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981.
A microwave-assisted sequential extraction of water and dilute acid soluble arsenic species from marine plant and animal tissues 总被引:1,自引:0,他引:1
This paper describes the use of dilute nitric acid for the extraction and quantification of arsenic species. A number of extractants (e.g. water, 1.5 M orthophosphoric acid, methanol-water and dilute nitric acid) were tested for the extraction of arsenic from marine biological samples, such as plants that have proved difficult to quantitatively extract. Dilute 2% (v/v) nitric acid was found to give the highest recoveries of arsenic overall and was chosen for further optimisation. The optimal extraction conditions for arsenic were 2% (v/v) HNO3, 6 min−1, 90 °C. Arsenic species were found to be stable under the optimised conditions with the exception of the arsenoriboses which degraded to a product eluting at the same retention time as glycerol arsenoribose. Good agreement was found between the 2% (v/v) HNO3 extraction and the methanol-water extraction for the certified reference material DORM-2 (AB 17.1 and 16.2 μg g−1, respectively, and TETRA 0.27 and 0.25 μg g−1, respectively), which were in close agreement with the certified concentrations of AB 16.4 ± 1.1 μg g−1 and TETRA 0.248 ± 0.054 μg g−1.To preserve the integrity of arsenic species, a sequential extraction technique was developed where the previously methanol-water extracted pellet was further extracted with 2% (v/v) HNO3 under the optimised conditions. Increases in arsenic recoveries between 13% and 36% were found and speciation of this faction revealed that only inorganic and simple methylated species were extracted. 相似文献
982.
利用等体积浸渍法制备Cu-Ce/γ-Al2O3催化剂,并在无H2存在的条件下对硬脂酸进行催化水热液化。对催化剂进行BET比表面积分析和X射线衍射(XRD)分析可知,Cu-Ce/γ-Al2O3催化剂中存在CuO和CeO2两种晶型,在300℃条件下水热反应12 h后具有更好的热稳定性。通过对硬脂酸进行水热液化实验和对生物油进行气相色谱-质谱(GC-MS)分析发现,加入Cu-Ce/γ-Al2O3催化剂能够获得最高的硬脂酸转化率(94.71%)和总烃产率(81.41%),水热液化脱氧效果最好。分析正烷烃的产率,结果发现硬脂酸在高温水热条件下主要发生脱羧反应。Cu-Ce/γ-Al2O3催化剂的加入能够同时促进反应过程中脱羧反应、加氢脱氧反应和裂化反应。此外,Cu-Ce/γ-Al2O3还能够促进羰基基团的脱除,有效减少产物中的醛和酮类物质。 相似文献
983.
M Suguna LakshmiB.S.R Reddy 《European Polymer Journal》2002,38(4):795-801
New epoxide and cyanate ester resins with an aromatic ester backbone namely 1,3-[di-(4-glycidyloxy diphenyl-2,2′-propane)]-isophthalate (DGDPI) and 1,4-[di-(4-cyanato diphenyl-2,2′-propane)]-terephthalate (DCDPT) were synthesized and the intermediates were characterized by IR, 1H-/13C-NMR spectroscopic methods. The cured products from DGDPI and DHDPI exhibited higher Tg compared with standard epoxy system. The increase in the Tg may be due to the cyanate ester and rigid aromatic backbones present in the curing system. 相似文献
984.
Stereoselective synthesis of (3S,4S)- and (3R,4R)-series of 3,4-dihydroxyglutamic acids was investigated. The key reaction in this synthesis is asymmetric reduction of meso-imide derived from meso-tartaric acid. Lewis acid-promoted cyanation of the obtained optically active lactam via the acyliminium intermediate followed by standard deprotection procedure afforded the desired 3,4-dihydroxyglutamic acids. 相似文献
985.
提出了一个广谱测定强酸、强碱溶液浓度的方法。用铂电极作工作电极,电位溶出法对溶液酸碱性产生响应。通过调节沉积时间和沉积电位,利用电位溶出法可以检测溶液酸、大致 的浓度范围为2.5mol/L H^ -1.0mol/L OH^-。详细研究了不同测定范围的实验条件,以及溶出过程的响应机理。在不同酸碱性溶液中电沉积产生的氢吸附于电极表面,溶出过程中被溶液中的氧氧化成氢离子,从而产生电位平台。该平台的出现还与随后的电极表面金属/金属氧化物电对电位值有关。 相似文献
986.
Liang Wang Jun Yue Bai Peng Fei Huang Hong Jing Wang Xiao Wei Wu Yu Qing Zhao 《Mikrochimica acta》2007,158(1-2):73-78
The electrochemical behaviors of uric acid (UA) at the penicillamine (Pen) self-assembled monolayers modified gold electrode
(Pen/Au) have been studied. The Pen/Au electrode is demonstrated to promote the electrochemical response of UA by cyclic voltammetry
(CV). The diffusion coefficient D of UA is 6.97 × 10−6 cm2 s−1. In differential pulse voltammetric (DPV) measurements, the Pen/Au electrode can separate the UA and ascorbic acid (AA) oxidation
potentials by about 120 mV and can be used for the selective determination of UA in the presence of AA. The detection limit
was 1 × 10−6 mol L−1. The modified electrode shows excellent sensitivity, good selectivity and antifouling properties. 相似文献
987.
