Complexation Gas Chromatography Research Articles

Transition metal complex stationary phases for the CGC analysis of ethers, thioethers and ketones

The use of polysiloxanes with cyano or thiol groups as stationary phases for complexation gas chromatography is discussed. The polymers were obtained via polycondensation followed by polymerisation of the corresponding dichloro- or dimethoxy-silanes. Both the phases were modified by bonding transition metal chlorides with were modified by bonding transition metal chlorides with cyano (CuCl2 or CoCl2) and thiol groups (NiCl2 or CoCl2). The phases were examined in order to determine their application to the analysis of ethers, thioethers and ketones. Due to the presence of lone electron pairs on oxygen or sulphur atoms, the compounds should be capable of specific interacting with the electron-withdrawing centre of the liquid stationary phases. A number of retention parameters (retention indices, molecular retention indices and specific retention volume) were determined, which allowed characterisation of specific interactions between the bonded metal and the compound analysed. The results also enabled assessment of the influence of the structure of the compounds on their retention. The measurements were also carried out for the phases with free SH and CN groups as reference phases. The work demonstrates that the phases obtained may be useful for effective separations.

Capillary complexation gas chromatography in analysis of halohydrocarbons

Investigations were carried out on capillary columns coated with liquid stationary phases possessing cyano (3-cyanopropylmethylpolysiloxane) and thiol (3-mercaptopropylmethylpolysiloxane) groups. These phases were modified by bonding CuCl2 and CoCl2 to cyano groups or NiCl2 and CoCl2 to thiol groups. The modified phases were examined in order to assess their usefulness for the analysis of aliphatic and aromatic halohydrocarbons. A number of retention parameters (I, ΔMe, Vg), which allow characterisation of the specific interactions between the bonded metal and the halohydrocarbon molecule, were determined for the columns both with and without the metal. The separations performed show that the columns with bonded metals are applicable for the practical analysis of the halohydrocarbons.

Synthesis and properties of mercaptosilicone modified by Ni(II) and Co(II) as stationary phases for capillary complexation gas chromatography

The synthesis of liquid stationary phases with mercaptopropylmethyl polysiloxane containing cations of Ni 2+ or Co 2+, bonded to the polymer via thiol groups, is described. Columns of 30 m×0.53 mm were coated with these stationary phases (film thickness of 0.5 μm). The columns are thermally stable up to 250°C. The average molecular masses of the prepolymer (805) and the polymer (10 612) were calculated. The Grob test was also performed. Retention factors ( k), retention indices ( I) and specific retention volumes ( V g) were found for the compounds of McReynolds series. The obtained polysiloxanes were characterised by means of spectroscopic techniques (UV–Vis, IR). The former technique has enabled to confirm the formation of a metal-phase bond, while the other provided information on polysiloxane chain length increase. Concentrations of metals in the phases containing metal complexes (Ni 2+/SH – 7.34×10 −3; Co 2+/SH – 4.52×10 −2) were determined by a voltammetric method. The stationary phases prepared were capable of interacting specifically with nucleophilic compounds.

Synthesis and properties of cyanosilicone stationary phases for capillary complexation gas chromatography

The synthesis of liquid stationary phases with cyanoproppylmethyl polysiloxane containing cations of Cu2+ or Co2+ which were bonded to the resulting polymer via cyano groups is described. Columns of 30m×0.53 mm were coated with these stationary phases (film thickness of 0.5 μm.). The characteristics of the polysiloxanes obtained were determined by the use of spectroscopic techniques (UV-vis, IR). The thermal stability of the columns was established and the average molecular mass of the polymer was calculated. The Grob test mixture was also used to evaluate the columns.

