一种全自动光度滴定仪

报道了改装７２１型分光光度计为光度滴定仪并联用８０３１单片微机构成一台全自动光度滴定仪，在单片机的控制下，实现取样，加试液，搅拌，开关光门，调零，调参比，滴定，测吸光度，数据处理，显示结果并打印，排除废液，冲洗滴定池等操作过程的全自动化，约１１０ｓ可完成一次测定，误差〈０．２％，ＲＳＤ〈１．５％，测定快速，准确，重复性好，可胜任在线监测工作，也可作常规滴定分析。     

Monte Carlo simulation of the chain length distribution in pulsed-laser polymerization experiments in microemulsion

The Monte Carlo method has been used for numerically simulating pulsed-laser polymerization (PLP) in microemulsion, in order to establish if a shift from inflection point to peak maximum as the best measure of the propagation rate constant, k_p, will occur theoretically. Termination is assumed to be instantaneous in the simulations as droplet sizes can be very small in microemulsions. From the results of the simulations it is found that instantaneous termination indeed causes the peak maximum to become the best measure of k_p. From these results it can be deduced that in bulk it is not simply the Poisson-broadening that causes the peak maximum to yield an overestimation of k_p. This overestimation is rather caused by the fact that the termination rate is finite leading to an asymmetrical peak in the molecular weight distribution. In combination with broadening this yields the inflection point to be the best measure of k_p in the bulk.     

Development of a multi-objective coagulation system for long-term fouling control in dead-end ultrafiltration

In this paper, a multi-objective control system has been developed and experimentally tested. The multi-objective control system can be effectively used to control short-term fouling as well as long-term fouling. In an earlier study it was found that coagulant dosing in ultrafiltration can be used effectively to control the short-term fouling resistance during several sequential filtration cycles. To control long-term resistance increase during sequential chemical cleaning cycles, usually, in open-loop setting of the cleaning frequency or variables which influence the cleaning efficiency, such as, the cleaning time and the chemical composition are adjusted. Additional introductory experiments showed that changes in the coagulant dosing have a more pronounced effect on long-term fouling than changes in the usual applied variables. For this reason, it was decided to develop a closed-loop multi-objective controller where the coagulant dosing is used as the manipulated variable to accomplish both control objectives namely the fouling resistance over multiple filtration cycles (the short-term objective), as well as the irreversible fouling resistance over multiple chemical cleaning cycles (long-term objective). However, the controller is too slow to deal with temperature changes influencing the effectiveness of the coagulant dosing. To handle these influences a kind of gain scheduler should be included in the control algorithm.     

Cartesian internal coordinates: translational and rotational invariance

Using translational and rotational invariance conditions for energy derivatives, we show that at a nonstationary point on the molecular potential energy surface the Hessian has at least three zero eigenvalues. Only at a stationary point can there be shown to be six (five for collinear geometries) zero eigenvalues. An infinitesimal transformation is defined such that the six (five for collinear geometries) transformed dependent Cartesian-like coordinates have zero gradients. From the form of this infinitesimal transformation, a translation-rotation free surface walking algorithm is defined. Numerical tests show that this surface walking procedure is practical for both non-collinear and collinear molecules.     

乳化剂分子亲水组分含量对相反转乳化过程的影响

高分子树脂水基分散体系 ,因其结构的可灵活调节性 ,在许多方面得到应用 ,又因其不含有机溶剂 ,能完全满足环境保护和生态的要求而备受关注 [1～ 3] .相反转乳化技术是制备高分子水基体系的新方法 ,它适用于制备包括加聚物和缩聚物的大多数高分子水基体系 ,大大拓宽了水基体系的范围 [4 ] .杨振忠等[5] 利用自己合成的高分子非离子型乳化剂将环氧树脂乳化成微粒尺寸小且分布窄的水基分散体系 ,对相反转机理和相反转技术进行了深入研究 .研究表明 ,乳化剂浓度和乳化温度对相反转后水基微粒尺寸和形态有重要影响 ,高乳化剂浓度和较低的乳化温…     

