电中性溶质在反相毛细管电色谱柱上峰展宽的研究

根据溶质在色谱柱中迁移的基本特征及柱分离过程弛豫理论的一般输运方程,在平衡色谱和不单独考虑逆向流的简化情况下,得到了能够说明多种因素对半峰宽影响的流出曲线的二阶中心矩表达式。通过反相毛细管电色谱实验,讨论了电压、柱长及保留因子等因素与峰展宽之间的关系,也探讨了溶质在色谱柱内峰展宽的规律。结果表明:半峰宽随柱长的增加和保留因子的增大而线性增加,随电压的增加而呈非线性减小。     

微流通道中溶质峰形不对称现象的研究

在微流控芯片分析中,由于微流通道微小的尺寸和检测器灵敏度的限制,容易出现诸如样品相对过载等引起溶质带偏离高斯分布(如前拖尾或者后拖尾等)的现象.引起溶质带峰形不对称的原因主要是由于吸附等温线^[1]和溶质带经过检测器时,由空间分布转化为时间分布所引起的扭曲所致^[2].     

高效液相色谱用线性梯度洗脱求保留值方程

〕提出了采用线性梯度洗脱求取未知样品中溶质保留值方程的原理及其计算方法,用光二极管阵列扫描检测器解决了梯度洗脱条件下色谱峰的归宿。实验证明：用所得的保留值方程预测等度洗脱下容量因子k'的相对误差不大于3%,而用梯度洗脱下的半峰宽规律可以估算未知样品容量因子k的分布范围,以解决对未知样品是采用等度或梯度洗脱方式。最后,借助计算机仿真方法用于样品的优化,获得了满意的结果。     

化学计量不确定度评定研究进展

测量不确定度是表征合理地赋予被测量之值的分散性的参数。本文针对化学计量不确定度评定基础模型仅适用于线性模型、概率分布为正态分布或缩放位移t分布等局限,介绍了近年来不确定度评定的研究热点:蒙特卡罗方法(Monte Carlo Method,MCM),不确定度评定的来源、评定概念、评估方法及其发展过程,扩大了测量不确定度评定与表示的适用范围。     

化学计量中不确定度评定研究进展

测量不确定度是表征合理地赋予被测量之值的分散性的参数。本文针对化学计量不确定度评定基础模型仅适用于线性模型、概率分布为正态分布或缩放位移t分布等局限,介绍了近年来不确定度评定的研究热点:蒙特卡罗方法(Monte Carlo Method,MCM),不确定度评定的来源、评定概念、评估方法及其发展过程,扩大了测量不确定度评定与表示的适用范围。     

吸附剂性能和操作参数对液相色谱流出峰不对称性的影响

色谱流出峰的拖尾现象普遍存在于制备和大型色谱分离过程中,它直接影响分离的产率和回收率．本文提出采用色谱流出峰形的不对称偏差度来表征色谱流出峰的拖尾程度;并基于液相制备色谱分离过程FAD－SMT模型及吸附速率理论,通过计算机模拟,定量分析了吸附剂性能和操作参数对色谱流出峰形不对称性的影响。结果表明：不仅是吸附剂的热力学和动力学性能（包括吸附相平衡关系、液固两相间的传质阻力）;而且柱的设计和吸附剂的装填状况（包括轴向扩散系数）,以及色谱分离的操作条件（进料时间、浓度和流速等）都直接影响色谱流出峰形的不对称性。随着吸附相平衡等温线的非线性程度增大,或者总传质系数的减小,色谱流出峰形的不对称偏差度明显增大;吸附剂吸附容量的减小也将引起色谱流出峰形的不对称偏差度的增加;色谱流出峰形的不对称偏差度与进科体积、浓度和流体线速,以及轴向扩散系数的增大成正比。     

分离度的探讨

按照国家标准《气相色谱法术语》定名的分离度(resolution)过去有称为分辨度或分辨率的。分离度在色谱法中是一个很重要的参数,它用以定量地描述混合物中具有相邻色谱峰的两个组分经过色谱柱分离后的情况,概括了色谱分离过程中的热力学和动力学的特性,因而可以比较全面地评价一根色谱柱的分离效能。 国家标准中规定分离度的定义是:“两个相邻色谱峰的分离程度,以两个组分的保留值之差与其平均峰宽之比表示”如图1所示:     

压力对加压电色谱分离选择性影响的研究

基于弛豫理论的基本原理,通过对溶质在加压电色谱中输运过程的研究,得到了溶质多种形态同时存在情况下反映其色谱行为与电泳行为对迁移时间影响的理论表达式。进一步研究了中性溶质与中性溶质、中性溶质与带电溶质以及带电溶质与带电溶质的分离选择性与压力、操作电压等的关系,结果表明：对于中性溶质的分离,尽管可以通过压力的改变调节峰间距和分离时间,但不会对出峰次序产生影响。对于中性溶质与带电溶质的分离以及带电溶质与带电溶质的分离,压力和电压皆可以便利地用于选择性的调节。     