Chemically bonded chelates as selective complexing sorbents for gas chromatography V. Silica chemically modified by Cu(II) complexes via amino groups

The synthesis of packings for complexation gas chromatography was performed by bonding aminosilane with a silica surface, and then bonding it with Cu(II) using the complexation properties of amino groups. Packings obtained in such a way were used for elemental analysis and differential scanning calorimetry and some retention parameters were determined for hydrocarbons, nitroalkanes and ethers. The chromatograms of test mixtures are presented in order to illustrate the separation properties of the packings. The thermal stability of the packings was determined by the use of the differential scanning calorimetry (DSC) technique. It was concluded that the modification of amino groups of N-(2-aminoethyl)-3-amino-propyltrimethoxysilane by Cu(II) cations allows use of these packings in the chromatographic analysis of hydrocarbons, ethers and nitroalkanes.

Chemically bonded chelates as selective complexing sorbents for gas chromatography IV. Silica surfaces modified with Co(II) and Ni(II) complexes

The synthesis of some new packings for complexation gas chromatography (CGC) is proposed in this article. These packings contain acetylacetonates and hexafluoroacetylacetonates of nickel(II) and cobalt(II), which are chemically bonded to a silica gel via β-diketonate groups. The effect of the structure and the configuration of some adsorbates (olefins, cyclic and aromatic hydrocarbons) on the retention of these compounds is determined. Moreover, the usefulness of the packings in the analysis of hydrocarbons is described. The results show the good applicability of the tested packings as well as their high selectivity towards compounds which contain π-electrons.

Chemically bonded chelates as selective complexing sorbents for gas chromatography III. Silica chemically modified by N-benzoylthiourea groups

High stability and simple synthesis from inexpensive starting materials make it possible to use the N-benzoylthiourea groups as modifiers of silica for complexation gas chromatography. Taking advantage of the chelating properties of N-benzoylthiourea, copper(II) ions were bonded with SiO 2 to give a packing capable of entering into π-type interactions with adsorbates with electron-donor properties such as linear and branched alkenes and aromatic and cyclic hydrocarbons. The high selectivity of the packing obtained permitted the separation of complex mixtures (including isomers) of different classes of organic compounds.

Enantiomer separation by complexation gas and supercritical fluid chromatography on immobilized polysiloxane-bonded nickel(II) bis[(3-heptafluorobutanoyl)-10-methylene-(1 R)-camphorate] (Chirasil-nickel)

The synthesis of a polysiloxane containing chemically bonded chiral metal complex derived from nickel(II) bis[(3-heptafluorobutanoyl)-10-methylene-(1 R)-camphorate] (Chirasil-nickel) and its effective immobilization on the inner surface of fused-silica capillaries by thermal treatment is described. As expected, the immobilization properties were found to be dependent on the content of residual reactive SiR groups in the polymer backbone (R = OCH 3, H). The immobilized Chirasil-nickel stationary phase was employed for the analytical enantiomer separation of coordinating solutes by high-resolution capillary gas and supercritical fluid chromatography. The increase in the relative retention monitored for racemic test solutes after rinsing the columns indicates a slight increase in the effective complex concentration which does not affect the chiral separation factor α. The temperature limit of analysis was raised to 170–180°C for temperature-programmed runs and to 140–150°C under iso thermal conditions, thus extending the scope of complexation gas chromatography considerably, as demonstrated by various enantiomer separations performed at elevated temperatures. When Chirasil-nickel is immobilized on the inner surface of short, narrow-bore capillaries (50 μm I.D.), it can be employed in complexation supercritical fluid chromatography, combining the high solvation strength of supercritical carbon dioxide with the benefit of low operating temperatures, enhancing enantioselectivity.

Investigation of the Enantiomerization Barrier of Homofuran by Computer Simulation of Interconversion Profiles Obtained by Complexation Gas Chromatography

AbstractBy computer simulation of experimental interconversion profiles, obtained by complexation gas chromatography, rate constants of enantiomerization have been determined for homofuran between 95 and 130°C. Since enantiomerization proceeds at similar rates in the mobile and stationary phase, the rate constants obtained by an Arrhenius plot are in excellent agreement with values determined independently by polarimetry between 60 and 90°C. We thus demonstrate that dynamic chromatography can be an easy means for the rapid determination of enantiomerization (or isomerization) barriers of ca. 70–120 kJ mol‐1 requiring only minute amounts of racemic sample.

