Prediction of internal standards in reversed-phase liquid chromatography. 1. Initial study on predicting internal standards for use with neutral samples based on linear solvation energy relationships

This paper describes the results of an initial study on the application of linear solvation energy relationships (LSERs) to the prediction of internal standard compounds in reversed-phase liquid chromatographic (RPLC) method development. Six neutral samples are separated on an Inertsil ODS(3) column by either acetonitrile-water or methanol-water mobile phases under either isocratic or linear gradient conditions. After the separation conditions are optimized, the desired positions for internal standard candidates are selected based on the "open windows" of the chromatograms. The compounds with the desired retention range are then predicted based on LSERs from a database consisting of more than 700 compounds with defined physicochemical properties. The prediction requires the use of LSER coefficients under the separation conditions for each sample. They are determined a priori by performing multivariable linear regression on the retention of 20 reference solutes against their physicochemical properties. It can be concluded from the study that LSER is an excellent approach to the selection of internal standard compounds for RPLC under either isocratic or gradient elution. The average prediction error is usually within 10%, but no more than 20%. Finally, LSER approach is fast and systematic, and will save a significant amount of time and resources during RPLC method development.     

Retention of ionizable compounds on HPLC. Modelling retention for neutral and ionizable compounds by linear solvation energy relationships

Summary A global LSER model that relates HPLC retention to mobile phase composition and pH is tested for a varied group of solutes, both neutral and ionizable, in a polymeric column and methanol-water mobile phases. It is compared to the local LSER model developed only for a given mobile phase, i.e., a fixed organic modifier content, and to the global LSER model set only for neutral solutes. The global LSER model for neutral and ionizable solutes requires a few supplementary parameters over the other models tested, but it accounts for retention under any experimental conditions for a given column and methanol-water mobile phases, describing properly the interactions established in the HPLC system (hydrophobicity, hydrogen-bond acidity and basicity, dipolarity/polarizability…). This paper is number 13 of a series with the same general title: “Retention of Ionizable Compounds on HPLC” published in various journals.     

Characterization of a novel pyridinium bromide surface confined ionic liquid stationary phase for high-performance liquid chromatography under normal phase conditions via linear solvation energy relationships

Utilizing linear solvation free energy relationship methodology, a novel pyridinium bromide surface confined ionic liquid (SCIL) stationary phase was characterized under normal phase high-performance liquid chromatographic conditions. A limited set of neutral aromatic probe solutes were utilized to rapidly assess the utility of the LSER model, using mobile phases of hexane modified with 2-propanol. The excellent correlation of the global fit across the mobile phase composition range used in this study for the experimental and calculated retention values (R(2)=0.994) indicates that the LSER model is an appropriate model of characterizing this polar bonded phase under normal phase conditions. For a limited subset of compounds, retention on the pyridinium bromide SCIL stationary phase is more highly correlated with that obtained on a cyano column than on a diol column under NP conditions.     

Characterization of stationary phases based on monosubstituted benzene retention indices using correspondence factor analysis and linear solvation energy relationships in RPLC

In reversed-phase liquid chromatography (RPLC), the comparison of experimental results obtained from different columns is a complex problem. A correspondence factor analysis (CFA) and a linear solvation energy relationship (LSER) were applied on retention data to characterize second-order intermolecular interactions responsible for retention on a set of RPLC columns. Seven octadecyl-C₁₈ columns with different packing materials are obtained from different manufacturers and one octyl-C₈ column. The retention data were determined under isocratic conditions using a methanol–water (65:35, v/v) mobile phase. The chromatographic retention indices based on alkan-2-ones and alkyl aryl ketones retention index scales are calculated using a multiparametric least-squares regressions iterative method. The CFA and LSER results permitted to highlight that the retention indices were appropriate for studying the second-order retention mechanisms on the eight chromatographic systems investigated and exhibited the best reproducibility. Although many earlier studies have reported the use of chemometric methods to characterize chemical factors affecting retention in RPLC using retention factors as retention parameters, this is the first study based on retention indices.     

Evaluation of the retention dependence on the physicochemical properties of solutes in reversed-phase liquid chromatographic linear gradient elution based on linear solvation energy relationships

This paper describes the results of the evaluation of retention dependence on the physicochemical properties of solutes in linear gradient elution by reversed-phase liquid chromatography (RPLC) based on linear solvation energy relationships (LSERs). Retention time data on Inertsil ODS(3) column by linear gradient elution were collected for both acetonitrile-water and methanol-water binary mobile phases under various gradient steepness. Based on the LSERs, the retention times were linearly correlated with the physicochemical properties (size, dipolarity, and hydrogen bond donor-acceptor acidity and basicity) of solutes. As predicted by LSERs, very acceptable linear relationships are observed for both mobile phases. While the magnitudes of the coefficients are modified by the gradient steepness, their signs are consistent with those obtained by isocratic elution. As obtained for isocratic elution, the dominant factors to retention in linear gradient elution of RPLC are the solutes' size and hydrogen bond acceptor basicity. The conclusions of the study allow us to predict retention in chromatographic method development by gradient elution.     

