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1.
Ultra-high-molecular-weight polyethylene (Mˉ
v: 5 × 106, 100-times elongated film) was irradiated with γ-rays under a 1,3-butadiene atmosphere at room temperature. Electron paramagnetic
resonance (EPR) measurements indicated that the radicals formed on the polyethylene substrate during the irradiation were
short-lived. EPR, Fourier transform IR spectroscopy, solid-state NMR, and differential scanning calorimetry of the as-irradiated
materials indicated that butadiene molecules were covalently bound to the polyethylene chains as pendant groups bearing trans-vinylene and vinyl functions in a ratio of 3:1. Some crosslinks among the pendants, or between pendants and the main chains
were produced. The number of unsaturated pendants introduced (including bridges) per carbon atom of the polyethylene main
chain was dependent on the irradiation dose and the butadiene pressure, and was 0.096 butadiene units for 10 kGy irradiation
under a 304 kPa butadiene atmosphere. The unsaturated pendants or bridges on the polyethylene chain thus introduced may be
good targets to functionalize polyethylene by covalent modification.
Received: 22 February 1999 Accepted in revised form: 30 June 1999 相似文献
2.
Anita Olszówka-Myalska 《Mikrochimica acta》2002,139(1-4):119-123
A composite material with aluminium matrix and alumina particles coated with nickel was investigated. The nickel coating
with thickness up to 1 μm formed by a chemical method consisted of a thin film directly on the alumina surface, porous zone
of grains 100 nm size and discontinuous zone of grain agglomerates. As a result of the interaction between the alumina particles
coated with nickel and the aluminium matrix, dissolution of nickel in aluminium occurred and reactive bonding took place.
In the interface characterized by SEM and TEM methods nickel aluminide and locally nickel-iron aluminide were identified.
The presence of complex aluminide was a result of local iron impurity in the aluminium powder. 相似文献
3.
Huseyin Bekir Yildiz Jaime Castillo Dmitrii A. Guschin Levent Toppare Wolfgang Schuhmann 《Mikrochimica acta》2007,159(1-2):27-34
An amperometric biosensor for the detection of phenolic compounds was developed based on the immobilization of tyrosinase
within an Os-complex functionalized electrodeposition polymer. Integration of tyrosinase within the redox polymer assures
efficient catechol recycling between the enzyme and the polymer bound redox sites. The non-manual immobilization procedure
improves the reproducibility of fabrication process, greatly reduces the desorption of the enzyme from the immobilization
layer, and, most importantly prevents fast inactivation of the enzyme by its substrate due to fast redox cycling.
A two-layer sensor architecture was developed involving ascorbic acid oxidase entrapped within an electrodeposition polymer
in a second layer on top of the redox polymer/tyrosinase layer. Using this sensor architecture it was possible to eliminate
the current interference arising from direct ascorbate oxidation up to a concentration of 630 μM ascorbic acid. The effects
of the polymer thickness, the enzyme/polymer ratio, and the applied potential were evaluated with respect to optimal sensor
properties. The sensitivity of the optimized sensors for catechol was 6.1 nA μM−1 with a detection limit of 10 nM, and for phenol 0.15 nA μM−1 with a detection limit of 100 nM. 相似文献
4.
Covalent modification of multiwalled carbon nanotubes with a low molecular weight chitosan 总被引:1,自引:0,他引:1
Gang Ke Wen Chao Guan Chang Yu Tang Zhen Hu Wen Jie Guan Dan Lin Zeng Feng Deng 《中国化学快报》2007,18(3):361-364
Covalent modification of shortened multiwalled carbon nanotubes (MWNTs) with a natural low molecular weight chitosan (LMCS) was accomplished by the nucleophilic substitution reaction. The LMCS modified MWNTs (MWNT-LMCS) were characterized by FTIR, solid-state 13C NMR, and XPS spectroscopies, thermogravimetric analysis, and transmission electron microscopy. The results revealed that amino and primary hydroxyl groups of the LMCS participated mainly in the formation of the MWNT-LMCS conjugates. The MWNT-LMCS consists of 58 wt.% LMCS, and about four molecular chains of the LMCS were attached to 1000 carbon atoms of the nanotube sidewalls. As a novel derivative of the MWNTs, the MWNT-LMCS not only solved in DMF, DMAc and DMSO, but also in aqueous acetic acid solution. 相似文献
5.
