Unified retention index of hydrocarbons separated on dimethylsilicone OV-101

Summary Gas chromatographic retention indices of 51 hydrocarbons were determined on OV-101 dimethylsilicone between 40 and 70°C. From the measured data the unified retention indices were calculated.     

手性有机酸薄层色谱保留指数的拓扑模型

基于Kier的分子连接性指数及邻接矩阵提出新型分子连接性指数（^mG_t^v）;引入手性指数（w_j）并建立了手性连接性指数（^mG_t^v）：^mG_t^v=^mG_t^v×w_j。^mG_t^v适用于手性分子、非手性分子及内消旋异构体的结构差异表征。用多元统计回归研究18种手性羟酸和氨基酸的薄层色谱保留指数（R_M）与^mG_t^v的定量构效关系,经最佳变量子集回归建立其四元数学模型,传统的判定系数（R²）为0.973,逐一剔除法（leave-one-out,LOO）的交互验证系数（Q²）为0.950,结果证明具有良好的稳健性及预测能力。根据进入该模型的4个手性连接性指数（⁰C_p^v、²C_p^v、C_ch^v、⁵C_p^v）可知,影响手性有机酸保留指数的主要因素是分子的二维结构特征和分子的手性特征以及柔韧性、折叠程度等三维结构因素。从上可见,新建手性连接性指数对手性有机酸的保留指数表征具有合理性与有效性,为预测手性有机酸的保留指数提供了一种有效方法。     

Unified retention indices of hydrocarbons on BP-1 dimethylsiloxane stationary phase

Summary Gas chromatographic retention indices for 23 hydrocarbons were determined on BP-1 dimethylsiloxane between 45 and 65°C. From the data measured unified retention indices were calculated. These values agree well with the corresponding experimental values. The values of unified retention indices obtained on BP-1 are compared with those determined on OV-101 and on squalane. The differences between the unified and the experimental retention indices on BP-1, OV-101 and squalane columns are shown.     

Effect of pressure on retention factors in HPLC using a non-porous stationary phase

Summary Pressure and temperature have significant influence on retention in HPLC. This study investigates the effect of pressure and temperature on the retention behavior of aromatic hydrocarbons (toluene, ethyl benzene, butyl benzene, pentyl benzene) and polar, acidic and basic samples (phenol, acetophenone, N,N-dimethyl aniline, benzophenone) on a reversed phase column. The effect has been studied on non-porous, tetradecyl (C₁₄) coated silica particles. We found that the adsorption-induced decrease of the partial molar volume of the solutes investigated was between ΔV _m =5–15 cm³ mol⁻¹. The increment of the decrease of the partial molar volume due to the addition of one CH₂ group, for the homologous series of the aromatic hydrocarbons is approximately ΔV _CH2 =2.3 cm³mol⁻¹. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001.     

Implicit characteristic parameter of a programmed temperature retention index database

In a programmed temperature retention index (PTRI) database, there exists a characteristic parameter rt0/β that can be calculated if the experimental parameters are clearly given. This characteristic parameter can be used to flexibly reproduce the original PTRI data under chromatographic conditions different from those originally given. As this characteristic parameter is not explicitly given, it is suggested to name this parameter as the implicit characteristic parameter (TCP) of a PTRI database. The ICP in White's PTRI database was easily found and used satisfactorily to reproduce PTRI of some test compounds using either a Hewlett-Packard ultra-performance OV-1 column or a self-coated OV-1 column. The reproduction of PTRI could not be realized on columns of different materials. The fact that several PTRI databases measured on glass capillary columns could not satisfactorily be reproduced on fused silica column is explained.     

Discrimination between linear and non-linear models describing retention data of alkylbenzenes in gas-chromatography

Summary Detailed statistical analysis is presented to describe the retention indices of alkylbenzenes as a function of their physical (boiling point, modrefraction) and topological (connectivity and complexity indices) properties. With the help of several statistical characteristics (examination of residuals, F test, partial F test, termination criteria, correlation indices) a discrimination is made among different models. A nonlinear equation was chosen which describes the retention data on slightly polar phases with the practically attainable precision. A comparison with literature sources shows that this equation provides the smallest residual error and, hence, it can be applied for prediction purposes. A correlation was found between the preexponential factor in the simple exponential model and the polarity of stationary phases on the Tarján scale.     

