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141.
142.
A. H. Jay W. W. Stevenson E. W. Colbeck S. W. Craven W. Murray N. T. Wilkinson W. J. Agnew R. Treje C. Benedicks G. A. Medwedewa W. P. Remin F. Willems J. J. Berzelius Ed. Houdremont P. Klinger G. Blaschczyk P. Klineer und W. Koch 《Fresenius' Journal of Analytical Chemistry》1944,127(1):43-46
Ohne Zusammenfassung 相似文献
143.
Raphael Ed. Liesegang 《Colloid and polymer science》1944,109(1):19-21
Zusammenfassung Ringbildung durch kapillare Wanderung in feuchtem Flie?papier (na? in na?) bei chemischem Umsatz mit langsamer Niederschlagsbildung,
wobei die Bildung des zweiten und der sp?teren konzentrischen Ringe nicht durch wiederholten Tropfenaufsatz des zweiten Reagenses
bedingt ist, sondern durch absatzweisen Wasserauftrag. Damit gelingt die st?rungsfreie Kreuzung von zwei Ringsystemen, die
bei Diffusionspr?paraten wegen der St?rungen durch Keimwirkungen unm?glich ist. Diese st?rungsfreie Kreuzung ist einer der
wenigen F?lle, bei denen z. B. bei fertigen geologischen Vorkommnissen entschieden werden kann, ob Kapillarit?t oder Diffusion
das Wesentliche war. Verwickeitere Verh?ltnisse, welche E. Deiss beschrieben hat, werden auf eine einfachere Weise zu deuten
versucht. 相似文献
144.
A new reversed-phase liquid chromatograhy/electrospray ionization tandem mass spectrometry method was developed for the analysis of perchlorate in water. The improved separation of perchlorate from common anions along with sample dilution effectively reduced matrix effects, primarily ion suppression caused by common anions. The (18)O-enriched perchlorate used as an internal standard provided further compensation for potential changes associated with instrument sensitivity, retention time shifting, peak broadening, ion suppression, and other matrix effects. The mean recoveries and relative standard deviations were 92-107% and 2.5-9.5% for simulated water matrix spikes at 0.05-1.0 microg/L, and 80-106% and 3.8-13% for real water sample matrix spikes at 2.0 microg/L, respectively. The method detection limits were 0.007 microg/L for reagent water and 0.014 microg/L for the simulated water matrix that contained 100 mg/L of SO(4)(2-), CO(3)(2-), and Cl(-) anions; 2 mg/L of PO(4)(3-) as P and NO(3)(-) as N; and 0.1 mg/L of Br(-), BrO(3)(-), ClO(2)(-), ClO(3)(-), and F(-) anions in reagent water, respectively. When using cartridge pretreatment to remove problematic SO(4)(2-), CO(3)(2-), and Cl(-) anions, the minimum reporting level could be set to 0.05 microg/L or lower. With 10-fold dilution, the minimum reporting level was conservatively set to 0.5 microg/L. 相似文献
145.
Analytical methods for the analysis of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) are widely available
and are the result of a vast amount of environmental analytical method development and research on persistent organic pollutants
(POPs) over the past 30–40 years. This review summarizes procedures and examines new approaches for extraction, isolation,
identification and quantification of individual congeners/isomers of the PCBs and OCPs. Critical to the successful application
of this methodology is the collection, preparation, and storage of samples, as well as specific quality control and reporting
criteria, and therefore these are also discussed. With the signing of the Stockholm convention on POPs and the development
of global monitoring programs, there is an increased need for laboratories in developing countries to determine PCBs and OCPs.
Thus, while this review attempts to summarize the current best practices for analysis of PCBs and OCPs, a major focus is the
need for low-cost methods that can be easily implemented in developing countries. A “performance based” process is described
whereby individual laboratories can adapt methods best suited to their situations. Access to modern capillary gas chromatography
(GC) equipment with either electron capture or low-resolution mass spectrometry (MS) detection to separate and quantify OCP/PCBs
is essential. However, screening of samples, especially in areas of known use of OCPs or PCBs, could be accomplished with
bioanalytical methods such as specific commercially available enzyme-linked immunoabsorbent assays and thus this topic is
also reviewed. New analytical techniques such two-dimensional GC (2D-GC) and “fast GC” using GC–ECD may be well-suited for
broader use in routine PCB/OCP analysis in the near future given their relatively low costs and ability to provide high-resolution
separations of PCB/OCPs. Procedures with low environmental impact (SPME, microscale, low solvent use, etc.) are increasingly
being used and may be particularly suited to developing countries.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
146.
