Validation of the accuracy of the perturbation peak method for determination of single and binary adsorption isotherm parameters in LC

An analytical validation of the precision and accuracy of the perturbation peak (PP) method for determination of single and competitive thermodynamic isotherm parameters was performed using frontal analysis as a reference. The isotherm parameters of 11alpha-hydroxyprogesterone were determined in an achiral system and the isotherm parameters of (+)-methyl L-mandelate and (-)-methyl D-mandelate were determined in a chiral system, both for the single components and for the competitive binary mixture. The experimental errors in the PP method using different injection techniques were investigated, and we devised a new injection technique for the determination of competitive isotherm parameters that considerably reduced the experimental errors and also made both perturbation peaks detectable. We showed that the PP method with the new injection technique can be used to determine isotherm parameters directly from a racemic mixture. These parameters agreed well with those determined using several enantiomer ratios. Elution-band profiles simulated using the isotherm parameters showed excellent agreement with experimental profiles.     

Validation of the accuracy of the perturbation peak method for determination of multicomponent adsorption isotherm parameters in LC

The isotherm parameters were for the first time determined for a quaternary mixture. This was done by the perturbation peak (PP) method using racemic mixtures of methyl and ethyl mandelate enantiomers. One complication with the PP method is that the traditional blank injection technique makes all perturbation peaks, except one, vanish at moderately nonlinear concentration plateaus. Therefore, we devised a new injection technique that made all four peaks on a quaternary component concentration plateau detectable, thereby making the determination of multicomponent competitive isotherm parameters possible. The measured quaternary perturbation data fitted well to the bi-Langmuir isotherm model and excellent agreement was found between experimental and simulated single-component and multicomponent profiles, thus validating the method and the determined isotherm parameters. The method (i) is valuable for computer-assisted optimization of preparative chiral chromatography and (ii) opens the possibility of quantifying competitive drug-target interactions for chiral drugs directly on racemic mixtures, which today is impossible with any nonlabeled technique including surface plasmon resonance technology.     

固体荧光样品寻峰方法探讨

特征激发峰值和发射峰值位置是荧光材料的两个重要参数。文中提出一种固体荧光样品的快速寻峰方法一固体对比法。该方法采用光谱平坦的高漫反射板为中介,利用测得的样品信号和高漫反射板信号间的内在联系,通过计算消除了仪器光源、探测器响应等诸多因素对测量结果的影响,保证了测量结果的正确可靠。该方法对非白校准型荧光光谱仪以及白校准型荧光光谱仪均能适用,且测量过程简单,测量结果精度高。     

Method for determination of association and dissociation rate constants of reversible bimolecular reactions by isothermal titration calorimeters

The rate law equation for reversible bimolecular reactions, which are describable by association and dissociation rate constants (k1 and k-1), is not solvable to a plain formula under stoichiometric reaction conditions. Therefore, it is a general technique to observe such reactions under pseudo first-order conditions, which make the reactions a single-exponential process, and enable us to determine k1 and k-1 without any complicated iterative computations needed to analyze the same reactions under stoichiometric reaction conditions. However, the accelerated reaction rates under pseudo first-order conditions are not always favorable to the physicochemical tools employing a slow or medium response time, such as thermal analysis instruments. In this study, we have developed a simple non-iterative analytical method to determine k1 and k-1 of reversible bimolecular reactions under stoichiometric conditions on the basis of experimental data of isothermal titration calorimetry (ITC), which is generally used to determine thermodynamic parameters rather than kinetic constants. Our method is principally based on the general principle of chemical bindings caused along with the titration processes, that is, the chemical relaxation kinetics, which had been hitherto considered in the analysis on the ITC data.     