色谱峰拐点和底宽的经验表示式

根据ＥＭＧ函数和线性回归,给出了色谱峰两拐点与峰顶在横轴上投影距离的表示式,给出了底宽和半高峰宽或１／１０峰高处峰宽之间关系的表示式,在不对称度为１．０９～３．００范围内,相关系数均在０．９９８以上。     

色谱流出曲线的曲线拟合法

通常人们把色谱流出曲线假设为高斯分布函数,但实际上真正的高斯峰很难由实验获得。由于实际峰型是非高斯型分布,往往使得理论预测值与实验值之间存在一定误差。例如由高斯计算的分离度K_1(及K_3)总是大于实测值。这主要由于实际峰往往是不对称的拖尾峰,峰尾使得实际分离度不如理论上由高斯对称曲线所预测的结果。为了定量描述拖尾峰的特征,许多作者采用了按指数规律卷积的高斯分布曲线数学模型:     

Liquid chromatography analysis of monosubstituted sulfobutyl ether-beta-cyclodextrin isomers on porous graphitic carbon

The retention behaviour of the three positional isomers of monosubstituted sulfobutyl ether-beta-cyclodextrin was investigated on a porous graphitic carbon (PGC) column. The influence of the mobile phase composition (nature and concentration of organic and electronic modifiers) was studied as well as the effect of column temperature. These hydrophilic and anionic analytes were highly retained on the PGC stationary phase compared to octadecyl bonded phases. The retention is mainly governed by a reversed-phase mechanism with electronic interaction playing a secondary role. An increase in solute retention and efficiency with temperature was observed. Successful isocratic separation with satisfactory baseline resolution of the three isomers of monosubstituted sulfobutyl ether-beta-cyclodextrin was achieved at 75 degrees C on a Hypercarb column by using ammonium acetate as electronic modifier in water-acetonitrile (83:17). The chromatographic methodology developed can be easily used for relative quantification of each isomer within a mixture and can be applied for semi-preparative purification of each one. The evaporative light scattering detector allows the detection of these non UV-visible absorbing molecules.     

CFD simulation of oil–water separation characteristics in a compact flotation unit by population balance modeling

Huge amounts of produced water are generated in offshore oil production. The Compact Flotation Unit (CFU) is an excellent pretreatment technology of produced water with high separation efficiency, low residence, and small split ratio. The Computational Fluid Dynamics-population balance model (CFD-PBM) method is used in the present work to study the oil–water separation characteristics in the self-developed Beijing Institute of Petrochemical Technology Compact Flotation Unit (BIPTCFU) at both micro-scale and macro-scale, which would help us gain more insights into the mechanism and the influence of flow field on the oil–water separation process such as the oil droplets’ diameter distribution and separation efficiency. The effects of the inlet diameter, the height of the preliminary separation zone, and the width of the annular space on the oil–water separation characteristics of CFU were discussed systematically. It is illustrated that the appropriate increase of inlet velocity, decrease of annular gap width, and increase of the height in the preliminary separation zone can effectively promote the collision and coalescence process of oil droplets. However, the overlarge height of the preliminary separation zone and the too narrow width of the annular space will both have a significant negative effect on the migration and separation of oil and water and lead to the decrease of separation efficiency.     

On the Geometry and Topology of 3D Stochastic Porous Media

The nature of geometric and topological information contained in statistical correlation functions was investigated systematically using simulated porous media, generated by the level-cut of Gaussian random fields. Pore space partitioning techniques based on multiorientation scanning were implemented to determine the pore and neck size distributions, coordination number distribution, and genus of a number of model porous media. These results were correlated with the statistical properties (porosity and correlation function) of the microstructure, revealing for the first time the extent of morphological diversity of a broad class of stochastically reconstructed porous media. It was found that the dominant factor explaining microstructural variability among the media studied is the dimensionless length of spatial correlation. Accordingly, the resolution at which the void space is discretized during simulation was shown to affect significantly the resulting pore and neck size distributions and specific genus. It was also found that the average coordination number of simulated porous media is independent of correlation length, but decreases slightly with decreasing porosity. Copyright 2000 Academic Press.     

