摘要:

AbstractDuring the past few years there has been a resurgence of interest in kinetic aspects of analytical chemistry and in kinetic methods of analysis. The increased activity is a result of advances that have been made in instrumentation and in data processing techniques. Still, the kinetic approach is not widely applied by practicing analytical chemists. Why is this true? Why are kinetic methods not among the most common methods in use by analytical chemistry? This paper discusses the advantages and limitations of kinetic methods and addresses the probable reasons that they are not widely used. Several new principles have cmerged that are guiding the development of new kinetic‐based determinations. These developments have made it possible to compensate for errors that result from changes in reaction conditions and to determine accurately multiple components in mixtures. With these advances kinetic methods are approaching the reliability of traditional equilibrium‐based determinations and should be re‐evaluated by analytical che

ISSN:0009-4536    

DOI:10.1002/jccs.199400034

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe serotonergic neurotransmitter 5‐hydroxytryptamine (5‐HT), the catecholaminergic neurotransmittcr dopaminc (DA) and various tetrahydroisoquinoline (TIQ) and tetrahydro‐β‐carboline (THβC) alkaloids are all easily oxidized compounds. Aberrant oxidative transformations of 5‐HT and other central indoles might be involved in neurodegenerative Alzheimer's Disease (AD). Changes in the oxidation chemistry of DA appear to be fundamental in substantia nigra neurons in Parkinson's Disease (PD). Various TIQ and THβC alkaloids are elevated in the brain as a result of ethanol drinking. Recent studies into the electrochemical oxidation chemistry of 5‐HT, DA and various TIQ and THβC alkaloids have been reviewed. The potential roles of the oxidation chemistry of these compounds in neurodegenerative AD, PD and alcoholis

ISSN:0009-4536    

DOI:10.1002/jccs.199400035

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractTo extend the applicability of electrokinetic chromatography (EKC), two new types of pseudostationary phases have been introduced. A high‐molecular surfactant, butyl acrylate/butyl methacrylate/methacrylic acid copolymer (BBMA) is employed as a micellar forming surfactant for miccllar electrokinetic chromatography (MEKC). The critical micelle concentration of BBMA is essentially zero, which means the micellar concentration is constant irrespective of temperature and buffer. Some characteristic features of BBMA as the pseudostationary phase for MEKC is investigated in comparison with conventional ionic surfactants. Ovomucoid and avidin, which are proteins isolated from egg white, have been found to be useful chiral selectors in affinity EKC. A few examples of the separation of enantiomers with these proteins are show

ISSN:0009-4536    

DOI:10.1002/jccs.199400036

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractSelected prominent problems in the analysis of advanced ceramic materials are surveyed. The importance of reliability of results is discussed in the field of elemental trace‐ and microanalysis in view of its interaction with economy, power of detection, local resolution and speciation selectivity. Particular problems in the analysis of major constituents, trace components and microlocal distributions are based on the striking propertics of ceramics; they are exemplified. Analytical assistance must start from the beginning of the production processing, in the preparation of the powdered base materials. Determination of the stoichiometry requires high accuracy and differentiation of chemical species in bulk and surface analysis of ceramic base powders. Element trace determination by direct instrumental methods requires standard reference materials for calibration; these are currently inavailable in a sufficient variety. For optimum reliability and power of detection, element traces must be prepared in isolated form in a small excitation volume for analysis.A review on the state‐of‐the‐art of wet‐chemical combined procedures is presented. Decomposition position procedures are emphasized, due to their risk of contributing severe systematic error. Combustion in elementary fluorine is presented for decomposition of refractory materials. The performance of some direct procedures is discussed. Very efficient methods are available for element trace determinations in ceramic materials, offering high detection power. Several approaches for high‐resolution local microanalysis in non‐conductive ceramic materials are identified as the most promising development in the analysis of sintered compact ceramic product

ISSN:0009-4536    

DOI:10.1002/jccs.199400037

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe vibrational spectroscopy by way of vibrational sum‐frequency generation (VSFG) has been made of formic acid adsorbed on MgO(001) surface and of n‐alkyltrichlorosilanes chemisorbed on quartz plates. It was revealed that the species on the MgO surface was formate ion (HCOO+) with CH bonds standing vertical to the surface and that the different adsorption sites showed up on repeated cycles of adsorption‐desorption processes. The results of chemisorbed films indicated that the g‐t and/or g‐t‐g′ conformational scquences of n‐alkyl chains occurred more frequently by the length of alkyl chain and that the surface hydroxyls, which are the sites of chemisorption, are ripped off by pre‐exposure of substrate

ISSN:0009-4536    

DOI:10.1002/jccs.199400038

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Non‐Methane Hydrocarbon Intercomparison Experiment (NOMHICE) is described. This experiment has been designed to evaluate analytical techniques currently being used by scientists throughout the world to measure ambient atmospheric hydrocarbon concentrations. NOMHICE consists of a series of planned experiments designed to identify existing problems in participating scientist's laboratories and to correct them. The various experimental steps (or phases) have been scheduled in order of increasing complexity so that problems can be addressed as they arise. Results are presented for the initial phases of this program. Phase 1 involved the circulation of a 2 component gravimetrically prepared standard to 40 laboratories throughout the world. Participants were asked to quantify but not identify the components. Phase 2 involved the circulation of a more complex 16 component gravimetrically prepared mixture to 32 participants. Participants were asked to identify and quantify the components. Further tasks are described which will be carried out in the futur