微波模板交联壳聚糖吸附剂对镉离子的吸附机理

通过IR、XPS及化学分析方法研究了微波模板法交联壳聚糖吸附剂(CCTSCd)对Cd2+的吸附机理及其选择记忆性。IR谱图表明,模板法保护了一部分氨基,未与Cd2+发生配位作用的一部分活性氨基参与了交联反应。对比吸附前后CCTSCd的XPS谱图,CCTSCd中O1s和C1s的结合能基本没有变化,N1s和Cd(II)Cd3d 5/2和Cd3d 3/2的特征峰发生化学位移,通过分峰拟合分析,Cd2+与CCTSCd中-NH2基团发生了配位反应。CCTSCd对Cd2+吸附符合Freundlich吸附等温方程。     

An improved method of calculating the peak stress distribution for a broad‐band random process

An improved method of fast fatigue life prediction under broad‐band random loading is proposed, which is based on the power spectral density of stress in the critical points of structures and the peak stress distribution of a stationary Gaussian random process. The improved method has higher precision than other existing approximate methods that are based on the peak stress distribution.     

660 MW燃煤机组瞬态过程NOx生成及脱除特性

燃煤机组为完成电网负荷调峰任务,锅炉负荷长期频繁波动,对氮氧化物的生成及脱除效果有显著影响。以某660 MW燃煤机组瞬态过程氮氧化物的生成及脱除特性为研究目标,建立了机组瞬态过程氮氧化物生成预测模型,开展了变负荷过程中氮氧化物生成预测研究。针对燃煤机组变负荷过程燃烧器切换的特点,发现新增燃烧器的负荷点越高时,越能有效避免氮氧化物的生成值增大。另外,分析了选择性催化还原（selective catalytic reduction,SCR）动态特性,分别研究了SCR入口氮氧化物浓度、喷氨浓度、烟气流速和反应温度等阶跃变化对氮氧化物脱除的动态特性影响,为后续瞬态过程喷氨优化控制逻辑提供参考。     

Highly sensitive hydrogen detection of catalyst-free ZnO nanorod networks suspended by lithography-assisted growth

We have successfully demonstrated a ZnO nanorod-based 3D nanostructure to show a high sensitivity and very fast response/recovery to hydrogen gas. ZnO nanorods have been synthesized selectively over the pre-defined area at relatively low temperature using a simple self-catalytic solution process assisted by a lithographic method. The conductance of the ZnO nanorod device varies significantly as the concentration of the hydrogen is changed without any additive metal catalyst, revealing a high sensitivity to hydrogen gas. Its superior performance can be explained by the porous structure of its three-dimensional network and the enhanced surface reaction of the hydrogen molecules with the oxygen defects resulting from a high surface-to-volume ratio. It was found that the change of conductance follows a power law depending on the hydrogen concentration. A Langmuir isotherm following an ideal power law and a cross-over behavior of the activation energy with respect to hydrogen concentration were observed. This is a very novel and intriguing phenomenon on nanostructured materials, which suggests competitive surface reactions in ZnO nanorod gas sensors.     

Quantitative study of concentration overload,peak asymmetry,and efficiency loss in micellar electrokinetic chromatography

An equation is derived for the velocity of a thin zone of specific analyte concentration in micellar electrokinetic chromatography. The velocity varies with analyte concentration, because micellar solubilization changes electrical conductivity, micellar electrophoretic mobility, and the partitioning of anabyte between mobile and micellar phases. Two studies based on a weakly and a strongly retained neutral analyte are made to test a limiting form of the equation in which the first two changes are ignored. In the first study, peak asymmetries are characterized and plate numbers are measured in two types of experiments: one of fixed surfactant concentration and variable analyte concentration and one of fixed analyte concentration and variable surfactant concentration. In the second study, the isotherm describing both experiment types is measured and interpreted by the Langmuir model to evaluate the velocity equation. The equation of continuity is solved numerically for the peak profiles governed by the velocity equation. In all but one case, a good agreement is found between theoretical and experimental peak asymmetries and plate numbers in both experiment types. An equation is derived for the relative change of analyte velocity caused by the Langmuir isotherm. The change depends on the relative migration time, micellar saturation, and retardation factor. The predicted velocity changes correlate well with peak asymmetries and efficiency losses.     

