梯度洗脱

柱液相色谱有等度（isocratic）和梯度（gradient）2种洗脱方式．等度洗脱时,流动相的组成在色谱分离过程中保持不变;梯度洗脱是控制流动相的组成,使其在色谱分离过程中发生连续的变化．现在,很多HPLC实验室的仪器都有梯度洗脱的功能,为了充分利用仪器的这种功能,本文将讨论以下3个问题：一是为什么要使用梯度洗脱;二是如何对梯度洗脱程序进行优化;三是使用梯度洗脱时常见的问题．     

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。     

计算机预测液相色谱梯度洗脱程序

用高效液相色谱法分析复杂样品时,往往会遇到样品中各物质的保留时间分布很宽的问题。溶剂梯度洗脱技术为解决这一问题开辟了一条有效的途径。但此技术在应用过程中,由于大多凭借经验设定溶剂梯度洗脱程序,所以,建立起一个比较好的程序就需要摸索较长的时间。近年来,国内外某些色谱工作者试图用计算机预测溶剂梯度洗脱程序,但有关详细情况迄今尚未见报道。     

反相高效液相色谱流动相组分最优化中初始条件的迅速选择

〕本文从梯度和等浓度两方面讨论了反相色谱流动相组分最优化过程中初始条件的迅速选择。讨论了不同梯度参数对确定初始流动相组分的影响;对不适于梯度洗脱的情况,提出了用逐步逼近的等浓度洗脱过程确定初始流动相组分的方法。以多环芳烃和去痛片组分为例验证了方法的可靠性。     

高效液相色谱梯度洗脱中弱溶剂的在线净化

利用一个在线净化预柱减少了高压梯度洗脱中由于试剂纯度不够造成的基线噪音。预柱的位置在溶剂泵Ａ和流动相混合器之间,由一个六通阀来控制。在线净化结果良好,有效地除去了空白梯度色谱图中的杂质峰,提高了梯度洗脱的分离重现性。该方法对开展梯度洗脱有实用价值。     

液相色谱-串联质谱外标法定量分析中基质效应的评估

以苯巯基尿酸为目标化合物,考察了色谱分离条件(即强洗脱、弱洗脱及梯度洗脱)对采用外标法定量的液相色谱-串联质谱(LC-MS/MS)分析中基质效应的影响。试验表明:①对无基质标准溶液的分析,以强洗脱条件下的灵敏度最高,且可实现高通量分析;②对同一基质不同浓度的试液,弱洗脱条件的基质效应明显改善,而梯度洗脱的结果最好;③对不同来源的基质和不同浓度的试验,在3种不同的色谱分离条件中以梯度洗脱效果最好,提高了分离度,减少了共流出,有效地降低了基质效应对目标物分析的影响。因此,在LC-MS/MS分析中,色谱分离条件的改善对降低基质效应对测定的影响十分重要。     

高效液相色谱梯度洗脱同时测定化妆品中防腐剂、抗氧化剂和杀菌剂

建立了一种灵敏、快速的高效液相色谱梯度洗脱同时测定化妆品中防腐剂、抗氧化剂和杀菌剂的方法。采用C8柱，以甲醇和水为流动相梯度洗脱。在检测波长273nm用二极管阵列检测器，17min内可将4种防腐剂、2种抗氧化剂和2种杀菌剂分离测定。方法快速准确，用于实际样品的测定。     

用反相液相色谱分离多肽时峰容量与色谱柱长度关系的研究

在蛋白质组学研究中,多肽混合物的有效分离对蛋白质鉴定和蛋白质之间相互作用的研究起着决定性的影响。基于此,用反相液相色谱研究了在两个不同长度的色谱柱上分离多肽混合物时色谱柱长度与峰容量的关系,同时考察了梯度洗脱时间对峰容量和峰宽的影响。实验结果表明,色谱柱长度对峰容量有显著的影响,而延长梯度洗脱时间不仅可以增加峰容量,而且可以增加峰宽。这说明用毛细管液相色谱 串联质谱联用方法对多肽混合物进行分离鉴定时,采用较长的色谱柱和较长的梯度洗脱时间有利于对更多的多肽进行分析鉴定。     

高效液相色谱中用于梯度洗脱的有机溶剂的纯度测试

在反相高效液相色谱中,空白梯度基线的漂移和杂质峰,可能由含水溶剂和有机溶剂中杂质所引起的。当含水溶剂通过预柱在线净化后,根据空白梯度色谱图可测试有机溶剂的纯度。按照此法,对国产不同等级的乙腈和甲醇进行了测试,指明这些试剂用于梯度洗脱的可能性。     

液相色谱梯度洗脱中的谱带压缩效应

谱带压缩效应是梯度洗脱区别于等度洗脱的重要特征。经典的范德姆特(van Deemter)理论塔板高度方程基于等度洗脱推导得到,因此不能对谱带压缩效应进行描述。在梯度洗脱中,保留因子(k)会随流动相组成(φ)的改变而发生变化,这就使得对梯度洗脱机理的研究要比等度洗脱复杂许多。该文对近10年来谱带压缩效应的研究进展,特别是溶剂强度模型(即描述ln k与φ关系的数学表达式)的非线性特征对谱带压缩因子(G)的影响进行了述评,指出为了更好地认识谱带压缩效应需要将这种非线性因素考虑在内。     

新型程序涂渍色谱柱程序效应的研究

新型程序涂渍色谱柱程序效应的研究许鸿生，洪辉（湘潭大学化学系，湘潭，４１１１０５）关键词新型程序柱，程序效应，气相色谱关于程序涂渍色谱柱的问题，国内外研究指数函数程序柱的较多［１～３］，色谱柱涂渍结构改变后，组分的保留行为及柱效能都发生较大变化．作者...     

