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71.
72.
A simple, rapid and economic method has been developed for the reduction of potassium permanganate in alkaline carbonate uranium leach liquors to a colourless solution. The pink colour of permanganate, if not reduced, seriously impedes the determination of carbonate, bicarbonate and phosphate by titrimetry and spectrophotometry. Out of 17 reductants investigated, commercial sugar has been found to be the most effective, rapid, simple and interference free for further estimations. To the best of the authors' knowledge, this is the first time that sugar as a reductant has been made use of in analytical investigations. 相似文献
73.
A procedure is described for the estimation of fluorine in microgramme quantities by the steam-distillation of the samples with sulphuric or phosphoric acid. Traces of the acid carried over are precipitated from the distillate as silver or barium salts, in order to eliminate their interference in the subsequent titration of fluorine. The results obtained compare favourably with those of the conventional perchloric acid method. By avoiding the latter, the present method offers the advantage of both safety and simplicity. 相似文献
74.
The oxygen to uranium ratio in uranium oxides such as U(3)O(8), UO(2+x) powders and UO(2) fuel pellets has been determined by a new spectrophotometric method. The method can be used for determination of O/U ratio in UO(2) pellets and powders on a routine basis. In the described method, uranium oxides in the powder form are dissolved in 2M sulphuric acid containing a few drops of HF. The concentrations of U(IV) and U(VI) are directly determined by means of the absorbances of these species at different wavelengths. For determination of the O/U ratio in U(3)O(8) powder samples, 630 and 310 nm are the wavelengths chosen for U(IV) and U(VI), respectively. For UO(2+x) powder, where the O/U ratio lies between 2.04 to 2.15, U(IV) and U(VI) are determined at 630 and 300 nm respectively, whereas for UO(2) fuel pellets, where the O/U ratio is less than 2.01, 535 and 285 nm are used. The molar absorptivity of U(IV) at 630 and 535 nm is 21.4 and 6.8 l.mole(-1).cm(-1) and that of U(VI) at 310, 300 and 285 nm is 178.1, 278.6 and 585 l.mole(-1).cm(-1), respectively. Standard deviations of +/-0.002 O/U ratio units for pellets and +/-0.004 O/U ratio units for powders have been achieved. 相似文献
75.
Summary An amperometric determination of tin with potassium dichromate has been described. The advantage of the cathodic polarograms of Cr2O2
7- and Sn2+ in formate media was taken and titrations were performed at –0.8 V vs. S.C.E. at pH 3.0. It is shown that tin upto 10 mg may be determined accurately within the limits of experimental errors.
Zusammenfassung Eine Methode wird beschrieben zur amperometrischen Bestimmung von Zinn mit Kaliumdichromat unter Ausnutzung des kathodischen Polarogramms von C2O7 2– und Sn2+. Die Titration wird bei –0,8 V (gegen S.K.E.) und PH 3,0 ausgeführt. Zinn kann in Mengen bis zu 10 mg mit guter Genauigkeit bestimmt werden. Die Fehler liegen inner-halb der experimentellen Grenzen.相似文献
76.
The class of realn × n matricesM, known asK-matrices, for which the linear complementarity problemw – Mz = q, w 0, z 0, w
T
z =0 has a solution wheneverw – Mz =q, w 0, z 0 has a solution is characterized for dimensionsn <4. The characterization is finite and practical. Several necessary conditions, sufficient conditions, and counterexamples pertaining toK-matrices are also given. A finite characterization of completelyK-matrices (K-matrices all of whose principal submatrices are alsoK-matrices) is proved for dimensions <4.Partially supported by NSF Grant MCS-8207217.Research partially supported by NSF Grant No. ECS-8401081. 相似文献
77.
Murty A.R.C. Bulusu Peter Waldstätten Thomas Tricotett Gerhard Schulz 《Tetrahedron letters》2004,45(12):2527-2530
A novel photochemical amide cleavage reaction of (6S)-methoxyascomycin opening a pathway for the selective cleavage of the pipecolic acid, is described. The scope of this reaction with several analogues carrying suitable protecting groups is examined. 相似文献
78.
Oxiranes undergo ring opening rapidly with sodium azide in a [bmim]BF4/H2O or [bmim]PF6/H2O (2:1) solvent system, under mild and neutral reaction conditions to afford the corresponding 2-azidoalcohols in high to quantitative yields. The remarkable features of this procedure are improved yields, enhanced reaction rates, high regioselectivity and ease of recyclability of ionic liquids (ILs). The recovered ionic liquid can be reused for four to five times but with gradual decrease in activity. 相似文献
79.
Conditions were established for the determination of ascorbic acid using phsophovanadotungstic acid as reagent. The method was applied to the determination of ascorbic acid in pure form, pharmaceutical preparations and fruit juices. The method is sensitive (2-24 micrograms ml-1 of ascorbic acid) and rapid and tolerates the presence of common ingredients usually found in fruit juices. The results obtained with the proposed method showed good agreement with those given by the standard method. 相似文献
80.
Murty A.R.C Bulusu Peter Waldstätten Thomas Tricotet Christophe Rochais Andrea Steck Markus Bacher 《Tetrahedron letters》2004,45(30):5833-5836
6-Vinyl (12) and (5R)- and (5S)-vinylproline (18, 19) analogues of ascomycin are synthesised starting from the known suitably protected (6S)-methoxy-9-hydroxy derivative (4) of ascomycin. The strategy involves hydrolytic cleavage of the Cε-N bond of the pipecolic acid moiety, extension of the amino acid side chain by two or one carbon units, functional group manipulations, Pd-catalysed reinstallation of the Cε-N or Cδ-N bonds, followed by deprotection and oxidation. 相似文献