1,720,988 research outputs found
Multivariate Charts for Quality Control of Multiresidue Analytical Methods
No full textModern analytical chemistry involves more and more the use of statistical, mathematical and computer tools, both during the methods validation and, successively, during the internal quality control (IQC). Although these activities are far-back mandatory for the official laboratories which are accredited to ISO/IEC 17025 international standard, in practice analysts are not always sufficiently familiar with the statistical process control (SPC) theory. Furthermore, especially for multiresidue methods, the implementation of an ICQ using single univariate Shewhart charts for each quality characteristic (analyte) of the process can be very misleading [1]. This happens because in practice these quality characteristics are correlated. For this reason and to improve the effectiveness of IQC procedures, multi-analyte methods should also be controlled by multivariate methods that consider the joint distribution of variables. From this perspective, the Hotelling T2 chart represents an extension of the usual Shewhart charts to the multivariate case, and it is the most popular tool used for monitoring multivariate processes.
So far there have been few known applications of multivariate statistical control in analytical chemistry, probably due to the lack of adequate skills among chemists. The aim of this work is, therefore, to present a user friendly add-on package, called “izsqcc”, for the R statistical software
Monthly variability of heavy metal accumulation and detoxifying response of freshwater Copepoda, Cyclops abyssorum
No full textReaction of allyl acetates and ketene silyl acetals catalyzed by Palladium (0) complexes part II. Cyclopropanation vs. allylic alkylation
No full textPlatinacyclobutane complexes from nucleophilic attack at a coordinated allyl group and catalytic formation of cyclopropanes in the presence of platinum complexes
No full textExpeditious synthesis of substituted 2-thiazolin-4-ones by one-pot reaction of some conjugated azoalkenes with thioamides
No full textDeterminazione rapida di residui di fitofarmaci nel miele mediante SPME-HRGC con rivelazione NPD ed ECD
No full textNucleophilic Attack at the Central Allyl Carbon atom in [(eta3-allyl)ML2]+Complexes (M = Pd, Pt). Experimental Facts and New Theoretical Insights
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A liquid chromatography-high resolution mass spectrometry method for the determination of thirty-three per- and polyfluoroalkyl substances in animal liver
No full textAn analytical method for the quantification of thirty-three perfluoroalkyl and polyfluoroalkyl substances (PFASs) in animal liver was developed applying the isotopic dilution methodology with twenty-one labelled isotopologues of native compounds. The proposed protocol involved the determination of short and long aliphatic chain PFASs (C4[sbnd]C18) extracting liver with acetonitrile followed by two clean-up steps. The instrumental analysis was performed with liquid chromatography coupled to high-resolution mass spectrometry. The acquisition method combined full MS/dd-MS2, t-SIM/dd-MS2 and SIM experiments with variable resolution in order to maximize in one chromatographic run accuracy, sensitivity and selectivity. An eight-level validation study was performed evaluating linearity, trueness, precision, quantification and detection limits. Trueness was from 94 to 126% with intra-laboratory reproducibility lower than 20%. Limits of quantification were in the range 2–100 pg g−1, except for 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-propanoic acid, HFPO-DA (500 pg g−1). The analysis of a certified reference material (IRMM-427) and participation in a proficiency test scheme (FAPAS – 0687) confirmed these satisfactory performances. Finally, the application of the developed procedure to detect PFASs in sixteen liver samples of farm animals revealed that chicken was the less contaminated species
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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