Computer-Assisted Modeling, Prediction, and Multifactor Optimization of Hydrophobic Compounds in Liquid Chromatography

The traditional overlapping resolution mapping (ORM) scheme was modified for application in HPLC with the flow rate of the mobile phase as a new factor. The mobile phase composition and a flow rate were taken as parameters to influence effective resolution and elution time. Chromatograms were obtained for the separation of the 16 compounds for ten trial conditions. Computer-assisted mathematical simulation was used to obtain optimum conditions for resolution and separation time of the compounds. The validity of the model developed was confirmed by experiments.     

Application of Iso-Selective Gradient Elution for the Separation of Selected Phthalates

Abstract

In this paper, the overlapping resolution mapping scheme was applied to the gradient HPLC separation of selected phthalates. The procedure employs a minimum of seven experiments for the determination of the optimum mobile phase gradient for the desired separation. In the present work, solvent systems for iso-selective multisolvent gradient elution were used. The overlapping resolution mapping procedure was found to be a rapid and systematic approach for optimizing HPLC separations.     

Resolution optimization in micellar electrokinetic chromatography using two different overlapping resolution mapping schemes

Summary An appropriate optimization strategy should be able to find good separation conditions in the shortest time with only a few experiments, to assure the baseline-separation of all components. In this paper, the use of two optimization schemes has been studied using 10 substituted benzene as model compounds. The triangular overlapping resolution mapping (ORM) scheme and cubic ORM scheme were compared to optimize the three relevant parameters-the concentration of surfactant, the concentration of HP-β-cyclodextrin and pH. By conducting experiments that span the maximum working range of the system, overall optimum conditions for separation can be obtained. To confirm the validity of the two ORM schemes, additional experiments using the predicted optimum conditions were performed. Finally, 10 substituted benzene compounds were completely separated within 20 min by both sets of optimized conditions.     

Combination of orthogonal array design and triangle overlapping resolution mapping scheme for resolution optimization in micellar electrokinetic chromatography.

This paper describes the application of a combined orthogonal array design and overlapping resolution mapping to the optimization of miceller electrokinetic chromatography for the separation of 10 substituted benzenes. The most important factors were first determined according to an OA16(2(15)) through 16 pre-designed experiments; a second set of experiments was carried out according to a triangle overlapping resolution mapping scheme, in which 7 pre-planed experiments were executed and global optimum conditions for the separation were obtained.     

重叠分辨图法用于毛细管电泳优化分离

采用重叠分辨图法对毛细管电泳的分离过程进行了研究，实验以扑草净等5种农药分离的条件为例，考察了影响分离的三个主要因素（溶液的pH、表面活性剂浓度和有机改性剂浓度）对分离度的影响，分离过程首先通过11次初步实验建立目标函数，这样可预测其它条件下的最小分离度，从最终的重叠分辨图可得到分离的最佳条件，在选定的优化条件下，5种组分可达到基线分离。     

反相高效液相三元流动相台阶梯度分离条件的快速优化方法

 根据溶质在柱内的迁移规律 ,建立了一种利用线性梯度实验快速获得溶质保留值方程系数 ,然后以串行响应函数为优化指标进行多台阶梯度分离条件优化的方法。与利用等度实验获得保留值方程的方法相比 ,该法可以大大缩短优化时间。通过该方法对芳香胺和衍生化氨基酸样品进行了分离 ,获得了满意的分离度 ,表明该方法的预测精度很好。     

Optimization of solvent selectivity for the chromatographic separation of fat-soluble vitamins using a mixture-design statistical technique

Summary A systematic approach, using a mixture-design statistical technique, has been developed for selecting the optimum mobile phase for the separation of fat-soluble vitamins in reversed-phase high-performance liquid chromatography. A quaternary mixture of methanol, acetonitrile, tetrahydrofuran and water was used as mobile phase. Retention time and peak width were recorded in ten runs augmented with five replicates and the data were subsequently fitted to special cubic polynomial models. The resulting mathematical equations enabled prediction of resolution over the entire parameter space. Contour plots of minimum effective resolution and maximum retention time as a function of mobile phase composition are presented and discussed. Visual inspection of these plots provides an overview of the quality of the separation and the analysis time required for each possible mobile-phase composition with n the parameter space. It is demonstrated that the methodology followed was an important tool which enabled the taking of informed decisions necessary for selection of the optimum mobile phase for a chromatographic separation. A combination ofR _S minimum andt _R maximum as optimization criteria in a multicriteria decision-making plot using pareto-optimality concept is discussed. This combination enabled visual demonstration of the compromise between separation quality and the economics of analysis time. Our methodology has been compared with the common used technique of ‘overlapping resolution mapping’.     

