吸附剂性能和操作参数对流相色谱流出峰不对称性的影响

色谱流出峰的拖展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,并基于液相色制备色谱分离过程ＦＡＤ－ＳＭＴ模型及吸附速率计算机模拟,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。     

液相制备吸附色谱流出峰对称性的若干影响因素

在色谱分离连续性方程和质量传递速率方程基础上,对色谱分离过程进行计算机模拟,定量分析了分离体系的热力学、动力学参数和操作条件对色谱流出峰形对称性的影响。结果表明,吸附相平衡关系、液固两相间的传质阻力及进料体积、进料浓度和流体线速等都将直接影响色谱流出峰形的对称性。流出峰形的不对称程度随着吸附等温线的非线性程度、液固两相间的传质阻力、流体线速、进料体积、进料浓度的增大而增大;在线性条件下,随着吸附剂吸附容量的减小而增大。     

大型液相色谱分离甘露醇和山梨醇的热力学及动力学参数辨识

本文研究了液相色谱分离过程的吸附平衡常数、传质系数参数的估值模型，用色谱技术和以惰性物示踪的扰动应答实验技术测定甘露醇和山梨醇在钙型吸附剂上的吸附相平衡常数和总传质系数以及床层中的轴向扩展系数，结果表明：吸附平衡常数和吸附剂的选择性随温度的升高而下降；液固相间的总传质系数随温度的升高而增大；轴向扩散系数随流速的增大而增大，参数灵敏度分析的结果表明，相平衡关系，尤其是吸附选择性，对色谱分离的影响有较     

柱吸附容量对蔗糖还原糖色谱分离过程产率和回收率的影响

本文采用了能反映流体轴向扩散的大型液相色谱分离过程数学模型,应用计算机模拟分析蔗糖和还原糖的色谱分离过程,从吸附剂吸附容量和柱装填密度两个方面;考察柱吸附容量对大型色谱分离的产率和回收率的影响。研究结果表明：在色谱柱中流体线速度恒定的条件下对多组分分离,回收率是随吸附剂吸附容量以及床层装填密度的增大而增大的;产率先随吸附剂吸附容量的增大而增大,而在出现峰值后下降;随着床层装填密度的增大,产率增加,但与此同时轴向扩散系数也增大,从而降低分离效率,导致在较高装填密度的范围内产率增力。的幅度减少。在相同的吸附剂用量下,采用短柱高装填密度的色谱柱将比长柱低装填密度色谱柱能获得更高的回收率和产率。     

非平衡塔板理论的几个问题

本文用非平衡方法对塔板理论进行了重新处理,导出了描述塔板过程的统一方程（平衡或非平衡）如下：（注：符号ｐｆ（ｒ,ｎ）表示交换ｎ次后第ｒ号塔板流动相中的物质分数;符号ｑｆ（ｒ,ｎ）表示交换ｎ次后第ｒ号塔板固定相中的物质分数）经计算机数值计算,得到如下初步结果：（１）色谱峰是不对称峰,其形状与流速有关。流速增大,不对称性将增大。流速的改变,也会引起峰形的其它改变。（２）色谱峰的峰宽与流速有关。流速增大,峰宽（以塔板数为量纲）将增大。（３）色谱峰的峰高与流速有关。流速增大,峰高将减小。     

连续旋转环状色谱的数学模型参数分析

连续旋转环状色谱用数学模型模拟时,模拟结果的精确度和所采用参数的“灵敏”程度有关。为此,探讨了相平衡常数、相间传质系数、弥散返混系数等对色谱峰质量浓度最高点位置角度（保留值）、分离度、峰宽和产率等参数的灵敏度并对它们逐一进行了分析。认为相平衡关系对分离效果最为敏感。筛选吸附量大、选择性好的吸附剂是改进操作效果的最佳途径。     

液相色谱技术测定葡萄糖果糖在Ca型吸附剂上相平衡常数和总传质系数

]考虑轴向扩散的影响,导出液相色谱技术测定吸附相平衡常数和总数传质系数参数估值模型,测定葡萄糖果糖吸附相平衡常数和总传质系数,研究流速、温度对这些参数的影响。获得理论计算与色谱分离实验流出曲线相吻合结果。     

塔板理论流出曲线的统计特征

直接从原始塔板理论的级数形式色谱流出曲线表达式出发,得到了流出曲线一级原点矩及二,三级中心矩的数学表达式,并依此讨论了色谱峰的形状特征及各种因素对峰形的影响规律.本文结果直接证实原始塔板理论曲线为不对称分布,描述峰型不对称性的偏态系数与塔片数及容量因子有关,且随容量因子的增大逐渐变小.当塔片数很大时,容量因子不很小的组分流出曲线有相似的对称性.     