A method of nonaqueous capillary electrophoresis was established for the separation and determination of alanine, phenylalanine,
isoleucine and valine after derivatization with 4-chloro-7-nitrobenzo-2-oxa-1, 3-diazol in nonaqueous media. The derivatization
and separation conditions were optimized. The optimum derivatization conditions were 70 min for the reaction time, 55 °C for
the reaction temperature and 20 mM ammonium acetate in methanol for the derivatization buffer. The most suitable running buffer
was composed of 60 mM ammonium acetate, 10% acetonitrile in methanol with a fused-silica capillary column (47 cm × 75 μm i.d.),
20 kV applied voltage and 20 °C capillary temperature. The correlation coefficients were better than 0.995 in the investigated
concentration ranges. The relative standard deviation (R.S.D.) (n = 5) of the migration times and peak areas were 2.0–4.3%
and 1.9–4.5%, respectively. The method was applied to the determination of four compounds in two compound amino acid injections,
with the exception of phenylalanine, the recoveries for the other three compounds ranging between 88–116%. 相似文献
6.
A simple and sensitive sensor is described for the determination of acetylspiramycin (ASPM) based on a single-wall carbon
nanotubes (SWNTs)-dihexadecyl hydrogen phosphate (DHP) film coated glassy carbon electrode (GCE). Compared with a bare GCE,
the SWNTs-DHP film modified GCE exhibits excellent enhancement effects on the electrochemical oxidation of ASPM. A well-defined
oxidation peak of ASPM occurs at 0.89 V in 0.1 mol·L−1 phosphate buffer (pH 5.5), which was used to determine ASPM. The electrochemical behavior of ASPM at the SWNTs-DHP modified
GCE was examined by cyclic voltammetry and differential pulse voltammetry. The experimental parameters were optimized and
a direct electrochemical method for the determination of ASPM is proposed. Under optimum conditions, the oxidation peak current
is linear to the concentration of ASPM in the range of 5.0–100 μg·mL−1, with a detection limit of 1 μg·mL−1. The SWNTs-DHP film modified electrode also provides an efficient way of eliminating interferences from some inorganic species
in the solution. This sensor was successfully utilized to determine ASPM in drugs. 相似文献
7.
Six chelating matrices have been prepared by anchoring 2,3-dihydroxypyridine (DHP) and 2-{[1-(3,4-dihydroxyphenyl)methylidene]amino}benzoic
acid (DMABA) onto Amberlite XAD-2 and XAD-16 and 3,4-dihydroxybenzaldehyde (DHB), and iminodiacetic acid (IDA) onto silica
gel. The materials were explored for enrichment of palladium followed by its determination with flame AAS. The optimum pH
ranges for quantitative solid phase extraction by these matrices are from 4.0–5.5 to 5.5–7.0. The flow rates (column procedure)
and concentration of HCl required for desorption have been optimized. Thiourea (∼3%) is essential for quantitative recovery
of Pd. The t1/2 values are between 5 and 15 min. The sorption capacity varies from 38 to 192 μmol g−1 (highest for silica gel loaded with iminodiacetic acid). The preconcentration factors were found in the range 20–150. Tolerance
limits of foreign species in the enrichment are reported. The enrichment procedures coupled with FAAS determinations were
applied to synthetic solutions corresponding to standards GBW07293 and NIST SRM 2557 successfully. 相似文献
8.