Responsive polymers have been the focus of many studies during the past decade because of their ability to change according to environmental stimuli. In this paper, we report on the development of a method to synthesize a pH/temperature‐sensitive linear copolymer, poly(N‐isopropylacrylamide‐ co‐acrylic acid)(poly(NIPAAm‐co‐AAc)), with a molecular weight of about 106–105 Da in water using azobisisobutyronitrile (AIBN) as the initiator. The effects of the following on the lower critical solution temperature (LCST) of the copolymer and homopolymer of NIPAAm were investigated: the type of buffer salts and pH changes of test solutions, molecular weight and concentration of homopolymer/copolymer solutions, and AAc monomer molar feed ratio (mol%). The effects of different synthesis methods on the molecular weight and on the AAc content were also evaluated. The mechanism of action in environments with different pH values is discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
988.
1INTRODUCTION In recent years,dicarboxylic acids have been wide-ly used as poly-dentate ligands involved in various metal chelation reactions to form transition or rare earth metal complexes with interesting properties in material science[1~3]and biological systems[4~7].For example,Kim,Y.and his coworkers focus on the syn-theses of copper(II)complexes containing ligands of malonate and pyrazine to study their electronic con-ductivity and magnetic property[8].The importance of Tr(II)/dic… 相似文献
989.
Four new two-ligand complexes of copper(II) with 2,2′-bipyridine and one of three different α-hydroxycarboxylic acids (lactic, H2LACO; 2-methyllactic, H2MLACO; and mandelic, H2MANO) were prepared. Complexes 1–3 of general formula [Cu(HL)2(bipy)]·nH2O (HL=monodeprotonated acid), were characterized by elemental analysis, IR, electronic and EPR spectroscopy, magnetic measurements and thermogravimetric analysis. Complexes 1 (HL=HLACO, n=2), 2 (HL=HMLACO, n=1) and 3a (the result of attempted recrystallization of 3, of formula [Cu(HMANO)(bipy)2](HMANO)·H2MANO·CH3CN were studied by X-ray diffractometry. The copper atom is in an elongated, tetragonally distorted octahedral environment in 1 and 2 and in 3a has a coordination polyhedron intermediate between a square pyramid and a trigonal bipyramid, as evaluated in terms of the parameter τ. In 1 and 2 the α-hydroxycarboxylato ligand is bidentate and monoanionic but in 3a there are three forms: a monodentate monoanion, a monoanionic counterion, and a neutral molecule. 相似文献
990.
Synthesis and characterization of block copolymers from 2‐vinylnaphthalene by anionic polymerization
Faquan Zeng Mu Yang Jianxin Zhang Sunil K. Varshney 《Journal of polymer science. Part A, Polymer chemistry》2002,40(24):4387-4397
The anionic polymerization of 2‐vinylnaphthalene (2VN) has been studied in tetrahydrofuran (THF) at ?78 °C and in toluene at 40 °C. 2VN polymerization in THF, toluene, or toluene/THF (99:1 v/v) initiated by sec‐butyllithium (sBuLi) indicates living characteristics, affording polymers with predefined molecular weights and narrow molecular weight distributions. Block copolymers of 2VN with methyl methacrylate (MMA) and tert‐butyl acrylate (tBA) have been synthesized successfully by sequential monomer addition in THF at ?78 °C initiated by an adduct of sBuLi–LiCl. The crossover propagation from poly(2‐vinylnaphthyllithium) (P2VN) macroanions to MMA and tBA appears to be living, the molecular weight and composition can be predicted, and the molecular weight distribution of the resulting block copolymer is narrow (weight‐average molecular/number‐average molecular weight < 1.3). Block copolymers with different chain lengths for the P2VN segment can easily be prepared by variations in the monomer ratios. The block copolymerization of 2VN with hexamethylcyclotrisiloxane also results in a block copolymer of P2VN and poly(dimethylsiloxane) (PDMS) contaminated with a significant amount of homo‐PDMS. Poly(2VN‐b‐nBA) (where nBA is n‐butyl acrylate) has also been prepared by the transesterification reaction of the poly(2VN‐b‐tBA) block copolymer. Size exclusion chromatography, Fourier transform infrared, and 1H NMR measurements indicate that the resulting polymers have the required architecture. The corresponding amphiphilic block copolymer of poly(2VN‐b‐AA) (where AA is acrylic acid) has been synthesized by acidic hydrolysis of the ester group of tert‐butyl from the poly(2VN‐b‐tBA) copolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4387–4397, 2002 相似文献