Business-objective-directed, constraint-based multivariate optimization of high-performance liquid chromatography operational parameters

The goal of a separation can be defined in terms of business needs. One goal often used is to provide the required separation in minimum time, but many other goals are also possible. These include maximizing resolution within an analysis-time limit, or minimizing the overall cost. The remaining requirements of the separation can be applied as constraints in the optimization of the goal. We will present a flexible, business-objective-based approach for optimizing the operational parameters of high performance liquid chromatography (HPLC) methods. After selecting the stationary phase and the mobile-phase components, several isocratic experiments are required to build a retention model. Multivariate optimization is performed, within the model, to find the best combination of the parameters being varied so that the result satisfies the goal to the fullest extent possible within the constraints. Interdependencies of parameters can be revealed by plotting the loci of optimal variable values or the function being optimized against a constraint. We demonstrate the concepts with a model separation originally requiring a 54 min analysis time. Multivariate optimization reduces the predicted analysis time to as short as 8 min, depending on the goals and constraints specified.     

应用扩展的重叠分辨率法优化液相色谱条件分离二茂铁类化合物

本文对优化液相色谱分离条件的重叠分辨率法进行了改进与扩展：首先利用全范围的二元线性梯度淋洗进行溶剂强度的优化，再通过重叠分辨率法进行了溶剂选择性的优化，并且建立了计算机系统，使此方法程序化。利用此方法建立了分离Ｎ－二茂铁甲酰基－Ｎ＇－芳基硫脲类衍生物的最佳流动相体系。     

Experimental design optimization of the separation of the aromatic compounds in petroleum cuts by supercritical fluid chromatography

A experimental design optimization method is demonstrated for evaluation of the resolution of the performance mixture used in the proposed ASTM test to determine the aromatic content of aviation fuels. The method uses a Doehlert experimental matrix test to optimize the resolution and analysis time by varying the pressure and temperature of the supercritical carbon dioxide mobile phase. The separation between saturated and aromatic compounds was optimized using only seven experiments. With this procedure, the analysis time required for determination of the total aromatic content of more complex samples can be reduced to less than 10 min.     

Optimization of supercritical fluid chromatographic separation of nitroaromatics by the overlapping resolution mapping scheme

The use of an interpretative optimization method to predict optimum conditions for the supercritical fluid chromatographic separation of nitroaromatics is demonstrated. The scheme utilizes the overlapping resolution mapping (ORM) procedure for multivariate prediction of the pressure gradient and temperature in order to separate eight nitroaromatics. Using the ORM scheme, only seven experiments were conducted before a global optimum was revealed. All the peaks were satisfactorily separated using experimental conditions derived from the scheme.     

Separation strategy for acidic chiral pharmaceuticals with capillary electrochromatography on polysaccharide stationary phases

The effect of five factors on the capillary electrochromatographic enantioseparation of acidic compounds was studied using an experimental design. The studied factors were pH, acetonitrile content in the mobile phase, temperature, buffer concentration, and applied voltage. These experiments allowed defining a generic separation strategy applicable on acidic compounds with chemical and structural diversity. The starting screening conditions consist of a 45 mM ammonium formate electrolyte at pH 2.9 mixed with 65% acetonitrile, an applied voltage of 15 kV, and a temperature of 25 degrees C. The screening phase occasionally can be followed by an optimization procedure. Evaluation of the proposed strategy pointed out that it allows achieving baseline resolution within a relatively short time when a beginning of separation is obtained at the starting conditions. This strategy revealed enantioselectivity for 11 compounds out of 15, of which 10 could be baseline-separated after the proposed optimization steps.     

Computer-aided target optimization for traditional Chinese medicine by ultra-performance liquid chromatography

A new strategy of target optimization was developed for resolving the separation problems of complex samples. Computer-aided target optimization for separation of complex samples by ultra-performance liquid chromatography (UPLC) was studied. Taking traditional Chinese medicine (TCM) (Rhizoma Coptidis) as an example, separation conditions of target compounds - overlapping peaks and all components - were optimized based on moved overlapping separation ranging map (OSRM) and artificially intervention. After calculating retention parameters and peak shape parameters of the target peaks, the optimization was operated in an emulational picture through the computer without further experiments. The emulational chromatogram was proved to be authentic by the estimated values, which were almost identical to experimental results. The method was very helpful for obtaining the satisfied separation conditions of target compounds rapidly and efficiently.     

The principle of optimization of binary mobile phase composition of multi-step linear gradient elution

The basic principle of optimal method called “moving overlapping resolution mapping method” to select the optimal binary mobile phase composition of multi-step linear gradient liquid chromatography is discussed with simultaneously considering effects of position of solute inside the column and mobile phase composition on peak resolution and retention value, then a BASIC program based on this principle is developed in IBM-PC computer. The validities of both principle of optimization and BASIC program are confirmed by separation of samples containing bile acids and PAHs in RP-HPLC.     

