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141.
Simultaneous electrochemical determination of nitrate and nitrite in aqueous solution using Ag-doped zeolite-expanded graphite-epoxy electrode 总被引:2,自引:0,他引:2
In this work a new electrochemical sensor based on an Ag-doped zeolite-expanded graphite-epoxy composite electrode (AgZEGE) was evaluated as a novel alternative for the simultaneous quantitative determination of nitrate and nitrite in aqueous solutions. Cyclic voltammetry was used to characterize the electrochemical behavior of the electrode in the presence of individual or mixtures of nitrate and nitrite anions in 0.1 M Na2SO4 supporting electrolyte. Linear dependences of current versus nitrate and nitrite concentrations were obtained for the concentration ranges of 1-10 mM for nitrate and 0.1-1 mM for nitrite using cyclic voltammetry (CV), chronoamperometry (CA), and multiple-pulsed amperometry (MPA) procedures. The comparative assessment of the electrochemical behavior of the individual anions and mixtures of anions on this modified electrode allowed determining the working conditions for the simultaneous detection of the nitrite and nitrate anions. Applying MPA allowed enhancement of the sensitivity for direct and indirect nitrate detection and also for nitrite detection. The proposed sensor was applied in tap water samples spiked with known nitrate and nitrite concentrations and the results were in agreement with those obtained by a comparative spectrophotometric method. This work demonstrates that using multiple-pulse amperometry with the Ag-doped zeolite-expanded graphite-epoxy composite electrode provides a real opportunity for the simultaneous detection of nitrite and nitrate in aqueous solutions. 相似文献
142.
Mihaela Badea Rodica Olar Dana Marinescu Valentina Uivarosi Teodor Octavian Nicolescu Daniela Iacob 《Journal of Thermal Analysis and Calorimetry》2010,99(3):829-834
A series of new complexes with mixed ligands of the type RuL
m
(DMSO)
n
Cl3·xH2O ((1) L: oxolinic acid (oxo), m = 1, n = 0, x = 4; (2) L: pipemidic acid (pip), m = 2, n = 1, x = 2; (3) L: enoxacin (enx), m = 2, n = 1, x = 0; (4) L: levofloxacin (levofx), m = 2, n = 2, x = 8; DMSO: dimethylsulfoxide) were synthesized and characterized by chemical analysis, IR and electronic data. Except oxolinic
acid that behaves as bidentate, the other ligands (quinolone derivatives and DMSO) act as unidentate. Electronic spectra are
in accordance with an octahedral stereochemistry. The thermal analysis (TG, DTA) in synthetic air flow elucidated the composition
and also the number and nature of both water and DMSO molecules. The TG curves show 3–5 well-separated thermal steps. The
first corresponds to the water and/or DMSO loss at lower temperatures followed either by quinolone thermal decomposition or
pyrolisys at higher temperatures. The final product is ruthenium(IV) oxide. 相似文献
143.
Rodica Luca 《Mediterranean Journal of Mathematics》2012,9(2):379-392
We study the existence of positive solutions for a higher-order nonlinear differential system subject to some m-point boundary conditions. As applications of the main results, we present two existence theorems for the positive solutions of a higher-order nonlinear differential equation with boundary conditions of the same form as those for the studied system. 相似文献
144.
145.
146.
Rodica Olar Andreea Dogaru Dana Marinescu Mihaela Badea 《Journal of Thermal Analysis and Calorimetry》2012,110(1):257-262
Three new complexes with formula [VOL2]·xH2O [(1) HL: N,N-dimethylbiguanide, x?=?0.5; (2) HL: 1-phenylbiguanide, x?=?0; (3) HL: 1-(o-tolyl)biguanide, x?=?0.5] were synthesised and characterised. The IR and UV?CVis spectral data indicate that these biguanide derivatives act as bidentate chelating anionic ligands and generate VO(II) complexes with a square?Cpyramidal stereochemistry. The thermal analysis (TG, DTA) elucidated the composition and also the number and nature of the water molecules. 相似文献
147.
