System peaks in capillary zone electrophoresis of anions with negative voltage polarity and counter-electroosmotic flow

The system peaks that often appear on electropherograms in anion separation by CE with indirect spectrophotometric detection, negative voltage polarity and cathodic EOF are studied. The system peaks are shown to correspond to the zones with the changed concentration of the BGE constituents; they appear while the zone of each analyte anion passes through the outlet end of the capillary and are transported to the detector by EOF. An equation is suggested for predicting migration times of the system peaks with an error of 1%. The ratios of the system peak area to the analyte peak area are found to amount to 20%. It is shown that it is possible to avoid overlapping of the system peaks and analyte peaks by controlling the EOF velocity owing to hydrodynamic pressure. Using the mathematical simulation of CE shows that the system peaks and baseline shift can result from changing the transference numbers of the BGE ions and analyte ions at the capillary edge. The cases when the system peak may be incorrectly identified as the peak of analyte ion are considered. In order to avoid such errors, some practical recommendations are given.     

Computational Chemistry techniques: covering orders of magnitude in space, time, and accuracy

Computational Chemistry is the branch of chemistry which uses extensively computer models to simulate real systems. Model systems are made to fit the real system in intended respects and with the intended accuracy of the creator or user of the model. The building blocks of model systems and the interactions between them are abstractions of the building blocks of real system and the interactions between them. In computer models a system must be represented by data which are stored in data structures, the interactions between them are represented by mathematical functions or sets of rules. Properties of the model system are calculated with various algorithms, both numerical and non-numerical. A computational chemist must decide which computer model is best suited to represent a real system so that its essential properties can be simulated as intended. Doing computational chemistry means to apply the right computer models to describe a real system or, if necessary, design new computer models.     

A statistical model for instable thermodynamical systems

A generic model is presented for statistical systems which display thermodynamic features in contrast to our everyday experience, such as infinite and negative heat capacities. Such system are instable in terms of classical equilibrium thermodynamics. Using our statistical model, we are able to investigate states of instable systems which are undefined in the framework of equilibrium thermodynamics. We show that a region of negative heat capacity in the adiabatic environment, leads to a first order like phase transition when the system is coupled to a heat reservoir. This phase transition takes place without a phase coexistence. Nevertheless, all intermediate states are stable due to fluctuations. When two instable system are brought in thermal contact, the temperature of the composed system is lower than the minimum temperature of the individual systems. Generally, the equilibrium states of instable system cannot be simply decomposed into equilibrium states of the individual systems. The properties of instable system depend on the environment, ensemble equivalence is broken.     

Chemical Equations for Multireaction Systems

While the balanced chemical equations for a multireaction system are generally not unique, the minimum number of independent equations, R, is a characteristic property of the system. Deleting one nonspectator species from the system leads to a system with R reduced by one. In this way each system can be reduced to a single-reaction system and ultimately to a no-reaction system. The least number of chemical species that can be deleted to obtain a no-reaction system equals R. Every multireaction system, therefore, can be reduced to a number of single-reaction equations which can be balanced by any one of the standard techniques. Some examples are given where balancing by inspection is employed.     

Wide area access to central corporate spectroscopic databases

Summary The reasons for the choice of a corporate spectroscopic datasystem are presented. In some companies research is spread world-wide. This leads to the need to design the system for wide area network operations. The system in ICI is an example of such a system, and some of the design considerations for the ICI system are presented.     

Programming the HP 48 Calculator to Control the Lab Works Interface

While the balanced chemical equations for a multireaction system are generally not unique, the minimum number of independent equations, R, is a characteristic property of the system. Deleting one nonspectator species from the system leads to a system with R reduced by one. In this way each system can be reduced to a single-reaction system and ultimately to a no-reaction system. The least number of chemical species that can be deleted to obtain a no-reaction system equals R. Every multireaction system, therefore, can be reduced to a number of single-reaction equations which can be balanced by any one of the standard techniques. Some examples are given where balancing by inspection is employed.     

Analytical methods and monitoring system for E-beam flue gas treatment process

The results of reliable and precise measurement of gas composition in different key points of e-beam installation are necessary for its proper operation and control. Only the composition of flue gas coming into installation is adequate to composition of flue gas emitted from coal-fired boiler. At other points of e-b installation the gas composition is strongly modified by process conditions therefore specific measuring system (sampling and conditioning system and set of gas analyzers) for its determination are required. In the paper system for gas composition measurement at inlet and outlet of e-b installation are described. Process parameters are continuously monitoring by CEM system and occasionally by the grab sample system. Both system have been tested at pilot plant at EPS Kaw czyn.     