TR组件测试系统功率参数校准技术

研究工作状态下TR组件测试系统功率参数的校准方法,介绍了在脉冲峰值功率条件下功率参数测量标准的仪器组成,分析其功率参数校准的定标方法,并给出相应实验数据。     

基于复解析带通滤波的自由衰减振动信号的频谱校正法

通过复解析带通滤波构造时域信号的解析信号,消除因时域实信号作FFT时由于时域截断产生的负频率成分能量泄露对正频率成分的干扰,从而提高自由衰减振动信号频谱校正精度。仿真分析及工程实测结果表明,当各个固有频率相隔较远时,校正精度很高。但在各阶固有频率靠得很近时不能直接使用这种方法。     

Injection technique for generating accurate adsorption isotherm data using the elution by characteristic points method

With the use of the elution by characteristic points (ECP) method, the adsorption isotherms are rapidly determined from the diffusive part of an overloaded elution profile. However, very large injection volumes are required, which lead to extremely tailed rears of the injection profiles. The ECP method is based on a theory assuming rectangular injection profiles and can therefore not account for such profiles. Consequently, the use of the ECP method in the traditional way, with classical full-loop injections, results in serious errors on the determined adsorption isotherm parameters which has not been demonstrated until this study. Therefore, we developed and validated a new experimental injection method, here denoted the "cut-injection" technique where instead nearly rectangular injection profiles are generated. The result convincingly shows that adsorption isotherms acquired by using the new cut-injection technique nearly totally coincide with adsorption isotherms determined using the accurate reference methods.     

Theoretical maximal precision for mass-to-charge ratio, amplitude, and width measurements in ion-counting mass analyzers

A theory previously developed for spectra with detector-limited (i.e., signal-independent) Gaussian-distributed noise is applied to calculate the maximal precision with which mass spectral peak parameters (mass-to-charge ratio, amplitude, width) can be determined from a discrete spectrum with source-limited Poisson-distributed noise. The precision depends in a calculable way upon the peak shape, signal-to-noise ratio, and number of data points per peak width. Those dependencies are tested by analysis of simulated data. The theory provides estimates for the precision of a repeated experiment, based on data from a single discrete mass spectrum whose parameters are extracted by a least-squares fit to a specified line shape. The relevance of the predictions to present and potential time-of-flight performance is discussed.     

Detection of oxygen consumption of cultured adherent cells by bead injection spectroscopy

This paper describes a method for detecting oxygen consumption of adherent cell cultures. The sensing is based on oxygen-dependent quenching of the phosphorescence of a Pt-porphyrin complex immobilized on microcarrier beads, which are used as the cell culture substrate. Bead injection, a recent variant of the flow injection technique, is used to pack an aliquot of the beads into a small sensing layer that can be easily and rapidly renewed. The technique is tested on a model system of Chinese Hamster Ovary M1 cells grown on Cytodex-3 microcarrier beads. Cellular respiration is monitored through O2 consumption measured across a period of 3 min. The method is validated by detecting the impairment of aerobic metabolism caused by 1.5 mM amobarbital. Further, it is shown to have enough precision to distinguish even more subtle changes, such as the increase in oxygen consumption caused by stimulation of the muscarinic m1 receptor with 100 microM carbachol.     

脉冲激光峰值／平均功率测试方法研究

为解决生产过程中所用脉冲激光光源输出峰值/平均功率测试的量值准确一致及其量值溯源问题,确保生产过程受控。文章以激光能量计作为量值传递标准,采用脉冲激光能量法实现脉冲激光峰值功率量值溯源;并运用波形半宽度分析法进行有效测试。     

弱电机房空调节能方案的探讨

为了降低恒温、恒湿精密空调运行耗电量,笔者提出了一种利用室外冷源来减少制冷系统运行周期,从而降低能耗的方案.经过方案描述、分析比较得出:对系统进行小量改动后即可大大降低空调设备的故障率及维修成本,且使设备节能(西安地区)34.6％以上.     

Hartley/Hilbert transform spectroscopy: absorption-mode resolution with magnitude-mode precision.

