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1.
Prenesti E Ferrara E Berto S Fisicaro P Daniele PG 《Analytical and bioanalytical chemistry》2007,388(8):1877-1883
A method that uses a Harned cell to perform potentiometric pH measurements has been optimized and applied to an aqueous solution
of simulated seawater that contains sodium perchlorate, sodium sulfate, sodium hydrogen carbonate and boric acid and has an
ionic strength I of 0.57 mol kg−1. The standard metrological approach developed for the measurement of pH in low ionic strength aqueous solutions was maintained,
but a few modifications were necessary, and measurement procedures and calculations were modified ad hoc from those adopted
in conventional protocols. When determining the standard potential of the cell, E°, NaClO4 salt was added to a 0.01 mol/kg HCl solution to attain the same ionic strength as the test solution and to investigate possible
specific effects related to the high levels and the nature of the background electrolyte. An appropriate value of γ
±HCl (0.737) was then selected from the literature, based on a realistic value for I. Finally, in order to convert the acidity function at zero chloride molality into pH, a suitable value of γ
Cl (0.929) was calculated. As a result, we obtained pH = 8.18 (T = 25 °C) with an associated expanded uncertainty U = 0.01 (coverage factor k = 2). The aim was to establish a sound basis for the pH measurement of seawater by identifying the critical points of the
experimental and theoretical procedure, and to discuss further possible developments that would be useful for achieving a
reference solution. 相似文献
2.
The redox characteristics of the drug domperidone at a glassy-carbon electrode (GCE) in aqueous media were critically investigated
by differential-pulse voltammetry (DPV) and cyclic voltammetry (CV). In Britton–Robinson (BR) buffer of pH 2.6–10.3, an irreversible
and diffusion-controlled oxidation wave was developed. The dependence of the CV response of the developed anodic peak on the
sweep rate (ν) and on depolizer concentration was typical of an electrode-coupled chemical reaction mechanism (EC) in which an irreversible
first-order reaction is interposed between the charges. The values of the electron-transfer coefficient (α) involved in the rate-determining step calculated from the linear plots of E
p,a against ln (ν) in the pH range investigated were in the range 0.64 ± 0.05 confirming the irreversible nature of the oxidation peak. In
BR buffer of pH 7.6–8.4, a well defined oxidation wave was developed and the plot of peak current height of the DPV against
domperidone concentration at this peak potential was linear in the range 5.20 × 10−6 to 2.40 × 10−5 mol L−1 with lower limits of detection (LOD) and quantitation (LOQ) of 6.1 × 10−7 and 9.1 × 10−7 mol L−1, respectively. A relative standard deviation of 2.39% (n = 5) was obtained for 8.5 × 10−6 mol L−1 of the drug. These DPV procedures were successfully used for analysis of domperidone in the pure form (98.2 ± 3.1%), dosage
form (98.35 ± 2.9%), and in tap (97.0 ± 3.6%) and wastewater (95.0 ± 2.9%) samples. The method was validated by comparison
with standard titrimetric and HPLC methods. Acceptable error of less than 3.3 % was also achieved.
Figure In aqueous media at pH 7.6- 8.4, the DPV and cyclic voltammetry of the drug domperidone (I) at GCE showed an irreversible
and diffusion controlled oxidation wave. The values of the electron transfer coefficient (α) involved in the rate determining
step were found in the range 0.64± 0.05 confirming the irreversible nature of the peak. The analysis of the drug in pure form
and in wastewater samples was successfully achieved 相似文献
3.
