Chemical Titration Method Research Articles

Nuclear magnetic resonance spectroscopy spectroscopic investigation of the aging mechanism of polyethylene terephthalate vascular prostheses

AbstractThis article attempts to develop and prove a technique to determine the degradation of polyethylene terephthalate (PET) for vascular prostheses. The implicit goal is to be able to quantify the amount of degradation to study the effect of in vivo aging. Nuclear magnetic resonance spectroscopy (1H‐NMR) provides a comprehensive view of chemical macromolecular structures. Examination of a series of PET vascular prostheses showed significant chemical differences between the virgin prostheses and the explants collected after aging, especially for diethylene glycol and cyclic oligomers groups. Aging was investigated in terms of chemical scission of ester and ether linkages caused by hydrolytic reaction during the in vivo stay. Besides, we extended this 1H‐NMR technique to determine hydroxyl end‐group concentrations and therefore the average number of macromolecular weight. To validate 1H‐NMR results, complementary techniques, the chemical titration method and the classical viscosimetric method, were used. The results showed an increase of hydroxyl end‐group concentration and a decrease in the macromolecular weight for the explants. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Sulfate-Ion Diffusion Regularity and Reaction Mechanism of Sodium Sulfate Attack on Carbonized Concrete

The experiment has been carried out to study the sodium sulfate attack on carbonized concrete. The concrete specimens with strength grade of C50 were first carbonized for 28d in the carbonation box after standard curing, and then immersed into the sodium sulfate solutions of three different concentrations. When the immersed time were up to 30d, 90d, 180d, 270d and 360d, the sulfate-ion concentrations of every layer from the surface to the inside of concrete specimen were measured by the chemical titration method. Based on the test results, the sulfate-ion diffusion regularity and the reaction mechanism of carbonized concrete are analyzed. It can be concluded that the sulfate-ion diffusion regularity and the reaction mechanism of carbonized concrete is completely different from that of un-carbonized concrete, the diffusion of sulfate-ion occupies advantage in the pore water of carbonized concrete, which increases the depth of concrete specimen attacked by sulfate solution.

Effect of chain density and conformation on protein adsorption at PEG-grafted polyurethane surfaces

Polyurethanes were modified using monobenzyloxy polyethylene glycol (BPEG) which possesses a bulky hydrophobic benzyloxy group at one end and a hydroxyl group at the other end as a preconstructed BPEG layer, and poly(ethylene glycol) (PEG) and monomethoxyl poly(ethylene glycol) (MPEG) with various chain lengths as fillers. Our objective was to investigate the effect of PEG graft density and conformation on protein adsorption at PEGlated surface. The graft density was estimated by a chemical titration method. The combination of ATR-FTIR, AFM and titration results provide evidences that the graft density can be increased by backfilling PEG or MPEG to a BPEG layer. However, fibrinogen and albumin adsorption significantly increased on all surfaces after PEG or MPEG backfilling. We conclude that the conformation of hydrophobic benzyloxy end groups of the BPEG layer plays a key role. The benzyloxy end groups of preconstructed PEG chains stretch to the surface after PEG backfilling, which possibly accounts for the observed increase in protein adsorption. The BPEG conformation change after backfilling with PEG or MPEG was also suggested by contact angles. Additionally, protein adsorption was slightly influenced by the length of filler, suggesting a change in surface morphology.

Hydroperoxide build-up in the thermal oxidation of polypropylene – A kinetic study

The thermal oxidation of unstabilised polypropylene (PP) was studied at 80 °C under various oxygen pressures: 0.02, 0.5 and 5.0 MPa, and, under 5.0 MPa oxygen pressure at various temperatures: 60, 80, 100 and 120 °C. Hydroperoxides were titrated using a chemical titration method and modulated DSC (taking an enthalpy of −325 kJ mol −1). Starting from a previous kinetic analysis of carbonyl growth in same exposure conditions, we have tried to simulate experimental results by a model based on the classical mechanistic scheme in which initiation results from POOH (mainly bimolecular) decomposition. The model, which takes into account substrate consumption and does not rely on usual simplifying assumptions (steady state for radicals, long kinetic chains, interrelations between termination rate constants), generates kinetic curves with the same shape as experimental ones and predicts well the effect of O 2 pressure and temperature on hydroperoxide and carbonyl concentrations.