Rafael A. de Sousa Anderson S. Ribeiro Mariana A. Vieira Adilson J. Curtius Nivaldo Baccan Solange Cadore 《Mikrochimica acta》2007,159(3-4):241-246
In order to determine inorganic constituents and contaminants in liquid aspartame sweeteners, different brands of this product
were analyzed by ICP OES and ICP-MS. The samples were submitted to acid digestion and parameters such as internal standardization
and wavelengths, in the case of ICP OES, and a recovery test were evaluated. The analytes studied were As, Ca, Cd, Co, Cu,
K, Fe, Mg, Mn, Na, Ni, Pb, Se and Zn. Since there is not a certified reference material for sweeteners, the accuracy of the
proposed method was evaluated by recovery tests and the values were in the range of 90–110% for the majority of the analytes.
The detection limits for the elements determined by ICP OES were in the range 0.01 (Mn)– 2.0 (K) μg g−1 while those determined by ICP-MS were 0.001 μg g−1 for all the elements except Mn and As (0.002 μg g−1). The relative standard deviations were below 12% for ICP OES and below 14% for ICP-MS determinations. The mean concentration
of the elements detected by ICP OES (Ca, Fe, K, Mg, Na, and Zn) varied according to the brand. The other analytes, were determined
by ICP-MS. For these elements, a significant variation in their concentrations was also found for different samples, except
for Co and Ni. The use of both multielemental techniques allowed the evaluation of the inorganic composition and the rapid
determination of several elements in aspartame sweeteners, with adequate accuracy. 相似文献
9.
Monte Carlo simulation of electron transport in solids is widely used in electron microscopy, spectroscopy and microanalysis.
The reliability of physical models incorporated in a Monte Carlo code is usually checked by comparing with experimental results.
Elastic or inelastic collisions are usually considered as the basic interactions of electrons with atoms. In our Monte Carlo
code the single scattering model is employed for simulation of X-ray emission from thin films of Au on the Si substrate. The
electron beam energy was in the range 10–30 keV, the take-off-angle was 40°. The simulated values of X-ray production were
calculated in our Monte Carlo code using several models of ionisation cross-sections. For the emitted intensities the depths
of inelastic collision and X-ray absorption were taken into account, then the k-ratios were calculated. These data were compared with experimental values of k-ratios calculated from X-ray intensities of Au M and Au L characteristic lines. We followed mainly the dependence of the
k-ratios of the film element on film thickness. The film thickness was in the range 0.05–1 μm. Reasonably good agreement was
found for dependences of X-ray intensity on film thickness in the whole energy range and for both lines, especially for Powell’s
model of the ionisation cross-section. 相似文献
10.
Arsenic speciation is of increasing interest to the food industry, as concerns about high total arsenic concentrations in
food can often be alleviated to a great extent if the ratio of toxic, less toxic and non-toxic arsenic compounds in the sample
is known.
The lipid matrix of fish oil is a challenge in the determination of arsenic species, as current methods for this type of analysis
require the analyte to be water-soluble. In this study, two sample preparation techniques were applied. One the one hand water-soluble
species were extracted with methanol/water, on the other, acid digestion was applied to release lipid-soluble arsenic compounds
into the aqueous phase. Ion chromatography – inductively coupled plasma mass spectrometry (IC-ICP-MS) was used for separation
and sensitive element-specific detection of arsenic compounds. Additional experiments, including alkaline hydrolysis, were
carried out to find out more about the type of lipids arsenic is bound to in fish oil.
Up to eight different arsenic species were detected and quantified in fish oil with dimethylarsinate being the major compound
both in the aqueous extract and in the acid digest. No inorganic arsenic was detected in the aqueous extract, and the maximum
concentration of arsenate determined in the acid digest was 0.05 μg g−1.
The total arsenic concentration determined by ICP-MS ranged from <0.1 to 5 μg g−1. With regard to the mass balance, approximately 1% of the total arsenic content was extractable with methanol/water, whereas
the sum of arsenic species quantified after acid digestion yielded 85–100% of the total arsenic content. It was confirmed
that the large fraction of arsenic in fish oil not extractable on an aqueous basis consists of organoarsenic compounds.
This new approach in sample preparation makes the complete characterization of the arsenic content in the sample possible
with regard to the respective species, providing necessary information required for risk assessment. 相似文献
11.