Light‐Driven Coordination‐Induced Spin‐State Switching: Rational Design of Photodissociable Ligands

The bistability of spin states (e.g., spin crossover) in bulk materials is well investigated and understood. We recently extended spin‐state switching to isolated molecules at room temperature (light‐driven coordination‐induced spin‐state switching, or LD‐CISSS). Whereas bistability and hysteresis in conventional spin‐crossover materials are caused by cooperative effects in the crystal lattice, spin switching in LD‐CISSS is achieved by reversibly changing the coordination number of a metal complex by means of a photochromic ligand that binds in one configuration but dissociates in the other form. We present mathematical proof that the maximum efficiency in property switching by such a photodissociable ligand (PDL) is only dependent on the ratio of the association constants of both configurations. Rational design by using DFT calculations was applied to develop a photoswitchable ligand with a high switching efficiency. The starting point was a nickel–porphyrin as the transition‐metal complex and 3‐phenylazopyridine as the photodissociable ligand. Calculations and experiments were performed in two iterative steps to find a substitution pattern at the phenylazopyridine ligand that provided optimum performance. Following this strategy, we synthesized an improved photodissociable ligand that binds to the Ni–porphyrin with an association constant that is 5.36 times higher in its trans form than in the cis form. The switching efficiency between the diamagnetic and paramagnetic state is efficient as well (72 % paramagnetic Ni–porphyrin after irradiation at 365 nm, 32 % paramagnetic species after irradiation at 440 nm). Potential applications arise from the fact that the LD‐CISSS approach for the first time allows reversible switching of the magnetic susceptibility of a homogeneous solution. Photoswitchable contrast agents for magnetic resonance imaging and light‐controlled magnetic levitation are conceivable applications.     

Development of diffuse double layers in column-wicking experiments: Implications for pH-dependent contact angles on quartz

The pH dependence of contact angles in quartz powder beds was studied by column wicking. The rate of capillary penetration was found to be highest at the isoelectric point of quartz which, by applying the classical Washburn equation, results in a minimum contact angle at the isoelectric point. Direct contact angle measurements however show that the contact angle is at a maximum at the point of zero charge (see e.g. [1], [2], [3], [4], [5] and [6]). By measuring the permeability of powder columns with aqueous solutions of varying pH, it is shown that the permeability reaches a maximum at the isoelectric point. This suggests that the rate of capillary penetration is influenced by the permeability of the powder columns towards respective aqueous solutions. The difference in permeability can be explained by the notion of an electroosmotic counter-pressure which was already recognized by Klinkenberg [7]. An approach is presented that involves the calculation of capillary constants from permeability measurements of the corresponding aqueous solutions. An equation is derived that takes direct account for the electroosmotic counter-pressure. Application of this equation combined with capillary constants calculated from permeabilities of the corresponding aqueous solutions results in the expected contact angle-pH relationship.     

NMR study of polymer surfactant interaction in the system HPMC/SDS/water

The interaction between the nonionic water soluble polysaccharide hydroxypropylmethyl cellulose (HPMC) and the low molecular weight amphiphile sodiumdodecyl sulphate (SDS) has been studied by NMR¹H-chemical shift measurements and by self-diffusion NMR measurements. The polymer concentration has been kept sufficiently dilute to avoid coil overlap and the SDS composition range goes from zero up to well above the normal CMC point. Although a different fraction was used, the present results agree well with previous results for the same system obtained by techniques other than NMR and show very clear break points that can be related to the polymer surfactant interaction. Furthermore, it can be inferred from the chemical shift measurements that the structure of the micellar clusters are similar whether polymer is present or not. From a combination of chemical shift and self diffusion measurements it is also found that neither the size nor the shape of the clusters seem to change significantly in the composition interval investigated.     

An algorithm for the location of branching points on reaction paths

A branching point is a point on a reaction path leading from reactants to products (via a transition state) at which it is energetically favorable for the system to break symmetry. Such a point can be defined in terms of normal modes along the reaction path and corresponds to zero curvature (a zero Hessian eigenvalue) along a symmetry-breaking mode. An effective method for the location of such points is presented and realized in an efficient, practical algorithm designed for use in the ab initio program package Gaussian 82.     