Relation between Viscous Characteristics and Dextrose Equivalent of Maltodextrins

AbstractRelation between viscous characteristics of different maltodextrins and degree of starch hydrolytic conversion expressed as DE value (dextrose equivalent) was deduced.Reduced viscosity of diluted solutions of maltodextrins linearly increased with maltodextrin concentration in the range 0.2×10−2 to 1×10−2 g/cm3. Values of intrinsic viscosity decreased with increasing degree of hydrolysis, which is expressed by DE values. Values of intrinsic viscosity of maltodextrins are independent of the botanical source of a particular starch but are dependent on molecular properties of samples that influence its friction characteristics in solution. When in diluted solutions, maltodextrins behave like macromolecules and obey the Staudinger‐Mark‐Houwink equation. Two ranges of DE value were established: DE = 0.5–10, in this range maltodextrin molecules in solution are randomly coiled (a = 0.53); and DE = 10–20, where the molecules are stretched (a = 1).Equations for determination of DE value by viscometric measurements were derived for each of the two established DE ranges. DE values calculated from the equations show good agreement with the ones obtained by standard chemical titration methods.

Sensitive Determination of Oxygen Solubility in Alkali Carbonate Melts

The solubility of in Li-K and Li-Na eutectic carbonate melts has been estimated in the range 600-700°C using a highly precise chemical titration method. In general, oxygen solubility is found to be distinctly higher in the Li-K than in the Li-Na eutectic with a tendency for such a solubility difference to disappear at 600°C. The precise determination of solubility values at different and partial pressures allowed evaluation of plausible oxygen dissolution mechanisms by a data fitting procedure. Our results support the assumption of a predominant superoxide formation at 650 and 700°C in both melts, with the difference that in Li-Na carbonate oxygen appears to dissolve also through formation of peroxymonocarbonate ions. At 600°C, molecular oxygen is found to be the major oxygen component. © 2004 The Electrochemical Society. All rights reserved.

Comparação dos métodos de Atenuação de Energia Radiante e Titulométrico para a determinação de Etanol no sangue

A comparison of Radiative Energy Attenuation and Titrimetric methods for the analysis of ethanol in blood. The alcohol determination in the blood was evaluated through the comparison of two analytical techniques, the method of radiative energy attenuation (REA) and the chemical titration method (TIT). The sensibility of REA was 0.4g/L and of TIT was 0.1g/L. The curve standard of etanol was linear up to 2.5g/L and 4.0g/L for methods REA and TIT, respectively. The coefficient of variation was 1.5% to 3.9% and 0.6% to 3.2% in the same day, and day-to-day coefficient of variation was 2.5% to 12.8% and 0% to 3.3% for methods REA and TIT, respectively. The tests of recovery presented the following results, 105% for REA and 88% for TIT. In 70 studied samples, the coefficient of correlation (r) was 0,9681 and the result of the test-t of Student was -1,294.

Fluoropolyethers end‐capped by polar functional groups. III. Kinetics of the reactions of hydroxy‐terminated fluoropolyethers and model fluorinated alcohols with cyclohexyl isocyanate catalyzed by organotin compounds

AbstractThe kinetics of the dibutyltin dilaurate (DBTDL)‐catalyzed urethane formation reactions of cyclohexyl isocyanate (CHI) with model monofunctional fluorinated alcohols and fluoropolyether diol Z‐DOL H‐1000 of various molecular weights (100–1084 g mol−1) in different solvents were studied. IR spectroscopy and chemical titration methods were used for measuring the rate of the total NCO disappearance at 30–60 °C. The effects of the reagents and DBTDL catalyst concentrations, the solvent and hydroxyl‐containing compound nature, and the temperature on the reaction rate and mechanism were investigated. Depending on the initial reagent concentration and solvent, the reactions could be well described by zero‐order, first‐order, second‐order, or more complex equations. The reaction mechanism, including the formation of intermediate ternary or binary complexes of reagents with the tin catalyst, could vary with the concentration and solvent and even during the reaction. The results were treated with a rate expression analogous to those used for enzymatic reactions. Under the explored conditions, the rate of the uncatalyzed reaction of fluorinated alcohols with CHI was negligible. Moreover, there was no allophanate formation, nor were there other side reactions, catalysis by urethane in the absence of DBTDL, or a synergetic effect in the presence of the tin catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3771–3795, 2002

Lattice parameter as a measure of electrochemical properties of LiMn 2O 4

Many factors affect the electrochemical properties of LiMn 2O 4. Among these factors the amount of Mn 3+ is an important factor which largely influences the capacity and capacity fading. However, it is difficult to detect the amount of Mn 3+ by chemical titration method. In this research we try to relate the amount of Mn 3+ with the lattice parameter. Lattice parameter is easy to measure. Therefore, if the amount of Mn 3+ can be deduced by the lattice parameter, it will be very helpful to control and design the electrochemical properties of LiMn 2O 4. The results show a good relationship among the lattice parameter, the amount of Mn 3+ and the capacity. Thus, lattice parameter could be used to deduce the electrochemical properties of LiMn 2O 4, although many works are still needed to construct a firm relationship.