Effect of Ionic Liquid on Retention of Solutes on C_(18) Column Based on Linear Solvation Energy Relationships

Several chromatography systems with ionic liquids and a mixture of water with the modifier as mobile phase were characterized via the linear solvation energy relationships(LSER) model. The effects of the ionic liquids and modifier(methanol) concentrations on the retention of 10 solutes(caffeine,pyridine,aniline,phenol,methylparaben,acetopenone,m-cresol,p-cresol,o-cresol,and benzene) were discussed. The LSER model demonstrated high potential to predict retention factors with high squared correlation coeffici...     

Influence of column characteristics on retention and selectivity in RP-HPLC

Summary Eight commercially available reversed-phase (RP) columns of widely different characteristics were evaluated and compared using the linear solvation energy relationships (LSER). Retention factors of 32 solutes of different types were determined under isocratic conditions using an acetonitrile-water (30∶70) mobile phase. Stationary phase properties were compared by the fitting coefficients of the LSER-based regression equations which are characteristic of the individual stationary phases and represent the extent of various molecular interactions contributing to the retention process. The good agreement between the calculated and measured logk values for different type of compounds support the adequacy and applicability of the LSER model to describe chromatographic retention. Characterization of column performance for the separation of various type of compounds was established by the determination of the different selectivity factors representing hydrophobic selectivity, polar selectivity and specific selectivity.     

线性溶剂-能量关系模型法评价纤维素三(3,5-二甲基苯基氨基中酸酯)涂敷手性固定相的作用力及其对手性拆分的影响

利用线性溶剂-能量关系模型(LSER)对分别以氨丙基硅胶(APS)和硅胶(SiO2)为基质的两种纤维素三(3,5-二甲基苯基氨基甲酸酯)(CDMPC)手性固定相(CSP)存在的作用力进行研究.利用33种分析物的LSER描述符号及分析物在固定相上的保留时间进行多元线性回归,通过对回归所得到的系统参数的分析来评价固定相存在的作用力.分析表明:两种固定相在正相条件下存在较弱的π-π作用力,较强的偶极-偶极作用力.而氢键作用力的大小受到基质的影响,以APS为基质的固定相给电子能力较强;而以SiO2为基质的固定相给质子能力较强.     

Applicability of mass spectrometry to detect coeluting impurities in high-performance liquid chromatography

This paper describes the results of selectivity optimization and internal standard prediction for the quantitation of estradiol and levonorgestrel in transdermal patches by reversed-phase liquid chromatography (RPLC) based on the linear solvation energy relationships (LSERs). The patch samples are prepared by swelling with acetonitrile (ACN) and the separation is performed by Zorbax Eclipse XDB ODS columns. A proper retention range is first determined with a binary mobile phase of ACN and water based on the general resolution equation. The interference to estradiol from a levonorgestrel impurity is then eliminated by a ternary mobile phase of acetonitrile-methanol-water with a composition predicted by LSERs. When the resolution is optimized and the "open window" in the chromatogram for an internal standard is selected, LSERs are used to predict the candidate compounds to be evaluated as the internal standard. The approach described in this study can be used, in general, to considerably improve the efficiency of RPLC method development, particularly for neutral samples. Finally, the LSER approach for the selectivity optimization is compared with a statistical response surface methodology (RSM) based on a central composite design (CCD) in terms of the effectiveness and number of experiments. It is concluded that, although the predicted mobile phase composition to achieve the desired selectivity is about the same, the LSER approach is more efficient and fewer experiments are required.     

两种带有不同间隔臂的环糊精键合固定相保留行为的评价

选取14种模型化合物对两种带有不同间隔臂的环糊精键合固定相(Click Alkyl-CD、Click OEG-CD)进行了反相液相色谱模式下的保留行为评价。通过梯度洗脱条件下保留参数计算方法和CSASS软件,根据3次线性梯度的保留值数据,测出14种溶质分子在两种固定相上的保留参数,在此基础上考察流动相含乙腈浓度与保留因子的关系后发现,Click Alkyl-CD和Click OEG-CD在分离非极性和中等极性化合物时主要基于反相液相色谱模式,而某些化合物(如吲唑)在Click OEG-CD上的保留受多种作用力影响,并不基于反相液相色谱模式。疏水性评价结果表明,反相分离模式下Click Alkyl-CD的保留参数和正辛醇-水分配常数的相关性较好(R=0.7),说明其具有比较强的疏水性;而Click OEG-CD的相关性不高(R＜0.3),说明疏水作用力以外的其他作用力对化合物在反相模式下的保留影响较大。