Bernard R Cornu D Scharff JP Chiriac R Miele P Baldeck PL Caslavský J 《Inorganic chemistry》2006,45(21):8743-8748
Single- and multibranched centrosymmetric derivatives incorporating B12 clusters [B12H11-N(H)=C(H)-C6H4-C6H4-C(H)=(H)N-B12H11]2- (3) and [1,3,5-(4-(B12H11-N(H)=C(H))-C6H4)-C6H3]3- (5) have been synthesized. Both derivatives were characterized by multinuclear NMR and ESI-MS analyses. To the best of our knowledge, compound 5 is the first example of a multicage derivative bearing three B12 units. Compounds 3 and 5 are only slightly yellowish colored. The UV-vis absorption curves of 3 and 5 show intense absorption bands at 360 and 314 nm, respectively. This result permits us to confirm the strong donor effect of the B12 cluster. The hypsochrome effect observed for compound 5 compared to that of compound 3 confirms the interest in multibranched derivatives for the preparation of two-photon absorption materials active in the visible range. 相似文献
148.
Mircea Chipara Ioan Morjan Rodica Alexandrescu Jeffrey M. Zaleski Nicholas Remmes David V. Baxter 《Journal of polymer science. Part A, Polymer chemistry》2005,43(23):3432-3437
The preparation and characterization of titanium-doped iron oxides–styrene isoprene styrene block copolymer composites is reported. The precursor, as-synthesized nanoparticles, contains akaganeite, maghemite, and titanium-doped maghemite. Hysteresis loops obtained by SQUID measurements revealed an exchange biased field assigned to the presence of akaganeite nanoparticles. It was found that the coercive field and the exchange bias field decreases as the temperature of the sample is increased. The temperature dependence of the magnetization revealed a blocking temperature of about 220 K. The ESR spectra in the temperature range 150 K to about 300 K are single broad resonance lines. It was observed that the resonance line position is strongly temperature dependent due to the combined action of the external and molecular magnetic fields. The decrease of the resonance line width as the temperature is increased is governed by the reorientation of the magnetization. Thermally activated movements of magnetic nanoparticles within the soft phase (polyisoprene) of the matrix may also contribute to resonance line narrowing. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3432–3437, 2005 相似文献
149.
Mihaela Badea Rodica Olar Dana Marinescu E. Segal A. Rotaru 《Journal of Thermal Analysis and Calorimetry》2007,88(2):317-321
A series of new complexes with mixed ligands
of the type M(4,4’-dipy)(C3H3O2)2(H2O)y ((1) M=Mn, y=2; (2) M=Ni, y=2; 4,4’-dipy: 4,4’-dipyridyl and C3H3O2 is acrylate anion) and respectively M2(4,4’-dipy)(C3H3O2)4(H2O)y
((3) M=Cu, y=0; (4) M=Zn, y=1). The
modification evidenced in IR spectra was correlated with the presence of acrylate
ion as unidentate in the case of complex (1)
and as bidentate for others complexes. The electronic reflectance spectra
showed the d–d
transition for complex (1) and (2) characteristic for the octahedral surrounding while
the spectrum for complex (3) have the characteristic
pattern for square-pyramidal stereochemistry. The thermal behaviour steps
were investigated. The thermal transformations are complex processes according
to TG and DTG curves including dehydration, acrylate ion oxidative degradation
and thermolysis process of aromatic amine. The final products of decomposition
are the most stable metal oxides. 相似文献
150.
The determination of the load on the machine tool is crucial in the mechanics of metal forming processes as it has a critical influence over the deformation of the material into a new shape and the optimal conditions for the process. The problems of strip, wire, tube drawing without plug, tube drawing with floating plug [1-4] viscoplastic deformation has no exact solutions, but this paper addresses them using an approximate method. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献