The chemical control of colossal magnetoresistance (CMR) in the new two-dimensional La1.2(Sr1.8−xCax)Mn2O7 system

The magnetic and electrical properties of the colossal magnetoresistance (CMR) La1.2(Sr1.8−xCax)Mn2O7 materials have been investigated. Based on the chemical titration method, the valence of Mn was determined to be 3.39±0.04 for all measured La1.2(Sr1.8−xCax)Mn2O7. The magnetoresistance ratio [ρ(0)/ρ(H)] was efficiently increased from ∼192% (135 K, 1.5 T) for x=0 to 208% (102 K, 1.5 T) for x=0.4 in La1.2(Sr1.8−xCax)Mn2O7. Moreover, the Curie temperature (Tc) decreased with increasing x and was strongly dependent on the apical bond lengths of Mn–O(2).

Temperature Dependent Rate Coefficient for the Reaction O(3P) + NO2 → NO + O2

Nitrogen oxides, NO and NO{sub 2} (collectively called No{sub x}), play a crucial role in atmospheric ozone chemistry: they lead to photochemical ozone production in the troposphere and catalytic ozone destruction in the stratosphere. The rate coefficient (k{sub 1}) for the reaction O({sup 3}P) + NO{sub 2} {r_arrow} O{sub 2} + NO was measured under pseudo-first-order conditions in O({sup 3}P) atom concentration over the temperature range 220--412 K. Measurements were made using pulsed laser photolysis of NO{sub 2} to produce oxygen atoms and time-resolved vacuum UV resonance fluorescence detection of O atoms. The NO{sub 2} concentration was measured using three techniques: flow rate, UV absorption, and chemical titration (NO + O{sub 3} {r_arrow} NO{sub 2} + O{sub 2}). The NO{sub 2} UV absorption cross section at 413.4 nm was determined as a function of temperature using the chemical titration and flow methods. Including the low-temperature data of Harder et al., the temperature-dependent No{sub 2} cross section is given by {sigma}{sub 413.4}(T) = (9.49 {minus} 0.00549 T) {times} 10{sup {minus}19} cm{sup 2} molecule{sup {minus}1}. The measured rate coefficients for reaction 1 can be expressed as k{sub 1}(T) = (5.26 {+-} 0.60) {times} 10{sup {minus}12} exp[(209 {+-} 35)/T] cm{sup 3} molecule{sup {minus}1}more » s{sup {minus}1}, where the quoted uncertainties are 2{sigma} and include estimated systematic errors. This result is compared with previously reported measurements of k{sub 1}.« less

Investigation of the Reaction Pathways in Selective Catalytic Reduction of NO with NH 3 over V 2O 5 Catalysts: Isotopic Labeling Studies Using 18O 2, 15NH 3, 15NO, and 15N 18O

Isotopic tracer studies were performed to investigate the reaction network of selective catalytic reduction of nitric oxide over vanadia catalysts having preferential exposure of different crystal planes. The catalysts were characterized using BET surface area analysis, X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, 3-D imaging, and thermal analysis techniques. The product analysis was carried out by a combination of chemiluminescence NO x analysis, gas chromatography-mass spectrometry, and chemical titration methods. The isotopic labeling experiments were performed under steady-state reaction conditions by using NH 3 + NO + 16O 2 → NH 3 + NO + 18O 2, 14NH 3 + NO + O 2 → 15NH 3 + NO + O 2, NH 3 + 14NO + O 2 → NH 3 + 15NO + O 2, and NH 3 + 14NO 16O + 16O 2 → NH 3 + 15NO 18O + 18O 2 switches. Interaction of NO with the vanadia surface was also studied using a 14NO 16O → 15NO 18O switch. The results obtained in these experiments were combined with the tracer studies performed in ammonia oxidation reactions over the same catalysts to elucidate the reaction pathways involved in SCR reactions, to compare the surface residence times of nitrogen containing species, as well as to quantify the role of ammonia oxidation in SCR reactions.

Ethoxy Radical Yield in the System C2D5OH plus F(2P) plus F2 at P = 1 Torr and T = 223-423 K

A discharge flow reactor with mass spectrometric detection has been used to determine the fractional yield of ethoxy, Y(EtO), from the reaction of F( 2 P) with C 2 D 5 OH. The chemical titration method that was used depends only upon the occurrence of the fast chain reaction, F 2 +C 2 D 4 OH→C 2 D 4 OH+F, and the ability to measure relative concentrations of ethoxy radical. Ethoxy concentration was proportional to the detected ion count signal at m/z 50. [Ethoxy] was titrated to an asymptote with a large excess of F 2 . The titration removes hydroxyethyl radicals and regenerates F so that, at the asymptote, each F initially present will have formed one ethoxy radical

