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991.
C. Brunori M. B. de la Calle-Gunti?as R. Morabito 《Fresenius' Journal of Analytical Chemistry》1998,360(1):26-30
Parameters for the reduction of Se(VI) to Se(IV) in HCl medium by heating in a microwave oven have been optimized. The reduction
resulted to be quantitative applying 100% power, corresponding to 600 W heating for 2 min in 6 mol/L or for 3 min in 4 mol/L
HCl. The behavior of selenomethionine and selenocystine under the optimized reduction conditions was studied in order to evaluate
a possible interference of these selenium species in the determination of Se(VI). The final determination of Se(IV), and Se(VI)
were done by hydride generation-atomic absorption spectrometry. The analytical merits of the method are reported. The method
was applied to the selective determination of Se(IV), and Se(VI) in spiked river and lake water.
Received: 6 December 1996/Revised: 1 April 1997/Accepted: 3 April 1997 相似文献
992.
Sáenz-Carbonell Luis Loyola-Vargas Víctor M. 《Applied biochemistry and biotechnology》1997,61(3):321-337
Hairy roots are less susceptible to manipulation by changes in medium composition than callus and cell suspension cultures.
However, when the individual components of the Gamborg’s B5 medium were modified one by one, several of them modified the yield of root cultures. Nitrogen (N) source changes, the absence
of phosphorus (P), calcium (Ca), and cobalt (Co), and the increase in the sucrose content of the medium increased the level
of alkaloids inDatura stramonium hairy root cultures. The use of ammoniun as N source provoked the alkaloid excretion into the medium. The addition of different
auxins inhibited the alkaloid accumulation, but the addition of abscisic acid (ABA) did not change the alkaloid content of
the cultures. The use of MeJa increased the content of hyoscyamine to 100%. 相似文献
993.
A. Narros Sierra J. S. Durand Alegría A. Cabrera Martín 《Fresenius' Journal of Analytical Chemistry》1993,345(6):437-440
Summary A chemiluminescent method for the determination of vanadium in steel with cinchomeronic hydrazide as analytical reagent is proposed. The optimum conditions are pH 11.75 (phosphate buffer), 1.0×10–3 mol/l cinchomeronic hydrazide, 6.6×10–3 mol/l hydrogen peroxide and 2.8×10–3 mol/l V(IV). The maximum chemiluminescent emission is obtained at 420 nm. A linear relationship exists in the range of 0.04–1.00 g/ml of V(IV) with a 3.6% variation coefficient at 0.50 g/ml of V(IV) level for ten replicates. Cobalt(II), copper(II) and chromium(VI) show strong interference and a chloroform extraction procedure with -benzo-inoxime is recommended to avoid these interferences. This method has been applied to determine vanadium in a certified steel with excellent results.Presented at Euroanalysis VII 相似文献
994.
Fondo M García-Deibe AM Ocampo N Sanmartin J Bermejo MR 《Dalton transactions (Cambridge, England : 2003)》2004,(14):2135-2141
The heptadentate Schiff base H(3)L can react with zinc acetate to form the discrete dinuclear complex Zn(2)L(OAc)(H(2)O), 1.H(2)O. The reaction of 1.H(2)O with NMe(4)OH.5H(2)O both in air and under an argon stream has been investigated. On one hand, this reaction in air yields the tetranuclear complex (Zn(2)L)(2)(CO(3))(H(2)O)(6), 2.5H(2)O, by spontaneous absorption of adventitious carbon dioxide. This process can be reverted in an acetic acid medium, whereas the treatment of 2.5H(2)O with methanoic acid yields crystals of [Zn(2)L(HCOO)].0.5MeCN.1.25MeOH.2H(2)O, 3.0.5MeCN.1.25MeOH.2H(2)O. On the other hand, the interaction under an argon atmosphere of 1.H(2)O with NMe(4)OH.5H(2)O in methanol allows the isolation of the dinuclear complex Zn(2)L(OMe)(H(2)O)(4), 4.4H(2)O. Recrystallisations of 1.H(2)O, 2.5H(2)O and 4.4H(2)O, in different solvents, yielded single crystals of 1.MeCN.2.5H(2)O, 2.4MeOH and 4.3MeOH.H(2)O, respectively. The crystal structure of 2.4MeOH can be understood as resulting from an unusual asymmetric tetranuclear self-assembly from two dinuclear units, and shows three different geometries around the four zinc atoms. 相似文献
995.
Mrcia Sousa Bispo Maria das Graas Andrade Korn Elane Santos da Boa Morte Leonardo Sena Gomes Teixeira 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):2175-2180
An analytical method for separation and pre-concentration of lead in seawater for determination by inductively coupled plasma optical emission spectrometry has been investigated. Lead was retained in the solid phase (0.5 g) composed of co-precipitated naphthalene and alizarin red. The solid phase quantitatively sorbs Pb(II) at pH 8–9, and the metal was eluted using 5.0 ml of 2 mol l−1 nitric acid. The effect of NaCl, KCl, BaCl2, CaCl2, Na2SO4, MgCl2 and Na3PO4 on the sorption of Pb(II) in the solid phase was studied. A set of solutions containing varying amounts of electrolytes (0.5; 1.0; 3.0 and 5.0% m/v) with Pb (50 μg) was prepared and the recommended procedure applied. The Na3PO4 was found to interfere; the other electrolytes did not interfere up to 5% m/v. A pre-concentration factor of 40 was obtained in this analytical procedure. The limit of detection and limit of quantification for Pb(II) were 53 and 176 μg l−1, respectively. Lead was determined in seawater samples collected in Salvador city, Bahia, Brazil. The precision, expressed as R.S.D., was 1.8–4.6%, and the recovery of lead added to seawater samples was 95–97%. 相似文献
996.
