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.     

A novel method for the calibration of Kováts retention indices using n-alkanes with a thermionic nitrogen-phosphorus specific detector

This paper describes a novel method for the detection of compounds that do not contain nitrogen or phosphorus by a thermionic nitrogen-phosphorus specific detector (NPD), which normally detects only nitrogen- or phosphorus-containing compounds. This method allows for the calibration of gas chromatographic columns with NPD detectors using n-alkanes instead of nitrogen-containing drug mixtures. This results in a more rapid and accurate calibration for the calculation of relative retention indices (RRI), such as Kováts indices, than was previously possible when employing an NPD detector. The proposed method describes the temporary conversion of the NPD detector into a detector with properties much like a flame ionization detector. After a deliberate increase in the hydrogen gas flow rate to the thermionic bead from 4 ml/min to 8 ml/min, the n-alkanes (containing no nitrogen) can be detected and used as RRI calibrators. Once the column has been calibrated, the hydrogen gas flow rate is lowered to the normal rate of 4 ml/min. The detector then behaves as a normal NPD, no longer detecting the n-alkanes.     

Identification of the constituents of a complex mixture by combined use of retention indices and specific multidetection responses

The ratio of the responses of two different specific detectors to a single compound has, when used in conjunction with the compound's retention index, been investigated as an identification criterion for the compound. The ECD:NPD and ECD:FPD response ratios have been used for the identification of some pesticides. Analyses were performed with a single column – dual parallel detection – personal computer system. The reliability of the detector response ratio (DRR) was demonstrated by the consistency of detector response with time, and the influence of the quantity of analyte and of the chromatographic operating conditions. These factors were selected in the expectation that the technique could be used for routine trace analysis.     

Instrumental method for automated on-line fraction analysis and peak deconvolution in multicomponent-overloaded high-performance liquid chromatography

A bi-dimensional (non-orthogonal) chromatographic system made of two columns of different length (longer along the first direction and shorter on the second) but packed with identical (or similar) materials has been employed to perform automated on-line fraction analysis and peak deconvolution of multicomponent overloaded band profiles. Multicomponent overloaded peaks, eluted from the first column, are sampled through a remotely-controlled switching valve and fractions are injected, under analytical conditions, directly into the second direction. This set-up serves a twofold purpose. First of all, it has been possible to use linear calibration curves for detector calibration (DC). Secondly, since single component peaks were resolved on the second direction, individual concentration profiles have been obtained beneath the envelop of overlapping bands. All the information necessary to operate the bi-dimensional system can be achieved by analyzing the chromatographic behavior of the mixture on the shorter column under linear conditions. Therefore, solutions of unknown concentration can be prepared and their composition reconstructed with a simple chromatographic run. Two- and three-component overloaded mixtures have been employed to validate the system.     

催化柴油中氮化物分布的气相色谱-原子发射光谱分析方法的研究

建立了催化柴油馏分中各种氮化物类型分布的气相色谱-原子发射光谱(GC-AED)分析方法,考察了色谱条件和不同的试剂气压力对各种氮化物分离和检测灵敏度的影响,定性(或归类)了某典型催化柴油中的73个氮化物,计算了程升条件下各种氮化物的保留指数,为不同实验室的定性比较提供了依据。以峰面积对质量浓度作图,氮化物在2.0~600 mg/L浓度范围内,AED检测器对不同氮化物有良好的线性响应,线性相关系数达0.998。几种氮化物(吲哚、1-甲基吲哚、C2-吲哚、咔唑、1-甲基咔唑、1,8-二甲基咔唑)峰面积的相对标     

Gas chromatographic separation of substituted pyridines

Capillary gas chromatographic methodology for separation of complex mixtures of substituted pyridines has been demonstrated on polar (CAM) and non-polar (DB-5) columns. Separations are characterized by high resolution, high sensitivity, a wide dynamic detector range, and good reproducibility. For the first time, Kováts retention indices have been calculated for pyridine and substituted pyridines. Correlations of retention indices with physico-chemical properties, such as hydrogen bonding, pyridine pKa and Hammett substituent constants are discussed.     

Analysis of Mixtures Containing Unknown Components by Gas Chromatography: Determination of Molecular Mass

New methods are proposed for the gas-chromatographic determination of the molecular masses of unknown components in complex mixtures within one cycle of analysis. The methods are based on the use of complex chromatographic data in the form of linear retention indices of compounds for a column with a nonpolar stationary phase and sensitivity indices of a thermal conductivity detector and a flame ionization detector.     

Development of a database of gas chromatographic retention properties of organic compounds

A comprehensive database of gas chromatographic retention properties of chemical compounds has been developed using multiple literature sources. The National Institute of Standards and Technology (NIST) database of retention data for non-polar and polar stationary phases currently contains 292,924 data records for 42,888 compounds. The database includes data for Kováts indices, linear indices, Lee indices, retention times and retention volumes. The first release of this database for non-polar stationary phases is available with NIST/US Environmental Protection Agency (EPA)/National Institutes of Health (NIH) Mass Spectral Database (June 2005) and through the internet (NIST Chemistry WebBook). The paper describes the database and the process by which it has been compiled. The format of data presentation and the quality control procedures are described. Data sources of gas chromatographic retention data are also discussed.     

