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1.
A new software-controlled volume-based system for sample introduction in process flow injection analysis was developed. By using a multi-syringe burette coupled with one or two additional commutation valves, the multi-commuted injection of precise sample volumes was accomplished. Characteristics and performance of the injection system were studied by injecting an indicator in a buffered carrier. Three configurations were implemented in order to achieve two different tasks: the single injection of a sample in a two- or three-channels manifold, and the dual injection into different streams. The two channel flow system using the single injection was applied to the determination of free acidity in diluted samples containing high levels of iron(III), by employing the single point titration methodology. The precipitation of ferric hydroxide was prevented using the ammonium and sodium salts of oxalate and acetate as buffer titrant. Methyl Red was employed as indicator. The procedure allows determination of acid concentration in solutions with a Fe(III)/H+ molar ratio up to 0.2. Samples with higher Fe(III)/H+ molar ratios were spiked with a known strong acid at dilution. The three-channel configuration was applied to the determination of ferric ions, using, as reagent, a merging mixture of sulfuric acid and potassium thiocyanate. The double injection system was implemented in series in a single (three-channel) manifold in such a way that a different injection volume and a changed reagent were used for each analyte. It was applied to the separated or sequential determination of free acidity and ferric ions. In this configuration, iron(III) was determined using 0.5-0.7% (w/v) sodium salicylate solution as reagent. The systems can operate at up to 100, 84 and 78 injections per hour, respectively. Determinations on synthetic and process samples compared well with the reference values and procedures. Recoveries of 95-102% with a maximum RSD value of 5.4% were found for acidity. The respective values obtained for iron determinations were 96-105% and 4.3%. 相似文献
2.
A very flexible modular system for use with a portable IBM PC for potentiometric titrations is described. The appropriate software has been developed in order to obtain automatic end-points, and conventional, first-derivative, second-derivative and Gran curves, as well as a listing of the potentiometric points expressed in different ways. All these alternatives are selectable on menu presentations. The potentiometric system has been applied both the research and routine problems. 相似文献
3.
The initial reaction rate is measured by monitoring the rate of increase of temperature of the solution with a thermistor; 0.2–2 mg l?1 copper in the final solution is determined, with very few interferences. 相似文献
4.
New cis-clerodane diterpenoids from Croton schiedeanus 总被引:1,自引:0,他引:1
Puebla P Correa SX Guerrero M Carron R San Feliciano A 《Chemical & pharmaceutical bulletin》2005,53(3):328-329
The acid fraction of extracts from the aerial part of Croton schiedeanus afforded six cis-clerodane type diterpenoids. Two of them (1 and 4) are new natural compounds. Structural elucidation was achieved on the basis of their spectral data. 相似文献
5.
The thermometric behaviour of three amidooximes (3,3′-oxy-, 3,3′-thio- and 3,3′-iminodipropioamidooxime) is studied in order to evaluate the errors in their thermometric titration with HCl and the corresponding neutralization enthalpies from the analysis of the enthalpograms. The dissociation parameters (ΔGi, ΔHi and ΔSi) of the three compounds at 25°C are evaluated from the pKa values and neutralization enthalpies. 相似文献
6.
Manuel A. Treto-Suárez Yoan Hidalgo-Rosa Eduardo Schott Ximena Zarate Dayan Páez-Hernández 《International journal of quantum chemistry》2020,120(3):e26083
The turn-on luminescent chemosensor [2-Hydroxy-1-naphthaldehyde-(2-pyridyl) hydrazone] (L), selective to Al3+ ions, was studied by means of density functional theory (DFT) and time-dependent-DFT quantum mechanics calculations. The UV-Vis absorption and the radiative channel from the adiabatic S1 excited state were assessed in order to elucidate the selective sensing mechanism of L to Al3+ ions. We found that twisted intramolecular charge transfer (TICT) and photoelectron transfer (PET), which alter the emissive state, are responsible for the luminescence quenching in L. After coordination with Al3+, the TICT is blocked, and PET is no longer possible. So, the emission of the coordination complex is activated, and a fluorescence effect enhanced by chelation is observed. For compounds with Zn2+ and Cd2+, the luminescence quenching is caused by PET, while for Ni2+, ligand to metal charge transfer is the prominent mechanism. To go into more detail, the metal-ligand interaction was analyzed via the Morokuma-Ziegler energy decomposition scheme and the natural orbital of chemical valence. 相似文献
7.