147.
V.O. Gelmboldt Ed.V. Ganin M.S. Fonari M.M. Botoshansky 《Journal of fluorine chemistry》2004,125(12):1951-1957
Preparation and characterization of the ammonium hexafluorosilicate salts, 2[R]+[SiF6]2− (R = 4-(aminosulfonyl)benzenammonium) (1), and 2[R]+[SiF6]2−.4H2O (R = 4-carboxybenzenammonium), (2), are described. These salts, prepared from the reaction of the 4-aminobenzenesulfonamide or the 4-aminobenzoic acid with fluorosilicic acid, were characterized by IR, mass spectrometry and X-ray diffraction. 1 and 2 crystallize in monoclinic crystal system (space group P21/c and P21/n, respectively), with Z = 2 in both cases. Compounds exhibit an extensive system of hydrogen bonding. 相似文献
148.
Segall M Champness E Leeding C Lilien R Mettu R Stevens B 《Journal of chemical information and modeling》2011,51(11):2967-2976
In this article we describe a computational method that automatically generates chemically relevant compound ideas from an initial molecule, closely integrated with in silico models, and a probabilistic scoring algorithm to highlight the compound ideas most likely to satisfy a user-defined profile of required properties. The new compound ideas are generated using medicinal chemistry 'transformation rules' taken from examples in the literature. We demonstrate that the set of 206 transformations employed is generally applicable, produces a wide range of new compounds, and is representative of the types of modifications previously made to move from lead-like to drug-like compounds. Furthermore, we show that more than 94% of the compounds generated by transformation of typical drug-like molecules are acceptable to experienced medicinal chemists. Finally, we illustrate an application of our approach to the lead that ultimately led to the discovery of duloxetine, a marketed serotonin reuptake inhibitor. 相似文献
149.
Stephen G. Urquhart Adam P. Hitchcock Archie P. Smith Harald W. Ade Werner Lidy Ed G. Rightor Gary E. Mitchell 《Journal of Electron Spectroscopy and Related Phenomena》1999,100(1-3):119-135
The successful application of X-ray spectromicroscopy to chemical analysis of polymers is reviewed and a detailed application to quantitative analysis of polyurethanes is presented. Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is the basis of chemical sensitive X-ray imaging, as well as qualitative and quantitative micro-spectroscopy. These capabilities are demonstrated by a review of recent work, and by presentation of new results outlining a methodology for quantitative speciation of polyurethane polymers. C 1s inner-shell excitation spectra of a series of molecular and polymeric model compounds, recorded by gas phase inelastic electron scattering (ISEELS) and solid phase NEXAFS techniques, are used to understand the spectroscopic basis for chemical analysis of polyurethanes. These model species contain the aromatic urea, aromatic urethane (carbamate) and aliphatic ether functionalities that are the main constituents of polyurethane polymers. Ab initio calculations of several of the model molecular compounds are used to support spectral assignments and give insight into the origin and relative intensities of characteristic spectral features. The model polymer spectra provide reference standards for qualitative identification and quantitative analysis of polyurethane polymers. The chemical compositions of three polyurethane test polymers with systematic variation in urea/urethane content are measured using the spectra of model toluene diisocyanate (TDI) urea, TDI-carbamate, and poly(propylene oxide) polymers as reference standards. 相似文献
150.
Bultinck P Augustynen S Hilbers HW Moret EE Tollenaere JP 《Journal of computational chemistry》2002,23(7):746-754
The program Generate, aimed at generating 3-D structures for peptides and peptidomimetics, is presented. The algorithm is based on a build-up procedure, using a library of conformations of amino acid residues. This library is built from conformational analysis of amino acids placed in a di- or tripeptide environment to mimic the surroundings of the amino acid in a true peptide, considering different positions of the residue in the peptide chain (peptidyl fragment, NH(+)(3)-terminus or COO(-)-terminus). Cis-trans isomerism in the amide bonds is taken into account by construction of rotamer libraries for different isomers. Water solvation is included through the GB/SA model. New amino acid residues can easily be added to the libraries, making it possible to generate conformations of peptidomimetics. 相似文献