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1.
Two independent methods for the determination of cadmium in cadmium-doped indium phosphide have been developed. Electrothermal
atomic absorption spectrometry (ETAAS) utilized both platform atomization and a chemical modifier composed of magnesium nitrate
and orthophosphoric acid. As the matrix mass was found to influence the cadmium sensitivity, matrix matched calibration standards
were necessary. The detection limit (3sB) is 0.20 μg/g for a 100 mg sample. The electrochemical method employed a solid-state cadmium sulfide-silver sulfide electrode
as potentiometric sensor. An excess of indium (III) influenced the electrode response. A preliminary chelation-extraction
of indium with acetylacetone at pH 5.0 in acetate buffer overcame the interference. The detection limit of the ISE-potentiometric
method is 10 μg/g for a 200 mg sample. Two indium phosphide single crystals grown from melts doped with cadmium sulfide or
cadmium telluride were analyzed for their cadmium content.
Received: 27 August 1996/Revised: 27 January 1997/Accepted: 30 January 1997 相似文献
2.
Emulsifier for microemulsion polymerization 总被引:3,自引:0,他引:3
By introducing an hydroxyl group and a lipophilic branch into the middle of lipophilic head of emulsifier 12-oxy-9-octadecenoic
acid, a new emulsifier was synthesized and applied in microemulsion polymerization. When the emulsifier content in the microemulsion
was kept to about 12%, the highest monomer content in microemulsion could achieve 35% for BA, 20% for St and MMA. The microemulsion
with high monomer content remained clear after polymerization, and the average diameters of polymer particles were 38.9 nm
for St microemulsion, 47.4 nm for BA, and 50.7 nm for MMA.
Received: 18 November 1997 Accepted: 16 January 1998 相似文献
3.
To understand the properties of colloidal dispersions it is often vital to prepare model materials with particles that have
a small polydispersity in order to make experimental tests of theories or models. However few preparations have been developed
that yield anisotropic particles with a narrow size distribution and precise shape. In this paper the preparation of a dispersion
of charge stabilized, tungstic acid particles is described. The particles are rectangular and have a length of 7.0 μm, a width
of 2.8 μm and a thickness of 0.2 μm. The polydispersity is 8% in length and 10% in width, making it one of the most monodisperse
dispersions of anisotropic particles. Each particle is monocrystalline and the crystal orientation is fixed with respect to
the particle morphology. Some interesting behavior is observed: these particles aggregate perpendicular and parallel to each
other to give flat, ordered flocs when the stability is reduced.
Received: 22 January 1998 Accepted: 4 February 1998 相似文献
4.
Monodisperse, cationic microgels were synthesized by surfactant-free emulsion copolymerization of 2-vinylpyridine and styrene,
using the cationic initiator 2,2′-azobis(2-amidinopropane) dihydrochloride. Low levels of divinylbenzene were employed as
a cross-linking agent. The particle morphologies and diameters were characterized by a combination of TEM and photon correlation
spectroscopy. At styrene contents less than 40% by weight, the particles were spherical with diameters of approximately 200 nm.
The diameter decreased with increasing styrene content and the morphology changed from spherical to irregular. The pH-dependent
swelling of the microgel particles was studied in constant ionic strength acetate buffers, as a function of styrene content
and cross-link density. Particle diameters increased sharply below pH 4.6 due to ionization of the 2-vinylpyridine residues.
At higher styrene levels, the transition pH is shifted to lower values and the extent of swelling is reduced. The pH at which
swelling occurred was identical for the three cross-linker levels (0.25, 0.50 and 1.5 wt%), but the extent of swelling decreased
in this order as expected. The rate of swelling of the particles was investigated by stopped-flow spectrophotometry; as microgels
swell the turbidity of the dispersions decreases and this was followed as a function of time. Higher styrene contents not
only reduce the extent of swelling, but also the rate at which maximum swelling is reached, whereas the level of cross-linker
employed in this study has no effect on the rate of swelling.
Received: 26 May 1997 Accepted: 16 July 1997 相似文献
5.