Simultaneous parameter compensation in the replication of programmed temperature gas chromatographic retention measurements

Tables of relative retention times, retention indices or emergence temperatures obtained under one set of chromatographic conditions can be used for the tentative identification of unknowns determined under an entirely different set of conditions. This can be accomplished for a particular liquid phase if the emergence temperature of a reference compound is maintained while one or more chromatographic parameters are changed to compensate for the changes in other parameters. The advantage of using proximal standards for the determination of both relative retention times and emergence temperatures is demonstrated in this report.     

Alkylphenol retention indices

A novel type of retention indices for alkylphenols and related compounds are proposed. The alkylphenol retention indices (APRI) use para-substituted n-alkylphenols as reference series. APRI for para-n-alkylphenols are per definition equal to the number of carbon atoms in the alkyl substituent; the value for phenol is zero. Application of the APRI system with different types of derivatisation of the phenolic hydroxy group showed that the derivatisation has limited influence on these indices. Especially para-substituted alkylphenols gave APRI values that could be transferred with high accuracy from one type of derivative to another. By comparing results obtained with different gradients in temperature-programmed GC, it was also shown that APRI is less affected by chromatographic conditions than retention indices based on n-alkanes.     

Prediction of gas chromatographic retention indices of polychlorinated dibenzothiophenes on non-polar columns

Polychlorodibenzothiophenes (PCDTs) have been found in several kinds of environmental samples. The lack of reference compounds has meant that very little is known about their gas chromatographic behavior. Here we discuss the retention of 19 authentic PCDTs and their sulfones on the widely used gas chromatographic stationary phases DB-5 and DB-5ms. The retention order is different from that of the polychlorodibenzofurans. The data generated allowed us to carry out a multiple linear regression to generate parameters for predicting the retention indices of unknown congeners based only on their structural features.     

饱和醇结构-保留定量相关的人工神经网络模型

以拓扑指数为结构描述符，用基于Levenberg-Marquardt优化的BP神经网络建立了醇类化合物的结构与色谱保留值的相关性模型，用于未知醇类化合物在SE－30和OV－3两根色谱柱上保留指数的同时预测，其学习速率优于文献中普通BP神经网络法，预测准确度与普通BP神经网络法接近，但优于多元线性回归法，因而是一种较好的预测有机化合物气相色谱保留指数的方法。     

γ-干扰素在反相高效液相色谱柱上色谱行为与分离的研究

用高效液相色谱法对基因工程下游包涵体所含目标蛋白进行分离纯化,较系统地研究了γ－干扰素在反相柱上的色谱行为及其影响因素。结果表明,复性后γ－干扰素伴有错配聚合体产生,其保留行为及洗脱谱图随构象不同而改变。分离系统的疏水性和粘度是影响γ－干扰素在固定相与流动相间传质扩散的重要因素。     

Molecular parameters and retention characteristics of unsubstituted polyaromatic hydrocarbons in HPLC

Summary The present research studies the possibility of using the correlation dependence between molecular parameters of unsubstituted polyaromatic hydrocarbons (PAH) and their retention in reversed-phase liquid chromatography to optimize the conditions for the separation and identification of unknown peaks on the chromatograms of multicomponent mixtures. A linear correlation equation, that takes the number and environment of the carbon atom in the PAH molecule into account as well as the differences in the specific interactions of isomeric molecules with polar eluent, has been proposed. The adequacy of the proposed PAH retention model was verified by comparing the calculated retention values with the experimental data. The possibility of identifying unsubstituted PAH according to the number of carbon atoms of various types and according to the values of the molecules lengths (calculated on the basis of the retention of these substances under different eluent compositions) was exemplified by various chromatographic systems (reversed phase-eluent-PAH molecules).     

Retention indices as identification tool in pyrolysis-capillary gas chromatography

Pyrolysis-capillary gas chromatography (Py-cGC) represents important method to identify the analytes in the mixture after thermal degradation. This combines high effective analyte separation on-line coupled with thermal degradation process that depends on analyte structure. System of retention indices has been used for identification of the analytes after on-line pyrolysis and chromatographic separation. The pyrolysate composition has been studied during thermal degradation of polymethylmethacrylate (PMMA) at different pyrolysis temperatures and chromatographic column conditions. Homologues series of n-alkanes have been used for calculation of pyrolysate Kováts retention indices (I) and compared with mass spectrometric (MS) data of pyrolysate model mixture. To identify PMMA thermal degradation products the high density polyethylene (HDPE) as additive standard producing triplets of the olefin homologous series during co-pyrolysis has been used. These homologous series enable to calculate programmed temperature retention indices (ITPGC) to identify the analytes present in the pyrolysate. Calculated I values were compared with published I values databases to identify analytes yielded at different pyrolysis temperatures.     

