Behaviour of copper(II) and nickel(II) dialkyldithiocarbamates on polar and non-polar stationary phases

Summary Fifteen Dialkyldithiocarbamate complexes each of copper(II) and Ni(II) have been prepared and the retention times of these complexes have been measured on the non-polar OV-101 phase and the polar NGA and OV-225 phases. The relationship has been studied between the retention characteristics of the complexes and their structure. The lenght of the alkyl substituent, regarded as a steric hindrance, turned out to affect the retention of the complexes on the non-polar phases.

---

Verhalten von Kupfer(II)- und Nickel(II)-dialkyldithiocarbamaten auf polaren und unpolaren stationären Phasen

Zusammenfassung Je 15 Dialkyldithiocarbamatkomplexe von Kupfer(II) und Nickel(II) wurden dargestellt und ihre Retentionszeiten auf der unpolaren Phase OV-101 sowie den polaren Phasen NGA und OV-225 gemessen. Die Beziehung zwischen der Retentionscharakteristik der Komplexe und ihrer Struktur wurde untersucht. Es zeigte sich, daß die Länge des Alkylsubstituenten (als sterische Hinderung) die Retention auf der unpolaren Phase beeinträchtigt.

     

Relationship between the gas chromatographic behaviour and the molecular structure of hydrocarbon samples and various stationary phases

Summary Retention parameters of different hydrocarbon classes were determined on non-polar and medium-polar stationary phases. The relationship between the retention indices, the physicochemical properties and the chemical structure of the solutes (samples) and solvents (liquid phases) was investigated.     

The dynamic chromatographic behavior of tri-o-thymotide on HPLC chiral stationary phases

The interconverting stereoisomers of tri-o-thymotide have been separated by HPLC on chiral stationary phases and the temperature dependence of the dynamic chromatographic patterns has been interpreted in terms of exchange between enantiomeric propeller and helical conformations. Computed low energy structures and CD spectra were used in absolute configuration assignment.     

Elution behavior of polyethylene in polar mobile phases on a non-polar sorbent

Linear polyethylene standards in the range of 1-500 kg/mol, dissolved in 1,2,4-trichlorobenzene, were injected into a column packed with oligo(dimethylsiloxane) modified silica gel. Fifteen polar solvents (cyclohexanone, cyclohexylacetate, cyclohexanol, nonylalcohol, dimethylformamide, dimethyl sulfoxide, ethylene- and diethylene glycol monobutyl ether, benzylalcohol, hexylacetate, bis(2-ethyl-hexyl)phthalate, N,N-dimethylacetamide, propylene carbonate, dipropylene glycol and N-methyl-pyrrolidone) were evaluated as mobile phases. Depending on the type of mobile phase evaluated, different elution behaviors are observed for polyethylene: (1) polyethylene was eluted in the size exclusion mode, (2) polyethylene was eluted together with the sample solvent peak at constant elution volume, (3) polyethylene was partially or fully retained on the column. The retained polymer was easily removed from the column by injecting a small volume of trichlorobenzene. The use of ethylene glycol monobutyl ether as the mobile phase enabled separation of the polyethylene from polypropylene. In this case polypropylene is eluted in the size exclusion mode, while polyethylene is eluted at a constant elution volume or remains in the column.     

Thermodynamic evaluation of the interaction of fatty acid methyl esters with polar and non-polar stationary phases,based on their retention indices

Summary Kovát retention indices are used to determine the partial molar free energies of solution of 39 methyl esters of saturated (normal and branched), mono- and poly-unsaturated higher fatty acids in the non-polar phase Se-30 and the polar phase SILAR 5CP. Contributions of double bonds as a function of their number and position in the acid chain to the partial molar free energies of solution (G) are evaluated quantitatively. Linear equations are suggested for the calculation of G of any compounds from their retention indices measured in columns with SE-30 and SILAR 5CP.     

