Grafting acrylic acid onto polypropylene by reactive extrusion with pre-irradiated PP as initiator

In this paper, the modification of polypropylene (PP) with acrylic acid (AA) by reactive extrusion using pre-irradiated PP (rPP) as initiator was investigated. It was found the relatively high graft degree (Gd) and slight degradation of modified PP was obtained when 20 wt% rPP was used. This result can be explained in terms of effective concentration of free radicals.

Preparation and Characterization of Melt Grafting 2-acrylamido-2-methyl-1-propanesulfonic Acid onto Pre-Irradiated Linear Low Density Polyethylene

Linear low density polyethylene (LLDPE) was functionalized with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) by using -ray pre-irradiation in air in a twin-screw extruder. Fourier-transformed infrared spectroscopy (FT-IR) and electron spectroscopy for chemical analysis (ESCA) were used to characterize the formation of LLDPE-g-AMPS copolymers. The content of AMPS in LLDPE-g-AMPS was determined by using element analysis instrument. The effects of concentrations of monomer, reaction temperature and pre-irradiation dose on degree of grafting were investigated. The critical surface tension of LLDPE-g-AMPS was measured by using contact angle method. The influences of the degree of grafting on crystallization properties were studied by using DSC. Compared with neat LLDPE, the crystallization temperature increased about 4C, and crystallinity decreased with increasing degree of grafting. Crystallization rates of grafted LLDPE were faster than that of plain LLDPE at the same crystallization temperature.

The preparation of high activity DMFC Pt/C electrocatalysts using a pre-precipitation method

It is suggested that a Pt/C cathodic catalyst for the direct methanol fuel cell (DMFC) can be prepared with a pre-precipitation method, in which, H2PtCl6 is precipitated onto the carbon black as (NH4)(2)PtCl6 before H2PtCl6 is reduced to Pt. The electrocatalytic activity of this Pt/C-A catalyst for oxygen reduction is excellent because the Pt/C catalyst prepared with this pre-precipitation method possesses a small average particle size, low relative crystalinity and a large electrochemically active surface area. In addition, the pre-precipitation method is simple and economical and it can be used to prepare a Pt/C catalyst on a large scale.

Electrochemical H2S sensor with H2SO4 pre-treated Nafion membrane as solid polymer electrolyte

It is reported for the first time that the performance of the electrochemical H2S sensor with the Nation membrane pre-treated with the concentrated H2SO4 as the solid electrolyte is much more stable than that for the sensor with the Nation membrane without H2SO4 pretreatment. The sensitivity of the sensor is about 2.92 muA/ppm. The response time of the sensor is about 9 s. The detection limit is about 0.1 ppm. Therefore, this kind of the electrochemical H2S gas sensor may be desirable for the practical application.

Self-assembly of the pre-formed inclusion complexes between cyclodextrins and alkanethiols on gold electrodes

A new kind of self-assembled monolayer (SAM) formed in aqueous solution through the pre-formed inclusion complexes (abbreviated CD . C-n) between alpha-, beta-cyclodextrins (CDs) and alkanethiols (CH3(CH2)(n-1)SH, n = 10, 14 and 18) was prepared successfully on gold electrodes. High-resolution H-1 NMR was used to confirm the formation of CD . C-n. X-ray photoelectron spectroscopy, cyclic voltammetry and chronoamperometry were used to characterize the resulting SAMs (denoted as M-CD . Cn). It was found that M-CD . Cn were more stable against repeated potential cycling in 0.5 M H2SO4 than SAMs of CH3(CH2)(n-1)SH (denoted as M-Cn), with a relative sequence of Mbeta-CD . Cn > Malpha-CD . Cn > M-Cn. In addition, an order of blocking the electron transfer between gold electrodes and redox couples (both Fe(CN)(6)(3-) and Ru(NH3)(6)(3+)) in solution, M-CD . C10 > M-CD . C14 > M-CD . C18, was observed. A plausible explanation is provided to elucidate some of the observations. (C) 1997 Elsevier Science S.A.

