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991.
萃取分光光度法测定水和硫酸中的硒 总被引:3,自引:0,他引:3
本文提出一种测定硒的分光光度法。在酸性介质中,四价硒氧化I成为I3,I3-和结晶紫形成的离子缔合物用二甲苯萃取,进行分光光度测定。硒的检出限是0.05μg/mL。用磷酸和EDTA消除Fe^3+,Pb^2+,Hg^2+等离子的干扰影响。本法可不和硫酸中四价硒。 相似文献
992.
A facile and environment friendly approach was developed to graft vinyl acetate (VAc) onto plastic articles in an aqueous solution using tert‐butyl alcohol (TBA) as a compatiblizer and benzoyl peroxide (BPO) as an initiator. In a novel setup, excessive monomer suspended in a water phase, VAc could be conveniently grafted on the model substrate of low‐density polyethylene (LDPE) film and the graft percentage (GP) could be developed up to 7.3%. Reaction temperature could increase GP significantly, while adding monomer over a critical volume did not influence GP. By adding some paradioxybenzene, i.e. 0.06–0.08% in VAc phase, homopolymer PVAc could be avoided practically, while graft polymerization proceeded favorably in aqueous solutions. It was proved by attenuated total reflection‐infrared (ATR‐IR) spectroscopy that grafted VAc was located mainly at the surface of the LDPE film and hydrophilic nature of both grafted and alcoholyzed films were improved via contact angle measurements. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
993.
We investigate the shape deformation of an infinite membrane anchored by a rigid rod. The density profile of the rod is calculated by the self-consistent-field theory and the shape of the membrane is predicted by the Helfrich membrane elasticity theory [W. Helfrich, Z. Naturforsch. 28c, 693 (1973)]. It is found that the membrane bends away from the rigid rod when the interaction between the rod and the membrane is repulsive or weakly attractive (adsorption). However, the pulled height of the membrane at first increases and then decreases with the increase of the adsorption strength. Compared to a Gaussian chain with the same length, the rigid rod covers much larger area of the membrane, whereas exerts less local entropic pressure on the membrane. An evident gap is found between the membrane and the rigid rod because the membrane's curvature has to be continuous. These behaviors are compared with that of the flexible-polymer-anchored membranes studied by previous Monte Carlo simulations and theoretical analysis. It is straightforward to extend this method to more complicated and real biological systems, such as infinite membrane/multiple chains, protein inclusion, or systems with phase separation. 相似文献
994.
An on-line and fully automated method was developed for the continuous and dynamic in vivo monitoring of four arsenic species [arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)] in urine of living organisms. In this method a microdialysis sampling technique was employed to couple on-line with high performance liquid chromatography (HPLC) and hydride generation atomic absorption spectrometry (HGAAS). Dialysates perfused through implanted microdialysis probes were collected with a sample loop of an on-line injector for direct and automated injection into HPLC system hyphenated with HGAAS. The saline (0.9% NaCl) solution was perfused at the rate of 1 microl min(-1) through the microdialysis probe and the dialysate was loaded into 50 microl of sample loop. The separation conditions were optimally selected to be in phosphate buffer solution at a pH 5.2 with a flow rate of 1.2 ml min(-1). The effluent from the HPLC was first mixed on-line at the exit of the column with HCl (1 M) solution and then mixed with a NaBH4 (0.2% m/v) solution. Based on the optimal conditions obtained, linear ranges of 2.5-50 ng ml(-1) for AsIII and 6.75-100 ng ml(-1) for the other three arsenic species were obtained. Detection limits of 1.00, 2.18, 1.03 and 2.17 ng ml(-1) were obtained for AsIII, DMA, MMA and AsV, respectively. Typical precision values of 3.4% (AsIII), 5.4% (DMA), 3.6% (MMA) and 7.5% (AsV) were obtained, respectively, at a 25 ng ml(-1) level. Recoveries close to 100%, relative to an aqueous standard, were observed for each species. The average in vivo recoveries of AsIII, DMA, MMA and AsV in rat bladder urine were 56+/-5%, 60+/-9%, 49+/-3% and 55+/-7%, respectively. The use of an on-line microdialysis-HPLC-HGAAS system permitted the determination of four urinary arsenic species in the bladder of an anesthetized rat with a temporal resolution of 50 min sampling. 相似文献
995.
996.
997.
对氯柱硼镁石(2MgO•2B2O3•MgCl2•14H2O)在4.5%H3BO3水溶液40 ℃的溶解及相转化过程进行了动力学研究.对不同时间取出的液相的化学分析及不同阶段分离固相的鉴定结果表明,该复盐在溶解阶段出现与前所报导不同的同步溶解,最终产物是库水硼镁石(2MgO•3B2O3•15H2O).提出了库水硼镁石的形成条件和溶解及相转化动力学机理,利用单纯形优化法配合Runge-Kutta微分方程组数值解法对实验数据进行处理,给出了转化结晶动力学方程. 相似文献
998.
Cheng MS Wang QL Tian Q Song HY Liu YX Li Q Xu X Miao HD Yao XS Yang Z 《The Journal of organic chemistry》2003,68(9):3658-3662
Methyl protodioscin (1), otherwise known as 3-O-[alpha-L-rhamnopyranosyl-(1-->2)-[alpha-L-rhamnopyranosyl-(1-->4)]-beta-d-glucopyranosyl]-26-O-[beta-D-glucopyranosyl]-22-methoxy-25(R)-furost-5-ene-3 beta,26-diol, has been synthesized for the first time from diosgenin through nine steps in an overall yield of 7.8%. 相似文献
999.
A convergent selective route to (+)-brefeldin A (BFA) and 7-epi-BFA was developed, with the crucial C-4/C-5 stereogenic centers were established using Crimmins asymmetric aldolization. 相似文献
1000.
纳米晶MgSO4·5Mg(OH)2·3H2O合成与表征 总被引:5,自引:0,他引:5
纳米材料由于具有表面、体积和量子尺寸效应的特殊性而受到广泛重视[1~3]. 微米级硫氧镁晶须作为塑料添加增强和阻燃剂已有报道[4~7]. 纳米晶MgSO4*5Mg(OH)2*3H2O不仅对塑料起补强作用, 而且其粒度小, 使塑料变得更致密, 强度、韧性与防水性能大大提高. 目前纳米材料的合成方法多种多样[8~10], 本文采用水热法制得纳米硫氧镁晶粒, 产物纯度高、分散性好且粒度易控制. 相似文献