Simulations of energy and switching in AFLCDs with different boundary conditions

Using standard expressions for the various terms in the Gibbs free energy, the switching in antiferroelectric liquid crystal (AFLC) displays is simulated and the time evolution of various energy terms and of the liquid crystal director distributions are calculated. It is shown that when returning from a strong positive voltage to zero, one can reach two types of antiferroelectric state: the normal alternating state with the two bulk polarizations perpendicular to the electrodes and opposite to each other, and the alternative splayed symmetric state with two bulk polarizations parallel to the electrodes and again opposite to each other. The former case gives rise to tri-state switching characteristics, the latter to V-shaped switching. In general strong polar interaction with the alignment layer favours V-shaped switching while weak or no polar interaction give rise to tri-state switching characteristics. Since the V-shaped characteristic has so far only been demonstrated experimentally in ferroelectric liquid crystals (or antiferroelectric liquid crystals being in the ferroelectric state), the difference in AFLCs is discussed and the conditions for continuous switching are modelled. The simulations show that the switching characteristics of the antiferroelectric display can be controlled by the surface parameters.     

Molecular implementation of sequential and reversible logic through photochromic energy transfer switching

Photochromic spiropyrans modified with fluorophores were investigated as molecular platforms for the achievement of fluorescence switching through modulation of energy transfer. The dyads were designed in such a way that energy transfer is only observed for the open forms of the photochrome (merocyanine and protonated merocyanine), whereas the closed spiropyran is inactive as an energy acceptor. This was made possible through a deliberate choice of fluorophores (4‐amino‐1,8‐naphthalimide, dansyl, and perylene) that produce zero spectral overlap with the spiro form and considerable overlap for the merocyanine forms. From the Förster theory, energy transfer is predicted to be highly efficient and in some cases of 100 % efficiency. The combined switching by photonic (light of λ>530 nm) and chemical (base) inputs enabled the creation of a sequential logic device, which is the basic element of a keypad lock. Furthermore, in combination with an anthracene‐based acidochromic fluorescence switch, a reversible logic device was designed. This enables the unambiguous coding of different input combinations through multicolour fluorescence signalling. All devices can be conveniently reset to their initial states and repeatedly cycled.     

SAXS determination of the amorphous surface layer thickness of polymer single crystals

Polyethylene single crystals were grown from 0.1% solutions in xylene at 80 and 87°C. Oriented mats were made from each preparation and the small-angle x-ray scattering (SAXS) profiles obtained. Following treatment of the raw data for main-beam position and width, background scatter, and the Lorentz factor, five Bragg reflections were resolved. A one-dimensional lattice was used as a model for the oriented mats of single crystals. This model contains three parameters. An additional parameter G_x was also introduced to demonstrate the general effect of a broadening factor on the model. The effect of each parameter on the calculated diffraction pattern was examined. From this examination it was found that by assuming that the broadening functions are zero we can determine directly from the number of observable peaks the maximum possible thickness of the amorphous surface. Further, we find that the thickness of the amorphous layer must be less than the maximum value calculated if G_x is assigned values greater than zero. A “best-fit” diffraction pattern was generated in order to estimate how much smaller the surface thickness can be such that one can still resolve five diffraction maxima. The range of amorphous surface thicknesses found from the calculated diffraction profile is 12–20 Å. This is in good agreement with complementary studies performed on the same crystal preparations.     

Quantum Control of Coherent ρρ‐Electron Dynamics in Chiral Aromatic Molecules

Control of mobile π‐electrons is one of the fundamental issues in the organic optoelectronics for designing the next generation ultrafast switching devices. The optimal control simulations of coherent π‐electron rotations in (P)‐2,2’‐biphenol, which is the typical nonplanar aromatic molecule with axial chirality, were performed by taking into account two types of the control targets: one is generation of the maximum π‐angular momentum, and the other is the maintaining of the generated unidirectional angular momentum during a setting time duration. The optimal control pulse for each target is designed. The analysis of the simulation results shows that the effective maintaining of the unidirectional angular momentum can be realized by applying 2π pulse to one of the electronic excited states forming the coherent electronic state. The 2π pulse prevents the reverse rotation of the π‐electrons by dumping the excited state population to the ground state and subsequently by pumping the population back to the excited state. The present results provide a theoretical basis for the designing next generation ultrafast switching devices made by organic aromatic molecules.     