In this work turbidimetric and nephelometric techniques have been used to study the homocoagulation of aqueous dispersions
of uniform spherical particles of surfactant-free latexes. Cationic and anionic latexes of similar particle sizes (361 and
370 nm) and different surface charge densities (+16.4 and −3.6 μC/cm2) were used throughout. The kinetic constants which control the aggregation processes when the electrical repulsion disappears
were estimated by both techniques at different particle concentration and wavelength in order to establish the experimental
conditions which provided reliable and similar values for the coagulation rate constant. Both experimental techniques (turbidity
and nephelometry) and two ways of fitting the data have been used with both latexes. For the first method, the initial slope
of turbidity or total scattered intensity versus time curves were used to calculate the kinetic constants. In the second method,
the whole turbidity or total scattered intensity versus time curves were fitted and the kinetic constants calculated. An unambiguous
experimental value for the doublet rate constant in diffusion conditions is obtained by turbidity and nephelometry techniques.
By nephelometry both data treatments have permitted a distinction between the doublet rate constant and the global rate constant
in diffusion conditions.
Received: 2 June 1997 Accepted: 14 August 1997 相似文献
6.
Temperature-sensitive micron-sized monodispersed composite polymer particles were prepared by seeded copolymerization of
dimethylaminoethyl methacrylate and ethylene glycol dimethacrylate with 1.77 μm-sized monodispersed polystyrene seed particles.
The change in surface property at temperature above and below 35 °C was examined by differential scanning calorimetry, trypsin
activity and the adsorption/ desorption behaviors of low molecular weight cationic emulsifier as well as biomolecules.
Received: 6 August 1997 Accepted: 16 January 1998 相似文献
7.
Summary The cross-linkings of the surface polymer layer on mono disperse, poly(maleic anhydride-styrene)-modified silica particles
by the reaction with diisocyanate were studied. The extent of cross-linking was estimated by the weight decrease by immersing
the particles in the buffer solution of pH 2.0, 4.0 and 9.0 at a room temperature for 24 h. The reaction of the polymer-modified
silica with 1,6-diisocyanatohexane afforded relatively stable composite particles which lost less than 5 wt% of the polymer
in aqueous solution in the pH range 2.0–9.0. The diisocyanate was a preferable cross-linker to 2,4-diisocyanatotoluene in
terms of stability in acidic or basic aqueous solution. The flexibility of the cross-linker molecule possibly plays an important
role in the cross-linking reaction. The carboxyl and amino groups were formed by treating the cross-linked composite particles
with diluted HCl solution; 5–6 and 0.5–1.1 μmol g-1, respectively. The cross-linked composite particles exhibited the characteristic property of ζ-potential, −44 to −47 mV and
−102 to −107 mV in a neutral aqueous solution and ethanol, respectively.
Received: 26 May 1997 Accepted: 4 August 1997 相似文献
8.
Dispersion behavior of aqueous solutions containing oleic acid (RH), sodium oleate (R-Na+), and NaCl was investigated by turbidity and dynamic light-scattering measurements. Changes of the size of scattering particles
in solution composed of 1 mM oleic acid and 100 mM NaCl were traced as a function of the degree of ionization α, in terms
of radius of the equivalent hydrodynamic sphere. Large associated micelles with a radius of 30 nm appeared by a slight decline
of α and existed at α higher than 0.75. They were responsible for the three-phase equilibrium (solution, micelle and aggregated
micelle, and acid–soap, (R-Na+)3RH) characterized by a constant pH of 9.75. The appearance of a new phase, (R-Na+)3RH, contributed to increase both the turbidity and averaged scattering particle size. As the breakdown of the three-phase
equilibrium, radius of scattering particles increased significantly. Finally, oleic acid oil droplets were separated from
aqueous phase at low α. When the system was buffered by tris(hydroxymethyl)aminomethane (Tris), scattering particles with
a weight-averaged hydrodynamic radius of 75 nm existed in a wide range of α from 0.85 to 0.65. In Tris buffered solution,
turbidity formation was induced by the increase in the number of aggregated particles.
Received: 12 November 1996 Accepted: 4 April 1997 相似文献
9.