An analytical method using alumina modified with water-soluble polyacrylic acid polymer for the simultaneous separation and
preconcentration of trace Cu and Cd in a column system, and their determination by flame atomic absorption spectrometry was
developed. The conditions for coating Al2O3 with polyacrylic acid were optimized, then the column was packed with 50 mg of this sorbent. Cd and Cu solution was passed
through a glass column at pH 4.5, and elution was carried out with 5 mL of 0.05 M HCl at a flow rate of 1 mL min−1. A sorption capacity of 10 mg Cu and 12 mg Cd was obtained for 1 g sorbent. The detection limit was calculated as 4.5 μg L−1 for Cu and 1.54 μg L−1 for Cd in the final solution. Enrichment factors of 300 for Cd and 400 for Cu were obtained. 相似文献
12.
DNA films immobilized on an indium tin oxide (ITO) electrode surface were detected and determined employing a high-affinity
intercalator, Ru(bpy)2(dppz)2+ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a:2′,3′-c]phenazine), as a redox indicator, and oxalate as a sacrificial electron
donor in solution to chemically amplify the voltammetric signal of the indicator. Nucleic acids were immobilized on ITO by
layer-by-layer electrostatic adsorption, using avidin as the first layer and nucleic acid as the second layer. In quartz crystal
microbalance (QCM) measurements on an avidin-coated gold surface, the amount of adsorption from a 200 μg mL−1 nucleic acid solution was found to be 3.2 ng mm−2 for both double-stranded (ds-) and single-stranded (ss-) calf-thymus DNA as well as polycytidylic acid (Poly-C). After binding
with Ru(bpy)2(dppz)2+ (Ru-dppz), voltammetry of the ds-DNA film on ITO was carried out in an indicator-free phosphate buffer. An anodic peak at
about 1.15 V was observed, and it was assigned to Ru-dppz oxidation. When measured in an oxalate buffer, however, a catalytic
current was observed due to the oxidation of oxalate by electrochemically generated Ru(bpy)2(dppz)3+, resulting in a 120-fold increase in the signal. Since oxalate itself produces a very low oxidation current on ITO, catalytic
voltammetry produces about a 14-fold improvement in the signal-to-blank ratio over the non-amplified determination. As a result,
ds-DNA adsorbed from 20 ng mL−1 solution could be detected, which was estimated by QCM to be 160 pg mm−2 on the surface. The catalytic current of ds-DNA was substantially higher than that of ss-DNA and poly-C, indicative of selective
binding of the redox indicator to ds-DNA. The results serve as a basis for the catalytic voltammetric detection of DNA hybridization
in future work. 相似文献
13.
A pre-concentration procedure using cloud point extraction is presented for the determination of uranium in natural water
using molecular absorption spectrometry. The ligand used was 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) and
the micellar phase was obtained using the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) and centrifugation.
Interferences were eliminated using a masking solution containing trans-1,2-cyclohexanediaminetetraacetic acid (CDTA), sodium
fluoride and sulphosalicylic acid. The optimization step was performed using a two-level factorial design and a Doehlert matrix,
involving the factors pH, centrifugation time and buffer concentration.
The method allows the determination of uranium in water samples with a detection limit of 0.15 μg L−1, a quantification limit of 0.50 μg L−1 and a precision expressed as relative standard deviation of 1.8 and 2.3% for uranium concentrations of 5 and 10 μg L−1, respectively (n = 8). The accuracy was confirmed by analysis of two certified samples of natural water. This method was
applied to the determination of uranium in superficial water samples collected at a uranium mine in Brazil. For five samples
analyzed, the concentration of uranium varied between 1.1 and 18.1 μg L−1. Tests of addition/recovery were performed for all these samples, and the results varying between 98 and 105% also proved
that this procedure is not affected by the matrix and can be applied satisfactorily to the determination of uranium in water
samples. 相似文献
14.