仪器与设备自动化管理系统方案

结合仪器与设备的管理现状，提出了仪器、设备自动化管理系统软件开发的整体思路。介绍了软件中的建立档案、查询资料、修改档案、打印报表、更新资料、作废仪器与设备目录、帮助、退出8个子系统的功能。     

Automation and Computerization of NAA

A PC controlled automatic INAA system is briefly introduced. The unique features of the system in software, hardware, and quality control procedures are described. Major performances are given to show the analytical quality and productivity of the system.     

New hybrid method for reactive systems from integrating molecular orbital or molecular mechanics methods with analytical potential energy surfaces

A computational approach to calculating potential energy surfaces for reactive systems is presented and tested. This hybrid approach is based on integrated methods where calculations for a small model system are performed by using analytical potential energy surfaces, and for the real system by using molecular orbital or molecular mechanics methods. The method is tested on a hydrogen abstraction reaction by using the variational transition-state theory with multidimensional tunneling corrections. The agreement between the calculated and experimental information depends on the quality of the method chosen for the real system. When the real system is treated by accurate quantum mechanics methods, the rate constants are in excellent agreement with the experimental measurements over a wide temperature range. When the real system is treated by molecular mechanics methods, the results are still good, which is very encouraging since molecular mechanics itself is not at all capable of describing this reactive system. Since no experimental information or additional fits are required to apply this method, it can be used to improve the accuracy of molecular orbital methods or to extend the molecular mechanics method to treat any reactive system with the single constraint of the availability of an analytical potential energy surface that describes the model system.     

硫化镉纳米微粒作探针共振瑞利散射测定某些蒽环类抗癌药物

在pH=5.0—9.0的水溶液中, 硫化镉纳米微粒[(CdS)n]与蒽环类抗生素米托蒽醌(MXT)、 表柔比星(EPI)和柔红霉素(DNR)凭借静电引力及疏水作用力结合, 形成粒径更大的聚集体, 导致共振瑞利散射(RRS)的增强并产生新的RRS光谱, 最大的RRS峰位于292 nm(MXT体系)、 285 nm(DNR体系)和315 nm(EPI体系). 与此同时还观察到二级散射(SOS)和倍频散射(FDS)强度明显提高. 其最大SOS峰位于540 nm(MXT体系)和560 nm(EPI及DNR体系), 而最大的FDS峰分别位于335 nm(MXT体系)、 320 nm(EPI体系)和330 nm(DNR体系). 在一定条件下, 3种散射强度(ΔI)均与药物的浓度成正比, 反应具有高灵敏度, 对于3种药物的检出限在3.6—9.1 ng/mL之间. 其中(CdS)n-MXT体系灵敏度最高, 对MXT的检出限分别为4.1 ng/mL(RRS)、 3.8 ng/mL(SOS)和3.6 ng/mL(FDS). 据此发展了一种用纳米硫化镉作探针, 灵敏、 简便并快速测定蒽环类抗癌药物的共振瑞利散射新方法.     

Two-dimensional multiple entrance-slit vidicon spectrometer for simultaneous multielement analysis

A new type of wavelength dispersion system for use with a multichannel detector has been developed for simultaneous multielement analysis. The system employs a monochromator with fixed grating position, and incident angle varied by horizontal displacement of the entrance slits. The overlapping spectral windows which result can be arranged to produce a composite spectrum having minimal interference from emissions by other sample constituents. Entrance slits may also be displaced vertically to create a two-dimensional system in which spectra are stacked one above the other and scanned by use of a multi-raster scanning pattern. A number of optical and performance characteristics of the system are evaluated in both the one- and two-dimensional modes, and the system is applied to the determination of Ca, Na and K in blood serum and to the determination of the exchangeable cations Ca, Na, Li and K in clay. The advantages of this system for simultaneous multielement analysis are discussed.     