N.O. Rojas M. Argentina E. Cerda E. Tirapegui 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,62(1):25-31
We study the patterns observed in the vicinity of a Faraday instability, in the limit of
a very thin layer of viscous fluid. We numerically solve our previous model [N.O. Rojas et
al., Phys. Rev. Lett. 104, 187801 (2010)] and compare our predictions to
experiments. Our model captures quantitatively the threshold of instability. The direct
simulation of our system permits us to predict the patterns observed in experiments. 相似文献
8.
Michael J. Nold Blas A. Cerda Chrys Wesdemiotis 《Journal of the American Society for Mass Spectrometry》1999,10(1):1-8
Dissociation of the amide bonds in a protonated peptide leads to N-terminal sequence fragments with cyclic structures and
C-terminal sequence fragments with linear structures. The ionic fragments containing the N-terminus (b
n
) have been shown to be protonated oxazolones, whereas those containing the C-terminus (y
n
) are protonated linear peptides. The coproduced neutral fragments are cyclic peptides from the N-terminus and linear peptides
from the C-terminus. A likely determinant of these structural choices is the proton affinity (PA) of the described peptide
segments. This study determines the PA values of such segments (Pep), i.e., cyclic and linear dipeptides and a relevant oxazolone,
based on the dissociations of proton-bound dimers [Pep + B
i
]H+ in which B
i
is a reference base of known PA value (Cooks kinetic method). The dissociations are assessed at different internal energies
to thereby obtain both proton affinities as well as entropies of protonation. For species with comparable amino acid composition,
the proton affinity (and gas phase basicity) follows the order cyclic peptide ≪ oxazolone ≈ linear peptide. This ranking is
consistent with dissociation of the protonated peptide via interconverting proton-bound complexes involving N-terminal oxazolone
(O) or cyclopeptide (C) segments and C-terminal linear peptide segments (L), viz. O ⋯ H+ ⋯ L ⇄ C ⋯ H+ ⋯ L. N-terminal sequence ions (b
n
) are formed with oxazolone structures which can efficiently compete for the proton with the linear segments. On the other
hand, N-terminal neutral fragments detach as cyclic peptides, with H+ now being retained by the more basic linear segment from the C-terminus to yield y
n
. 相似文献
9.
Alexander Carreño Eduardo Schott Ximena Zarate Juan Manuel Manriquez Juan C. Vega Miguel Mardones Alan H. Cowley Ivonne Chavez Juan P. Hinestroza Ramiro Arratia-Perez 《Chemical Papers》2017,71(6):1019-1030
Research in functionalized inorganic supports faces special challenges regarding the inmobilization of organic chains and efficient computational methods for the quantum chemical modeling of coordination compounds. The silylant 3-cloropropyltriethoxysilyl (R1) was anchored over silica gel in anhydrous conditions, in order to react with diethyl Iminodiacetate (DIDA) to obtain modified silica gel (R2), which was hydrolized in basic conditions previously synthesized and characterized by S BET, TGA and FTIR spectroscopy to obtain iminodiacetic acid groups IDA to prepare an modified inorganic support (R3) that is able to get hands on metals from the first transition series such as copper and nickel. The obtained experimental values showed that the functionalized grade of R3 corresponds to 0.1598 mmol of the nitrogen indicated that the adsorbed Cu(II) or Ni(II) have the stoichiometry for both cation of 1:1. Based on this relation, the three different structures were proposed to carry out the computational studies using density functional theory (DFT) in its LDA and PW91 with the TZP slater type basis set. The primary coordination sphere of copper(II) or nickel (II) ion in R3 are optimized, structural parameters are calculated, vibrational bands are assigned and energy gaps of frontier orbital (HOMO–LUMO) have been calculated. The calculated results reproduced the experimental data with good agreement. An energy decomposition analysis (EDA) of the different models proposed here was performed and suggest a 1:1 coordination form. 相似文献
10.