the sensitivity and relative error were proposed to evaluate the linearity of calibration curves. Of these, lack of fit was unable to detect appropriately the linearity mainly due to its sensitivity to the precision of analytical results. The rest of statistical parameters reported could be considered as starting point for comparative purposes, being useful as acceptance criteria. The principal advantage of the GC/ISTD analytical methodology was the normalization of the slopes obtained by the participating laboratories, being very helpful to the harmonization of results.
- Published
- 2015