Comparison of electrochemical characteristics of acetylcellulose microfiltration membranes and a model system

The electrokinetic properties of commercial acetylcellulose microfiltration membranes are compared to a model system, i.e., an acetylcellulose film applied to a plane-parallel capillary made of quartz glass. It is shown that the absolute magnitudes of the electrokinetic potentials of the model system are higher than those of the examined microfilters, seemingly because the latter are modified to increase their mechanical strength and elasticity. The dissociation constants of carboxyl groups and the adsorption potentials of potential-determining ions are found from the electrokinetic data on the model system.     

The 1-alkoxy-4-nitro-1,2,3-benzotriazole system

The 1-alkoxy-4-nitro-1,2,3-benzotriazole system was prepared using a phase transfer catalysis procedure. The physical and spectral properties of the system are reported. Molecular orbital calculations on the 1-methoxy derivative are used to explain the spectroscopic and electronic properties of the system.     

Internal Standard Correction of Results Obtained by Atmospheric Pressure Chemical Ionization Mass Spectrometry

An internal standard system has been developed for a mass spectrometer equipped with an atmospheric pressure chemical ionization source. The system has been used to overcome sensitivity drift problems that are commonly encountered when the spectrometer is used for long-term environmental monitoring. Additionally, the internal standard has been used to correct sensitivity changes induced by the matrix being analyzed. Principal components of the system are a low concentration internal standard source and a flow-delivery system for introducing the standard to the reagent gas delivery stream of the spectrometer. Following an experiment, real-time data are downloaded to a personal computer where internal standard correction and data analysis are performed. Application of the internal standard to the measurement of nicotine and pyridine is demonstrated.     

A centralized,hierarchically structured computer system for chemical research and analytical instrumentation

An hierarchically structured, centralized compute system, replacing an obsolete central DECsystem-10, can be used for all the computational tasks in chemical research, as well as for real-time data acquisition and evaluation for numerous analytical instruments, required in a large Institute. In this hierarchical system, the real-time tasks are done by local minicomputer satellites that are tailored to special requirements in the laboratories. All higher level data processing and data storage demands are covered by the central system, consisting of two VAX11/780 computers, to which all satellites as well as all user terminals are connected. The design criteria are described as well as some of the software packages developed for this system.     

聚合物—盐—水液—固萃取新体系的研究现状与前景

讨论了聚合物－盐－水液－固萃取体系的特点和研究现状，综述了该体系用地萃取分离金属离子及生物活性物质所取得的进展，提出了该体系研究中尚需解决的问题。     

Conformational sampling via a self-regulating effective energy surface

The difficulty of efficiently sampling the phase space of complex systems with rough energy surfaces is well known. Typical solutions to the problem involve accelerating the crossing of barriers, but such methods often have the secondary problem that the low-energy states of interest are inadequately sampled, unless the parameters of the search algorithm are modified as the system evolves. A method is presented to improve the sampling with particular emphasis on the low-energy conformations, which make the most important contributions to the thermodynamics of the system. The algorithm proposed here samples the details of the minima, while easily surmounting barriers. This is achieved by introducing a self-regulating sampling variable which depends on the current state of the system. Two replicas of the system are introduced and the sampling variable is treated as a particle coupled to the physical system. The method is illustrated with a simple model system and is applied to the realistic example of barrier crossing in a protein-ligand complex.     

Scenarios of human errors and their quantification in multi-residue analysis of pesticides in fruits and vegetables

A total of 54 scenarios of human errors in multi-residue analysis of pesticides in fruits and vegetables are mapped in a routine monitoring laboratory. The likelihood and severity of the errors and the ability of components of the laboratory quality system to prevent/block human errors, as well as the effectiveness of the quality system as a whole, are evaluated using expert judgments. It is shown that human errors in sampling are prevented less by the quality system than other steps of the analysis. Training and supervision are found as the quality system components having the highest priorities. Effectiveness of the quality system obtained a good score value of 71 % (in comparison with an ideal system preventing human errors with 100 % effectiveness). Variability of the score values resulting from changes of the expert judgments is discussed.     

A sensitivity analysis of the smith predictor controller

The sensitivity of the Smith predictor controller to variations in system parameters is analyzed. The parameters considered are system gain, time constant, and delay or dead time. Both simulated and experimental results are discussed. First- and second-order models are studied. For the first-order model, a proportional plus integral control is used with the Smith predictor. A proportional plus integral plus derivative control is used with the Smith predictor for the second-order system. The controller is implemented digitally. An application of the Smith predictor with a model of the system obtained by a nonlinear least-squares parameter identification method is demonstrated on an experimental system.