Empirical correlation equations describing retention data of hydrocarbons on dinonylphatalate and polyethyleneglycol 4000

Summary Relative retention data and Kováts retention indices were measured for several hydrocarbons (mainly for alkylbenzenes) on dinonylphtalate and polyethylenelycol 4000 stationary phase. Correlations were searched between these retention data and the following physical (boiling point, molrefraction, molvolume) and topological (connectiviity index and general index of molecular complexity) properties of solutes. The best fitting equations was choosen among more than 150 equations involving linear, quadratic, exponential, two variables linear and quadratic dependence of retention data and the properties mentioned as well as their inverses.     

Identification of FAMEs using ECL values and a three-dimensional Kováts retention index system

n-Alkanes and fatty acid methyl esters have been chromatographed on four capillary columns of different polarity (LM-1 (100% polydimethylsiloxane), CB-225 (25% cyanopropyl, 25% phenyl polysiloxane), LM-100 (immobilized polyethylene glycol), and BPX-70 (70% cyanopropyl polysiloxane)) with the goal of identifying the major fatty acid methyl esters obtained by derivatization of vegetable oils. Chromatographic retention data were employed for the construction of a three-dimensional Kováts retention index system and for the elaboration of a table of equivalent chain length values.     

QSPR study on GC relative retention time of organic pesticides on different chromatographic columns

In the present study, Lu index and distance-based atom type topological index (DAI) previously developed in our team, were introduced and combined with molecular electronegativity chi ep to characterize quantitative structure-property relationship of GC relative retention time (RRT) for several types of structurally diverse organic pesticides on the four kinds of chromatographic columns. Using multiple linear regression technique, four several-variable models are obtained with the estimations correlation coefficient (R(2)) being between 0.9655 and 0.9285, and the correlation coefficient (R(2)cv) in the leave-one-out cross-validation procedure are between 0.9560 and 0.9143, respectively. The results in this study indicate that the three topological indices Lu index, DAI, and molecular electronegativity chi ep can predict the gas chromatographic RRT of organic pesticides with diverse hetero-atoms.     

Identification of Dinocap in water using GC/IR and GC/MS

The determination of Dinocap, one of the most often used acaricides and contact fungicides, is complicated by the fact that it consists of several isomeric alkyldinitro-phenyl-crotonates. In a first step, GC/IR and GC/MS has been used to separate the mixture, to determine the chromatographic behaviour and to fully characterize the six different isomeric compounds. The structures of additional impurities in the commerical preparation were shown to be the correlating phenols. An extraction/preconcentration method has been devised based on Carbopack B, yielding recoveries between 75 and 98%. A qualified estimation of the total Dinocap content of drinking water can be made by this approach for concentrations well below the limits set by the European drinking water regulations. The development of a complete analytical procedure based on these results appears to be feasible.Dedicated to Professor Dr. Dr. h.c. mult J. F. K. Huber on the occasion of his 70th birthday     

应用人工神经网络预测多氯代二苯骈呋喃的色谱保留指数

以量子化学方法在密度泛函B3LYP/6-31G(d)水平上计算得到了多氯代二苯骈呋喃系列化合物(PCDF)分子的结构参数:最高占据轨道能(EHOMO)、最低空轨道能(ELUMO)、最正原子净电荷(q+)、最负原子净电荷(q-)、分子偶极矩(μ)、极化率(α)、分子平均体积(Vm)、恒容热容(C■V).采用误差反向传播(BP)算法的人工神经网络,建立了EHOMO、ELUMO、q+、q-、μ、α、Vm、C■V与PCDF色谱保留指数之间关系的模型,检测样本的预报值与实验值相对误差范围为-1.66%².39%,平均相对误差为0.31%,达到了很好的预测效果.     

Utilization of Rohrschneider's concept and Tekler equation in linear temperature programmed GC. Precalculation of retention data

Summary An extension of Rohrschneider's concept to the field of the linear temperature programmed gas liquid chromatography, is proposed, which is based on Antoine's equation for the temperature dependence of the reduction index of Takács et al. and Tekler. The new method presented in this paper, applied to retention data of two stationary phases of low polarity, PS-255 and OV-105, gives a new possibility of precalculating retention data.     