Simultaneous determination of monoamine and amino acid neurotransmitters in rat endbrain tissues by pre-column derivatization with high-performance liquid chromatographic fluorescence detection and mass spectrometric identification

A sensitive and efficient method for simultaneous determination of glutamic acid (Glu), gamma-amino-butyric acid (GABA), dopamine (DA), 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) in rat endbrains was developed by high-performance liquid chromatography (HPLC) with fluorescence detection and on-line mass spectrometric identification following derivatization with 1,2-benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC). Different parameters which influenced derivatization and separation were optimized. The complete separation of five neurotransmitter (NT) derivatives was performed on a reversed-phase Hypersil BDS-C-18 column with a gradient elution. The rapid structure identification of five neurotransmitter derivatives was carried out by on-line mass spectrometry with electrospray ionization (ESI) source in positive ion mode, and the BCEOC-labeled derivatives were characterized by easy-to-interpret mass spectra. Stability of derivatives, repeatability, precision and accuracy were evaluated and the results were excellent for efficient HPLC analysis. The quantitative linear range of five neurotransmitters were 2.441-2 x 10(4) nM, and limits of detection were in the range of 0.398-1.258 nM (S/N = 3:1). The changes of their concentrations in endbrains of three rat groups were also studied using this HPLC fluorescence detection method. The results indicated that exhausting exercise could obviously influence the concentrations of neurotransmitters in rat endbrains. The established method exhibited excellent validity, high sensitivity and convenience, and provided a new technique for simultaneous analysis of monoamine and amino acid neurotransmitters in rat brain. (C) 2008 Elsevier B.V. All rights reserved.

Determination of aliphatic amines from soil and wastewater of a paper mill by pre-column derivatization using HPLC and tandem mass spectrometry (HPLC-MS/MS)

A pre-column derivatization method for the sensitive determination of aliphatic amines using the labeling reagent 1,2-benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC) followed by HPLC with fluorescence detection and APCI/NIS identification in positive-ion mode has been developed. The chromophore of 2-(9-carbazole)-ethyl chloroformate (CEOC) reagent was replaced by the 1,2-benzo-3,4-dihydrocarbazole functional group, which resulted in a sensitive fluorescence derivatizing reagent, BCEOC, that could easily and quickly label amines. Derivatives were stable enough to be efficiently analyzed by HPLC and showed an intense protonated molecular ion corresponding m/z [M + H](+) with APCI/MS in positive-ion mode. The collision induced dissociation of the protonated molecular ion formed characteristic fragment ions at m/z 264.1, m/z 246.0 and m/z 218.1, corresponding to the cleavages of CH2CH2O-CO, CH2CH2-OCO, and N-CH2CH2O bonds. Studies on derivatization conditions demonstrated that excellent derivatization yields close to 100% were observed with a 3 to 4-fold molar reagent excess in acetonitrile solvent, in the presence of borate buffer (pH 9.0) at 40 degrees C for 10 min. In addition, the detection responses for BCEOC derivatives were compared with those obtained with CEOC and FMOC as labeling reagents. The ratios I-BCEOC/I-CEOC and I-BCEOC/I-FMOC were, respectively, 1.40-2.76 and 1.36-2.92 for fluorescence responses (here, I was the relative fluorescence intensity). Separation of the amine derivatives had been optimized on an Eclipse XDB-C-8 column. Detection limits calculated from an 0.10 pmol injection, at a signal-to-noise ratio of 3, were 18.65-38.82 fmol (injection volume 10 mu L for fluorescence detection. The relative standard deviations for intraday determination (n = 6) of standard amine derivatives (50 pmol) were 0.0063-0.037% for retention times and 3.36-6.93% for peak areas. The mean intra-and inter-assay precision for all amines were <5.4% and 5.8%, respectively. The recoveries of amines ranged from 96 to 113%. Excellent linear responses were observed with correlation coefficients of >0.9994. The established method provided a simple and highly sensitive technique for the quantitative analysis of trace amounts of aliphatic amines from biological and natural environmental samples.

