RESUMEN
Uncertainty associated with nuclear counting analyses are attributed to two main components of uncertainty; one is related to sampling, the other to sample preparation and the subsequent nuclear counting. The ISO/IEC 17025 standard of 2017 require accredited laboratories carrying out their own sampling to estimate the uncertainty associated with sampling in the field. This study presents the results of a sampling campaign and analysis by gamma spectrometry to determine the sampling uncertainty related to the measurement of radionuclides in soil.
RESUMEN
Measurement uncertainty is an important variable, to be accounted for when decisions have to be made based on measurement results. Measurement uncertainty is composed of two main components; one is related to the primary sampling, the other to the sample preparation and the subsequent analysis of the sample. The component related to the sample preparation and the analysis is commonly well evaluated in proficiency testing while there is generally no straightforward similar approach to evaluate sampling uncertainty. ISO 17025:2017 explicitly requires that testing laboratories performing sampling and analyses determine the uncertainty related to the primary sampling. In order to determine uncertainty arising in the primary sampling of 222Rn in water destined for human consumption, three laboratories IRE (BE), DiSa (LU) and SCK CEN (BE) initiated a joined sampling and measurement campaign. The dual split sample method in combination with ANOVA was used to evaluate the primary sampling uncertainty (precision) of the different methods. The tests showed that sampling bias is very probably, but that with good laboratory practice the sampling uncertainty precision and respectively bias can be kept below 5%.
RESUMEN
Calix[4]arenes substituted by four urea functions are self-complementary molecules that spontaneously combine in apolar solvents in the presence of an ammonium salt to form dimeric capsules held together by a belt of hydrogen bonds. In the presence of tetraethylammonium salts, the Et4N+ cation is included as a guest. The sorting between dimeric capsules formed in a mixture of calix[4]arenes directly depends on the steric crowding of the substituents grafted on the urea groups whether aromatic derivatives or aliphatic chains linking urea functions in mono-, di-, or tetraloop structures. Simple rules allow one to anticipate which capsules will be exclusively formed when calix[4]arenes are mixed in different proportions. The stabilization of the dimeric structures by hydrogen bonds is thwarted by the overlaps of aliphatic loops and/or by bulky groups that cannot pass through these loops. Despite the structural similarity of the calixarenes, the exclusive formation of dimers of well-defined compositions and clear titration breaks are observed by electrospray mass spectrometry. This technique yields reliable information on stoichiometries and composition despite measurements in the gas phase rather than in solution and it does not suffer from excessive peak overlaps in contrast with NMR.
Asunto(s)
Calixarenos/química , Fenoles/química , Urea/química , Dimerización , Espectroscopía de Resonancia Magnética/métodos , Modelos Moleculares , Estructura Molecular , Estereoisomerismo , Urea/análogos & derivadosRESUMEN
Two different strategies were used to synthesize tri(2-alkoxy-5-nitrophenyl)methanes 6a,b. The X-ray structures of 6a and its precursor 5 show the molecules in a conformation with a syn-orientation of the nitro and alkoxy groups. Hydrogenation and acylation by the appropriate active ester gave the corresponding tri-CMPO derivatives 4a,b. Their ability to complex lanthanide ions was studied by NMR spectroscopy and by nuclear magnetic relaxation dispersion and further characterized by quantum mechanical calculations. Extraction experiments from acidic solution to dichloromethane reveal a reasonable selectivity of Am(III) over Eu(III), but in contrast to similar tetra-CMPOs derivatives of calix[4]arenes the distribution coefficients strongly decrease with increasing concentration of HNO(3).