Preparation and gas chromatographic characterization of dibenzyl crown ether stationary phases

Summary Two crown ethers, di(tert-butylbenzo)-propyl-15-crown-5 polysiloxane (PSO-DTB-15C5) and dibenzo-propyl-15-crown-5 polysiloxane (PSO-DB-15C5) have been synthesized and coated onto fused-silica capillary columns. The chromatographic characteristics, including column efficiency, polarity, phase transition temperature, operating temperature range and selectivity, were studied.Excellent selectivity was obtained for the separation of polar position isomers, especially phenol and dinitrotoluene isomers. The separation mechanism is discussed.     

Gas chromatographic retention indices of trimethylsilyl derivatives of mono- and diglycerides on capillary columns with non-polar stationary phases

Mono- and diglycerides play an important role in the metabolism of plants and animals. They are usually constitutive elements of complex mixtures and are not always as main components, which considerably hinder the identification of these analytes. This work communicates about a synthesis of a wide range of esters of glycerol and aliphatic C(6)-C(20) acids and presents gas chromatographic characteristics of 32 compounds in the form of the most reproducible parameters-linear-programmed retention indices on high-performance capillary columns with non-polar stationary phases. The article also presents mass spectra for a series of those glycerides which were not characterized earlier by these parameters.     

Study of the gas chromatographic behavior of selected alcohols and amines

The gas chromatographic behavior of selected linear and non-linear alcohols and amines was investigated using four capillary columns containing phenyl substitution levels of 0%, 5%, and 50% and 50% cyanopropyl substitution. In a previous study, the positions of specific compounds inside the capillary column were iteratively modeled using only two thermodynamic parameters (ΔH and ΔS). The present study addresses the validation of the two-parameter model for retention time prediction for selected alcohols and amines using thermodynamic data obtained from as few as two data points. The difference between predicted and observed retention times under different temperature conditions was generally less than 1% of the experimental value and the predicted order of elution was correct in the used model.     

Interactions between 33 solutes and four cyano-containing stationary phases: gas chromatographic activity coefficients and the solvation parameter model

Infinite-dilution gas–liquid chromatographic activity coefficients at 393.15 K (with their thermal and athermal components) and derived excess partial molar Gibbs energies, enthalpies, and entropies have been determined for each of 33 solutes of different polarity on four stationary phases with cyano groups, using retention data taken from the literature. The strongest interactions predicted by the solvation model are the dipolarity/polarizability, the acidic solute–basic stationary phase interaction, and nonpolar cavity formation and dispersion. These interactions were compared with those evaluated from the solute activity coefficients; the effect of the solute connectivity index and dipole moment on nonpolar and polar interactions, respectively, is discussed. The dependence of the thermal activity coefficient on nonpolar interactions, and the influence of stationary phase polarity on the four solute–stationary phase interactions, were evaluated. The nonpolar interaction increases with increasing connectivity and with increasing athermal activity coefficient. The dipolarity/polarizability interaction increases with increasing solute dipole moment. Finally, polar interactions increase with increasing stationary phase polarity whereas the nonpolar interaction is independent of stationary phase polarity.     

Choice of preferred stationary phases for gas chromatography. Part II

Summary The regularities of changes of the polarity factors with the composition of mixed stationary phases are discussed. Values of the polarity factors of active solids, partitioning liquids and also colloidal stationary phases are compared. Part I: ref. [1].     

The correlation between molecular polarizability of PAHs and their retention data on various stationary phases in reversed-phase HPLC

Summary The equation for the potential energy of interactions established for gas-liquid chromatography has been confirmed in reversed phase liquid chromatography. Equations derived for molecular polarizabilities of PAHs and their retention data have very high correlation coefficients. The results indicate that the inductive effect between solute and stationary phase is the main one and the dispersive effect is very small compared with the inductive effect but its contribution increases with the carbon chain length of the stationary phase.     

Calculation of the polychlorinated terphenyl congener distribution and gas chromatographic retention behavior of selected single standards on four stationary liquid phases

The distribution of the 8557 theoretically possible structures of polychlorinated terphenyls (PCT) over the different degrees of chlorination and basic terphenyl backbones has been calculated and is presented in detail. As congeners missing chlorine atoms in an ortho position are suspected to be as noxious to organisms as dioxins, the number of these congeners is specified as well. The gas chromatographic retention behavior of 14 PCT single standards is studied on four stationary liquid phases for capillary columns (HP-Ultra 1, HP-5MS, RSL-300 and Polycarbonate) relative to 2,2′,3,4,4′,5,5′-heptachlorobiphenyl and shows no consequent separation of PCT in terms of the degree of chlorination. Individual congeners have been assessed for their suitability as internal standards in PCT analysis.     

