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1.
Capillary electrophoresis (CE) is a powerful separation method based on the migration of charged species under the influence of electric field. The main merits of CE are high separation efficiency, short analysis time and small consumption of solvents and samples. However, the main drawbacks of CE are generally lower sensitivity compared to classical column-chromatographic methods.Selectivity and/or sensitivity of CE separation can be improved by forming complexes between analytes and a complex-forming reagent present as an additive in the background electrolyte (BGE). We focus this review primarily on the application of inorganic complex-forming reagents added to the BGE to separate organic ligands. We briefly mention common CE separations of inorganic analytes (mainly metal ions) using BGEs with organic ligands (e.g., hydroxycarboxylic or aminopolycarboxylic acids) as selectors.The review involves brief theoretical consideration of the significance of the effect of complex formation on separation selectivity and/or sensitivity in CE, but the major topic is critical evaluation of different inorganic complex-forming reagents used recently in the CE analysis of organic compounds, including:
- (i)
- borate, tungstate and molybdate in separating organic compounds possessing vicinal -OH groups;
- (ii)
- ligand-exchange CE and capillary electrochromatography in chiral analysis; and,
- (iii)
- the role of metal ions as central ions employed for selectivity enhancement of CE separation of various classes of organic compounds, including biopolymers.
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Challenging applications offered by direct analysis in real time (DART) in food-quality and safety analysis 总被引:1,自引:0,他引:1
Direct analysis in real time (DART) is an ambient ionization technique undergoing rapid development. With minimal sample pre-treatment, ionization of analyte molecules outside the mass spectrometry (MS) instrument in the ordinary atmosphere is feasible. This ionization approach relies upon the fundamental principles of atmospheric pressure chemical ionization.The current review highlights and critically assesses application of DART (and some related desorption/ionization techniques) coupled to various types of MS analyzers for both target and non-target analysis of complex food matrices. Based on existing studies, DART-MS is presented as a simple, high-throughput tool for:
- (i)
- qualitative confirmation of chemical identity;
- (ii)
- metabolomic fingerprinting/profiling; and,
- (iii)
- quantification of low-molecular-weight food components, including some trace organic contaminants.
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Gerra L. Bosco 《Trends in analytical chemistry : TRAC》2011,30(8):1189-1211
This report of the 2011 James L. Waters Symposium at Pittcon 2011 highlights the powerful imaging technologies of electron microscopy (EM) and ion microscopy (IM). The four speakers each provided a window into a specific subset of the field:
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- David Bell described the history, development, application, and commercialization of transmission EM (TEM) and scanning TEM (STEM);
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- David Martin presented the challenges and methodologies of imaging ordered polymers and biomaterials with TEM;
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- Joseph Michael explained the history of the commercialization of scanning EM (SEM) and its modern applications; and,
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- David Joy, who submitted his talk in absentia, provided a history of EM and a summary of the advantages of IM versus EM.
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Roberto Todeschini Viviana Consonni Andrea Mauri Manuela Pavan 《Analytica chimica acta》2004,515(1):199-208
Regression models with good fitting but no predictive ability are sometimes chance correlations and often show some pathological features such as multicollinearity, overfitting, and inclusion of noisy/spurious variables. This problem is well known and of the utmost importance. The present paper proposes some criteria that are to be fulfilled as conditions for model acceptability, the aim being to recognize linear regression models with pathology. These criteria have been thought of in order to face the following problems:
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- model instability due to outliers and influential objects;
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- predictor multicollinearity;
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- redundancy in explanatory variables;
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- overfitting due to chance factors.
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5,6-Dihydrobenz[c]acridines were synthesized by the reaction of 1-chloro-3,4-dihydro-2-naphthaldehyde with aromatic amines under three different conditions:
- a.
- Thermolysis of 1-chlorovinyl-(N-aryl)imines prepared from 1-chloro-3,4-dihydro-2-naphthaldehyde.
- b.
- Acid catalyzed cyclization of 1-(N-aryl)amino-3,4-dihydro-2-naphthaldehydes.
- c.
