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The 14C method can be successfully applied for determination of biogenic component in any type of samples. For a special case of liquid fuels, the „direct LSC method“ for measurement 14C activity by a liquid scintillation counter (LSC) has been recognized as a powerful and reliable method of determination of biogenic component. Laboratories of the Ruđer Bošković Institute (RBI) in Zagreb, the Jožef Stefan Institute (JSI) in Ljubljana, and at the Faculty of Science of the University of Novi Sad (UNS) in Novi Sad implemented the direct LSC method and optimized slightly different measurement and evaluation procedures (Krajcar Bronić et al., 2017, Krištof and Kožar Logar, 2013, Stojković et al., 2017). They defined limits of applicability of the direct LSC method by the values of the Standard Quench Parameter SQP(E) determined by the LSC Quantulus 1220. The laboratories participated in the international inter-laboratory comparison study ILC/2018 „Content of biocomponent in liquid fuel samples“, which was organized in 2018 by the Institute of Ceramics and Building Materials (Opole, Poland). Here we present the results obtained by these 3 laboratories and compare the fbio results with the expected fbio-exp values. Seven samples of diesel type of fuel having different concentrations of biocomponent and different colours were obtained. The results for samples with the SQP(E) values well above the limits of applicability of the direct LSC method were satisfying in all three laboratories. Qualitatively acceptable, but quantitatively unacceptable results, were obtained for a sample in the SQP(E) region of limited applicability. One of the samples exhibited a high quench level, so the SQP(E) parameter was below the limits of applicability of the direct LSC method in all 3 laboratories, (SQP(E) < 600). The RBI laboratory applied accelerator mass spectrometry (AMS) technique to determine fbio in this highly-quenched sample as well as in the sample without 14C (SQP(E) > 800) and in the sample having SQP(E) in the limited region of applicability (600 < SQP(E) < 700). The JSI laboratory applied the direct absorption of CO2 in an absorption-scintillation cocktail (DA) technique for the highly-quenched sample (SQP(E) < 600). The UNS laboratory used the biogenic oil for calibration and also the internal standard method (IntSt), and the latter resulted in better agreement with the expected values. Although there were some differences in details of the applied direct LSC methods in the three laboratories, the presented intercomparison results showed that all the methods were suitable for determination of the fbio in liquid fuels, providing the correctly defined limits of applicability for highly quenched samples. Laboratories that have possibility of applying a different 14C measurement technique can satisfactorily determine fbio also in highly quenched samples. |