毛细管电泳分离过程的不可逆热力学模型及优化控制仿真

以非平衡热力学分离理论为框架,建立了毛细管电泳分离大系统的分离模型。以分离过程的操作电压U为控制量,以溶质体系的净分离熵S~S作为目标函数,通过对分离大系统的优化设计,得到了最优操作电压控制轨线U^*(t)。通过仿真,证明了分离大系统在此最优控制规律作用下,分离效果最好。     

Chiral separations by host-guest complexation with cyclodextrin and crown ether in capillary zone electrophoresis

Summary Capillary zone electrophoresis using cyclodextrins and a chiral crown ether as buffer constituents was studied for the enantiomeric separation of drugs and amino acids. Based on results obtained from separation of racemic -amino acids both chiral selectors are compared with respect to resolution, efficiency and retention time. For (±)-Quinagolide effects of buffer composition and temperature are examined using -cyclodextrin as chiral agent. Optimum conditions were pH 2.5 at 30 mmol L^–1 -cyclodextrin. A linear dependence of retention on -cyclodextrin concentration allowed calculation of formation constants of the host-guest complexes. Buffer concentration and temperature also influence resolution. The application of a chiral crown ether to the separation of optical isomers in capillary zone electrophoresis is described for the first time. Chiral recognition of solutes depends on the formation of protonated alkyl amines and separation is attributed to the formation of diastereomeric host-guest complexes with different interactions for each enantiomer. The effects of crown ether concentration on resolution are presented.     

Method to predict the bandwidth of elution profile under the linear gradient elution in reversed‐phase HPLC

Solute migration in a chromatographic column is an important consideration when designing batch or continuous chromatographic separation processes. Most design methods for the chromatographic processes are based on the equilibrium theory which concerns only the migration velocity of the solute. However, in real cases, it is important to predict the zone spreading which occurs by axial dispersion and mass transfer resistance. To predict the actual solute profiles in the column or effluent stream, numerical methods to solve nonlinear partial differential equations have been used. However, these methods involve much time and expense. In this work, two different rate factors are considered to predict the characteristics of the solute profiles. The first is solute migration velocity and the second is the zone spreading rate. The zone spreading rate can be estimated by the apparent axial dispersion coefficient which is obtained from the height of the equivalent theoretical plate in particular. Four benzene derivatives (benzene, toluene, p‐xylene, and acetophenone) were used as model solutes, and two mobile phase systems, water/methanol and water/ACN, were used in RP‐HPLC. The bandwidths and retention times of the solutes were predicted under several linear gradient conditions. The predicted and experimental bandwidths and retention times showed good agreement.     

Metrics of separation performance in chromatography. Part 1. Definitions and application to static analyses

Earlier introduced metrics of separation performance are described in a systematic way. After providing the definitions of the metrics suitable for a broad variety of applications, the study focuses on static analyses (isothermal GC, isocratic LC, etc.) and their general separation performance. Statistically expected number of resolved (adequately separated) single-component peaks is treated as the ultimate metric of general separation performance of chromatographic analysis. That number depends on the peak capacity of the analysis and the number of components in a test mixture. The peak capacity, in turn, depends on the separation capacity of a column and the lowest separation required by the data-analysis system for resolving poorly separated peaks. The separation capacity is a special case of a broader metric of the separation measure which is a function of column efficiency, solute separability, and the level of the solute interaction with a column stationary phase. The formulae for theoretical prediction of all these metrics for arbitrary pairs of peaks in static analyses are derived. To provide a better insight into the basic metrics of the separation performance, additional metrics such as the solute discrimination (relative difference in solute velocities), utilization of separability (solute discrimination per unit of their separability), specific separation (the separation per unit of separability), and others are defined and found for static analyses.     

Evaluation of the van Deemter equation in terms of open‐ended flow to chromatography

Plate theory and adsorption theory are the main tools available for understanding chromatographic experiments. Both theories predict a Gaussian distribution of solute molecules within the tubular system. However, Gaussian concentration distributions are observed predominantly at slow linear flow rates, while asymmetric concentration distributions are observed at the linear flow rates most used in chromatography. Allegedly, this asymmetry originates from an inhomogeneous distribution of grain sizes in the column and column overload. However, it is an experimental fact that the distribution of chemicals within an injected volume of solute changes as a function of time, while the response is measured simultaneously. Accordingly, the obtained signal cannot be compared to the theory before some type of time‐based deconvolution of the data has been performed. Adjustments to high‐performance liquid chromatography data were thus proposed through empirical equations that describe the relevant time values, peak height, peak area, and parameters of the van Deemter equation. It was proposed that the transfer of solute from the front to the rear part of the pulse during laminar open‐ended flow occurs at rate that depends on the linear flow rate, and to a lesser extent, on properties of the response function.     

特征线法在求解非线性液相吸附色谱模型中的应用

本文应用特征线法求解非线性液相吸附色谱分离过程模型，论述了特征线法的原理和步骤，讨论了时间步长和空间步长对模型数值解的影响，并用色谱分离甘露醇和山梨醇以及分离蔗糖和还原糖的实验进行验证，用特征线法计算的理论流出曲线与实验流出线吻合较好。本文还分折了模型中各个参数的灵敏度，结果表明：吸附等温方程Q＝Ci*／（ai＋biCi*）中参数ai比参数bi以及总传质系数ki有更高的灵敏度。