Isotope ratio measurements characterizing 202Hg/200Hg in NIST SRM 3133 Mercury Standard Solution were undertaken by multicollector inductively coupled plasma mass spectrometry
employing NIST SRM 997 Tl for mass bias correction by use of the slope and the intercept obtained from a natural logarithmic
plot of each session of measurements of 202Hg/200Hg against 205Tl/203Tl. The calculated value of 1.285333 ± 0.000192 (mean and one standard deviation, n = 40) for the mass bias corrected 202Hg/200Hg was then used for mass bias correction of other Hg isotope pairs. Ratios of 0.015337 ± 0.000011, 1.68770 ± 0.00054, 2.3056 ± 0.0015,
1.3129 ± 0.0013, 2.9634 ± 0.0038, and 0.67937 ± 0.0013 (expanded uncertainty, k = 2) were obtained for 196Hg/198Hg, 199Hg/198Hg, 200Hg/198Hg, 201Hg/198Hg, 202Hg/198Hg, and 204Hg/198Hg, respectively. Reduction of Hg(II) to Hg0 in solutions of SRM 3133 was then undertaken using SnCl2, NaBH4, UV photolysis in the presence of formic acid, and ethylation of Hg(II) using NaBEt4. These reactions induced significant isotope fractionation with maximum values of 1.17 ± 0.07, 1.08 ± 0.09, 1.34 ± 0.07, and
3.59 ± 0.09‰ (one standard deviation, 1SD, n = 5) for δ
202/198Hg relative to the initial isotopic composition in the solution following 85–90% reduction of the Hg by SnCl2, NaBH4, UV photolysis, and ethylation with NaBEt4, respectively. Mass-dependent fractionation was found to be dominant for all reduction processes.
Figure Mass dependence of fractionation for all samples from Hg fractionation experiments using NaBEt4. Solid lines are the theoretically predicted MDF based on δ′ 202/198
Hg using equation 7. Error bars displayed are one standard deviation of the mean of 5 measurements of each sample 相似文献
4.
Bojana Beljkaš Jovana Matić Ivan Milovanović Pavle Jovanov Aleksandra Mišan Ljubiša Šarić 《Accreditation and quality assurance》2010,15(10):555-561
The objective of this research was to test suitability of the Dumas combustion method to completely substitute the Kjeldahl
method in routine laboratory determination of crude protein content in cereals and oilseeds. The validation of the method
demonstrated that it is able to determine crude protein content in cereals and oilseeds in an efficient and accurate manner,
with a detection limit w(N) = 0.006%, quantification limit w(N) = 0.019%, repeatability precision RSD
r = 0.41%, intra-laboratory reproducibility precision RSD
R = 0.74%, trueness, expressed in terms of bias b = 0.43%, and linear response between (2.36–19.2) mg N. Measurement uncertainty, expressed as relative expanded uncertainty
(coverage factor k = 2, confidence level 95%), was calculated from validation data (U
rel = 2.24%). In order to examine the relationship between two methods, 15 cereal grain and oilseed samples were analyzed using
Dumas and Kjeldahl procedure. The Kjeldahl procedure gave slightly lower w(N) values than the Dumas procedure: w
K(N) = 0.9905 w
D(N) = 0.0376 (R
2
= 0.9996). Relative standard deviations and results of homogeneity test obtained during analysis of complex cereal products
(cereal breakfast and muesli bars) show that the Dumas combustion method may be less suitable for analysis of such samples
compared to Kjeldahl method. 相似文献
5.
Francisco Ros Pilar Jiménez María Victoria Roux 《Monatshefte für Chemie / Chemical Monthly》2007,138(10):941-949
Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate,
−47.7 ± 0.1 kJ mol−1 (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol−1, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose
the vibrational energy using the Debye energy function (E
vib 835.0 kJ mol−1 (78.6°C), E
0 included). E
kin for the crystal (771.1 kJ mol−1 (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy.
The cohesion energy of the racemic crystal, −44.2 kJ mol−1, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol−1, 83.3°C) and E
kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential
energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E
vib + rot for the liquid in the way as to E
vib for the gas, the Debye entropy function being increasedly suited for the liquid (E
vib + rot 763.4 kJ mol−1 (115.4°C)). Positive ΔE
pot, 13.0 kJ mol−1, arised from the increase in electronic energy (Δ
l
νmean − 154.3 cm−1, by the dielectric nature of the liquid), added to the cohesion energy. 相似文献
6.
Radix Scrophulariae (Xuanshen) is one of the famous Chinese herbal medicines widely used to treat rheumatism, tussis, pharyngalgia, arthritis,
constipation, and conjunctival congestion. Harpagoside and cinnamic acid are the main bioactive components of Xuanshen. The
purpose of this study was to develop an HPLC–UV method for simultaneous determination of harpagoside and cinnamic acid in
rat plasma and investigate pharmacokinetic parameters of harpagoside and cinnamic acid after oral administration of Xuanshen
extract (760 mg kg−1). After addition of syringin as internal standard, the analytes were isolated from plasma by liquid–liquid extraction. Separation
was achieved on a Kromasil C18 column, and detection was by UV absorption at 272 nm. The described assay was validated in terms of linearity, accuracy,
precision, recovery, and limit of quantification according to the FDA validation guidelines. Calibration curves for both analytes
were linear with the coefficient of variation (r) for both was greater than 0.999. Accuracy for harpagoside and cinnamic acid ranged from 100.7–103.5% and 96.9–102.9%, respectively,
and precision for both analytes were less than 8.5%. The main pharmacokinetic parameters found for harpagoside and cinnamic
acid after oral infusion of Xuanshen extract were as follows: C
max 1488.7 ± 205.9 and 556.8 ± 94.2 ng mL−1, T
max 2.09 ± 0.31 and (1.48 ± 0.14 h, AUC0–24 10336.4 ± 1426.8 and 3653.1 ± 456.4 ng h mL−1, 11276.8 ± 1321.4 and 3704.5 ± 398.8 ng h mL−1, and t
1/2 4.9 ± 1.3 and 2.5 ± 0.9 h, respectively. These results indicated that the proposed method is simple, selective, and feasible
for pharmacokinetic study of Radix Scrophulariae extract in rats.
Figure Radix Scrophulariae 相似文献
7.
Francisco Ros Pilar Jiménez María Victoria Roux 《Monatshefte für Chemie / Chemical Monthly》2007,28(4):941-949
The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate,
−47.7 ± 0.1 kJ mol−1 (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol−1, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose
the vibrational energy using the Debye energy function (E
vib 835.0 kJ mol−1 (78.6°C), E
0 included). E
kin for the crystal (771.1 kJ mol−1 (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy.
The cohesion energy of the racemic crystal, −44.2 kJ mol−1, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol−1, 83.3°C) and E
kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential
energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E
vib + rot for the liquid in the way as to E
vib for the gas, the Debye entropy function being increasedly suited for the liquid (E
vib + rot 763.4 kJ mol−1 (115.4°C)). Positive ΔE
pot, 13.0 kJ mol−1, arised from the increase in electronic energy (Δ
l
νmean − 154.3 cm−1, by the dielectric nature of the liquid), added to the cohesion energy. 相似文献
8.
Photoelectrochemical measurements have been performed at a polybithienyl (PBT) film (doping level of 1 × 1018/cm3) deposited on a platinum electrode. The cathodic photocurrents and negative slope of the Mott-Schottky plot indicate that
the PBT film has the features of a p-type semiconductor. The cathodic photocurrents are interpreted in terms of the Gaertner-Butler
model on the basis of the theory of the semiconductor|solution interface. The (i
ph
hν)2/n vs. hν plots taken from the photocurrent spectra show two linearities for n=1 in the wavelength range from 460 nm to 490 nm and for n=4 in the wavelength range λ > 490 nm. The band gaps of the PBT film were determined to be 2.05 ± 0.05 eV for n=1 and 1.55 ± 0.05 eV for n=4. The flat-band potential is 0.33 V (vs SCE). From the slope of the Mott-Schottky plot at the modulation frequency of 3 kHz,
the dielectric constant ɛ of the film and the thickness of the depletion layer W
0 of the PBT film were determined to be 7.4 and 0.29 μm, respectively.
Received: 6 January 1999 / Accepted: 6 June 1999 相似文献
9.
Giovannoli C Anfossi L Baggiani C Giraudi G 《Analytical and bioanalytical chemistry》2008,392(3):385-393
Experimental work performed was aimed at the assessment of a competitive capillary electrophoresis immunoassay with laser-induced
fluorescence (CEIA-LIF) detection for the determination of the Cry1Ab endotoxin from Bacillus thuringensis. The binding constant of a monoclonal antibody, raised against the insecticide protein Cry1Ab, was determined on a microplate
by indirect enzyme-linked immunosorbent assay (ELISA) and compared with that obtained in-capillary under nonequilibrium separation
conditions. The two binding constants appear comparable—(5.0 ± 1.2) × 106 M−1 and (9.06 ± 5.7) × 106 M−1—reflecting good preservation of the antibody binding behavior in the capillary electrophoresis format. These results allow
use of a calibration curve possible between 0.2 and 150 nM of endotoxin protein, with a limit of detection of 0.5 nM (33 μg L−1). Preliminary recovery experiments on maize extracts spiked with known amounts of Cry1Ab endotoxin also showed promising
results in detecting the toxin in complex real matrices. 相似文献
10.
The electrode characteristics and selectivities of PVC-based thiocyanate selective polymeric membrane electrode (PME) incorporating
the newly synthesized zinc complex of 6,7:14,15-Bzo2-10,11-(4-methylbenzene)-[15]-6,8,12,14-tetraene-9,12-N2-1,5-O2 (I
1
) and zinc complex of 6,7:14,15-Bzo2-10,11-(4-methylbenzene)-[15]-6,14-diene-9,12-dimethylacrylate-9,12-N2-1,5-O2 (I
2
) are reported here. The best response was observed with the membrane having a composition of I2:PVC:o-NPOE:HTAB in the ratio of 6:33:59:2 (w/w; milligram). This electrode exhibited Nernstian slope for thiocyanate ions over working concentration range of 4.4 × 10−7 to 1.0 × 10−2 mol L−1 with detection limit of 2.2 × 10−7 mol L−1. The performance of this electrode was compared with coated graphite electrode (CGE), which showed better response characteristics
w.r.t Nernstian slope 59.0 ± 0.2 mV decade−1 activity, wide concentration range of 8.9 × 10−8 to 1.0 × 10−2 mol L−1 and detection limit of 6.7 × 10−8 mol L−1. The response time for CGE and PME was found to be 8 and 10 s, respectively. The proposed electrode (CGE) was successfully
applied to direct determination of thiocyanate in biological and environmental samples and also as indicator electrode in
potentiometric titration of SCN− ion. 相似文献
11.
Electrochemical investigations of the reaction mechanism and kinetics between riboflavin immobilised on zirconium phosphate
(ZPRib) in carbon paste and NADH showed results yielding reliable information about aspects on the mechanism of the electron
transfer reaction between the flavin and NADH. The formal potential (E°′) of the adsorbed riboflavin was −220 mV versus SCE at pH 7.0. A shift about 250 mV towards a more positive potential compared
with its value in solution was assigned to the interaction between the basic nitrogen of riboflavin and the acid groups of
ZP. The invariance of the E°′ with the pH of the contacting solution and the effect of different buffer constituents were attributed to the protection
effect of ZP over the riboflavin. The electrocatalytic oxidation of NADH at the electrode was investigated using cyclic voltammetry
and rotating disk electrode methodology using a potential of −50 mV versus SCE. The heterogeneous electron transfer rate constant,
k
obs, was 816 M−1 s−1 and the Michaelis-Menten constant, K
M, was 1.8 mM (confirming a charge transfer complex intermediate in the reaction) for an electrode with a riboflavin coverage
of 6.8 × 10−10 mol cm−2. This drastic increase in the reaction rate between NADH and the immobilised riboflavin was assigned to the shift of the
E°′. A surprising effect with addition of calcium or magnesium ion to the solution was also observed. The E°′ was shifted to −150 mV versus SCE and the reaction rate for NADH oxidation increased drastically.
Received: 22 February 1999 / Accepted: 10 March 1999 相似文献
12.
E. Makrlík P. Toman P. Vaňura V. Kašička R. Rathore 《Journal of solution chemistry》2011,40(8):1418-1426
From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag+(aq) + 1⋅Cs+(nb) ⇆ 1⋅Ag+(nb) + Cs+(aq) taking part in the two-phase water–nitrobenzene system (where 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated to be log 10
K
ex(Ag+, 1⋅Cs+) = −1.0±0.1. Further, the stability constant of the hexaarylbenzene-based receptor⋅Ag+ complex (abbreviation 1⋅Ag+) in nitrobenzene saturated with water, was calculated at a temperature of 25 °C: log 10
β
nb(1⋅Ag+) = 5.5±0.2. By using quantum mechanical DFT calculations, the most probable structure of the 1⋅Ag+ complex species was solved. In this complex having C3 symmetry, the cation Ag+ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene ring via cation–π interaction. 相似文献
13.
A fast and sensitive liquid chromatography–mass spectrometry method was developed for the determination of ursolic acid (UA)
in rat plasma and tissues. Glycyrrhetinic acid was used as the internal standard (IS). Chromatographic separation was performed
on a 3.5 μm Zorbax SB-C18 column (30 mm × 2.1 mm) with a mobile phase consisting of methanol and aqueous 10 mM ammonium acetate
using gradient elution. Quantification was performed by selected ion monitoring with (m/z)− 455 for UA and (m/z)− 469 for the IS. The method was validated in the concentration range of 2.5 − 1470 ng mL−1 for plasma samples and 20 − 11760 ng g−1 for tissue homogenates. The intra- and inter-day assay of precision in plasma and tissues ranged from 1.6% to 7.1% and 3.7%
to 9.0%, respectively, and the intra- and inter-day assay accuracy was 84.2 − 106.9% and 82.1 − 108.1%, respectively. Recoveries
in plasma and tissues ranged from 83.2% to 106.2%. The limits of detections were 0.5 ng mL−1 or 4.0 ng g−1. The recoveries for all samples were >90%, except for liver, which indicated that ursolic acid may metabolize in liver. The
main pharmacokinetic parameters obtained were T
max = 0.42 ± 0.11 h, C
max = 1.10 ± 0.31 μg mL−1, AUC = 1.45 ± 0.21 μg h mL−1 and K
a = 5.64 ± 1.89 h−1. The concentrations of UA in rat lung, spleen, liver, heart, and cerebellum were studied for the first time. This method
is validated and could be applicable to the investigation of the pharmacokinetics and tissue distribution of UA in rats. 相似文献
14.
A kind of erbium hexacyanoferrate (ErHCF)-modified carbon ceramic electrodes (CCEs) fabricated by mechanically attaching ErHCF
samples to the surface of CCEs derived from sol–gel technique was proposed. The resulting modified electrodes exhibit well-defined
redox responses with the formal potential of +0.215 V [vs saturated calomel electrode (SCE)] at a scan rate of 20 mV s−1 in 0.5 M KCl (pH 7) solution. The voltammetric characteristics of the ErHCF-modified CCEs were investigated by voltammetry.
Attractively, the ErHCF-modified CCEs presented good electrocatalytic activity with a marked decrease in the overvoltage about
400 mV for l-cysteine oxidation. The calibration plot for l-cysteine determination was linear at 5.0 × 10−6–1.3 × 10−4 M with a linear regression equation of I(A) = 0.558 + 0.148c (μM) (R
2 = 0.9989, n = 20), and the detection limit was 2 × 10−6 M (S/N = 3). At last, the ErHCF-modified CCEs were used for amperometric detection of l-cysteine in real samples. 相似文献
15.
Measurements of the electrophoretic mobility (u
E) of particles of colloidal α-alumina were made as a function of pH, electrolyte concentration and electrolyte type (NaCl,
NaNO3 and KCl) using two similar instrumental techniques. Significant differences (50% or less) in the values of u
E of particles in NaCl were obtained from the two instruments; however, the isoelectric points (IEPs) (the pH at which u
E=0), estimated from the two sets of measurements, occurred at 7.5 ± 0.3 and 7.8 ± 0.05 and were not significantly different.
The latter estimate corresponds with those for particles in KCl and NaNO3 of 8.05 ± 0.11 and 7.95 ± 0.18, respectively, made using the same instrument and indicate that the IEP was a weak function
of electrolyte type. When cations acted as counterions (pH > IEP), the absolute magnitudes and the ranges of u
E with electrolyte concentration were found to be significantly less than when anions acted as counterions (IEP > pH). Estimates
of the zeta potential (ζ), made using various procedures, showed variations of up to 25% at low ratios of electrical-double-layer
thickness (κ
−1) to particle radius (a) (κa∼10) and were of a similar scale to differences in u
E, but no significant variations (95% confidence) in ζ were obtained at high values (κa∼200).
Received: 12 July 2000 Accepted: 17 October 2000 相似文献
16.
A new high α1A adrenoreceptor (α1AAR) expression cell membrane chromatography (CMC) method was developed for characterization of α1AAR binding interactions. HEK293 α1A cell line, which expresses stably high levels of α1AAR, was used to prepare the stationary phase in the CMC model. The HEK293 α1A/CMC-offline-HPLC system was applied to specifically recognize the ligands which interact with the α1AAR, and the dissociation equilibrium constants (K
D) obtained from the model were (1.87 ± 0.13) × 10−6 M for tamsulosin, (2.86 ± 0.20) × 10−6 M for 5-methylurapidil, (3.01 ± 0.19) × 10−6 M for doxazosin, (3.44 ± 0.19) × 10−6 M for terazosin, (3.50 ± 0.21) × 10−6 M for alfuzosin, and (7.57 ± 0.31) × 10−6 M for phentolamine, respectively. The competitive binding study between tamsulosin and terazosin indicated that the two drugs
interacted at the common binding site of α1AAR. However, that was not the case between tamsulosin and oxymetazoline. The results had a positive correlation with those
from radioligand binding assay and indicated that the CMC method combined modified competitive binding could be a quick and
efficient way for characterizing the drug–receptor interactions. 相似文献
17.
Catherine Tessini Claudia Mardones Lorena Rivas Dietrich von Baer 《Accreditation and quality assurance》2009,14(7):381-387
High-performance liquid chromatography (HPLC) to determine shikimic acid is used as a complementary tool to differentiate
wine varieties. In order to correctly classify, measurement uncertainty of shikimic acid by HPLC in red wine was estimated
considering the following components: uncertainty associated with the preparation of shikimic acid stock solution, uncertainty
associated with quantification using a calibration curve, and uncertainty associated with precision. The most important contribution
to total uncertainty was the method precision. The expanded uncertainty (U) for different wine varieties was between 2.6 and
8.5%. The method was applied to determine the concentration of shikimic acid in different emerging wine varieties cultivated
in Chile, such as Carmenère, Shiraz, and Pinot Noir, comparing them with classical varieties, such as Cabernet Sauvignon and
Merlot. Shiraz wines presented lower shikimic acid concentrations (between 27 and 86 mg L−1 with U
(k=2) = 2.6%) than Cabernet Sauvignon wines (between 41 and 142 mg L−1 with U
(k=2) = 8.1%), but their concentrations were higher than found in Merlot (from 9 to 41 mg L−1 with U
(k=2) = 4.3%) and Carmenère wines (between 7 and 49 mg L−1 with U
(k=2) = 5.8%). Pinot Noir was the variety with the lowest concentration of this acid (7–14 mg L−1 with U
(k=2) = 8.5%).