Fourier transformation (FT) of an N-point time-domain discrete signal produces, after phase correction, two independent data sets: an N/2-point absorption spectrum, A(omega), and an N/2-point dispersion spectrum, D(omega), each with the same information content. Usually only A(omega) is kept. The dispersion-mode information has conventionally been recovered in either of two ways. First, the N/2-point magnitude-mode spectrum, M(omega) = ([A(omega)]2 + [D(omega)]2)1/2, offers a square root of 2 improvement in precision compared with the original N/2-point absorption spectrum, but with poorer resolving power (factor ranging from square root of 3 to 2 for unapodized data). Alternatively, zero-filling the initial time-domain data to 2N data points prior to Fourier transformation results in an N-point absorption-mode spectrum with the same peak width and peak-height-to-noise ratio as the original N/2-point absorption spectrum, but with a square root of 2 improvement in precision. Thus, magnitude-mode display improves FT spectral precision at the expense of a loss in resolving power, whereas zero-filling improves precision at the expense of having to store twice as many data points. In this paper, we present a third method of recovering the dispersion information.(ABSTRACT TRUNCATED AT 250 WORDS)     

Argentometric titration for the determination of liquid chromatographic injection reproducibility

The reproducibility of autosamplers for high-performance liquid chromatography can be checked by the injection of a sodium chloride solution without an installed column. The dispensed chloride plug is analyzed quantitatively by argentometric titration. If the titration can be performed with high enough precision, the autosampler performance is investigated without additional effects. Experiments with a 20-microL loop were performed. We found the following repeatabilities (relative standard deviations): titration, 0.07%; 10-microL "pull loop" injection (partial filling of the loop), 0.6%; and 20-microL "full loop" injection, 0.1%. In contrast to these data, the relative standard deviations obtained from chromatographic peaks include the steps of injection, separation, detection, and integration without any knowledge of the individual contributions. Such values are higher; we found for chromatographic peak areas of parabens 2% under pull loop conditions and 0.17% by full loop. The titration approach allows the determination of the contribution of the injection to the uncertainty budget of a liquid chromatographic analysis.     

Comparison of linear and non-linear method in estimating the sorption isotherm parameters for safranin onto activated carbon

Comparison analysis of linear least square method and non-linear method for estimating the isotherm parameters was made using the experimental equilibrium data of safranin onto activated carbon at two different solution temperatures 305 and 313 K. Equilibrium data were fitted to Freundlich, Langmuir and Redlich-Peterson isotherm equations. All the three isotherm equations showed a better fit to the experimental equilibrium data. The results showed that non-linear method could be a better way to obtain the isotherm parameters. Redlich-Peterson isotherm is a special case of Langmuir isotherm when the Redlich-Peterson isotherm constant g was unity.     

Method for the sequential online analysis of enzyme reactions based on capillary electrophoresis

We have developed an easy-to-operate and effective method for performing the sequential online analysis of enzyme reactions based on capillary electrophoresis (CE). The system was constructed by passing two capillaries through a sample vial at a distance of 5 μm between the capillary ends. Direct online sample injection and sequential CE analysis were achieved by periodically switching the high-voltage power supply off and on, without any physical disturbance of the capillary inlet. The sample was injected via concentration diffusion with in-column derivatization of the amino acids occurring at the interface of the capillaries. High reproducibility of the sequential injections was demonstrated with relative standard deviation values (n = 20) of 1.01%, 1.25%, and 0.80% for peak height, peak area, and migration time, respectively. Sequential online CE enzyme assay of a glutamate pyruvate transaminase catalyzed enzyme reaction was carried out by simultaneously monitoring the substrate consumption and the product formation every 30 s from the beginning to the end of the reaction. The Michaelis constants for the reaction were obtained and were found to be in good agreement with the results of traditional off-line enzyme assays. Our method has great potential for usage in sequential online CE analysis of chemical reactions with in-column chemical derivatization of the analytes for ultraviolet or laser-induced fluorescence detection.