Pre-column derivatization of amines with 1,2-benzo-3,4-dihydrocarbazole-9-isopropyl chloroformate followed by LC-fluorescence and LC-APCI-MS

A pre-column derivatization method for the sensitive determination of amines using the labeling reagent 1,2-benzo-3,4-dihydrocarbazole-9-isopropyl chloroformate (BCIC-Cl) followed by high-performance liquid chromatography with fluorescence detection has been developed. Identification of derivatives is carried out by high performance liquid chromatography/atmospheric pressure chemical ionization (LC-APCl-MS-MS). The chromophore of 2-(9-carbazole)-ethyl chloroformate (CEOC) reagent is replaced by 1,2-benzo-3,4-dihydrocarbazole-9-isopropyl functional group, which results in a sensitive fluorescence derivatizing reagent BCIC-Cl. BCIC-Cl can easily and quickly label amines. Derivatives are stable enough to be efficiently analyzed by high-performance liquid chromatography and show an intense protonated molecular ion corresponding m/z [MH](+) under APCl in positive-ion mode. The collision-induced dissociation of protonated molecular ion formed a product at m/z 260 corresponding to the cleavage of CH2-OCO bond. Studies on derivatization demonstrate excellent derivative yields over the pH 9.0-10.0. Maximal yields close to 100% are observed with a 3 to 4-fold molar reagent excess. In addition, the detection responses for BCIC derivatives are compared with those obtained using CEOC and FMOC as derivatization reagents. The ratios of l(BCIC)/l(CEOC) and l(BCIC)/l(FMOC) are, respectively, 1.23-3.14 and 1.25-3.08 for fluorescent (FL) responses (here, l is relative fluorescence intensity). Separation of the derivatized amines had been optimized on reversed-phase Eclipse XDB-C-8 column. Detection limits are calculated from 1.0 pmol injection, at a signal-to-noise ratio of 3, are 10.6-37.8 fmol. The mean interday accuracy ranges from 94 to 105% for fluorescence detection with the largest mean %CV < 7.5. The mean interday precision for all standards is < 6.0% of the expected concentration. Excellent linear responses are observed with coefficients of > 0.9997.

非均匀性对岩石破裂过程影响的研究

Rock heterogeneity plays an important role in rock fracturing processes. However, because fracturing is a dynamic process and it is very difficult to quantify materials' heterogeneity, most of the theories dealing with local failure were based on the homogeneity assumption, very few involving stress distribution heterogeneity and successive local failure due to rock heterogeneity. Therefore, based on various references, the author studied the laws and mechanism of influences of heterogeneity on rock fracturing processes, under the frame of the project "Study on Associate Mechanism between Rock Mass Fracture and Strength Failure", funded by Nation Natural Science Fund. the research consists of such aspects as size effect correction to rock fracture parameters, SEM (Scanning Electron Microscope) real-time observation on rock samples under different loads, micro-hardness testing, and numerical simulating based on microstructure. There are some important research results as followed: 1. Unifying formula for nonlinear and non-singularity correction, simplifying the complex process of correcting size effect on rock fracture toughness. 2. Using the methods of micro-hardness testing mineral grain and random jointing micrograph digitizing mineral slice, preliminarily solving the problems of numerical simulating and quantitatively describing the heterogeneous strength and its distribution rules, which has certain innovation and better practicability. 3. Based on SEM real-time observation, studying the micro-process of fracturing in marble, sandstone, granite, and mushroom stone samples with premanufactured cracks under tension, pure-shear and compression-shear conditions. Strength Failure was observed: there was some kind failure occurred before Fracture Failure in marble and sandstone samples with double cracks under pure-shearing. It is believed that the reason of strength failure developing is that stress concentrations is some locations are larger than that near the end of pre-manufactured cracks. 4. Based on the idea that rock macro-constitute is composed of complex microstructure, the promising method used to handle heterogeneity considers not only the heterogeneity of the rock medium, but also the heterogeneity of the rock structure. 5. Putting forward two types of rock strength failure: medium strength failure induced by heterogeneity of rock medium and structure strength failure induced by heterogeneity rock structure. 6. By evaluating potential fracture cell with proper failure priority, the numerical simulating method solved the problem of simulating the coextensive strength failure and fracture failure with convention strength failure rules. The result of numerical analysis shows that the influence of heterogeneity on rock fracturing processes is evident. The sinuosity of the rock fracture-propagation path, and the irregular fluctuation of loading displacement curve, is mainly controlled by the heterogeneity of rock medium.