塔板理论流出线的统计特征

直接从原始塔板理论的级数形式色谱流出曲线表达式出发,得到了流出曲线一级原点矩及二、三级中心矩的数学表达式,并依此讨论了色谱峰的形状特征及各种因素对峰形的影响规律。本文结果直接证实原始塔板理论曲线为不对称分布,描述峰型不对称性的偏态系数与塔片数及容量因子有关,且随容量因子的增大逐渐变小。当塔片数很大时,容量因子不很小的组分流出曲线有相似的对称性。     

色谱柱分离过程弛豫理论——流出曲线的动力学本质

在分析型线性色谱中,流出曲线一般表现为拖尾的形式,这种现象可以采用多种机理加以解释。模仿动力学弛豫理论的假设条件,认为溶质在柱过程中的迁移以跃迁形式完成,得到了浓度分布曲线的数学表达式。分别探讨跃迁次数、两相间跃迁速率及溶质在流动相中的轴向跃迁对峰形的影响,进一步说明了色谱流出曲线的动力学本质     

SYSTEM IDENTIFICATION METHOD OF LINEAR AND NON-LINEAR LIQUID PREPARATIVECHROMATOGRAPHIC SEPARATION

1.INTRODUCTIONThechromatographicproblemistorelatetheconcentrationprofileofthebandattheoutletofthecolumntotheequilibriumisothelm,themasstransferkineticsandtheprofileoftheinjectionbandandperformtheoptimumdesignofseparationprocess['J.Togettheobjective,Itisnecessarytoidentifythesystemof.ProjectsupPOrtedbyTheNationalNaturalScienceFoundationofChinatheliquidadsorptionchromatographylinearornon-linear,andthendeterminethethermodynamicanddynamicsparametersofthesystemaccuratelysothatthecomputersim…     

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。     

双柱交替循环色谱分离甘露醇山梨醇过程

本文在非线性非平衡双柱循环色谱分离过程数学模型的基础上,进行了双柱交替循环色谱分离甘露醇山梨醇的实验,对模型进行了实验验证。结果表明：采用非线性非平衡双柱循环色谱模型计算的流出曲线与实验结果相吻合。计算机模拟的结果从理论上证明了对本实验体系采用双柱交替循环色谱分离模式比采用传统的色谱分离模式能获得更高的分离产率,产率随循环次数的增加而增加,使用双柱交替循环色谱分离操作模式获得的分离效率超过使用传统长色谱柱操作模式获得的分离效率。当轴向扩散比较严重、液固两相间的传质阻力较大,或者吸附的表观选择性系数较小时,采用双柱循环色谱模式比使用传统单柱色谱模式能获得更高的产率。     

Simple and Efficient Solution for Robustness Testing in Gradient Elution Liquid Chromatographic Methods

In this paper, an efficient way for robustness testing of gradient elution liquid chromatographic methods is proposed and tested on model mixtures comprising cilazapril, hydrochlorothiazide, and their degradation products, solutes that differ not only in polarities, but also in solubility and absorption characteristics. In general, the robustness could be tested with respect to various responses: resolution, retention factor, selectivity factor, change of detector response, etc. In chromatographic methods, the separation of the adjacent peaks is mandatory, and, consequently, the resolution is usually used as response. In isocratic elution methods, the resolution threshold depends on many factors, such as sizes of adjacent peaks, peak shapes, and asymmetry factor. At the same time, the situation is even more complex in gradient elution methods, because separation depends on a larger number of parameters, such as gradient profile, column geometry, mobile phase flow rate, column equilibration between gradient runs, etc. To ensure baseline separation, the authors propose application of separation criterion (s) as response and indirect modeling in the robustness evaluation. Examined response in this approach is represented by the difference between the retention time of the beginning of the peak and the retention time of the end of the previously eluting peak of the critical pair. Moreover, the proposed methodology included reusing experiments from the optimization phase to define a robust chromatographic region without increasing the number of experiments. It was shown that method robustness can be easily and efficiently evaluated by this methodology.     