Enantio- and regioselectivity in the epoxide-hydrolase-catalyzed ring opening of simple aliphatic oxiranes: Part I: Monoalkylsubstituted oxiranes.

The in vitro conversion of chiral aliphatic monoalkylsubstituted oxiranes into 1,2-diols catalyzed by epoxide hydrolase of rat liver microsomes occurs with substrate enantioselectivity and regioselectivity. Substrate enantioselectivity is generally low, and has the same sense, for methyloxirane, vinyloxirane, epichloro-, and epibromohydrin. In the hydrolysis of t-butyloxirane inhibitory effects are involved leading to a complex pattern of enantioselectivity. All investigated monosubstituted aliphatic oxiranes are hydrolyzed with high regioselectivity by nucleophilic attack of water at the unsubstituted ring carbon atom. The enantiomeric excess of the unreacted oxirane substrates and the diol metabolites formed were determined by complexation and inclusion gas chromatography.

Semi-preparative enantiomer separation of 1-chloro-2,2-dimethylaziridine by complexation gas chromatography -absolute configuration and barrier of inversion

1-Chloro-2.2-dimethyl-aziridine has been resolved into its enantiomerically pure invertomers by semi-preparative complexation gas chromatography at 25°C. The absolute configuration has been correlated with the chromatographic elution order. An inversion barrier of ΔG‡ = 115.5 kJ/mol was determined in the gas phase at 338.6 K.

Use of two-dimensional gas chromatography in the direct enantiomer separation of chiral essential oil components

The enantiomeric excess of a component of an essential oil can be determined on-line with normal gas chromatographic analysis by applying two-dimensional gas chromatography with a second column coated with a chiral stationary phase. The enantiomeric excess for the examples reported was evaluated by complexation gas chromatography, which was demonstrated to give successful enantiomer separations without derivatization of several monoterpenoids and compounds peculiar to the essential oil field.

The absolute configuration of 6,8-dioxabicyclo[3.2.1]octane and several methyl substituted derivatives

The enantiomers of 6,8-dioxabicyclo[3.2.1]octane and the alkyl substituted derivatives, exo- and endo-7-methyl, exo- and endo-5,7-dimethyl, 7,7-dimethyl, and exo- and endo-7-ethyl-5-methyl ( exo- and endo-brevicomin), were synthesized stereoselectively with known configuration by standard synthetic methods, or with baker's yeast, or both. The correlation between the absolute configuration of the bicyclic rings and the optical rotation was established by means of chiral complexation gas chromatography for two molecules for which this correlation was not known previously. In all cases, the (1R) enantiomer exhibits positive rotation. The absolute configurations were established for the yeast products which were always produced in high optical purity.

Enantiomer Separation of n-1-Alkenyl-3-Acetates and of Alkyl Substituted 1,3-Dioxolanes by Complexation Gas Chromatography

ABSTRACT The simultaneous enantiomer separation of a homologous series of n-1-alkenyl-3-acetates on nickel(II)bis[3-(heptafluorobutanoyl)-(1R)-camphorate] and of alkyl-substituted 1,3-dioxolanes containing three chiral centers on nickel(II)bis[3-(heptafluorobutanoyl)-(1R)-camphorate] and on nickel(II)bis [3-(heptafiuorobutanoyl)-(1R,2S)-pinan-4-onate] by complexation gas chromatography is described. The method allows the rapid screening of the stereochemistry of the title compounds in biological mixtures.

Gas‐Chromatographic Enantiomer Separation of Unfunctionalized Cycloalkanes on Permethylated β‐Cyclodextrin

In contrast to established procedures for the gas‐chromatographic separation of enantiomers (use of amide phases, complexation gas chromatography), which require the presence of polar functional groups in the compounds being separated, a new procedure now makes it possible to discriminate between the enantiomers of unfunctionalized hydrocarbons. This communication describes the enantiomer separation of cis‐l‐ethyl‐2‐methylcyclohexane, trans‐1,1,3,5‐tetramethylcyclohexane, and other alkyl‐substituted cyclohexanes on glass capillary columns containing permethylated β‐cyclodextrin in polysiloxane solution (inclusion mechanism).

