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Method validation for the determination of fraction of modern (F14C) in wood samples using conventional method

Baydoun R., El Samad O., Nsouli B., Younes G.

Geochronometria

2018

Vol. 45, no. 1

68--73

The radiocarbon laboratory at the Lebanese Atomic Energy Commission is undertaking environmental studies, in order to determine the anthropogenic impact of technologies on the ecosystem through the determination of radiocarbon content in tree leaves and plants. Thus, it was important to validate the method used to demonstrate that the applied procedure gives reliable results. Method validation is universally applied in analytical laboratories as an essential part of quality assurance system and as a basic technical requirement of the ISO 17025 standard. The conventional method used for determination of Fraction Modern (F14C) is a standard method issued by the American Society for Testing and Materials in 2011 with a code ASTM-D 6866-11 Method C. According to Eurachem guide, internal validation was expressed in terms of accuracy that was evaluated by trueness and precision. Trueness was expressed in terms of relative bias, while for precision ten consecutive replicates were carried out to under repeatability conditions and five duplicates were analyzed under reproducibility conditions. The limit of detection and the minimum detectable activity (MDA) were calculated. Uncertainty sources were defined and their relative standard uncertainties were calculated in order to determine the combined standard uncertainty. Five reference samples of different matrices were analyzed; calculated z score values were acceptable as being between –2 and +2. The calculation and results are presented in this work.

Set-up, optimization and first set of samples at the radiocarbon laboratory in Lebanon

Baydoun R., El Samad O., Aoun M., Nsouli B., Younes G.

Geochronometria

2014

Vol. 41, no. 1

87--91

A new radiocarbon laboratory has been established recently at the Lebanese Atomic Ener-gy Commission. This laboratory consists of benzene synthesis line and a low background liquid scin-tillation counter, Tri-Carb 3180 TR/SL for measurements with Bismuth Germanate (BGO) guard de-tector. The effectiveness of the benzene line was tested firstly by preparing benzene from a wood sample after carbide and acetylene receiving. Normalization and standardization of the liquid scintil-lation counter was carried out, as well as the Factor of Merit (E2/B) was determined for three differ-ent counting regions. To assure accuracy and reliability of results, reference materials were used. Based on z-score and u-score evaluation, as well as Student's t-test, acceptable data were obtained from travertine and wood samples available through the International Atomic Energy Agency (IAEA-C2 and IAEA-C5), and humic acid (U) and murex shell (R) from the Fifth International Radiocarbon Intercomparison (VIRI). After that, a preliminary study was done, which is the base for future re-search in order to assess the anthropogenic impact and degree of environmental pollution in terms of radiocarbon isotope ratio (Δ14C) deduced from the Percent Modern Carbon or PMC. This work repre-sents the results of four reference materials and those of five green grass samples. The Δ14C of green grass samples collected from two different clean zones were found to be 50‰ and 52‰, while the values of those collected from different polluted zones were 23‰, 7‰ and 15‰.