可移动式微量氧分析仪检定装置研制

研制一种新型可移动式微量氧分析仪检定装置。该装置由标准气体、零点气、脱氧纯化器、减压阀、调节阀、4通阀、5通阀、不锈钢管路、流量控制系统、移动平台等组成。该装置气密性好,15 min内可将装置内氧气浓度由20.9%降至不大于0.1μmol/mol,对于0~10μmol/mol的微量氧分析仪检定结果的扩展不确定度为Urel=1.7%FS(k=2)。该装置满足气体标准物质的连续切换和在线检定的需要,检定时间短,结果准确可靠,可为在线式和非在线式微量氧分析仪的量值溯源提供有效保障。     

Separation of Twenty Biogenic Amines and Derivatives by a High-performance Liquid Chromatographic Column Switching Technique with On-line Fluorimetric and Electrochemical Detections

Abstract

A new high-performance liquid chromatographic technique including the use of an automated column switching system has been developed for the study of dopamine, norepinephrine, epinephrine and serotonin and their related metabolites in biological samples. Through two runs, it has been possible to separate twenty derivatives and three internal standards which have to be added to samples prior to the extraction procedures. In each case, the column switching system allowed to obtain a clear separation of all the compounds, which will be of importance to avoid any expected interference from other endogenous substances, while decreasing the analysis time. By coupling on-line fluorimetric and electrochemical detections the specificity of the technique was enhanced, since the ratio of the responses of both detectors was an index of the purity of the peaks. In addition, fluorimetric detection was found of value to free the determination of some compunds from the effects of solvent front while electrochemical detection increased the sensitivity. Finally, the column switching system allowed a rapid cleaning of the columns between two analyses. A typical application to a human urine sample was shown.     

Determining the zeta-potential of ceramic microfiltration membranes using the electroviscous effect

The possibility of measuring the zeta-potentials of porous membranes using the electroviscous effect was investigated. The zeta-potential of Membralox^® ceramic microfiltration membranes was determined both with the newly developed electroviscous technique and by streaming potential measurements. It was found that the electroviscous technique provided a simple means of obtaining accurate values of zeta-potential, especially for higher zeta-potentials. The streaming potential measurements were found to be more suitable for the determination of the iso-electric point, i.e. the pH at which the zeta-potential is zero.The iso-electric points of new α-alumina, zirconia, and titania membranes were found to be 8.5, 8.0, and 6.3, respectively. Upon using the membranes and cleaning them with a detergent, the iso-electric point of the α-alumina membrane decreased to 6.5, and that of the zirconia membrane decreased to 5.2, while the iso-electric point of the titania membrane stayed virtually constant. Cleaning these membranes with a strong acid or base could not reverse the observed decreases in iso-electric point.     

Ferroelectrically Switching Helical Columnar Assembly Comprising Cisoid Conformers of a 1,2,3‐Triazole‐based Liquid Crystal

The 1,2,3‐triazole molecule, which is a product of click chemistry, possesses a high dipole moment and can be a useful polar motif for ferroelectric columnar liquid crystal (LC) materials—though it has not been used to date. Herein, we report the helical assembly and ferroelectric switching properties of a columnar liquid crystal comprising a naphthalene core and 1,2,3‐triazolyl linkages. The molecule assembles into a double‐stranded helical columnar LC structure (Col_hel). The X‐ray simulations of cisoid and transoid columnar models suggest that the helical assembly comprises cisoid conformers with a non‐zero dipole moment. The helical columns in the Col_hel phase are aligned homeotropically under an electric field. The ferroelectric switching of the axial polarization can be observed in the temperature range of 105–115 °C in the Col_hel phase, wherein the triazolyl hydrogen bonding along the column axis is weakened. The ferroelectric switching event is attributed to the rotation of the polar triazolyl units in response to the electric field.     