Alessandro Borghi Roberto Compagnoni Roberto Cossio Lorenzo Giuntini Mirko Massi Filippo Olmi Alba P. Santo Gloria Vaggelli 《Mikrochimica acta》2006,155(1-2):105-112
We present a multi-analytical and multi-instrumental approach to a petrologic study of garnets from metapelites characterized
by different metamorphic grades. The comparison between major, minor and trace element (Y) distribution in garnets crystallized
at different temperatures was performed by electron microprobe (EDS and WDS) and the Proton Induced X-ray Emission microprobe
(μ-PIXE).
Two garnet samples were selected from metapelite rocks at different metamorphic grades from the tectonic unit of Stilo, Calabrian–Peloritanian
Arc, Southern Italy. Quantitative spot analysis profiles and compositional X-ray maps of major elements and yttrium are reported.
The major element zoning of garnets is mostly characterized by a smoothed and gradual concentric variation of all elements
from core to rim. The Y concentration reveals a marked zoning with its distribution decreasing from about 7000 ppm to about
100 ppm from core to rim, respectively. The precise determination of the Y content by μ-PIXE technique allowed us to better
define the rock thermal history, by applying the Y geothermometer. In particular, a common starting temperature of about 450 °C
was calculated for the beginning of the garnet growth from all over the unit, but different temperatures in the range from
520 °C to 670 °C were estimated for the peak event in garnets from different areas, in agreement with the P–T values given
by the main rock mineral assemblages, reflecting a different metamorphic grade. 相似文献
15.
A novel method is described for the preconcentration of ultratrace amounts of lead in water. Dithizone is employed as a chelator
forming a neutral lead-dithizone complex to extract lead ions from aqueous solution into the ionic liquid 1-octyl-3-methylimidazolium
hexafluorophosphate. Under optimal conditions, the extraction efficiency in one step and back-extraction efficiency with 5 mL
of 0.1 mol L−1 nitric acid were 99.9 and 99.8% for 20 μg of lead in 1 L of water solution, respectively. Preconcentration coupled with graphite
furnace atomic absorption spectrometry was developed for the determination of lead in environmental water samples. The calibration
graph was linear with a correlation coefficient of 0.998 at levels near the detection limits up to at least 0.1 μg L−1. The detection limit, calculated as three times the standard error of the estimated calibration graph, is 1.0 ng of lead
per liter of water sample. The determination of lead was free from interference from almost all cations and anions, and from
humic acid in water from plant rot. Lead recoveries between 97.8 and 100.8% for spiked samples prove the accuracy of the method. 相似文献
16.
T. Basinska S. Slomkowski A. Dworak I. Panchev M. M. Chehimi 《Colloid and polymer science》2001,279(9):916-924
Polystyrene microspheres with polyglycidol (polyGL) in a surface layer were synthesized in batch radical emulsifier-free
emulsion copolymerizations of styrene and surfmers, α-t-butoxy-ω-vinylbenzyl-polyGL macromonomers (VB-polyGL). Macromonomers
with number-average molecular weight Mˉ
n=950 (VB-polyGL950) and Mˉ
n=2700 (VB-polyGL2700) were used for these polymerizations. In all syntheses the initial concentrations of styrene and initiator
(K2S2O8) were constant. The initial macromonomer-to-styrene ratios were varied from 1.10 × 10−3 to 1.64 × 10−2 mol/mol and from 3.46 × 10−4 to 3.47 × 10−3 mol/mol for VB-polyGL950 and VB-polyGL2700, respectively. The diameters of microspheres obtained were smaller for the syntheses
with higher concentrations of macromonomers. Syntheses with VB-polyGL950 yielded microspheres with number-average diameters
(Dˉ
n) from 216 to 900 nm and with a bimodal diameter distribution. The number-average diameters of microspheres obtained with
VB-polyGL2700 varied from 220 to 650 nm, depending on the initial concentration of macromonomer. Their diameter distributions
were monomodal, with a diameter polydispersity parameter (ratio of weight-average and number-average diameters) in the range
1.007≤Dˉ
w/Dˉ
n≤1.022. For each type of microsphere the fraction of polyGL in a surface layer and the surface concentration of sulfate anions
were determined. The fraction of polyGL in the surface layer was related to the initial monomer composition in the polymerizing
mixture. Adsorption of human serum albumin onto surfaces of some poly(styrene/VB-polyGL) microspheres was up to 10 times lower
than for the polystyrene microspheres obtained in a similar emulsifier-free emulsion polymerization of styrene.