模拟移动床色谱法拆分甲霜灵对映体

模拟移动床(SMB)色谱作为一种精确、高效的制备色谱技术引起研究者的极大关注。本文以EnantioPak OD填料为手性固定相,正己烷-乙醇(70 : 30, v/v)为流动相,在四区模拟移动床上手性拆分甲霜灵外消旋体。采用旋光检测器研究甲霜灵异构体在手性柱上的洗脱顺序;探讨进样浓度、进样流速、各区流速和切换时间等条件对手性分离甲霜灵外消旋体的影响,并与制备色谱进行比较。结果表明:S-(+)-甲霜灵先于R-(-)-甲霜灵被流动相洗脱,R-(-)-甲霜灵在色谱柱上的保留强于S-(+)-甲霜灵;在线性和非线性条件下,模拟移动床都能很好地拆分甲霜灵外消旋体,在优化SMB工艺条件下,S-(+)-甲霜灵和R-(-)-甲霜灵的光学纯度都大于99%;在样品质量浓度为15 mg/mL的条件下,模拟移动床色谱分离的样品量显著高于制备色谱,而流动相消耗仅为后者的1/9。这对于发展大规模色谱拆分甲霜灵工艺具有良好的指导意义。     

脂肪醇气相色谱保留指数与结构的相关性研究

在分子图的邻接矩阵基础上,构建了一个化合物均价连接性指数mL,mL=∑(Ai·Aj·Ak…)-0.5,其中一阶指数1L及定位基参数β与25种脂肪醇在6种固定相(SE-30,OV-3,OV-7,OV-11,OV-17和OV-25)上的气相色谱保留指数I显著相关,相关系数均大于0.98。所建定量结 构-保留关系(QSRR)模型具有良好的稳定性和预测能力,较好地揭示了脂肪醇在不同固定相上气相色谱保留指数的变化规律。     

High-performance liquid chromatographic separation of dihydropyrimidine racemates on polysaccharide-derived chiral stationary phases

The chromatographic behavior of a set of racemic dihydropyrimidines (DHPMs) has been evaluated on two polysaccharide-derived chiral stationary phases under normal phase conditions. One of these is coated, the other chemically immobilized. The outstanding solvent compatibility of the immobilized chiral stationary phase (CSP) permits the use of solvents such as ethyl acetate (EtOAc) that are unsuitable for coated supports, for which traditional 2-propanol:hexanes mixtures have been employed. Drastic changes in the chromatographic retention and resolution of DHPMs and, in general, in the separation performances have been observed for the two systems. From a practical point of view, EtOAc has been proven to be a better choice for the separation of this important class of compounds. By comparing molecules different in specific positions of their scaffolds, hypotheses concerning the role of individual chemical groups on retention and selectivity have been done. These effects have been quantified, in some cases, in terms of standard Gibbs energy variations. Even if no chromatographic measurements have been made under nonlinear conditions, clear indications of the potential use of immobilized chiral adsorptive media operated with EtOAc:hexanes mixtures for preparative separations of DHPMs have been evidenced.     

Analysis of triacylglycerols on porous graphitic carbon by high temperature liquid chromatography

The retention behaviour of several triacylglycerols (TAGs) and fats on Hypercarb, a porous graphitic carbon column (PGC), was investigated in liquid chromatography (LC) under isocratic elution mode with an evaporative light scattering detector (ELSD). Mixtures of chloroform/isopropanol were selected as mobile phase for a suitable retention time to study the influence of temperature. The retention was different between PGC and non-aqueous reversed phase liquid chromatography (NARP-LC) on octadecyl phase. The retention of TAGs was investigated in the interval 30-70 degrees C. Retention was greatly affected by temperature: it decreases as the column temperature increases. Selectivity of TAGs was also slightly influenced by the temperature. Moreover, this chromatographic method is compatible with a mass spectrometer (MS) detector by using atmospheric pressure chemical ionisation (APCI): same fingerprints of cocoa butter and shea butter were obtained with LC-ELSD and LC-APCI-MS. These preliminary results showed that the PGC column could be suitable to separate quickly triacylglycerols in high temperature conditions coupled with ELSD or MS detector.     

大豆异黄酮指纹图谱中保留时间漂移的校正研究

选取5个极性不同的化合物作为标准样品,在不同仪器及不同色谱柱上采用已建立的大豆异黄酮高效液相色谱(HPLC)指纹图谱条件进行测定,以它们在不同色谱仪(或柱)上的保留时间进行线性回归,并用得到的线性方程对相同条件下测得的大豆异黄酮指纹谱中峰面积为总峰面积1.5%以上的色谱峰的保留时间进行校正,通过校正使保留时间的最大绝对误差由5.868 min减小为0.854 min。采用该方法可以校正相同色谱条件但不同实验室间指纹图谱保留时间的漂移,提高HPLC指纹图谱的重现性。