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11.
Ravindra K. Agrawal 《Journal of Thermal Analysis and Calorimetry》1989,35(3):909-917
In this article, the facts and fictions surrounding the compensation effect is explored. False compensation effect occurs mainly due to: propagation of computational and experimental errors resulting in inaccurate estimates of the Arrhenius parameters; and, the natural compensation between InA andE. Since Arrhenius parameters are sensitive to errors in temperature; the errors due to uncertainty in temperature should be minimized to eliminate false compensation effect. Increasing the experimental temperature range is helpful in minimizing errors due to uncertainty in temperature. A point of concurrence in a plot of Ink and 1/T establishes the occurrence of true compensation effect. True compensation effect has been shown to be a useful tool in chemical research for: identifying the governing reaction mechanism; predicting the effects of various reaction parameters; and, correlating and reducing experimental data.
The author would like to thank the reviewer for his constructive criticisms. 相似文献
Zusammenfassung In dieser Mitteilung werden Fakten und Vorstellungen betreffs des Kompensationseffektes untersucht. Falsche Kompensationseffekte werden hauptsächlich verursacht durch: eine ungenaue Ermittlung der Arrheniusparameter durch die Fortpflanzung von rechnerischen und experimentellen Fehlern sowie dem natürlichen Kompensationseffektes zwischen InA undE. Das Arrheniusparameter gegenüber Fehler im Temperaturwert sehr empfindlich sind, sollten Temperaturungenäuigkeitsfehler zur Vermeidung eines falschen Kompensationseffektes minimalisiert werden. Zur Verminderung der aus der Temperaturungenauigkeit resultierenden Fehler ist es von Nutzen, den Temperaturbereich des Experimentes zu erweitern. Ein wahrer Kompensationseffekt wird durch einen Schnittpunkt in einem Ink-1/T Diagramm angezeigt. Es wird gezeigt, daß der wahre Kompensationseffekt ein nutzvolles Mittel in der chemischen Forschung darstellt: zur Feststellung des dominierenden Reaktionsmechanismus, zur Vorhersage der einflüsse verschiedener Reaktionsparameter und zur Aufarbeitung und Schlußfolgerung von bzw. aus experimentellen Daten.
, . , , lnA E. , , . . Ink-1/T . , , , .
The author would like to thank the reviewer for his constructive criticisms. 相似文献
12.
A sensitive and selective method has been developed for the micro-determination of Mn(II) by the selective extraction of the yellow Mn(II)-8-hydroxyquinolinate complex with a liquid ion-exchanger, Aliquat 336, from basic medium. The molar absorptivity of the complex is 2.2 x 10(4)1.mole(-1).cm(-1) at 420 nm and the colour system obeys Beer's law in the range 0.1-3.5 ppm Mn(II) in the final solution. The composition and stability of the complex are discussed. Potential interferents have been examined and the method is applied to analysis of standard steel and bronze samples. 相似文献
13.
A simple and sensitive method for the determination of isoproturon, a widely used herbicide is described here which is based on alkaline hydrolysis of isoproturon to its corresponding primary amine followed by diazotization and coupling with p-aminoacetophenone in alkaline medium. The absorption maxima of the coloured compound formed is measured at 525 nm. Beer's law is obeyed over the concentration range of 0.5-5.0 mug in a final solution volume of 25 ml (0.02-0.2 ppm). The molar absorptivity and Sandell's sensitivity were found to be 8.6x10(5) l mol(-1) cm(-1) and 0.0002 mug cm(-2), respectively. The method has been satisfactorily applied to the determination of isoproturon in environmental and biological samples. 相似文献
14.
Summary A study of the Cd(CN)2 +x X– [Cd(CN)2X
x
]
x–
equilibrium (where X = Cl, Br or CNS) has been carried out at 18° and 38° by measuring the solubility of cadmium cyanide in potassium chloride, bromide and thiocyanate at various concentrations, and at a high ionic strength (6 M) maintained with sodium perchlorate to minimise the effect of activity coefficients. Equilibrium constants forx = 1 and 2 have been calculated and clearly favour the situation wherex = 1. H values for the dissociation of [Cd(CN)2X]– have also been calculated. 相似文献
15.
A sensitive and reproducible method is described for the quantitative determination of metadoxine in the presence of its degradation products. The method was based on high performance liquid chromatographic separation of the drug from its degradation products on the reversed phase, kromasil column [C18 (5-micron, 25 cm × 4.6 mm, i.d.)] at ambient temperature using a mobile phase consisting of methanol and water (50: 50, v/v). Flow rate was 1.0 mL min?1 with an average operating pressure of 180 kg cm?2 and t R was found to be 2.85 ± 0.05 min. Quantitation was achieved with UV detection at 286 nm based on peak area with linear calibration curves at concentration range 10–100 μg mL?1. This method has been successively applied to pharmaceutical formulation. No chromatographic interference from the tablet excipients was found. The method was validated in terms of precision, robustness, recovery and limits of detection and quantitation. Drug was subjected to acid, alkali and neutral hydrolysis, oxidation, dry heat, wet heat treatment and photo and UV degradation. As the proposed method could effectively separate the drug from its degradation products, it can be employed as stability indicating one. Moreover, the proposed HPLC method was utilized to investigate the kinetics of the acidic, alkaline and oxidative degradation processes at different temperatures and their respective apparent pseudo first order rare constant, half-life and activation energy was calculated with the help of Arrhenius plot. In addition the pH-rate profile of degradation of metadoxine in constant ionic strength buffer solutions with in the pH range 2–11 was studied. 相似文献
16.
A spectrophotometric method for determination of a microgram quantity of cerium with N-p-tolyl-p-chlorobenzohydroxamic acid is described. The orange-red-colored complex is extracted from chloroform at pH 9 which absorbs between 460 and 465 nm. Beer's law is obeyed at this wavelength. A clean-cut separation from many commonly occurring metal ions is easily accomplished. The system obeys Beer's law within the range of 0.5–28 ppm of cerium(IV). The molar absorptivity of cerium-N-p-tolyl-p-chlorobenzohydroxamic acid complex is 4.5 × 103 liters mol?1 cm?1. 相似文献
17.
Noor-ul H. Khan Santosh Agrawal Rukhsana I. Kureshy Sayed H.R. Abdi Surendra Singh Raksh V. Jasra 《Journal of organometallic chemistry》2007,692(20):4361-4366
An efficient method for the addition of trimethylsilyl cyanide (TMSCN) to various aldehydes and ketones has been described using Fe(Cp)2PF6 (2.5 mol%) as a catalyst under solvent free condition. Excellent yields of trimethylsilylether of cyanohydrin up to (94%) was achieved within 10 min. 相似文献
18.
A new crown hydroxamic acid, 5,14-N,N'-hydroxyphenyl-4,15-dioxo-1,5,14,18-tetraaza hexacosane (NHDTAHA) for the extraction and spectrophotometric determination of lanthanum(III) is described. Lanthanum(III) forms a yellow coloured complex with NHDTAHA, which is extracted with chloroform, having molar absorptivity 7.7 x 10(3) 1 mol(-1) per cm at 372 nm. The system obeys Beer's law in the range 1.2-20 ppm of lanthanum. The extract is directly aspirated for ICP-AES measurements, the limits for estimation are 5-140 ppb of lanthanum. Lanthanum has been determined in monazite sand and standard samples. 相似文献
19.
Summary Polarographic studies have been made of the reaction between Cerium(IV) and potassium thiocyanate in acidic medium. CeIVin the concentration range 2 · 10–4 M to 5 · 10–3 M was found to be reduced to CeIII by thiocyanate ion. One equivalent of thiocyanate reduced 4–6 equivalents of CeIV in the concentration range studied.
Zusammenfassung Die Reaktion zwischen CerIV und Kaliumthiocyanat wurde in saurem Medium polarographisch untersucht. CerIII wurde im Bereich von 2 · 10–4 m bis 5 · 10–3 m von Thiocyanat zu CerIII reduziert. In diesem Konzentrationsbereich entsprachen einem Äquivalent Thiocyanat 4–6 Äquivalente CerIV.相似文献
20.
S. P. Agrawal R. C. Aggrawal T. N. Srivastava 《Fresenius' Journal of Analytical Chemistry》1959,171(2):91-95
Summary p-Cresotic acid and its nitro, bromo, sulfo, acetyl, benzoyl and hydrazine derivatives and 5-methyl salicylic-o-aeetic acid have been used for the estimation of thorium and zirconium. The precipitates obtained have in all cases been ignited and weighed as oxides. These reagents have been found under suitable experimental conditions to effect the separation of Th as well as Zr from cerite earths. 相似文献