Received: 26 September 2000/Accepted: 19 February 2001 相似文献
17.
Tomás Pérez-Ruiz Carmen Martínez-Lozano Virginia Tomás José Fenoll 《Mikrochimica acta》2003,141(1-2):73-78
The chemiluminescence reaction of lucigenin with glucose and fructose in the presence of Brij-35 and in alkaline solution
was used to develop kinetic methods for the determination of both hexoses individually and mixed together. A stopped-flow
mixing module coupled to a photomultiplier tube allowed kinetic and equilibrium measurements, which were used for the individual
determination of glucose and fructose. The same measurements were used to analyse the mixture of both sugars using a two equation
system, which was resolved by multiple linear regression. The ranges of the calibration graphs obtained by using kinetic and
equilibrium measurements were 25–1000 μg ml−1 and 75–1100 μg ml−1, respectively, for glucose and 1–350 μg ml−1 and 5–250 μg ml−1, respectively, for fructose. Mixtures of glucose and fructose in ratios between 1:0.4 and 40:1 were satisfactorily resolved.
Received February 27, 2002; accepted August 6, 2002 相似文献
18.
《中国化学快报》1993,(5)
Photoisomerization of a new polymer: monoesters of polymaleic acid containing naphthalene-azo-anthraquinone groups in side chains at the air-water interface of a Langmuir trough wan detected by recording the development of surface pressure with time. This process wan found to be a first-order reaction and complete within several minutes. 相似文献
19.
Kanchi Suvardhan Kailasa Suresh Kumar Dasari Rekha Pantrangam Subrahmanyam Kapuvedi Kiran Bellum Jayaraj Surasura Ramanaiah Kandhukuri Janardhanam Pattium Chiranjeevi 《Mikrochimica acta》2007,157(3-4):237-244
Cloud point extraction was applied as a method for preconcentration of rhodium after formation of a complex with 2-propylpiperidine-1-carbodithioate
(2-PPC), and later determined by flame atomic absorption spectrometry using TritonX-114 as surfactant. Rhodium was complexed
with 2-PPC in an aqueous phase and kept for 15 min in a thermostatted bath at 40 °C. Separation of the two phases was accomplished
by centrifugation for 15 min at 4000 rpm. The chemical variables affecting the cloud point extraction were optimized and successfully
applied to rhodium determination in various water samples. Under optimized conditions, the preconcentration system (100 mL
sample) permitted an enhancement factor of 50. The detection limits obtained under optimal conditions was 0.052 ng mL−1. The extraction efficiency was investigated at different rhodium concentrations (7.0–42.0 μg mL−1), and good recoveries (96.42–99.14%) were obtained using this method. It has been applied to the determination of rhodium
in water and was compared with reported methods in terms of Student’s ‘t’-test and variance ratio ‘f’-test. 相似文献
20.
With the aim of avoiding cumbersome sample treatment, we present a device for the introduction of solid soil samples into
AAS-flames for gold determination, as well as the proposition of earth from anthills as a gold occurrence indicator. A previous
ground sample of anthill earth (0.50 mg) was weighed directly into a small recipient of polyethylene which was then connected
to a sampling boronsilicate glass chamber. The sample was carried by an airflow (5 L min−1) to a quartz cell positioned between the burner top and the optical beam. The generated atomic vapor produced a transient
signal which was totally integrated in three seconds. The performance was compared with conventional flame atomic absorption
spectrometry after proper sample digestion. No significant differences were observed between both procedures (mean deviation
±1.90%), and a LOQ of 0.03 μg Au was achieved using the proposed method. The anthill earth was found to be very suitable for
indication of gold occurrence in soils and related materials. 相似文献