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31.
Summary The kinetics of the silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate (pdp) was studied in acetate buffers. The rate law as represented by-d[pdp]/dt = {(k
1
K
inf2
sup-1
[H+]2 + k
2[H+] + k
3
K
3)/ ([H+]2/K
2 + [H+] + K
3)}[pdp][Ag(I)] conforms to the proposed mechanism. The rate is independent of malonic acid concentrations. Acetate ions do not affect the rate; however, the rate decreases as the ionic strength increases. A probable portrait of reaction events is suggested. A comparative analysis of the reactivity pattern of malonic acid towards peroxodiphosphate and peroxodisulphate in presence of silver(I) has been made. 相似文献
32.
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
33.
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
34.
The stability constants of the Cu2+, Zn2+, Ni2+ and Mu2+ complexes of N-phenyl-o-methoxybenzohydroxamic acid at 30° in 50% v/v aqueous dioxan are: log K1 10·45, 8·16, 7·52, 6·33; log K2 8·90, 6·70, 6·01, 5·59 (for the ions in the order given). 相似文献
35.
A solvent extraction separation of uranium, in the presence of thorium, cerium and lanthanides with a new calix[4]resorcinarene bearing eight hydroxamic acid groups (C4RAHA) is described. Quantitative extraction of uranium is possible in ethyl acetate solution of C4RAHA at pH 8.0. The lambda(max) and molar absorptivity (varepsilon) for uranium is 356nm and 8352Lmol(-1)cm(-1). The Binding ratio of uranium with C4RAHA as evaluated by Job's method is 4:1. The system obeys Beer's law over the range 0.075-6.0mugml(-1) of uranium with Sandell sensitivity 0.0284mugcm(-2). A preconcentration factor of 142 was achieved by directly aspirating the extract for GF-AAS measurements. The two-phase stability constant evaluated at 25 degrees C for uranium is 15.91. The complexation is characterized by favorable enthalpy and entropy changes. A liquid membrane transport study of uranium was carried out from source to the receiving phase under controlled conditions and a mechanism of transport is proposed. Uranium has been determined in standard and environmental samples. 相似文献
36.
V. K. Jain R. A. Pandya S. G. Pillai Y. K. Agrawal P. H. Kanaiya 《Journal of Analytical Chemistry》2007,62(2):104-112
In the present paper, solid-phase extractive preconcentration and separation of lanthanum(III) and cerium(III) using calix[4]arene-o-vanillinsemicarbazone
immobilized on a polymeric matrix, a Merrifield peptide resin, is proposed. The diamino derivative of calix[4]arene was first
diazotized and coupled with o-vanillinsemicarbazone to obtain a new “upper-rim” functionalized calix[4]arene-o-vanillinsemicarbazone.
It was then covalently linked to the Merrifield peptide resin and characterized by FT-IR and elemental analysis. Quantitative
studies were carried out by spectrophotometry and ICP-AES with a relative standard deviation of 1.7%. Various physicochemical
parameters like pH, concentration of eluting agents, flow rate, total sorption capacity, metal-ligand stoichiometry, exchange
kinetics, preconcentration factor, distribution coefficient, breakthrough capacity, resin stability, and effect of electrolytes
and associated metal ions have been studied. The uptake and stripping of these metal ions on the resin was fast, indicating
a better accessibility of La(III) and Ce(III) towards the chelating sites. Detection limits corresponded to three times the
standard deviation of the blank (3σB) and amounted to 3.05 and 6.86 μg/L, along with preconcentration factors of 153 and 133 for La(III) and Ce(III), respectively.
The robustness of the procedure is demonstrated by the recoveries obtained (>97.5%) for La(III) and Ce(III) in the presence
of several cations and anions. The proposed method was satisfactorily applied to the separation of La(III) and Ce(III) from
each other and also from U(VI) and Th(IV) by sequential acidic elution and varying pH. The validity of the method was tested
by analyzing these metal ions in monazite sand and standard geological materials.
The text was submitted by the authors in English. 相似文献
37.
38.
The Bianchi type II, VIII, and IX models are investigated in Lyra's geometry (in normal gauge) when the gauge function is time dependent. The physical behavior of these models in vacuum and in the presence of the Zeldovich fluid is discussed. 相似文献
39.
A sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic method of analysis of nevirapine both as a bulk drug and in formulations was developed and validated. The solvent system consisted of toluene-carbon tetrachloride-methanol-acetone-ammonia (3.5:3.5:2.0:1.0:0.05, v/v/v/v/v). Densitometric analysis of nevirapine was carried out in the absorbance mode at 289nm. This system was found to give compact spots for nevirapine (R(f) value of 0.44+/-0.02). Nevirapine was subjected to acid and alkali hydrolysis, oxidation, dry heat and wet heat treatment and photodegradation. The drug undergoes degradation under acidic, basic conditions and oxidation. Also the degraded products were well resolved from the pure drug with significantly different R(f) values. Linearity was found to be in the range of 30-1000ng/spot with significantly high value of correlation coefficient. The linear regression analysis data for the calibration plots showed good linear relationship with r(2)=0.998+/-0.002 in the working concentration range of 300ng/spot to 1000ng/spot. The mean value of slope and intercept were 0.073+/-0.005 and 36.78+/-1.50, respectively. The method was validated for precision, robustness and recovery. The limit of detection and quantitation were 5 and 10ng/spot, respectively. As the method could effectively separate the drug from its degradation products, it can be employed as a stability indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of acid degradation process. Arrhenius plot was constructed and activation energy was calculated. 相似文献
40.
Cerium and lanthanum were determined gravimetrically by selective precipitation with N-m-tolyl-m-nitrobenzohydroxamic acid and separated from several metal ions such as Ag(+), Be(2+) , Pb(2+) , Mn(2+) , Cu(2+), Zn(2+) , Cd(2+) , Hg(2+) , Pd(2+) , Ga(3+) A1(3+) , Bi(3+) , Sb(3+), Sn(4+), Ce(3+) , Pr(3+) , Nd(3+) , Ti(4+), Zr(4+), Th(4+), V(5+) , Mo(6+) and U(6+) . The precipitates were weighted directly after drying at 110 degrees . The analytical results indicated the composition of the complexes to be (C(14)H(11)N(2)O(4))(n)M. 相似文献