ISSN:0009-4536    

DOI:10.1002/jccs.199400039

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe temporal and concentration response of microdialysis probes in vivo was characterized. The temporal response was monitored using step changes in dopamine (DA) concentration which were followed with one minute sampling using smallbore HPLC. The response under three conditions was examined: in vitro sampling of DA, in vitro infusion of DA, and local infusion of DA. The dialysate DA concentration stabilized within two minutes after each change. These results suggest that relatively fast changes in DA levels in tissue can be followed by microdialysis probes. The rapid stabilization also suggests that the DA concentration profile does not extend very far from the probe.To characterize the concentration response, the linearity of the gain or loss of DA diffusing between the probe and tissue was determined. The difference in the inflow and outflow concentrations was plotted as a function of the inflow concentration. The correlation coefficient of the linear regression curve was 0.99. The zero point intercept, the extracellular concentration of DA, was 3.8 nM and the slope, or recovery, was 63.4%. There was no break at the zero point which is indicative of symmetrical diffusion into and out of the probe.

ISSN:0009-4536    

DOI:10.1002/jccs.199400040

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractVarious applications of laser‐enhanced ionization (LEI) in analytical chemistry are reviewed. This technique was applied to determine some physical quantities associated with a flame through development of an appropriate model. Determinations of flame temperature and atomization efficiency of an element in the flame are examples. As trace analysis is an important application of this technique, we compare the ion yield induced in a two‐step LEI with that in a one‐step LEI. The factors governing the ion enhancement via two‐step excitation are examined in order to make efficient use of the two‐step LEI apparatus. A novel technique was designed to couple flow‐injection analysis to a conventional LEI device; in this manner, electrical interference, a severe problem inherent in LEI, was successfu

ISSN:0009-4536    

DOI:10.1002/jccs.199400041

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractArtificial macrocyclic polyethers were synthesized and applied as neutral carriers for ion‐selective PVC membrane electrodes, ion‐chromatographic packing materials, extractants and adsorbents for ion separation, coating materials for piezoeletrical membrane sensors for organic species, and ion‐transport carriers through liquid membranes. Ion‐selective electrodes such as those for K+Na+, UO22+, Cs+, Pb2+, Fe3+, Hg2+and Ag+ions based on crown ether‐phosphotungstic acid (PW) precipitates and dithio crown ethers respectively were prepared and showed good sensitivity and selectivity. Crown ether‐PW precipitates were applied as adsorbents of rare‐earth ions and some common heavy‐metal ions. Some rare‐earth ions were easily extracted with crown ethers, especially 15‐crown‐5. Poly(stytene/divinyl benzene) cryptand‐22 resin was synthesized and applied as a bifunctional stationary phase of ion chromatography to separate bom cations and anions, even some organic carboxylate geometric isomers. Crown ethers such as mono‐benzo‐15‐crown‐5 was successfully applied as a coating material on piezoelectric quartz membrane sensors for some organic species. The oscillation frequency of the crown‐ether quartz‐membrane sensor was sensitive to organic vapours such as amines and alcohols. Upon adsorption of organic species on the crown‐ether quartz membrane, the oscillation frequency of the sensor decreased obviously. Special crown ether such as dibenzo‐16‐crown‐5‐oxyacetic acid, decyl‐cryptand‐22 and 1, 4‐dihydro‐pyridine‐18‐crown‐5 were synthesized and successfully applied as ion‐transport carriers (ionophores

ISSN:0009-4536    

DOI:10.1002/jccs.199400042

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractLiquid chromatography with pulsed amperometric detection (PAD) at an Au electrode was successfully applied for speciation of mercury: inorganic mercury, methylmercury and ethylmercury. The optimized conditions for triple‐step potential waveforms utilized in PAD were: E11800 mV, t150 ms; E2300 mV, t23850 ms; E3750 mV, t3100 ms; mercury oxidation was monitored at E3. With the eluent of HClO4(0.10 M) + KCl (1.0 mM) + CH3CN (1.0%) at a flow rate 0.80 mL/min, three mercury species were fully separated in 6 min on a glass column (3 mm × 10 cm) packed with Chemcosorb C18(5 μm). However, the first peak (inorganic mercury) was commonly overlapped by the solvent front. The relative standard deviations (n = 6) for methylmercury (15 ppb) and ethylmercury (30 ppb) were 4.2% and 2.8%, respectively. The linear range tested was 2 – 500 ppb (r = 0.9998) for methylmercury, and was 4 – 1000 ppb (r = 1.000) for ethylmercury. The detection limits (S/N = 3) were 1.2 ppb and 1.8 ppb for methylmercury and ethylmercury, respectively. The results of determination of the mercury‐containing species thimerosat in three commercial contact‐lens solutions agreed satisfactorily with the expe

ISSN:0009-4536    

DOI:10.1002/jccs.199400043

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY