共查询到20条相似文献,搜索用时 15 毫秒
1.
Sol and Gel state properties of aqueous gelatin solutions of concentrations 4%, 6%, 8% and 10% (w/v) have been investigated
through dielectric relaxation studies done at various temperatures in the range T=20–60 °C carried out over a frequency range f=20 Hz–10 MHz and no relaxation of any nature was observed. The sharp transition observed at the gelation temperature T
gel provided an excellent matching with the same measured through differential scanning calorimetry (DSC). The capacitance (C
p) values above f=100 kHz became increasingly negative as the gel was melted to the sol state. However, in the gel state C
p was found to be almost independent of temperature for frequencies above 100 kHz. At frequencies lower than 10 kHz, C
p measured was ∼105 F, implying pronounced interfacial polarization either due to electro-chemical reaction or because of ions getting trapped
at some interface within the bulk.
Received: 10 February 1997 Accepted: 2 September 1997 相似文献
2.
Silvana V. Rodrigues Decio Nepomuceno Luci Viana Martins W. Baumann 《Fresenius' Journal of Analytical Chemistry》1998,360(1):58-61
The solubility of two related series of each three triazine compounds has been determined in supercritical CO2, at 40 °C and pressures between 80 and 220⋅105 Pa. A high pressure small volume cell with adjustable optical path and built-in circulation pump has been constructed to
be used with quartz windows in a Perkin Elmer UV-VIS spectral photometer. At 220 bar solubilities are between 0.3 and 25 g/L,
dependent on the specific triazine structure. The isothermal pressure dependence of the solubility could be modelled using
the pressure dependent dielectric constant of CO2 as the only variable.
Received: 30 October 1996/Revised: 3 April 1997/Accepted: 13 April 1997 相似文献
3.
Stefan
amigasiewicz Bogdan Kowalski 《Journal of Polymer Science.Polymer Physics》1986,24(9):1961-1970
The dielectric relaxation of poly(bis-benzimidazobenzisoquinolinones) has been studied in the frequency range from 101 to 105 Hz and at temperatures from ?150 to +80°C. The data show that the relaxation is due mainly to diffusion of water in the polymer with simultaneous reorientation of water dipoles. 相似文献
4.
A new method for determining the static permittivity (dielectric constant) of extremely thin liquid interlayers is illustrated.
A special condenser, which can be filled with a test liquid, is constructed. Both condenser plates – one planar, the other
spherically curved – are made of vitreous carbon and are supplied with a high-grade politure.
In order to adjust plate separation distances from 10 nm up to about some μm the planar plate can be easily shifted by a piezoelectric
translation stage; the plate separation is monitored by an optical system supported by displacement transducers.
The measuring frequency was kept constant at 1 MHz. Water was chosen as the test liquid. At 19.8 °C thin water layers having
thickness smaller than 0.3 μm exhibit a decrease of the dielectric constant. The experimental data are consistent with a decay
length α-1 of the order of 1 nm which in view of the underlying crude model must be regarded as approximative.
Received: 28 May 1996 Accepted: 30 September 1996 相似文献
5.
Waxes were separated from needles by chloroform washing, drying and dissolving the residue in tetrahydrofuran (THF). Both
a THF solution of the wax and an aqueous solution of the Pd-Mg matrix modifier were sampled directly into the graphite tube.
The reaction conditions were optimised for the wax concentration of 45 mg ml-1 in THF and the Pd:Mg ratio of 1:1 in the matrix modifier. The atomisation and charring temperatures for As, Cd and Pb were
the same as those recommended for analysis of aqueous solutions except the charring temperature of Cd takes 200 °C lower.
The characteristic masses for As (26 pg), Cd (0.5 pg) and pb (9 pg) are also comparable to published data. The parameters
of calibration curves were identical for all three elements dissolved either in clear THF or in the wax solution. Elemental
concentrations were found to range from 0.1 to 1.0 mg g-1, increasing with needle age for As, Pb but not Cd.
Received: 20 September 1996 / Revised: 14 November 1996 / Accepted: 13 December 1996 相似文献
6.
Micron-sized monodispersed polystyrene (PS)/poly(n-butyl methacrylate) composite particles were produced as follows. First, 1.77 μm-sized monodispersed PS seed particles produced
by dispersion polymerization were dispersed in ethanol/water (1/2, w/w) medium dissolving poly(vinyl alcohol) as a stabilizer.
n-Butyl methacrylate (BMA) monomer dissolving benzoyl peroxide initiator was emulsified in ethanol/water (1/2, w/w) solution
of sodium dodecyl sulfate as emulsifier with ultrasonic homogenizer, and the BMA monomer emulsion was mixed with the PS seed
emulsion. The PS seed particles absorbed with a large amount of BMA (about 150 times weight of the seed particles) for 2 h
to about 10 μm in diameter while keeping good monodispersity and BMA droplets disappeared finally. The seeded polymerization
was carried out at 70 °C after a certain amount of water was added to depress the redissolving of BMA from the swollen particles
into the medium by raising from room temperature to the polymerzation temperature.
Received: 21 February 1996 Accepted: 4 September 1996 相似文献
7.
3]2+. Whereas the initial method is carried out in an aqueous solution, the improved one employs an aqueous micellar medium formed
by the cationic surfactant cetylpyridinium bromide (CPBR). The λmax in both methods is the same, i.e. 510 nm. The mean apparent
molar absorptivity (ɛ) and Sandell’s sensitivity (Ss) were calculated as ɛ=2.10×104 Lmol-1 cm-1 and Ss=8.37 ng cm-2 for the initial procedure, and ɛ=2.62×104 Lmol-1 cm-1 and Ss=6.72 ng cm-2 for the improved one. The regression line equation for the improved method was: A=1.487×10-1C −1.415×10-2 (r=0.9998). The accuracy and the precision of the improved method were investigated and the conclusions were satisfactory.
The results obtained for ASCA by both the described method and an official one, were statistically compared by means of the
Student’s t-test and by the variance ratio F-test; and no significant difference was observed.
Received: 15 January 1996/Revised: 7 March 1996/Accepted: 13 March 1996 相似文献
8.
P. Bermejo-Barrera Antonio Moreda-Piñeiro Jorge Moreda-Piñeiro Adela Bermejo-Barrera 《Analytical and bioanalytical chemistry》1997,358(7-8):844-847
Rapid methods were developed for the direct determination of Ag, Al, Cd and Mn in cocaine and heroin by ETAAS using programmes
omitting the charring step . Sample pretreatment was simple: dissolution in ultrapure water or in 35.0% (v/v) HNO3 for heroin or cocaine, respectively. Optimum drying temperatures were 250 °C for Ag, Al and Mn, and 300 °C for Cd. The run
cycles were 35 and 37 s, for Ag and Al respectively, and 36 s for Cd and Mn. The best results were obtained with Pd, Mg(NO3)2 and (NH4)2HPO4, as chemical modifiers. The limits of detection were 8.6, 55.9, 2.2 and 12.4 μg kg-1 for Ag, Al, Cd and Mn, respectively.
Received: 14 November 1996/Revised: 14 January 1997/Accepted: 18 January 1997 相似文献
9.
C. Vanderdonckt M. Krumova F. J. Baltá Calleja H. G. Zachmann S. Fakirov 《Colloid and polymer science》1998,276(2):138-143
Poly(ethylene terephthalate) (PET) was annealed in vacuum at different temperatures (190–260 °C) for different times (10 min–24 h)
in order to examine the mechanical properties (microhardness) of PET samples with a wide range of molecular weights (10 000–120 000).
Short annealing times result in a twofold decrease in mol. wt. due to hydrolytic decomposition. However, long annealing times
give rise to a substantial molecular weight increase. It is found that microhardness (H) rises linearly with the degree of crystallinity obtained during up-grading of mol. wt. and its extrapolation leads to H-values of completely crystalline PET, H
PET
c=405 MPa for samples with conventional mol. wt. and of 426 MPa for samples with mol. wt. higher than 30 000. It is shown that
the increase of mol. wt. for each set of samples with a given range of degree of crystallinity also causes a slight increase
of H. The influence of mol. wt. upon hardness is discussed in the light of the changes in the physical structure (crystallinity,
crystal thickness) which is formed at given heat treatment conditions.
Received: 29 April 1997 Accepted: 23 September 1997 相似文献
10.
M. A. Kabil S. E. Ghazy A. A. El-Asmy Y. E. Sherif 《Analytical and bioanalytical chemistry》1997,357(4):401-404
A sensitive and selective flotation procedure for the separation of microamounts of Co(II), Ni(II) and Cu(II) separately
or in admixture is described. The maximum separation rate (∼1) for 0.1 mmol/L of each analyte is achieved using 1 mmol/L of
both oleic acid (HOL) surfactant and 4-phenylthiosemicarbazide (HPTS) as a collector in the pH range 6–7. A method for the
simultaneous separation and microdetermination of the analytes is elaborated, based on adding excess HPTS and floating the
species with HOL at pH ∼6. The filtrate (which is clear brownish-yellow) obtained from the scum is used for the spectrophotometric
determination of Co(II) at 350 nm. The formation constants of 1:1 and 1:2 [Co(II):HPTS] species are 6.9×105 and 1.22×1010 L mol-1, respectively. Beer’s law is obeyed up to 9 μg/mL of Co(II) with a molar absorptivity of 1.15×104 L mol-1 cm-1. The precipitate in the scum layer is quantitatively collected, dissolved in aqua regia and aspirated directly into the flame
for the (AAS) determination of Ni and Cu. The procedure is successfully applied to some natural water samples. A mechanism
for the separation of the analytes is proposed.
Received: 23 January 1996/Revised: 1 April 1996/Accepted: 9 April 1996 相似文献
11.
J. E. Algie 《Colloid and polymer science》1969,234(2):1069-1078
Summary This paper contains data on the dielectric properties of wool with a range of water contents up to 30%, at temperatures of
0.5°, 21°, 32°, 48°, 70°, and 90 °C and for frequencies from 80 c/sec to 1.6 Mc/sec.
The dielectric loss data can be analysed into three absorption bands α, α′ andβ. Theα absorption is probably due to the motion of main chains, the α′ band is due to adsorbed water and theβ band is probably associated with the motion of side chains.
Water acts as a plasticiser and it is shown that a plot of the dielectric dispersion against water content does not show a
discontinuity indicating that there is no abrupt change in the nature of the absorbed water. 相似文献
12.
Solid-phase spectrophotometric microdetermination of iron with ascorbic acid and ferrozine 总被引:1,自引:0,他引:1
M. L. Fernández-de Córdova A. Ruíz-Medina A. Molina-Díaz 《Analytical and bioanalytical chemistry》1997,357(1):44-49
A very sensitive and selective method for the determination of trace amounts of iron has been developed, based on the reduction
of Fe(III) to Fe(II) by ascorbic acid, followed by chromogenic chelation of Fe(II) with ferrozine. The complex Fe(II)-ferrozine
is easily sorbed on a dextran-type anion-exchange gel packed in a 1 mm cell, and the absorbance of the gel is measured directly
at 569 and 800 nm. The extended linear range of the determination is 0.5–10 ng ml-1 of iron (apparent molar absorptivity=4.4×107 l mol-1 cm-1) and the precision (RSD) 1.3% for a concentration of 5 ng ml-1 of iron (n=10). The detection limit for a sample volume of 1000 ml, using 0.040 g of anion-exchanger, corresponds to 0.12 ng ml-1. The method has been successfully applied to the determination of iron in natural and waste waters, wine, soil extract and
previously digested vegetal tissues, drugs and human hair.
Received: 20 November 1995/Revised: 23 January 1996/Accepted: 26 January 1996 相似文献
13.
The association behaviour of triblock copoly(ethylene oxide/tetrahydrofuran/ethylene oxide), in particular E100T27E100, in aqueous solutions has been investigated by means of static and dynamic light scattering, nuclear magnetic reso-nance
(NMR) and surface tension techniques. On raising the polymer concentration at room temperature, the copolymer aggregates to
form micelles with an aggregation number of about 105 (R
G, mic≈15 nm and R
H, mic≈13 nm, as revealed by light scattering and FT-PGSE NMR measurements, respectively). The micelles are kinetically quite stable,
the micellar lifetime is shown to be more than 1 h. The residence time of a single unimer in a micelle is more than 140 ms.
The apparent radius of gyration R
G, mic is fairly independent of concentration, but large effects are observed on varying the temperature. Raising the temperature
initially results in an increase of the apparent micellar size, followed by a maximum at an intermediate temperature (≈45 °C).
At higher temperatures a contraction of the micelles is observed. The shape of the micelles also appear to vary in this temperature
interval. The interactions responsible for these phenomena are discussed in terms of, e.g., the temperature-dependent solubility
of the alkylene oxide segments in water and polydispersity effects.
Received: 29 January 1996 acccepted : 4 November 1996 相似文献
14.
A column preconcentration method has been established for the spectrophotometric determination of traces of nitrite using
diazotization and coupling on an naphthalene-tetradecyldimethylbenzylammonium (TDBA)-iodide (I) adsorbent. Nitrite ion reacts
with sulfanilic acid (SA) in the pH range 1.8–3.0 for the SA-1-naphthol system and in the pH range 2.3–3.2 for the SA-1-naphthylamine-4-sulfonate
system (SA-NAS system) in hydrochloric acid medium to form water-soluble colourless diazonium cations. These cations were
coupled with 1-naphthol in the pH range 1.6–4.6 and with NAS in the pH range 2.6–5.0 to be retained on naphthalene-TDBA-I
packed in a column. The solid mass was dissolved from the column with 5 mL of dimethylformamide (DMF) and the absorbance measured
at 418 nm for the SA-1-naphthol system and at 485 nm for the SA-NAS system. The calibration curve was linear over the concentration
range 0.02–0.87 mg/L for SA-1-naphthol and 0.02–0.80 mg/L in the sample for SA-NAS. The molar absorptivity was calculated
to be 1.70×104 L mol-1 cm-1 for SA-1-naphthol and 1.66×104 L mol-1 cm-1 for SA-NAS. The detection limits were found to be 0.014 and 0.016 mg/L for SA-1-naphthol and SA-NAS, respectively. The preconcentration
factors were 8 and 6 for SA-1-naphthol and SA-NAS, respectively. Replicate determinations of seven sample solutions containing
6.6 μg of nitrite for SA-1-naphthol and 5.3 μg of nitrite for SA-NAS gave mean absorbances of 0.486 and 0.382 with relative
standard deviations of 0.49 and 0.58%, respectively. Interferences due to various foreign ions have been studied and the method
has been applied to the determination of 27–65 μg/L levels of nitrite in natural waters. The recovery and relative standard
deviation for water samples were 98–102% and 0.49–0.58% for both systems.
Received: 1 December 1995/Revised: 22 April 1996/Accepted: 22 April 1996 相似文献
15.
Francisco Laborda María V. Vicente José M. Mir J. R. Castillo 《Analytical and bioanalytical chemistry》1997,357(7):837-843
Chromatographic effluents were on-line analyzed by Zeeman-ETAAS, using a flow-through cell placed in a graphite furnace autosampler
as interface. To obtain high sampling rates, the use of fast graphite furnace programmes was studied. Conventional programmes
of 96 s were reduced to 18 s by using hot injection (120 °C) and reducing the charring step to 2 s. The increase of the injection
volume from 20 to 60 μl lengthened the programme to 46 s. Nickel had to be added to get a comparable response for both inorganic
and organic selenium species (selenite and selenomethionine) and to reduce the interferent effect produced in presence of
the chromatographic eluent (TRIS 0.01 mol l-1, NH4NO3 0.1 mol l-1, pH 7). The optimized conditions were applied to the speciation of selenium in human erythrocyte lysates by size exclusion
LC-ETAAS. Using a high performance size exclusion column selenium could be assigned to proteins of 100 and 35 kDa. Detection
limits in the range of 1 ng (2 μg l-1 for 500 μl injection volume) were obtained for the combined technique.
Received: 9 October 1996/Revised: 8 July 1996/Accepted: 14 July 1996 相似文献
16.
Fourier transform infrared spectra in the wave number range 450–4500 cm-1 of poly (2-hydroxy-ethyl methacrylate) PHEMA have been studied as functions of water content in the range 38–2.6 wt% and
of temperature in the range 300–373 K. The results show changes in the intensities of the stretching frequencies of the carbonyl
band, H–O–H bending vibration and O–H stretching vibration with a change in water content and temperature. The results confirm
two types of water in the hydrogel polymer system, tightly bound water and loosely bound water. At low concentrations, water
is mainly hydrogen-bonded to the polymer and is described as tightly bound water. However, at water concentrations greater
than 18% by weight, part of the water exists in a different form and behaves as loosely bound water. For concentrations over
30%, there is some evidence that excess water behaves more loosely bound somewhat like bulk water. Infrared spectroscopic
results supplement those obtained by means of NMR by Smyth et al. and by dielectric spectroscopy. Our results also show that
some of the water continues to be hydrogen bonded to the polymer until at least a temperature of 373 K when the bulk water
should have evaporated. FTIR is found to yield greater site-specific insight into the local behaviour of water in hydrated
PHEMA.
Received: 22 August 1996 Accepted: 11 November 1996 相似文献
17.
A novel surfactant peptide consisting of an arginine cation with laurate anion has been synthesized, purified and characterized.
The critical micellar concentration (cmc) of peptide in aqueous solutions has been determined using spectroscopic techniques
and is found to increase from 0.06 to 0.11 mM with increasing temperature (15–45 °C). Cmc is also determined in the presence
of salts like NaCl, KCl and sodium acetate and it is found that these electrolytes hinder aggregation with a significant increase
in the case of sodium acetate. The aggregation number of the surfactant peptide has been determined using fluorescence quenching
measurements and is observed to decrease from 14 to 6 with increasing temperature (15–45 °C). The standard free energy change
(ΔG
0
m) and standard enthalpy change (ΔH
0
m) of the peptide aggregate are found to be negative with a small positive value for standard entropy change (ΔS
0
m). The peptide aggregate seems to undergo phase transition above 50 °C as observed from UV–vis and fluorescence spectroscopy.
From pyrene binding studies, it is shown that the interior dielectric constant increases from 5.08 at 34 °C to 8.77 at 50 °C
and further decreases with increase in temperature indicating a phase change at 50 °C. Also, the ratio of excimer intensity
to monomer intensity, which is a measure of microviscosity of the aggregate, decreases with increase in temperature with a
change at 50 °C indicating a phase change.
Received: 14 February 1997 Accepted: 13 August 1997 相似文献
18.
M. Fujiwara T. Okano T. -H. Nakashima A. A. Nakamura G. Sugihara 《Colloid and polymer science》1997,275(5):474-479
For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, critical micellization
concentration (CMC), solubility and degree of counterion binding (β) were determined by means of electrocon-ductivity measurements
at different temperatures (at every 5 °C) ranging from 15 to 50 °C. The phase diagram of 14SFNa in pure water was constructed
from the CMC- and solubility-temperature data, in which the Krafft temperature (critical solution temperature) was found around
0 °C. The changes in the Gibbs energy, ΔG
0
m, enthalpy, ΔH
0
m, and entropy, ΔS
0
m, upon micelle formation as a function of temperature were evaluated taking βvalues into calculation.
Received: 28 August 1996 Accepted: 5 November 1996 相似文献
19.
The characteristics of poly(oxyethylene) hydrogenated caster oil ether (HCO-10) vesicles were studied for the standpoints
of encapsulation efficiency, stability, solubilization and permeability or barrier efficiency. The vesicles of 5% HCO-10 had
6.24% of calcein-entrapment efficiency and 240 nm of mean diameter. The stability of HCO-10 vesicle suspensions was dependent
on their concentrations. In the vesicle suspensions of 10% HCO-10 or more, both the size of the vesicles and the fluidity
of the suspensions obviously varied with incubation time, indicating that a flocculation occurred; whereas, the vesicle suspension
of 5% HCO-10 was relatively stable. The solubilization process of HCO-10 vesicles by SDS was similar to that of EggPC liposomes.
The rate constants for permeation of Cl ion and calcein were 2.46×10-3 s-1 and 5.79×10-5 s-1, respectively, suggesting that HCO-10 vesicles possessed some barrier potential for Cl ion and calcein although they were
smaller than those of liposomes. Furthermore, the efflux of the solute such as calcein from HCO-10 vesicles was maximum at
37 °C, where the vesicle membrane was presumably destabilized by dehydration of EOs in HCO-10 molecules.
Received: 7 May 1996 Accepted: 3 September 1996 相似文献
20.
Anionic cartridge preconcentrators for inorganic arsenic, monomethylarsonate and dimethylarsinate determination by on-line HPLC-HG-AAS 总被引:1,自引:0,他引:1
M. Gómez C. Cámara M. A. Palacios A. López-Gonzálvez 《Analytical and bioanalytical chemistry》1997,357(7):844-849
Preconcentration anionic cartridges in combination with hyphenated FI-HG-AAS and HPLC-HG-AAS have been evaluated for the
preconcentration and quantification of total toxic arsenic and of inorganic arsenic, monomethylarsonate and dimethylarsinate
species, respectively. Optimum retention and elution parameters of the species on the anionic cartridges are evaluated and
the quality parameters of the analysis are reported. The detection limits for the arsenic species under study range from 0.1 μg L-1 to 0.6 μg L-1. The proposed method was successfully applied to the determination of arsenic species in spiked fresh water.
Received: 2 April 1996/Revised: 22 July 1996/Accepted: 25 July 1996 相似文献