Four monodisperse latices with particle size of 75, 135, 340 and 477 nm were synthesized. The rheo-logical properties of
mixture of the monodisperse latices were inves-tigated as a function of blending ratio, and compared with those of multi-modal
latices, in a range of shear rate from 0.2 to 100 s-1. The maximum packing (highest solid contents) was observed at a weight fraction 80% of large particles with respect to total
solids contents for both bimodal and trimodal latices, and the lowest viscosity was obtained when the ratio of large to medium
to small particles was approximately 80/10/10 (by wt.). It was also demonstrated that this minimum in the viscosity is not
strongly dependent on the actual size of each kind of particles present in the multimodal latices.
Received: 22 November 1996 Accepted: 26 November 1997 相似文献
10.
Subbiah Thirumaran Govindasamy Gurumoorthy Rajaram Arulmozhi Samuele Ciattini 《应用有机金属化学》2020,34(9):e5761
[ Ni(dtc)2] (dtc = N-(pyrrole-2-ylmethyl)-N-thiophenemethyldithiocarbamate ( 1 ), N-methylferrocenyl-N-(2-phenylethyl)dithiocarbamate ( 2 ), N-furfuryl-N-methylferrocenyldithiocarbamate ( 3 ), and (N-[pyrrole-2-ylmethyl]-N-thiophenemethyldithiocarbamato-S,S′)(thiocyanato-N)(triphenylphosphine)nickel(II) ( 4 ) complexes were prepared and characterized by elemental analysis, infrared, ultraviolet–visible, and nuclear magnetic resonance (1H and 13C) spectroscopies. The data were consistent with the formation of square planar nickel(II) complexes, which was confirmed by single-crystal X-ray diffraction studies on 2 and 4 . Fe···Fe interactions exhibited by complex 2 led to supramolecular aggregation. The structure of 4 reveals intermolecular and intramolecular C-H···Ni anagostic interactions. The anion-sensing properties of 2 were studied with halide ions by cyclic voltammetry. It was observed that 2 acts as sensor for bromide. Complexes 1 , 2 , and 3 , were utilized to prepare nickel sulfide, nickel–iron sulfide-1, and nickel–iron sulfide-2, respectively. The composition, structure, morphology, and optical properties of nickel sulfide and nickel–iron sulfides were examined using powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, ultraviolet–visible, fluorescence, and infrared spectroscopy. Powder X-ray diffraction patterns of nickel sulfide, nickel–iron sulfide-1, and nickel–iron sulfide-2 indicate the formation of orthorhombic Ni9S8, cubic NiFeS2, and cubic Ni2FeS4, respectively. The photocatalytic activities of as-prepared nickel sulfide and nickel–iron sulfide-1 nanoparticles were investigated for photodegradation of methylene blue and rhodamine-B under ultraviolet irradiation. Nickel–iron sulfide-1 nanoparticles show slightly higher photodegradation efficiency compared with the nickel sulfide nanoparticles. 相似文献
11.
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
12.
A. N. Araújo José A. M. Catita José L. F. C. Lima Elias A. G. Zagatto 《Fresenius' Journal of Analytical Chemistry》1998,360(1):100-103
A monosegmented flow system (MCFA) is proposed to achieve slow enzymatic spectrophotometric determinations, here applied
to the determination of triglycerides in blood serum. The sample (4.5 μL), enzymatic reagent (150 μL) and an air plug (100 μL)
are simultaneously inserted into a carrier stream buffered to pH 7.9 (Tris ⋅ HCl). In order to avoid the cumbersome step of
air removal, a relocating detector was used. This system handles about 60 samples/h, yielding precise results (r.s.d. usually<2.5%).
Sensitivity is 56 mAU ⋅ L/mmol up to 6 mmol/L triglycerides. Accuracy was assessed by running 50 samples already analysed
by a conventional procedure yielding the equation CMCFA(mmol/L)=1.00(±0.04) CRef(mmol/L)−0.03(±0.08); r=0.990.
Received: 22 January 1997/Revised: 12 March 1997/Accepted: 28 March 1997 相似文献
13.