Determination of alcohols by high-performance liquid chromatography with fluorimetric detection after pre-column derivatisation with carbazole-9-N-acetic acid and chromatographic behaviour of alcoholic derivatives

Alcohols were derivatised to their carbazole-9-N-acetic acid (CRA) esters with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC . HCl) as the dehydrating agent. Studies on derivatisation conditions indicated that the coupling reaction proceeded rapidly and smoothly in the presence of a base catalyst in acetonitrile to give the corresponding sensitively fluorescent derivatives. The retention behaviour of alcohol derivatives was investigated by varying mobile phase compositions (ACN-water and MeOH-water). The parameters from the equation log k'=A-BX were evaluated by retention data of derivatives using an isocratic elution with different mobile phases. The results indicated that the parameters derived allowed computation of retention factors in good agreement with experiments. At the same time, a general equation was derived that makes possible predictions of partition coefficient in binary mobile phases with different proportions of organic solvent to water based on some simple regression analysis. The LC separation for the derivatised alcohols containing higher carbon alcohols showed good reproducibility on a reversed-phase C-18 column with gradient elution. The detection limits (excitation at 335 nm, emission at 360 nm) for derivatised alcohols (signal-to-noise ratio=3:1) were in the range of 0.1-0.4 pg per injection. (C) 2001 Elsevier Science B.V. All rights reserved.

Synthesis of nanometric-size magnesium nitride by the nitriding of pre-activated magnesium powder

Magnesium nitride (Mg3N2) was synthesized by the reaction of magnesium in the highly reactive form (Mg*) with nitrogen at 450 degrees C under normal pressure. The effect of doping with nickel dichloride on the nitridation of Mg* was investigated. Differential thermal analysis (DTA) of Mg* systems and transmission electron microscopy (TEM) measurement of the product formed were carried out. TEM measurement showed that the particle size of the Mg3N2 synthesized was in the nanometric range. The dependence of nitridation of the NiCl2-doped Mg* on temperature was investigated at temperatures ranging from 300 to 500 degrees C. The nitridation of NiCl2-doped Mg* could occur even at temperature as low as 300 degrees C. (C) 1999 Kluwer Academic Publishers.

Application of liquid pre-column capillary electrophoresis technique to the study of interaction between drug enantiomers and human serum albumin

Based on the chiral separation of several basic drugs, dimetindene, tetryzoline, theodrenaline and verapamil, the liquid pre-column capillary electrophoresis (LPC-CE) technique was established. It was used to determine free concentrations of drug enantiomers in mixed solutions with human serum albumin (HSA). To prevent HSA entering the CE chiral separation zone, the mobility differences between HSA and drugs under a specific pH condition were employed in the LPC. Thus, the detection confusion caused by protein was totally avoided. Further study of binding constants determination and protein binding competitions was carried out. The study proves that the LPC technique could be used for complex media, particularly the matrix of protein coexisting with a variety of drugs.

Analysis of phenols by high-performance liquid chromatography with pre-column derivatization by 2-(9-carbazole)-ethyl-chloroformate

2-(9-Carbazole)-ethyl-chloroformate (CEOC), a novel pre-column fluorescence labeling reagent, has been synthesized and applied for the derivatization of phenols. Taken phenol, p-chlorophenol, 2,5-dimethylphenol, 2,4-dichlorophenol and 1,4-dihydroxybenzene as testing standards, the effects of derivatization conditions, such as pH of borate buffer, reaction time and fluorescent tagging reagent concentration, have been systematically studied. Under the optimized conditions, CEOC reacts readily with the phenols to form stable derivatives with excitation and emission wavelengths, respectively, at 293 and 360 nm. The single step derivatization reaction could be finished within 20 min even at room temperature. Such a method has been successfully applied to the analysis of phenols in printing ink by high-performance liquid chromatography. (c) 2005 Elsevier B.V. All rights reserved.