Hexamminecobalt(III)-tricarbonatocobaltate(III) was prepared, and its bicarbonate solution was standardized against ferrous ammonium sulfate using Ferroin indicator. The Co solution was used as an oxidimetric reagent for the determination of organic systems.Hydroquinone as a reversible system undergoes fast electrochemical reactions, so it can be determined with the Co(III) complex, which acts as an irreversible titrant. Thus it can be determined with both visual and potentiometric methods. Standardized hydroquinone solutions in H2SO4 medium gave very similar results when determined potentiometrically against standard Co(III) solution. The acid medium is important for liberating Co(III) ions. Hydrochloric acid behaves similarly but perchloric acid interferes with the reaction. Diluting the hydroquinone solutions had no effect on the determinations. The potentiometric endpoint coincides with the discharge of the color if Ferroin has been present.p-Aminophenol, p-phenylenediamine, and Metol (p-hydroxy-N-methylaniline), which slow or hinder the electrochemical reaction, do not indicate a distinct potential change at the endpoint, so cannot be determined potentiometrically. Their chemical reactions are fast enough to be titrated visually against Co(III) complex using Ferroin indicator. Titration curves representing biamperometric measurements of these solutions fulfill these results.Hydrazine sulfate and isonicotinic acid hydrazide as irreversible systems cannot react with Co(III) and thus cannot be determined either potentiometrically or visually as both electrochemical and chemical reactions are slow to be recognized. 相似文献
997.
V. Jedináková L. Kuča M. Vojtíšková 《Journal of Radioanalytical and Nuclear Chemistry》1980,59(1):125-132
We have investigated the effect of coextraction of lanthanides and yttrium on the distribution coefficients DAm in the extraction of americium by benzyldimethyldodecylammonium nitrate (BDMLNNO3) from nitrate solutions. In the coextraction of lanthanides, the extraction of Am(NO3)3 is suppressed, which is markedly manifested in the extraction of light lanthanides (La, Ce, Pr); of the series of lanthanides their extraction is the highest. The effect of nitric acid and the possibility of separation of lanthanides and americium by the application of three-stage multiple extraction is discussed. 相似文献
998.
Gracia CA Gómez-Barreiro S González-Pérez A Nimo J Rodríguez JR 《Journal of colloid and interface science》2004,276(2):408-413
Static (SLS) and dynamic (DLS) light-scattering techniques were applied to the study of the aggregation of dodecyl- (C12DBACl), tetradecyl- (C14DBACl), and hexadecyldimethylbenzylammonium (C16DBACl) chlorides in water and in 0.01 and 0.05 m NaCl aqueous solutions at 25 degrees C. Results of SLS measurements yielded critical micelle concentration (cmc) values for aqueous and NaCl solutions. The aggregation numbers of the micelles for the homologous surfactants are low but increase with chain length and ionic strength of the solution. Various patterns of changes of the diffusion coefficient, D, as a function of chain length, molality, and with ionic strength were found for the studied surfactants. Transformations in the structure of micelles of C14DBACl in 0.01 m NaCl occur at a concentration of surfactant of about 0.01 m. Such transformations, presumably due to rodlike structure, are the more extensive the higher the concentration of NaCl. The concentration of C16DBACl in 0.05 m NaCl covers the range where already repulsive interactions between micelles occur, as judged by the strongly negative slope of the D versus molality plot. To provide additional information on the suggested transformations, complementary viscosity measurements for C14DBACl in 0.01 m of NaCl have been performed. 相似文献
999.
Hevia E Pérez J Riera V Miguel D Campomanes P Menéndez MI Sordo TL García-Granda S 《Journal of the American Chemical Society》2003,125(13):3706-3707
As depicted in the scheme, the alkylidenamido complex 1, a N-rhenaimine, reacts with ketenes to afford the beta-lactams 2-4, which possess a {Re(CO)3(bpy)} fragment as substituent at nitrogen. Clean demetalations using HOTf or MeOTf yield the free beta-lactams or N-methyl-beta-lactams along with [Re(OTf)(CO)3(bpy)]. DFT calculations help to rationalize why the reaction is faster than those of non transition metal N-substituted imines. 相似文献
1000.
Erik Rakovský Ľudmila Žúrková Jaromír Marek 《Monatshefte für Chemie / Chemical Monthly》2002,133(3):277-283
Summary. Anhydrous 1,6-hexanediammonium dihydrogendecavanadate ((HdaH2)2H2V10O28, 1) was prepared by reaction of V2O5 with 1,6-hexanediamine in aqueous solution. The crystal structure of 1 was determined, and the proton positions in the H2V10O28
4− anion were calculated by the bond length/bond number method. The protons are bound to the centrosymmetrically oriented μ–OV3 groups of the decavanadate anion. Based on the analysis of IR spectra of 1 prepared from H2O and D2O, the absorption band at 871 cm−1 can be attributed to δ(V–Ob–H) vibrations.
Received August 3, 2001. Accepted (revised) October 8, 2001 相似文献