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
A. F. Santos L. Polese M. S. Crespi C. A. Ribeiro 《Journal of Thermal Analysis and Calorimetry》2009,96(1):287-291
The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent
kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably
managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(α)) could be calculated. Hence, the kinetic triplet (E±SD, logA±SD and f(α)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152±4 kJ mol−1, logA=14.1±0.2 s−1 for the kinetic model, and the autocatalytic model function was: f(α)=αm(1−α)n=α0.42(1−α)0.56. 相似文献
19.
Carina M. M. Machado Paula Gameiro Helena M. V. M. Soares 《Journal of solution chemistry》2008,37(5):603-617
The complexation behavior of eight M–(buffer)
x
–(OH)
y
systems involving two divalent ions (cobalt and nickel) and four zwitterionic biological buffers (AMPSO, DIPSO, TAPS and
TAPSO) were characterized. Complex formation was detected for all eight M–(buffer)
x
–(OH)
y
systems studied, but fully defined final models were obtained for only four of these systems. For systems involving cobalt
or nickel with AMPSO or TAPS, a complete characterization of the systems was not possible in the studied buffer pH-range.
Metal complexation was studied by glass-electrode potentiometry (GEP) and UV-Vis spectroscopy at 25.0 °C and I=0.1 mol⋅dm−3 KNO3 ionic strength. For the Ni–(L)
x
–(OH)
y
and Co–(L)
x
–(OH)
y
systems, with L = TAPSO or DIPSO, the proposed final models and overall stability constants were obtained by combining results
from both techniques. For the Ni–(L)
x
–(OH)
y
systems, the measured values of the stability constants are log 10
β
NiL=3.0±0.1 and log 10
β
NiL2=4.8±0.1 for L = TAPSO, and log 10
β
NiL=2.7±0.1 and log 10
β
NiL2=4.6±0.1 for L = DIPSO. For the Co–(L)
x
–(OH)
y
systems, the overall stability constants are log 10
β
CoL=2.2±0.1, log 10
β
CoL2=3.6±0.2 and log 10
β
CoL(OH)=7.6±0.1 for L = TAPSO, and log 10
β
CoL=2.0±0.1 and log 10
β
CoL(OH)=7.8±0.1 for L = DIPSO. For both buffers, the CoL(OH) species is characterized by a major structural rearrangement. 相似文献
20.
Krska R Schubert-Ullrich P Josephs RD Emteborg H Buttinger G Pettersson H van Egmond HP Schothorst RC Macdonald S Chan D 《Analytical and bioanalytical chemistry》2007,388(5-6):1215-1226
This paper presents results from the European Commission-funded project Doncalibrant, the objective of which was to produce
calibrators with certified mass fractions of the Fusarium toxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-Ac-DON), 15-acetyldeoxynivalenol (15-Ac-DON), and nivalenol (NIV),
in acetonitrile. The calibrators, available in ampoules, were sufficiently homogeneous, with between-bottle variations (s
bb) of less than 2%. Long-term stability studies performed at four different temperatures between −18 and 40 °C revealed no
significant negative trends (at a confidence level of 95%). Molar absorptivity coefficients (in L mol−1 cm−1) were determined for all four toxins (DON: 6805 ± 126, NIV: 6955 ± 205, 3-Ac-DON: 6983 ± 141, 15-Ac-DON: 6935 ± 142) on the
basis of a mini-interlaboratory exercise. The overall uncertainty of the calibrators’ target values for DON and NIV were evaluated
on the basis of gravimetric preparation data and include uncertainty contributions from possible heterogeneity, storage, and
transport. The Doncalibrant project resulted in the production of calibrators for DON (IRMM-315) and NIV (IRMM-316) in acetonitrile
with certified mass fractions of 25.1 ± 1.2 μg g−1 and 24.0 ± 1.1 μg g−1, respectively. Both CRMs became commercially available from the Institute for Reference Materials and Measurements (IRMM,
Geel, Belgium) at the beginning of 2007. 相似文献