Definitions and methods of calculation of the temperature-programmed retention index, ITP: II. Comparison of ITP values calculated according to different definitions

Temperature-programmed retention indices, I_TP, calculated according to three different definitions are compared. The advantages and shortcomings of these definitions are discussed in terms of their theoretical background, accuracy, ease of calculation and applicability. The Generalized Retention Index (GI) seems to be the best definition of I_TP, while Van den Dool's definition and the Extended Kováts Definition are approximate and can be applied only to simple temperature programme.     

Relationship between the average molecular polarizabilities of polycyclic aromatic hydrocarbons and their retention indices determined on various stationary phases

The Kováts retention indices of 10 polycyclic aromatic hydrocarbons were determined on SE-30, OV-101, SE-52, OV-7 and OV-17 stationary phases. A significant correlation has been found between the retention indices and the average molecular polarizabilities of the analyzed substances. Equations were derived for the direct determination of the average molecular polarizabilities from the retention index values. The influence of the temperature on this relationship is also indicated.     

Use of Local Lagrange Interpolation for calculation of retention indices in linear temperature-programmed gas chromatrography

Summary The influence of the isothermal temperature, program rate, initial temperature and flow rate on retention indices was studied. The methods of Kováts, Van Den Dool and Local Lagrange Interpolation are compared. Ten experimental measurements were carried out on a capillary column coated with OV-101 stationary phase.     

Factors affecting the reproducibility and reliability of retention simulation in any form of temperature programmed capillary GC

Conversion of Kováts retention indices on a given stationary phase into the thermodynamic parameters of compounds on a given column leads to a simplified method for retention simulation in isothermal, linear, and multi-ramp temperature programmed capillary gas chromatography. The influence of numerical methods used in the computation, the temperature coefficient of Kováts indices, and the experimental factors such as isothermal temperatures selected in the measurement of n-alkanes, column characterization and sample overloading, on the reproducibility and accuracy of simulation were discussed and examined. When the column used is properly characterized, the error between the simulated values and the experimental data is within ± 0.5 index unit or less than ± 1% of retention time.     

On the Relationship Between Kováts and Lee Retention Indices

A relationship between the Kováts and Lee retention indices was obtained for dimethylsilicone stationary phase and isothermal conditions. The temperature dependence of the retention indices was taken into account. Based on numerous experimental data for dimethylsilicone stationary phase, parameters of the linear temperature dependence of the Kováts indices were determined for the reference compounds of the Lee scale.     

Temperature programmed retention indices: Calculation from isothermal data. Part 1: Theory

Direct conversion of isothermal to temperature programmed indices is not possible. In this work it is shown that linear temperature programmed retention indices can only be calculated from isothermal retention data if the temperature dependence of both the distribution coefficients and the column dead time are taken into account. Procedures are described which allow calculation of retention temperatures and from these, accurate programmed retention indices. Within certain limits the initial oven temperature and programming rate can be chosen freely. The prerequisite for this calculation is the availability of reliable isothermal retention data (retention times, retention factors, relative retention times, or retention indices) at two different temperatures for one column. The use of compiled isothermal retention indices at two different temperatures for the calculation of retention temperatures and thus temperature programmed indices is demonstrated. For the column for which programmed retention indices have to be determined, the isothermal retention times of the n-alkanes and the column dead time as a function of temperature have to be known in addition to the compiled data for a given stationary phase. Once the programmed retention indices have been calculated for a given column the concept allows the calculation of temperature programmed indices for columns with different specifications. The characteristics which can be varied are: column length, column inner diameter, phase-ratio, initial oven temperature, and programming rate.     

Gas chromatographic — Mass spectrometric identification of alkylcyclohexanes and cyclohexenes

Summary A series of 34 alkylcyclohexane hydrocarbons structurally related top-menthane, including all saturated, monoolefinic and aromatic structural precursors from cyclohexane, have been characterized by GC and MS. Kováts retention indices have been determined on five stationary phases (squalane, SE-30, Apiezon L, OV-225, PEG 20M) and the corresponding polarity, temperature and structural increments have been calculated. From the information acquired 10 alicyclic hydrocarbons have been identified for the first time in a pyrolysis naphtha.     

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.     

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 numerical interpolation of Kováts indices without dead time correction

Summary Comparison with normal procedures shows that numerical interpolation of the logarithms of gross retention times generates quite useful Kováts indices for gas chromatographic analysis. The dead time concept is not used in the interpolation.     

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.     

