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D'Annibale A Ciaralli L Bassetti M Pasquini C 《The Journal of organic chemistry》2007,72(16):6067-6074
The ring-closing metathesis (RCM) reactions of homoallylic acrylates bearing alkyl substituents on various positions of their skeleton afford the corresponding pentenolides in the presence of carbene ruthenium catalysts. For R3 = R4 = H, or R3 = Me, R4 = H, the reactions are catalyzed by complex [RuCl2(PCy3)2(=CHPh)], while a second-generation Grubbs catalyst is required when R3 = H and R4 = Me, R3 = R4 = Me, or R3 = i-Pr and R4 = H. Alkyl substitution at the homoallylic carbon (R1, R2) increases the yield of the reaction when both the acrylic and/or homoallylic double bonds are methyl-substituted. The interaction of the catalyst with the substrate in the initiation stage involves the homoallylic double bond rather than the acrylic moiety, and the resulting alkylidene species from the first-generation Grubbs catalyst can be observed by 1H and 31P NMR. The racemic tobacco constituents 4-isopropyl-5,6-dihydropyran-2-one and 4-isopropyltetrahydropyran-2-one are prepared via a short reaction sequence, involving the RCM reaction as the key transformation. 相似文献
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M. Ciprotti A. Sorbo S. Orlandini L. Ciaralli 《Accreditation and quality assurance》2013,18(4):333-339
Laboratories dealing with the analysis of food of animal origin have to face the shortage of both appropriate certified reference materials and pertinent proficiency tests (PTs). Therefore, internal quality control (IQC) materials have to be prepared in-house. The combination matrix/analytes/concentration, as well as the physical state, is a key issue. The European Union Reference Laboratory for Chemical Elements in Food of Animal Origin (EURL-CEFAO), within its activity as PT provider, has set a procedure to prepare test items of liquid milk spiked with arsenic, cadmium and lead at adequate values of concentration. This work describes in detail the steps of this procedure. Homogeneity and stability of the PT test items thus prepared were evaluated by the EURL-CEFAO using a sensitive and accurate method accredited according to ISO/IEC 17025. The analyte concentrations in spiked milk were found stable up to 18 months which is of particular interest for cadmium due to the low value of spiking (roughly 5 μg/kg). The outcome proves that the procedure used to prepare liquid milk spiked with chemical elements is suitable to produce in-house reference materials stable enough for analytical purposes. Furthermore, this procedure is easy to perform and can be applied by routine laboratories to produce samples for their IQC. 相似文献
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Brookman Brian Butler Owen Ciaralli Laura Horsky Monika Laurent Caroline Noblett Tracey Örnemark Ulf Patriarca Marina Sibbesen Lorens P. Tiikkainen Ulla van Putten Kees Robouch Piotr 《Accreditation and quality assurance》2019,24(1):93-101
Accreditation and Quality Assurance - A summary of the working group discussions on proficiency testing (PT) and external quality assessment (EQA) held at the Eurachem Workshop, Portorož,... 相似文献
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Angela Sorbo Andrea Colabucci Laura Ciaralli 《Accreditation and quality assurance》2013,18(4):291-298
As proficiency tests (PTs) provider, the European Union Reference Laboratory for Chemical Elements in Food of Animal Origin (EURL-CEFAO) yearly organizes exercises on the determination of chemical elements within the area of its mandate. The scheme is addressed to the National Reference Laboratories (NRLs) of the European Union Member States. Each PT is planned giving priority to the matrices and elements for which maximum levels are set in Commission Regulation No. 1881/2006 and following amendments as well as to those mainly considered in National Residues Control Plans. Samples to be distributed are prepared in the Laboratory’s facilities using materials purchased on the market and often adjusting the concentration levels of the analytes around their maximum levels. In the 2006–2011 period, PTs were planned as a long-term programme pursuing the general objective of providing the NRLs with a scheme that can give them the opportunity to check and improve the performance of their analytical methods and to verify the effectiveness of any corrective actions through the repetition of the same matrix. Control charts give participants the possibility of a long-term follow-up of their performance promoting the improvement of Quality Control. To this aim, Shewhart and Cusum control charts for z-scores are prepared according to ISO 13528:2005 and updated after each PT for each laboratory. z-scores are assigned using values of σ pEURL-CEFAO that correspond to the level of performance appropriate to the demand. Cusum charts are also evaluated by EURL-CEFAO in order to identify problems that may cause a bias in the measurement method. 相似文献
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