Role of Ammonia Oxidation in Selective Catalytic Reduction of Nitric Oxide over Vanadia Catalysts

The role of direct oxidation of ammonia in SCR reactions and the catalytic anisotropy of V2O5 catalysts in this reaction network were investigated. The catalysts were characterized using BET surface area measurement, X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and 3-D imaging. Temperature-programmed reduction experiments using ammonia and hydrogen as reducing agents and temperature-programmed desorption studies were also performed. A steady-state fixed-bed reactor system was used for activity and selectivity measurements. The product analysis was carried out by a combination of techniques including chemiluminescence NOx analysis, on-line gas chromatography and on-line mass spectrometry, and chemical titration methods. The results obtained in this study, when combined with our previous studies in SCR reactions, indicate that over vanadium pentoxide catalysts, ammonia oxidation and NO reduction reactions are closely coupled. The results suggest that ammonia adsorption takes place on at least two types of sites located on the (010) and (100) planes of V2O5. The sites that selectively reduce NO to N2 are the VOV sites located on the side planes, whereas VO sites promote direct oxidation of ammonia to NO and the formation of N2O from NO and NH3 interaction more readily. It is found that the VO sites are more easily reduced with both hydrogen and ammonia.

Spectroscopic studies of organometallic compounds on single crystal metal surfaces: Surface acetylides of silver (110)

The nature of compounds formed by the reaction of organic molecules with metal surfaces can be studied with a battery of analytical methods based on both physicals and chemical understanding. In this paper the application of UPS, XPS, LEED and EELS as well as temperature programmed reaction spectroscopy (TPRS) and chemical titration methods to the characterization of surface complexes is discussed. Particular emphasis is given to the reaction of acetylene with a single crystal surface of silver, Ag(110). Previous work has shown that this surface, when clean, is unreactive to hydrocarbons, alcohols and carboxylic acids under ultra high vacuum conditions. Preadsorption of oxygen, however, renders the surface reactive, and a wide variety of organometallic surface compounds can be formed. As expected then, no stable adsorption state and no reaction was observed with clean Ag(110) following room temperature exposure to acetylene. Following exposure at 150 K, however, a weekly bound chemisorption state was observed to desorb at 195 K, indicating a binding energy to the surface of approximately 12 kcal/gmole. Reaction with preadsorbed oxygen gave water formulation upon dosing and produced surface intermediates which yeilded two acetylene desorption states at 195 and 175 K. Heating above 300 K to completely desorb the higher temperature state produced new, well-defined LEED Features due to residual surface carbon which disappeared when the surface was heated above 550 K. Clearly, there were distinc changes in the nature of the absorbed layer at 195, 300 and 550 K. These changes were reflected in XPS. For the weakly chemisorbed acetylene a large C(ls) peak at 285.6 eV with a small, broad, indistinc shoulder at higher binding energy (288.2) was observed. The spectrum of the species following acetylene desorption at 275 K, however, showed the formulation of a large C(ls) peak at 283.6 eV in addition to peaks characteristics of the weakly chemisorbed state. This result indicated that the carbon atoms in the surface acetylide became inequivalent. Heating to 300 K produced a single peak at 282.8 eV which reverted to 283.4 when heated above 550 K; the carbon atoms became chemically equivalent. This latter state could be removed completely by O 2 to form CO 2(3). The XPS results showed quantitative conversion of all surface carbon from each state observed. Conclusive evidence regarding the identity of these states was obtained with titration experiments with deuterated acetic acid. CH 3COOD was adsorbed on top of the acetylenic residues at 150 K and heated to note the isotopes of acetylene that desorbed. The 275 K acetylene desorption peak, which showed inequivalent carbon atoms, was titrated by CH 3COOD to form C 2HD, indicating C 2H as the stable surface species. The species formed above 300 K, which showed equivalent carbon atoms in XPS, titrated to form C 2D 2, indicating a C 2 surface species. In each case the formulation of surface acetate was quantitative. The structure of these species was probed further with high resolution electron energy loss spectroscopy. The weakly chemisorbed molecular state exhibited vibrational losses at 300, 700 and 3270 cm -1, characteristics of an acetylene-surface stretching motion, a C-C-H bend and the C-H stretch respectively. No C-C stretch was observed, indicating that the molecule lay parallel to the plane of the surface. For adsorbed C 2H, bands were observed at 300, 690 and 3250cm -1. The high C-H stretching frequency indicated that the C-C bound order was near three. The absence of a C-C stretch in the spectrum was somewhat surprising, but was explained by a σ-π bonded complex in which the -C=CH species was flattened toward the surface by an interaction of an Ag atom with the π system of the acetylide.