Robert Koeber R. Niessner Josep Maria Bayona 《Analytical and bioanalytical chemistry》1997,359(3):267-273
The performance of two liquid chromatography-mass spectrometry (LC/MS) interfacing techniques, thermospray (TSP) and atmospheric
pressure chemical ionization (APCI), for the analysis of benzo[a]pyrene (BaP) metabolites (hydroxy, epoxy and quinone derivatives) was compared. Interface and detection parameters such as
source temperature, eluent composition or flow rate were optimized using negative ion mode. In TSP, the main ions are mostly
[M]-, [M−H2O]- or [M+CH3COO]-, whereas APCI gives mainly the [M]- and [M−H]- ions. Quantification was carried out by flow injection. Calibration graphs were linear in the range of 10 ng to 1000 ng in
TSP and 0.1 ng to 10 ng in APCI. Detection limits were in the range of 1 ng to 20 ng in TSP and 0.002 ng to 0.2 ng in APCI.
The presence of BaP-1,6-dione, BaP-3,6-dione, and BaP-6,12-dione was confirmed in environmental samples of air particulate
matter.
Received: 6 January 1997/Accepted: 18 April 1997 相似文献
14.
Robert Koeber R. Niessner Josep Maria Bayona 《Fresenius' Journal of Analytical Chemistry》1997,359(3):267-273
The performance of two liquid chromatography-mass spectrometry (LC/MS) interfacing techniques, thermospray (TSP) and atmospheric
pressure chemical ionization (APCI), for the analysis of benzo[a]pyrene (BaP) metabolites (hydroxy, epoxy and quinone derivatives) was compared. Interface and detection parameters such as
source temperature, eluent composition or flow rate were optimized using negative ion mode. In TSP, the main ions are mostly
[M]-, [M−H2O]- or [M+CH3COO]-, whereas APCI gives mainly the [M]- and [M−H]- ions. Quantification was carried out by flow injection. Calibration graphs were linear in the range of 10 ng to 1000 ng in
TSP and 0.1 ng to 10 ng in APCI. Detection limits were in the range of 1 ng to 20 ng in TSP and 0.002 ng to 0.2 ng in APCI.
The presence of BaP-1,6-dione, BaP-3,6-dione, and BaP-6,12-dione was confirmed in environmental samples of air particulate
matter.
Received: 6 January 1997/Accepted: 18 April 1997 相似文献
15.
The analysis of the interaction of micelles formed by a blockcopolymer is given by means of small-angle X-ray (SAXS) and
small-angle neutron scattering (SANS). The blockcopolymer consists of poly(styrene) and poly(ethylene oxide) (molecular weight
of each block: 1000 g/mol) and forms well-defined micelles (weight-association number: 400, weight-average diameter: 15.4 nm)
in water. The internal structure has been studied previously (Macromolecules 29:4006 (1996)) by SAXS. There it has been shown
that the micelles are spherical objects. The structure factor S(q) as a function of the scattering vector q (q=(4π/λ) sin (θ/2); λ: wavelength of the radiation in the medium; θ: scattering angle) can be extracted from both sets of small-angle
scattering data (SANS: q≤0.4 nm-1; SAXS: q≤0.6 nm-1). It is shown that particle interaction in the present system can be described by assuming soft interaction which is modeled
by a square-step potential.
Received: 12 May 1997 Accepted: 9 July 1997 相似文献
16.
O. Quadrat L. Mrkvic˘ková Z. Walterová L. Titkova P. Bradna J. S˘n˘upárek 《Colloid and polymer science》1998,276(10):879-886
Changes in viscosity, pH and static light scattering behavior on alkali addition of model dispersions of statistical copolymers
of ethyl acrylate with 15 and 50 wt% of methacrylic acid prepared by semicontinuous emuslion copolymerization and crosslinked
with various amount of N,N′-methylenebisacrylamide were investigated. It was found that about 1% of crosslinking agent was sufficient to prevent unpredictable
disintegration of dispersion particles and gauranteed reproducible flow behavior of alkalinized dispersions. The viscosity
of alkalinized dispersions of crosslinked particles at low concentration is controlled by the effective hydrodynamic volume
of swelled particles which decreases with the crosslinking degree of copolymer. On the other hand, at higher particle concentration
close to critical concentration at which the space is filled up by swelled particles the influence of particle interaction
prevails and due to lower deformability of crosslinked particles viscosity increases with a crosslinking degree. In comparison
with similar dispersions prepared without a crosslinking agent these results indicated much uniform structure of dispersion
particles and suppression of influence of random crosslinking due to chain transfer reactions. The study shows that dispersions
of crosslinked copolymers of this type could be considered as thickners of latex binders with stable and reproducible thickening
properties.