Determination of thermodynamic characteristics from retention data in GC

Summary Retention data have been measured for model substances of different polarities under isothermal conditions at several temperatures using capillary columns coated with Carbowax-20M and SP-2100 stationary phases. By using the k capacity ratios obtained for various temperatures the thermodynamic characteristics of the partition process were determined. For homologous series linear relationships can be established between thermodynamic characteristics and carbon number. Thermodynamic characteristics can be used both to compare and evaluate column quality and to predict retention indices for different temperatures and linear programmed temperature conditions.Dedicated to Professor J. F. K. Huber on the occasion of his 60th birthday.     

iMatch: a retention index tool for analysis of gas chromatography-mass spectrometry data

A method was developed to employ National Institute of Standards and Technology (NIST) 2008 retention index database information for molecular retention matching via constructing a set of empirical distribution functions (DFs) of the absolute retention index deviation to its mean value. The effects of different experimental parameters on the molecules' retention indices were first assessed. The column class, the column type, and the data type have significant effects on the retention index values acquired on capillary columns. However, the normal alkane retention index (I(norm)) with the ramp condition is similar to the linear retention index (I(T)), while the I(norm) with the isothermal condition is similar to the Kováts retention index (I). As for the I(norm) with the complex condition, these data should be treated as an additional group, because the mean I(norm) value of the polar column is significantly different from the I(T). Based on this analysis, nine DFs were generated from the grouped retention index data. The DF information was further implemented into a software program called iMatch. The performance of iMatch was evaluated using experimental data of a mixture of standards and metabolite extract of rat plasma with spiked-in standards. About 19% of the molecules identified by ChromaTOF were filtered out by iMatch from the identification list of electron ionization (EI) mass spectral matching, while all of the spiked-in standards were preserved. The analysis results demonstrate that using the retention index values, via constructing a set of DFs, can improve the spectral matching-based identifications by reducing a significant portion of false-positives.     

Prediction of the chromatographic retention of saturated alcohols on stationary phases of different polarity applying the novel semi-empirical topological index

The novel semi-empirical topological index (I_ET), previously developed by Heinzen and Yunes, was extended to predict the chromatographic retention of saturated alcohols on low polarity stationary phases (OV-1). The predictive ability of I_ET was also verified on stationary phases of different polarity (SE-30, OV-3, OV-7, OV-11, OV-17 and OV-25). Simple linear regressions between the retention indices and the semi-empirical topological index (RI=a+bI_ET) were established for each stationary phase separately, showing good statistical parameters. Statistical analysis showed that the QSRR model used on stationary phases of low polarity (OV-1) has high internal stability and good predictive ability for external groups. The polarity of the SE-30, OV-3, OV-7, OV-11, OV-17 and OV-25 stationary phases, indicated by retention polarity (P_R) given by Tarján et al., is reflected in the ‘a’ (intercept) and ‘b’ (slope) coefficients of the equations obtained for each of these phases. The linear relationship between the ‘a’ coefficient and P_R showed satisfactory statistical quality. Thus, it was possible to generate a single combined model of QSRR, including a parameter that represents the property of the stationary phase P_R. The combined model also has a satisfactory predictive quality, as shown by the plot of calculated versus experimental retention indices for saturated alcohols on six stationary phases of different polarity (r²=0.9956; S.D.=9.54).     

The role of electric interaction in the retention index cencept. Universal interaction indices for GLC,HPLC and TLC

Summary New electric interaction indices are proposed which can universally be used in GLC, HPLC and TLC. These indices can easily be calculated from a variety of the commonly used retention parameters, such as Kováts' retention indices, relative retention times, capacity factors, or R_F values, and the average molecular polarizabilities of the reference compounds. Calculation examples for polycyclic aromatic hydrocarbons and n-alkanes are given. Application of the electric interaction indices for studying the retention mechanism is demonstrated.     

A method of calculating the second dimension retention index in comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

A method was developed to calculate the second dimension retention index of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC/TOF-MS) data using n-alkanes as reference compounds. The retention times of the C(7)-C(31) alkanes acquired during 24 isothermal experiments cover the 0-6s retention time area in the second dimension retention time space, which makes it possible to calculate the retention indices of target compounds from the corresponding retention time values without the extension of the retention space of the reference compounds. An empirical function was proposed to show the relationship among the second dimension retention time, the temperature of the second dimension column, and the carbon number of the n-alkanes. The proposed function is able to extend the second dimension retention time beyond the reference n-alkanes by increasing the carbon number. The extension of carbon numbers in reference n-alkanes up to two more carbon atoms introduces <10 retention index units (iu) of deviation. The effectiveness of using the proposed method was demonstrated by analyzing a mixture of compound standards in temperature programmed experiments using 6 different initial column temperatures. The standard deviation of the calculated retention index values of the compound standards fluctuated from 1 to 12 iu with a mean standard deviation of 5 iu.