Chemical Cleaning of Microfiltration Membranes Fouled by Whey

Millipore hydrophobic polyvinylidene fluoride (PVDF) microfiltration membranes were used for whey processing. Fouled membranes were cleaned with acid (HCl), alkaline (NaOH) and surfactant (Triton‐X100). The latter resulted in maximum flux recovery and resistance removal. Hydrochloric acid had a moderate effect and sodium hydroxide was the weakest cleaning agent. This is due to the cleaning strength of emulsifiers compared to acid or alkali. However acids are more efficient than alkaline solutions for removal of mineral compounds which remain on the membrane surface. Cleaning efficiency depends on the concentration of cleaning agent being higher for higher surfactant concentration. For acids and alkali, the efficiency increases with increasing the concentration of the reagent reaches a maximum (optimum concentration) and then decreases. This can be explained by changes in permeability of the deposit layer with the concentration of the cleaning agent. Another explanation is the breakage of proteins by acid or alkali which produces more fouling materials and causes less cleaning efficiency. Operating conditions affect the cleaning process. At higher stirring speeds (turbulent flow) or longer cleaning time better removal of deposits and higher cleaning efficiency were observed. The sequential cleaning process may or may not improve the cleaning efficiency. When acidic cleaning was followed by washing with a surfactant an improvement was achieved. This can be attributed to the incomplete removal of deposits by acid. However further cleaning with acid can not improve the cleaning efficiency. During whey processing fouling occurs by deposition of foulants of mostly proteins and macromolecules on the membrane surface or in the membrane matrix. Large substances (compared to the membrane pores) settle on the membrane surface and the small species penetrate and are adsorbed in the membrane pores. Cleaning dissolves and removes the adsorbed foulants from the membrane.     

Ultra‐high‐performance liquid chromatography with tandem mass spectrometry method for determination of four compounds in rat plasma after oral administration of Xanthii fructus and stir‐fried Xanthii fructus extracts

Xanthii fructus (XF), the fruit of Xanthium sibiricum Patr., is a traditional Chinese materia medica commonly used to treat allergic rhinitis and other rhinitis diseases. To uncover the mechanism of the stir‐frying process and its effect on the pharmacokinetic behavior of active compounds in model rats, four active compounds—chlorogenic acid, 4‐caffeoylquinic acid, 1,5‐O‐dicaffeoylquinic acid and apigenin—were selected based on previous spectrum‐effect experiments. High performance liquid chromatography tandem triple quadrupole mass spectrometry (UPLC–QqQ–MS) technology, an accurate and feasible method, was applied to measure the concentration of these four compounds in rat plasma. This validated method can accurately measure the concentration of each compound at each sampling point of rat plasma. This validated method shows good linearity, extraction recoveries, matrix effects, intra‐ and inter‐day precision and stabilities. Compared with the XF group, the maximum plasma concentration (C_max) value of 1,5‐O‐dicaffeoylquinic acid decreased remarkably (p < 0.05) after oral administration of stir‐fried Xanthii fructus (SXF) extract, while the other compounds showed no significant difference. The mean residence time value of chlorogenic acid (p < 0.05) and 1,5‐O‐dicaffeoylquinic acid (p<0.01) after oral administration of SXF extraction demonstrated significant differences compared with the XF group, while the other two compounds showed no statistical difference, indicating that the stir‐frying process prolonged the effect time and delayed the removal time of chlorogenic acid and 1,5‐O‐dicaffeoylquinic acid. The values of the area under the plasma concentration–time curve from zero to the last quantifiable time‐point, the area under the plasma concentration–time curve from zero to infinity, the time to maximum concentration and the elimination half‐life of four compounds in the SXF group showed no statistically significant difference from the XF group. From this data, we speculated that the stir‐frying process can not only keep the absorption of 4‐caffeoylquinic acid and apigenin, but also increase the effect time of chlorogenic acid and 1,5‐O‐dicaffeoylquinic acid, which could be the mechanism underlying the stir‐frying process enhancing the effects of XF.