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Chemical Literature (chemical + literature)
Selected AbstractsStudies on the adaptability of different Borgen norms applied in self-modeling curve resolution (SMCR) methodJOURNAL OF CHEMOMETRICS, Issue 6 2009Róbert Rajkó Abstract Lawton and Sylvestre, and later Borgen et al. provided first the analytical solution for determining feasible regions of self-modeling curve resolution (SMCR) method for two- and three-component systems, respectively. After 20 years, Rajkó and István recently revitalized Borgen's method given a clear interpretation and algorithm how to draw Borgen plots using computer geometry tools; later Rajkó proved the existence of the natural duality in minimal constrained SMCR. In both latter cases, 1-norm was used to normalize raw data; however Borgen et al. introduced a more general class of normalization. In this paper, the definition and detailed descriptions of Borgen norms are given firstly appearing in the chemical literature. Some theoretical and practical studies on the adaptability of some Borgen norms used for SMCR method are also provided. Copyright © 2009 John Wiley & Sons, Ltd. [source] Determination of rank by median absolute deviation (DRMAD): a simple method for determining the number of principal factors responsible for a data matrix,JOURNAL OF CHEMOMETRICS, Issue 1 2009Edmund R. Malinowski Abstract Median absolute deviation (MAD) is a well-established statistical method for determining outliers. This simple statistic can be used to determine the number of principal factors responsible for a data matrix by direct application to the residual standard deviation (RSD) obtained from principal component analysis (PCA). Unlike many other popular methods the proposed method, called determination of rank by MAD (DRMAD), does not involve the use of pseudo degrees of freedom, pseudo F -tests, extensive calibration tables, time-consuming iterations, nor empirical procedures. The method does not require strict adherence to normal distributions of experimental uncertainties. The computations are direct, simple to use and extremely fast, ideally suitable for online data processing. The results obtained using various sets of chemical data previously reported in the chemical literature agree with the early work. Limitations of the method, determined from model data, are discussed. An algorithm, written in MATLAB format, is presented in the Appendix. Copyright © 2008 John Wiley & Sons, Ltd. [source] Synthesis, Characterization and Thermal Behaviour of Guanidinium-5-aminotetrazolate (GA) , A New Nitrogen-Rich CompoundPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 4 2003Jochen Neutz Abstract This work describes the synthesis and the thermoanalytical characterization of guanidinium-5-aminotetrazolate (GA). GA is a new nitrogen-rich energetic material. It is not mentioned in the chemical literature so far. The molecular structure of the compound has been determined by IR, 1H-, 13C- and 15N-NMR spectroscopy. The thermal properties, the decomposition pathways and its volatile products were investigated by thermal analysis and are discussed. [source] Using a triple-quadrupole mass spectrometer in accurate mass mode and an ion correlation program to identify compounds,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2005Andrew H. Grange Atomic masses and isotopic abundances are independent and complementary properties for discriminating among ion compositions. The number of possible ion compositions is greatly reduced by accurately measuring exact masses of monoisotopic ions and the relative isotopic abundances (RIAs) of the ions greater in mass by +1,Da and +2,Da. When both properties are measured, a mass error limit of 6,10,mDa (<,31,ppm at 320,Da) and an RIA error limit of 10% are generally adequate for determining unique ion compositions for precursor and fragment ions produced from small molecules (less than 320,Da in this study). ,Inherent interferences', i.e., mass peaks seen in the product ion mass spectrum of the monoisotopic [M+H]+ ion of an analyte that are ,2, ,1, +1, or +2,Da different in mass from monoisotopic fragment ion masses, distort measured RIAs. This problem is overcome using an ion correlation program to compare the numbers of atoms of each element in a precursor ion to the sum of those in each fragment ion and its corresponding neutral loss. Synergy occurs when accurate measurement of only one pair of +1,Da and +2,Da RIAs for the precursor ion or a fragment ion rejects all but one possible ion composition for that ion, thereby indirectly rejecting all but one fragment ion-neutral loss combination for other exact masses. A triple-quadrupole mass spectrometer with accurate mass capability, using atmospheric pressure chemical ionization (APCI), was used to measure masses and RIAs of precursor and fragment ions. Nine chemicals were investigated as simulated unknowns. Mass accuracy and RIA accuracy were sufficient to determine unique compositions for all precursor ions and all but two of 40 fragment ions, and the two corresponding neutral losses. Interrogation of the chemical literature provided between one and three possible compounds for each of the nine analytes. This approach for identifying compounds compensates for the lack of commercial ESI and APCI mass spectral libraries, which precludes making tentative identifications based on spectral matches. Published in 2005 by John Wiley & Sons, Ltd. [source] | ||||||||||