Rediscovering the problem of interpretation of chromatographically determined enthalpy and entropy of adsorption of different adsorbates on carbon materials. Critical appraisal of literature data

Adsorbate-adsorbent and adsorbate-adsorbate interactions having decisive influence on the distribution of adsorbate between gas-solid phases in inverse gas chromatography (IGC) have been thermodynamically explained. Specific retention volumes, second adsorption virial coefficients and Kováts retention indices, likewise their dependencies on column temperature, T, number of carbon atoms, n(C) (or methylene groups CH(2)) and mutual ones have been briefly presented. The results of the molar differential enthalpy and entropy of adsorption obtained for different carbon materials employing inverse gas chromatography have been collected and interpreted. An attempt has been made to elucidate abnormal behaviour of the specific and net retention volumes, the second adsorption virial coefficients and the Kováts retention indices, e.g., the magnitudes on which the values of the afore-mentioned thermodynamic values have been determined and compared. The detailed analysis of the errors associated with the experimental parameters necessary for calculating retention volumes, second adsorption virial coefficients and Kováts retention indices has been presented.     

Comprehensive evaluation of lipophilicity of biogenic amines and related compounds using different chemically bonded phases and various descriptors

The retention behavior for a series of biogenic amines and related sympathomimetic drugs has been investigated in reversed-phase thin-layer chromatography using RP-2, RP-8, RP-18W, and Diol stationary phase and mixtures of phosphate buffer (pH = 7.10) and methanol in different proportions as mobile phases. Several methodologies like arithmetic mean of experimental retention values, extrapolation to zero methanol concentration procedure and principal component analysis were applied to retention data values (R(M)) in order to determine relevant parameters (mean of R(M) - mR(M), R(M0), and scores corresponding to the first principal component - PC1/R(M) respectively) encoding information on the lipophilic behavior of compounds. High similarities in lipophilicity behavior of investigated amines were highlighted by mR(M) and PC1/R(M) lipophilicity indices for all of the studied stationary phases. The experimental results were compared with some computed lipophilicity parameters expressed as distribution coefficients at working pH (logD), partition coefficients (logP(N), logP(I), and diff(logP(N-I))) concerning both neutral and fully protonated species and difference between both species, and also with various lipophilicity values (logP) generated by different commonly used software. Significant correlations were observed between the experimental lipophilicity indices mR(M) respectively PC1/R(M) and diff(logP(N-I) ) values in all cases.     

Forming taxonomic groups of organic compounds for calculating gas-chromatographic retention indices from physicochemical constants

The traditional approach to calculations of gas-chromatographic retention indices from physicochemical constants of organic compounds in homologous series does not encompass all possible objects. Forming different taxonomic groups of compounds by variations in the formal unsaturation, the number of atoms of different elements within molecules, or any complex fragments of structure/composition makes it possible to calculate unknown retention indices by several independent methods from different arrays of initial data. The application of simple three-parameter equations provides an accuracy comparable to the modern interlaboratory error of determination of retention indices for any compounds. St. Petersburg State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 6, pp. 176–182, November–December, 1994. Translated by L. Smolina     

Cyclam complexes of Cu(II) and Co(II) as stationary phases for gas chromatography

New macrocyclic stationary chemically bonded phases were synthesized and tested in gas chromatography conditions. The complexes of 1,4,8,11-tetraazacyclotetradecane with Cu(II) and Co(II) were bonded to the silica support through the (3-chloropropyl)triethoxysilane reactant. The packings obtained were analyzed by diffuse-reflectance ultraviolet–visible spectroscopy (DRUV–Vis), differential thermal gravimetry (DTG), porosimetry, and elementary analysis. Preliminary study of the novel silica gas chromatography (GC) stationary phases containing cyclam complexes was carried out using packed 1/8 in. i.d. columns. The study was conducted on: cyclic, linear and branched olefins, aromatic hydrocarbons and ethers. Characterization of interactions between the compounds mentioned and new stationary phases was based upon analysis of Kováts retention indices (I), difference between retention indices for two phases (ΔI), and molecular retention indices (ΔM_e). Results have shown that the new stationary phases interact sufficiently strongly with molecules of high electron density and can be applied in capillary gas chromatography for the analysis of light hydrocarbons.     

Kováts' coefficients for predicting polarities in silicone stationary phases and their mixtures

Summary A correlation between the retention polarity and the Kováts' coefficient has been found for a number of commercial stationary phases used in gas chromatography. The correlation has been used to predict the polarity of a few mixed stationary phase columns prepared as binary mixtures of OV-101 with OV-25, DC-550 or Carbowax 20M, and also mixtures of OV-225 with SP-2340. A linear relationship was found between polarity and mixture composition. The temperature dependence of the Kováts' coefficient was investigated and found to increase linearly with temperature, the rate of increase depending on the polarity of the stationary phase, with greater increases for more polar stationary phases.