- Thermolysis of N-arylenaminoimine hydrochlorides derived from 1-chloro-3,4-dihydro-2-naphthaldehyde in DMF medium.
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Yong-Liang Yu 《Trends in analytical chemistry : TRAC》2011,30(10):1649-1658
In the past decade, the lab-on-valve (LOV) system, as the third-generation of the flow-injection analysis technique, has exhibited powerful capability in instrument miniaturization and on-line sample pretreatment.This review presents and discusses the state of the art in the progress of the LOV system in the determination of metal species in two parts:
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- miniaturization of analytical instrumentations; and,
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- sample-processing front-ends.
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This work describes the effect of the molecular weight on the viscosimetric parameters of poly(4-vinylpyridine) (P4VP) polymers in ethanolic solution. Numerous studies concerning this question have been reported in very separate intervals of molecular weight. We have observed a discordance (discontinuity) in the variation of the intrinsic viscosity as a function of the molecular weight of these polymers ([η]=f(Mw)). In order to establish a general relationship between viscosimetric parameters and Mw, we have considered 10 P4VP samples in a wide interval of molecular weights: 0.75×104 to 153×104. These results have been compared and completed with that of the literature. We have observed that:
- (i)
- All viscosimetric parameters (intrinsic viscosity [η], Huggins constant kH, second virial coefficient, viscosimetric expansion coefficient αη, and critical concentration) change according to a continuous function without a break.
- (ii)
- The lower is the molecular weight of P4VP; the higher are the variations of the expansion coefficient and the interaction effects.
- (iii)
- The variation of the intrinsic viscosity versus the molecular weight follows a unique relation in the whole Mw range. In fact, the Berkowitz equation (1), described for a limited range of relatively high Mw (105 to 18.5×105) is extended for all Mw interval values.
- (iv)
- Empiric laws for [η], kH, A2 and C* and variations as a function of molecular weight were proposed for the P4VP in ethanol.
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André Leclaire 《Journal of solid state chemistry》2008,181(9):2338-2345
Through the study of the Cs-O bonds registered in the literature one observes that:
- (i)
- the bond lengths range from 2.46 to 3.60 Å;
- (ii)
- the preferential coordination numbers adopted by the caesium ions are 8, 9 and 10 but values from 1 to 12 also exist;
- (iii)
- the average bond lengths increase with the coordination (CN) of the caesium ions with the following values: 2.714 Å (CN=1), 2.98 Å (CN=2), 3.057 Å (CN=3), 3.104 Å (CN=4), 3.149 Å (CN=5), 3.188 Å (CN=6), 3.224 Å (CN=7), 3.245 Å (CN=8), 3.261 Å (CN=9), 3.269 Å (CN=10), 3.293 Å (CN=11) and 3.323 Å (CN=12).
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Zbigniew Dobkowski 《Polymer Degradation and Stability》2006,91(3):488-493
Routine DSC and TGA techniques, used to characterise polymer thermal stability, have been further used for assessment of comparative thermal stability of various polymer materials and for prediction of material lifetimes. The following materials were investigated: (1) commercial and experimental polymer materials - results for poly(vinyl chloride) (PVC) and bisphenol A polycarbonate (PC) are presented; (2) a polydimethylsiloxane-polytetrafluoroethylene (SIL-PTFE) coating system; and (3) commercially available linear low density polyethylene (PE-LLD), unmodified and modified chemically and physically. The plot of reciprocal temperature of initial decomposition 1/Tdi vs log heating rate β has been recommended for assessment of comparative thermal stability. The lifetime of polymer materials was calculated from the plots of log time-to-failure, log tf, vs reciprocal temperature 1/T, where tf values were obtained using Tdi from TGA measurements or directly from the oxidation induction time (OIT) data as criteria for initial deterioration of polymer thermal stability. The following sequences of increasing thermal stability were found for investigated materials:
- (1)
- PVC ? PC;
- (2)
- SIL < SIL-PTFE 20% < SIL-PTFE 50% ? PTFE;
- (3)
- (B) PE-LLD, grafted < (A) PE-LLD, unmodified < (C) PE-LLD, filled.