ChemInform Abstract: Evidence for a Temperature‐Independent Inversion of Enantiomeric Selectivity in the Complexation Gas Chromatography at Chiralic Phases

ChemInform Abstract: Evidence for a Temperature‐Independent Inversion of Enantiomeric Selectivity in the Complexation Gas Chromatography at Chiralic Phases

Evidence for a Temperature Dependent Reversal of the Enantioselectivity in Complexation Gas Chromatography on Chiral Phases

Great caution should be taken in attempting to derive configurations from the sequence of elution of enantiomers, according to the observations of Gil-Av et al. and Schurig et al. Both groups found a temperature dependence in the elution sequence obtained in the gas-chromatographic separation of enantiomers on chiral stationary phases, which led to lack of separation at the isoenantioselective temperature Tiso. defined by (a) and to a reversed order of elution above and below T.iso. Hydrogen-bond-forming systems (amino acids on diamide phases) and complex-forming selectand-selector systems (oxaspirocyclic compounds on nickel complexes) were investigated. The Tiso values were 130–150°C and 70–90°C, respectively. These findings show, at the same time, that below Tisothe elution sequence is determined by the differences in the interaction enthalpy as given by the Gibbs–Helmholtz equation (b) and that above Tiso it is determined by the interaction entropy.

Evaluation of nickel(II) bis[α-(heptafluorobutanoyl)-terpeneketonates] as chiral stationary phases for the enantiomer separation of alkyl-substituted cyclic ethers by complexation gas chromatography

A method is described which permits the determination of thermodynamic data for molecular association, as well as the enantioselectivity — Δ R,S (Δ G°), from relative retention data by complexation gas chromatography. Thus, the solute—solvent association equilibria between two achiral, and fifteen chiral alkyl-substituted cyclic ethers and twelve non-racemic nickel(II) bis[α-(heptafluorobutanoyl)terpeneketonates] in squalane have been measured at 60°C. The selectivity of the solute—solvent association between alkyl-substituted oxiranes and the twelve nickel terpeneketonates follows a common trend which is rationalized in terms of opposing electronic and steric effects of the Lewis bases. The origin of the striking influence of ring size of cyclic ethers on the association strength with the twelve nickel terpeneketonates, which varies by two orders of magnitude, is unknown. Improved chiral stationary phases for the enantiomer separation of alkyl-substituted cyclic ethers have been found. The highest enantiomeric bias on racemic oxiranes is induced by nickel(II) bis[3-(hepta-fluorobutanoyl)-(1 R,2 S)-pinan-4-onate], containing a bicyclic terpene structure, and by nickel(II) bis[5-(heptafluorobutanoyl)-( S)-carvonate], containing a monocyclic terpene structure, respectively. The enantioselectivity, — Δ R,S (Δ G°), is generally high when the solute—solvent interaction is intermediate. For chiral alkyl-substituted oxiranes a consistent relationship between molecular configuration and the order of elution is observed for almost all of the twelve nickel terpeneketonates used as solvent. The synthesis of these solvents is described in detail.

Cytochrome P-450-catalyzed asymmetric epoxidation of simple prochiral and chiral aliphatic alkenes: species dependence and effect of enzyme induction on enantioselective oxirane formation.

The enantioselectivity of the in vitro conversion of simple prochiral and chiral aliphatic alkenes into oxiranes by liver microsomes of untreated or induced (phenobarbital) rats, of untreated or induced (phenobarbital, benzo[a] pyrene) mice, and of humans was determined by complexation gas chromatography. The enantiomeric excess (ee) of the epoxides extends from 0 (trimethyloxirane) to 50% (ethyloxirane). The configuration (R or S) of the enantiomers formed in excess is consistent for homologous oxiranes but is species dependent and in some cases influenced by enzyme induction. Enantioselectivity differences of aliphatic alkene epoxidation by human liver microsomes of four individuals are negligible.

Resolution of rac-1,2-halohydrins by chiral complexation gas chromatography

Resolution of rac-1,2-halohydrins by chiral complexation gas chromatography