THE DETERMINATION OF ADSORPTION ISOTHERMS AND SOLID DIFFUSION COEFFICIENTS OF MANNITOL AND SORBITOL BY LIQUID CHROMATOGRAPHY TECHNIQUE

The parameter identification model is proposed for determining the linear adsorption isotherms and the solid diffusion coefficients by using adsorption chromatorgaphy.Axial dispersion coefficients is firstly determined by pulse-respond experiment technique with an inert substance as tracer,then the elution curves of chromatography separating the isomer mannitol and sorbitol are determined by the chromatographic measuring technique,and pinally the adsorption isotherms and the solid diffusion coefficients of mannitol and sorbitol on Ca^2+ resins are estimated by using this model.The results show that the axial dispersion coefficients increase with fluid velocity increasing,The adsorption equilibrium constants decrease with temperature rising;and the solid diffusion coefficients increase with temperature rising.The theoretical elution curves are good agreement with the experimental elution curves of the liquid adsorption chromatography separating the mannitol and the sorbitol.The model provides a simple and reliable procedure to estimate the kinetic and thermodynamic parmeters of the adsorption.     

THE DETERMINATION OF ADSORPTION ISOTHERMS AND SOLID DEFFUSION COEFFICIENTS OF MANNITOL AND SORBITOL BY LIQUIDCHROMATOGRAPHY TECHNIQUE

1INTRODUCTIONTheseparationprocessoflarge-scaleliquidchromatographyisaunstabletransferprocess.Theseparationefficiencyisaffecteddirectlybytheadsorptionisotherms,themasstransferresistancewithinsolidadsorbentparticleandtheoperationparametersinthesystem.Therefore,thedeterminationoftheisothermsandisnecessaryfordesigningandoptimizingthechromatographicprocess.Thereareseveralmethodstodeterminekineticparameters.Carl(1992)carriedoutthekineticexperimentoftheadsorptioninacontinuousstirredtankadsorberl…     

Dynamic chromatography: A stochastic approach

During the chromatographic separation process, analyte reactions are often observed leading to band broadening and/or elution of peak clusters. For many different chemical compounds the reaction can be reduced to a simple isomerisation kinetic scheme where elution is the result of adsorption–desorption on the surface stationary phase coupled with a flipping two-level reaction system. In this paper, the chromatographic peak shape for a reacting analyte is calculated in frequency domain when the reaction follows a simple reversible first order scheme. Both reaction and dynamic chromatographic systems have been considered. The derived solutions are expressed in closed form in the Fourier domain. Several limit solutions obtained under conditions of very slow and moderately fast kinetics are exploited. The effects of both kinetics rate constants and retention time on the chromatographic peak shape are singled out.     

Liquid chromatographic determination of sulindac and metabolites in serum

An improved liquid chromatographic procedure is described for the quantitative determination of sulindac, sulindac sulfone, and sulindac sulfide from serum. The procedure makes use of acetonitrile extraction of the compounds of interest from acidified serum samples. Under these conditions extraction efficiencies in the 85 percent range are obtained for each of the compounds. The liquid chromatographic separation of the compounds of interest and the internal standard (indomethacin) is accomplished in an isocratic elution procedure using a nitrile (CN) stationary phase. The HPLC separation procedure is completed in less than 10 minutes, giving excellent resolution and peak shape.     

Use of synthetic adsorbents in preparative normal-phase liquid chromatography

Normal-phase liquid chromatographic separation using polymeric synthetic adsorbents was investigated. The retention behavior of dialkyl phthalates under a hexane-isopropanol eluent system revealed that both polystyrenic and polymethacrylic adsorbents can be used for normal-phase liquid chromatography, and that the polymethacrylic adsorbent has stronger retentivity than the polystyrenic adsorbent. Applicability of these synthetic adsorbents, especially the polymethacrylic adsorbents, was verified by the separation of polyunsaturated fatty acids, schizandrin in Schisandra chinensis fruit, tocopherols and tocotrienols in vegetable oils using a 10-microm adsorbent packed into an HPLC column. Furthermore, the separation was expanded to preparative scale by using polymethacrylic adsorbents with 17- and 31-microm fine grade particle sizes. The effect of loading volume on the retention or separation was also examined, and separation was maintained up to the loading of several grams per liter adsorbent. These results demonstrate that commercially available synthetic adsorbents possess considerable performance as normal-phase chromatographic media for more precise purification of bioactive compounds. including pharmaceuticals and nutraceuticals with scale-up possibilities.