Optical intensity gradient by colloidal photonic crystals with a graded thickness distribution

Gradient colloidal crystals with a thickness gradient were prepared by the vertical deposition technique with vertically graded concentration suspensions. The thickness of the gradient colloidal crystal gradually changes at different positions along the specific gradient direction of the crystal. The thickness gradient was determined by the concentration gradient, depending on the initial colloidal concentration and the settling time. The optical transmission intensity at the dip wavelength can be tuned by changing the thickness of the colloidal crystals. The gradient colloidal crystals lead to a gradient of optical intensity at the dip in transmission light. The gradient of optical intensity at the dip increases as the thickness gradient of the colloidal crystal increases.     

Analytical equilibrium gradient methods

Analytical equilibrium gradient methods are non-linear separation methods in which the separation mechanism involves a force gradient along the separation channel. These methods can be classified into two categories: those in which the gradient is a field gradient applied along the separation channel (i.e., field gradient), and those in which the channel is subjected to a constant field with a gradient formed in some other property (i.e., constant field). Standard deviation of peak width, resolution and peak capacity are important parameters in characterizing equilibrium gradient methods, and general expressions can be obtained from considering both the point of force acting on the analyte and the basic flux equation. Several successful examples, such as density gradient sedimentation, isoelectric focusing and electromobility focusing are discussed. Based on equilibrium gradient methods in the field gradient category, a method to dynamically improve peak capacity is described. An example of such an approach is given using electromobility focusing.     

Mucin (MUC5AC) expression by lung epithelial cells cultured in a microfluidic gradient device

We have developed a microfluidic gradient device for controlling mucin gene expression of NCI-H292 epithelial cells derived from lung tissues. We hypothesized that gradient profiles would control mucin gene expression of lung epithelial cells. However, it was not possible to generate various stable gradient profiles using conventional culture methods. To address this limitation, we used a microfluidic gradient device to create various gradient profiles (i.e. non-linear, linear, and flat) in a temporal and spatial manner. NCI-H292 lung epithelial cells were exposed to concentration gradients of epidermal growth factor in a microfluidic gradient device with continuous medium perfusion. We demonstrated an effect of gradient profiles on mucin expression of lung epithelial cells cultured in the microfluidic gradient device. It was revealed that NCI-H292 lung epithelial cells exposed to the flat gradient profile of the epidermal growth factor exhibited high expression of mucin as compared with cells exposed to non-linear and linear gradient profiles. Therefore, this microfluidic gradient device could be a potentially useful tool for regulating the mucin expression of lung epithelial cells exposed to chemokine gradient profiles.     

Selective Adhesion and Directional Migration of Endothelial Cells Guided by Cys‐Ala‐Gly Peptide Density Gradient on Antifouling Polymer Brushes

Selective adhesion and directional migration of endothelial cells (ECs) on biomaterials is critical to realize the rapid endothelialization. In this study, a Cys‐Ala‐Gly (CAG) peptide density gradient is generated on homogeneous cell‐resisting poly(2‐hydroxyethyl methacrylate‐co‐glycidyl methacrylate) brushes by immersing the brushes in a complementary gradient solution of CAG and competitive mercapto‐terminated methoxyl poly(ethylene glycol). The adhesion and spreading of smooth muscle cells (SMCs) is impaired effectively on the gradient surface. About six folds of adherent ECs over SMCs are achieved at the position (10 mm) of highest CAG density on the gradient surface in a co‐culture condition. Due to the gradient cues, ECs migrate fastest with the best directionality of 86.7% at the middle of the gradient, leading to the maximum net displacement as well.     

Reaction path as a gradient line on a potential energy surface

The reaction path is shown to be always a gradient line on a potential energy surface (PES ) of a molecule. The properties of gradient lines on the PES are elucidated. Correct symmetry conservation rules along the gradient line are derived. The behavior of the gradient line on a PES with different topologies are considered. © 1994 John Wiley & Sons, Inc.     

程序涂渍柱“柱效能程序效应”的研究

本文从理论上给出程序柱“柱效能程序效应”的概念并导出了函数关系式,通过计算机可计算柱效能程序效应与柱内各变量之间的关系,实践证明实验数据的变化趋势与理论数据相符。     

高分子梯度溶液吸声机理的研究

Emphasis of this work was paid to the study on the sound absorption mechanism of gradient polymer solution. A specially designed gradient polymer solution and an uniform polymer solution were synthesized. The sound attenuation properties of the gradient polymer solution and the uniform polymer solution were measured in sound tube. Results show that the sound attenuation of the gradient polymer solution is larger than that of the uniform. Depending on the experimental result and the theory of sound wave propagation in layered medium, a mathematical model of sound attenuation in the gradient polymer solution was established. And a calculating program was carried out by Maple and Matlab. The calculated results are fairly in good agreement with the measured. So mechanism of the gradient polymer solution was developed. This mechanism can be described as follows: a polymer solution with the concentration gradient layer forms the gradient polymer solution. This gradient layer led to multiple reflection and absorption of sound when the sound wave propagated in it. Finally the sound energy was transferred into heat.