Received: 23 February 1998 Accepted: 11 June 1998 相似文献
17.
The emulsifier-free emulsion copolymerization of styrene and tetrahydrofurfuryl methacrylate (TMA) in aqueous phase is described.
Monodisperse latex particles with diameters from about 280 to 620 nm are obtained consisting of a hydro-phobic polystyrene
core and a hydrophilic poly-TMA shell. The influence of a variation of TMA, styrene and initiator (potassium persulfate) concentration
in the original emulsion on particle size, molecular weight and composition of the copolymer is described. The concentration
of TMA and initiator affects the number of primary particles but not the size of the final particles, whereas the styrene
concentration strongly influences the particle diameter, a large size being favored by a high styrene concentration. The molecular
weights of the polymers are between 6.2×104 and 7.0×105 g/mole. Size exclusion chromatography of polymer solutions in tetra-hydrofuran shows that high molecular weights are especially
found in large particles, which are preferentially formed in emulsions with a high concentration of styrene. 1H-NMR spectroscopy of the polymer shows that only about 50% of the initial TMA concentration are polymerized in the particles.
Thus the copolymers prepared at increasing styrene concentration and constant initiator concentration of the emulsion show
an increasing polystyrene content and are formed in particles of increasing size.
Received: 4 June 1997 Accepted: 19 August 1997 相似文献
18.
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
19.
Micron-sized mono-dispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles (PS/PBMA=2/1 by weight) having a heterogeneous structure in which many fine
PBMA domains dispersed in a PS matrix near the particle surface were produced by seeded polymerization of n-butyl methacrylate (BMA) of which almost all had been absorbed by 1.8 μm-sized monodispersed PS seed particles utilizing
the dynamic swelling method. The morphology was varied by changing the PS/BMA ratio and polymerization temperature. It was
concluded that the swelling state of 2 μm-sized BMA-swollen PS particles in the seeded polymerization process is one of the
important factors to control the morphology of the composite particles.
Received: 27 November 1996 Accepted: 21 March 1997 相似文献
20.
O. A. Platonova L. M. Bronstein S. P. Solodovnikov I. M. Yanovskaya E. S. Obolonkova P. M. Valetsky E. Wenz M. Antonietti 《Colloid and polymer science》1997,275(5):426-431
The preparation and properties of Co nanoparticles in polystyrene(PS)-poly-4-vinyl-py-ridine(PVP) micelles were studied.
Elementary Co was generated by two methods: (i) by reduction of micelles loaded with CoCl2, and (ii) by thermal decomposition of Co2(CO)8 in micel-lar solutions of such block copolymers. Co particles formed by both processes are effectively stabilized by the
block copolymer matrix and do not aggregate. For CoCl2 as a Co-source, the formed particles have a size less than 1 nm. Thermal treatment of such dried polymers at 200 °C for 2 h leads to spherical particles of 3–5 nm in size. The polymeric hybrid materials prepared in this way display remarkably
high values of magnetization at rather low Co contents in the polymer, i.e., we obtain a tenfold increase of the specific
magnetization density. Co2(CO)8 as a Co source, results in a more complex behavior. Co2(CO)8 dissolves in the solvent as well as in the micelle core where it is converted to an cationic–anionic complex involving the
4-VP units. The shape and size of the Co nanoparticles formed by thermolysis can be controlled by the balance of 4-VP/Co and
can be varied from spherical particles in the limit of lower Co loads being mainly attached to the micelle core to a star-like
and cubic morphology in case of excess of Co2(CO)8. Both superparamagnetic and ferromagnetic materials can be prepared. For ferromagnetic samples coercive force varies from
250 to 475 Oe depending on Co content and polymer sample.
Received : 27 September 1996 Accepted: 22 November 1996 相似文献