Prediction,optimization of separation,and identification of unknown compounds in capillary gas chromatography

A procedure for the identification and separation of unknown compounds by capillary gas chromatography is described. The procedure involves a live retention time database and optimization of the separation. After initial chromatography of the sample, a rough search lists all the possible compounds it might contain and the analyst then uses his experience to discard those compounds in the list which are unlikely to be present. The multi-component separation is then optimized over the whole range of defined starting temperatures and programming rates, in order to produce the best possible separation of the sample components, and the chromatography repeated using the results obtained from the optimization procedure. Further search operations within a given search window will then report the compound names, and related information, for each peak. Since the identification operation is performed at least twice during the procedure, and the optimization of the separation assists the identification by separating possibly overlapped peaks, the confidence of the qualitative analysis is higher than may be obtained using standards alone. If the reproducibility of isothermal indices measured on columns could be guaranteed, this procedure could be used instead of performing chromatography on standards of the compounds contained in the database, regardless of changes in column dimensions, phase ratio, and operating conditions in temperature programmed analysis.     

Implementation of a design of experiments to study the influence of the background electrolyte on separation and detection in non-aqueous capillary electrophoresis-mass spectrometry

Non-aqueous capillary electrophoresis (NACE) background electrolytes are most often composed of a mixture of methanol and acetonitrile (ACN) with soluble ammonium salts added as electrolyte. In this study on NACE-MS, we used a mixture of glacial acetic acid and ACN giving rise to an acidic background electrolyte (BGE) with a very low dielectric constant. Impressive changes in selectivity and resolution were observed for structurally closely related indole alkaloids including diastereomers upon addition of ammonium formate as electrolyte and upon variation of the solvent ratio. In order to obtain best separation and MS detection conditions and to reveal the influence of the parameters of the BGE on separation and detection and vice versa of the MS parameters on separation, an optimization strategy was employed using a design of experiments in a central composite design with response surface methodology. It was proven that at high electroosmotic flow conditions capillary electrophoretic separations and thus optimization can be realized without interference from the coupling to an MS system. Several significantly interacting parameters were revealed, which are not accessible with classical univariate optimization approaches. With this optimization, alkaloid mixtures from a plant extract of Mitragyna speciosa, containing a large number of diastereomeric compounds were successfully separated.     

Surface analysis of steel sheets with GDOS and EPMA

Summary In the field of steel sheet characterization, chemical surface analysis plays a very important role. Surface composition effects the surface properties of the final product. At Voest-Alpine Stahl Linz the analysis techniques GDOS and EPMA are routinely used to characterize the steel sheet surface. Some fundamental experiments are here described for the optimization of GDOS depth resolution. In the documentation for a semiquantitative approach for steel sheet analysis, investigations and experience about minimum detection limits are presented. Self developed methods for concentration mapping and thickness mapping are described in the field of electron probe microanalysis; Also an EPMA depth profiling method is highlighted. Finally practical examples demonstrate the wide application range of the analysis methods.     

Rapid 1H[13C]-resolved diffusion and spin-relaxation measurements by NMR spectroscopy

Hadamard-encoded heteronuclear-resolved NMR diffusion and relaxation measurements allow overlapping signal decays to be resolved with substantially shorter measuring times than are generally associated with 2D heteronuclear cross-correlation experiments. Overall measuring time requirements can be reduced by approximately an order of magnitude, compared to typical 2D heteronuclear single-quantum correlation-resolved diffusion or relaxation measurements. Specifically, in cases where chemical shift correlation information provides enhanced spectral resolution, the use of Hadamard encoding can be used to overcome uniqueness challenges that are associated with the analysis of concurrent dynamic processes and the extraction of time constants from overlapping exponential signal decays. This leads to substantially improved resolution of similar time constants than can be achieved solely through the use of post-acquisition processing techniques. In the ideal case of complete spectral separation of the signal decays, the usual constraint that time constants must be sufficiently different to resolve by exponential analysis can be circumvented entirely. Hadamard-based pulse sequences have been used to determine 1H[13C]-resolved diffusion coefficients and spin-relaxation time constants for the chemically similar components of an aqueous solution of ethanol, glycerol, and poly(ethylene glycol), and a dye-containing block-copolymer solution, which exhibit significant spectral overlap in their 1H NMR spectra.     

五味子提取物高效液相色谱分析方法的优化

针对五味子乙醇提取物的复杂体系,借助于复杂样品分析系统软件(CSASS),根据组分在4次简单线性梯度下42个峰的保留时间,快速准确地计算出各组分的液相色谱保留参数a,c值和峰形参数σ,W1/2。借助这些参数,对五味子色谱的分离情况进行高精度仿真预测。在此基础上,应用移动重叠分辨分离图和谱图仿真技术,发展了计算机辅助的五味子提取物的高效液相色谱全局优化方法。在优化条件下,五味子提取物的高效液相色谱分析可在40 min内完成,且常量成分和部分低含量成分都能够得到较好的分离。所建立的方法已成功地用于五味子中化合物保留时间及峰形的预测,并在此基础上对其色谱分离条件进行优化。     

用改进的重叠分辨率优化法于薄层色谱分离二茂铪化合物

在薄层色谱中分离一系列二茂铪化合物，首先利用黄金分割优选法优化二元展开剂体系，然后按优化结果把二元展开剂混合成四元溶剂体系，共用重叠分辨率法确定四元展开剂体系的最佳组成，分离结果令人满意，同时，本文还对等溶剂强度条件和不等溶剂强度条件下的优化结果做了比较和讨论。