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Optimization of the direct LSC method for determination of biogenic component in liquids by applying 14C

Krajcar Bronić, Ines; Sironić, Andreja; Barešić, Jadranka; Lovrenčić Mikelić, Ivanka; Borković, Damir (2021) Optimization of the direct LSC method for determination of biogenic component in liquids by applying 14C. In: LSC 2020 - International Conference on Advances in Liquid Scintillation Spectrometry - Abstract collection. Shenzen, China, LSC2020, pp. 41-42 .

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The 14C method can be successfully applied for determination of biogenic component in any type of samples and different measurement techniques can be applied. For a special case of liquid fuels, direct method by measurement 14C activity of liquid fuel samples in liquid scintillation counter (the „direct LSC method“) has been recognized as a powerful and reliable method of determination of biogenic component (fbio). In the Ruđer Bošković Institute (RBI) Radiocarbon Laboratory we have been implemented our own data evaluation method based on the quench properties of fuels (SQP(E) – Standard Quench Parameter in LSC Quantulus 1220) [1]. We participated in the international intercomparison 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 compare our fbio results with the fbio-ILC official results and report optimization of the direct LSC method. Laboratories obtained seven samples of diesel type of fuel having different colors. Consequently, the samples resulted in different SQP(E) values when the direct LSC methods was applied. Three samples were analyzed by the AMS (Accelerator Mass Spectrometry) method. The LSC results were quantitatively acceptable for four samples with SQP(E) values above 700 (Figure 1), which was taken as the lowest limit of quantitative fbio determination. Qualitatively acceptable, but quantitatively unacceptable results, were obtained for two samples with the SQP(E) values between 600 and 700, that was defined as the region of limited applicability. For one of the samples the quenching was high, SQP(E) < 600, and the direct LSC method did not give any result. However, all AMS results were acceptable (Figure 1) since AMS does not depend on the sample color. The obtained results have been used for further validation and optimization of the direct LSC method. We defined the limits of applicability of the direct-LSC method for both quantitative (SQP(E) > 700) and qualitative results (600 < SQP(E) < 700). A sample of used edible oil (UEO, laboratory code Z-7226) was used to test these limits. The UEO was a dark sample giving the SQP(E) value of 546 (below the limit of qualitative applicability), while the AMS revealed fbio = 97.9 ± 0.3 % (and δ13C = -29.6 ‰). We mixed the UEO with the (fossil) petrol (benzene) sample (laboratory code Z-6266), which we used as the background sample (fbio = 0 %) with good quenching properties (SQP(E) = 864). We monitored changes in the SQP(E) and fbio values in UEO-petrol mixtures in the concentration range 0 – 100 %. The total mixture volume was 10 mL and 10 mL of Ultima Gold F scintillation cocktail was added, i.e., the measurement was performed in the same manner as all other organic liquid samples [1]. Mixtures of 10 % and 20 % of UEO gave SQP(E) values of 773 and 759, and the fbio was calculated to be 104.0 ± 1.2 % and 101.1 ± 1.3 %, respectively, confirming the quantitative region of SQP(E) values above 700. Mixtures containing 30 – 50 % of UEO resulted in SQP(E) values between 671 and 609, while the fbio values were about 150 %, confirming qualitatively acceptable results. Mixtures containing more than 60 % of UEO had SQP values below 600 and fbio values had a large spread. The presented results showed that the direct LSC method with an evaluation method developed in our laboratory was suitable for determination of the fbio in liquid fuels, providing the correctly defined limits of applicability for highly quenched samples. The RBI Laboratory has a possibility of applying also AMS 14C measurement technique that can satisfactorily determine fbio also in highly quenched samples, but the AMS technique is more complicated and more expensive.

Item Type: Conference or workshop item published in conference proceedings (UNSPECIFIED)
Uncontrolled Keywords: 14C, biogenic component, fuels, direct method
Subjects: NATURAL SCIENCES > Physics
NATURAL SCIENCES > Interdisciplinary Natural Sciences
NATURAL SCIENCES > Interdisciplinary Natural Sciences > Environmental Science
NATURAL SCIENCES > Interdisciplinary Natural Sciences > Radiation Science
Divisions: Division of Experimental Physics
Depositing User: Ines Krajcar Bronić
Date Deposited: 11 Nov 2021 06:17

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