Multi-walled carbon nanotubes as the gas chromatographic stationary phase: role of their functionalization in the analysis of aliphatic alcohols and esters

Presented hereafter is the novel application of differently functionalized multi-walled carbon nanotubes (f-MWCNTs) as stationary phases for the GC separation of C(1)-C(5) alcohols and esters. Low-cost packed columns, easily prepared in laboratory, were used with satisfactory results. Depending on the functional groups introduced on the pristine MWCNTs, remarkably different behaviours have been observed, thus indicating that derivatization is a key factor to achieve optimal resolution. The best performance was shown by the 2,2'-(ethylenedioxy)diethylamine derivatized MWCNTs, allowing the separation of alcohol isomers, for this reason chosen for the investigation of fermentation by-products in distilled spirits. The degree of derivatization has been assessed for each packing material by thermogravimetric analysis (TGA). A computational study has been performed to correlate the physico-chemical properties of alcohol probes with the retention behaviour.     

Calculation of the polychlorinated terphenyl congener distribution and gas chromatographic retention behavior of selected single standards on four stationary liquid phases

The distribution of the 8557 theoretically possible structures of polychlorinated terphenyls (PCT) over the different degrees of chlorination and basic terphenyl backbones has been calculated and is presented in detail. As congeners missing chlorine atoms in an ortho position are suspected to be as noxious to organisms as dioxins, the number of these congeners is specified as well. The gas chromatographic retention behavior of 14 PCT single standards is studied on four stationary liquid phases for capillary columns (HP-Ultra 1, HP-5MS, RSL-300 and Polycarbonate) relative to 2,2′,3,4,4′,5,5′-heptachlorobiphenyl and shows no consequent separation of PCT in terms of the degree of chlorination. Individual congeners have been assessed for their suitability as internal standards in PCT analysis. Received: 16 January 1998 / Revised: 3 April 1998 / Accepted: 7 April 1998     

The effect of the structure of bonded cyanoalkyl stationary phases on their selectivity in the liquid chromatographic separation of polynuclear aromatic hydrocarbons

Summary The paper discusses the effect of the length and structure of the hydrocarbon chain connecting the nitrile group to the silica gel surface on the chromatographic properties of cyanoalkyl phases.When using non-polar and polar mobile phases, the selectivity of the cyanodecyl phases toward PAHs is higher than of the cyanopropyl phase and of hydroxylated silica gel.Polar additives to the mobile phase drastically decrease the retention on silica gel and on the cyanopropyl phase while affect the properties of cyanodecyl phases only to a considerably less degree. Newly synthesized phases with different structures of the hydrocarbon chain are compared with the commerical cyano-and ODS-phases. The retention mechanism on the cyanoalkyl phases is discussed.     

Relationship between the structure and properties of amino alcohols and their derivatives

Methods have been developed for the alkylation of imidazole by unsaturated compounds and -bromoacetophenone in the presence of weakly alkaline agents. Several new alcohols and ketones containing N-imidazolyl groups were obtained.See [1] for communication VIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 662–664, May, 1971.The authors thank M. A. Belousova and T. N. Dyumaeva for obtaining the IR spectra and A. I. Chernyshev for obtaining the PMR spectra.     

Relationship between the gas chromatographic behaviour and the molecular structure of hydrocarbon samples and various stationary phases Part I. Correlation of retention data and thermodynamic functions with chemical structure

Summary Retention parameters of different hydrocarbon classes were determined at 90–120°C on non-polar and medium-polar stationary phases. The specific retention volumes, and the thermodynamic functions of solution were calculated and the relationship between these data, the physicochemical properties and the chemical structure of the solutes (samples) and solvents (liquid phases) investigated.