Liquid Crystalline Stationary Phases Research Articles

New liquid crystalline stationary phases for gas chromatography of positional and geometrical isomers having similar volatilities

New liquid crystalline compounds of the type 2-methyl-4′-R-4-( p-methoxycinnamoyloxy)azobenzene, where R = methoxy, ethoxy, ethyl or n-butyl, were synthesized. Their properties as stationary phases for the gas chromatographic separation of positional isomers of xylene, dichlorobenzene, methoxynaphthalene and geometrical isomers of insect sex pheromones of similar volatilities have been investigated. The effect of temperature on the separation ability of the liquid crystalline compounds was studied. Large separation factors, α, for isomers were obtained on a column in its supercooled nematic state. The separation of insect sex pheromones was found to depend on the structure of the liquid crystalline compound used as stationary phase rather than on its nematic range.

Mesomorphous Properties of Azo- and Azoxyarylethanes as Potential Stationary Phases in Gas Chromatography

Abstract Two series of compounds have been synthesized: 1,2-bis(4′-butoxybenzeneazobenzene-4)ethanes and 1,2-bis(4′-butoxybenzeneazoxybenzene-4)ethanes. The effects of lateral substituents (CH3, Cl, CN) on temperature are tested as well as the molar enthalpies and entropies of their phase transitions determined. The application of those compounds as liquid-crystalline stationary phases in gas chromatography is suggested.

Selectivity and chemical structure of nematic mesophases in gas chromatography

The retention behaviour of geometrical isomers and Rohrschneider compounds was measured in the nematic range of liquid crystalline stationary phases having different chemical structures, in order to determine the influence of these structures on the polarity and selectivity of the phases. It was found that lateral substituents in mesogenic molecules effect a change in selectivity. The polarities of these phases are compared with those of conventional stationary phases, and the strong influence of the terminal groups of the liquid crystal molecules on Δ I values is discussed.

Liquid crystalline stationary phases with a cyclohexyl ring in the molecule

The selectivities and polarities of five liquid crystalline stationary phases, derived from cyclohexane and differing as regards the terminal substituents, were determined. The efficiency of the columns in which these stationary phases were deposited was established. The selectivities of the stationary phases are related to the type of mesophase and are comparable to those of other liquid crystalline stationary phases; likewise the effciencies of the columns with these phases are comparble but the polarity is low.

Glass capillary columns with liquid crystalline stationary phases for gas chromatography. The influence of the pretreatment of the inside tube wall

The importance of capillary columns prepared with a liquid crystalline stationary phase are increasing. It is known that the interaction of the liquid crystals molecules with the glass capillary wall may strongly influence selectivity and efficiency of the column. The paper reports on systematic investigations on the correlations between the pretreatment of the inside glass capillary surface, the chemical nature of the liquid crystal and the chromatographic properties of the columns obtained.

Disc-like liquid crystalline stationary phases from the triphenylene derivatives group

Disc-like liquid crystals belonging to the triphenylene derivatives group have been tested as stationary phases. Some relationships were determined as a function of the column temperature and separations a few substances were studied. Differences were found in the behaviour of disc-like and rod-like liquid crystalline stationary phases. On disc-like liquid crystals, compounds with a linear molecular structure are easily separated from those with a cyclic structure having similar boiling temperatures.

Comparison of diphenylethane derivatives with lateral substituents as liquid-crystalline stationary phases in gas chromatography

The separating properties of liquid-crystalline stationary phases with the same main chain but differing in the presence or absence of lateral substituents were compared. The effect of the kind and position of the lateral substituent on the effectiveness of separation was studied. Mixtures of polynuclear aromatic hydrocarbons and isomers of naphthalene and benzene derivatives and of other compounds were separated. Some relationships were found to exist between the presence of the lateral substituents, their position in the molecule and their polarity and the effectiveness of the separation of the mixtures of various groups of compounds.

Effect of lateral substituents on the properties of liquid crystal molecules as stationary phases in gas chromatography

The properties of liquid crystalline azo compounds with lateral substituents (CH 3, CN, Cl) have been tested from the point of view of their suitability as stationary phases in gas chromatography. The tested properties were compared with those of the unsbustituted compounds. The study consisted in comparing the retention properties of the test substances on the stationary phases and determining their selectivity and the efficiency of the columns containing these phases. It was found that minor changes in the liquid molecular structure affect the properties of the liquid crystalline stationary phases. The properties of the liquid crystal with respect to the test substance depend on the kind of substituent and its position. The interactions of liquid crystal molecules with the same substituents depend on the kind of substance chromatographed.

Liquid crystals : V. Comparative study of laterally halogen-substituted liquid crystalline stationary phases

Comparaison des temps de retention de composes benzeniques a differentes temperatures pour neuf phases substituees

Synthesis and testing of new high-temperature liquid crystalline stationary phases

Three new liquid crystalline Schiff's bases were synthesized that show wide mesophase ranges. The properties of these compounds as stationary phases and their separating capacities towards polynuclear hydrocarbons were tested.

Glass capillary column with nematogenic liquid crystals as stationary phases for separating polycyclic aromatic hydrocarbons

Use of the homologues and analogues of nematogenic liquid crystals of the type N,N′-bis(p-methoxylbenzylidene)-α,α′-bi-p-toluidine (BMBT) as stationary phases in glass capillary columns is described. These stationary phases are very useful for resolving closely related, rigid solute isomers of three-, four- and five-ring PAH. With these columns it is possible to achieve faster and more complete separation of PAH compared with packed columns with a liquid crystalline stationary phase.

Properties of single and mixed liquid-crystalline stationary phases : II. Mixed liquid-crystalline stationary phases

The properties of binary and ternary mixed liquid-crystalline stationary phases of eutectic composition have been tested. The experimental results are compared with theoretical ones obtained by assuming that the properties of the component phases are additive. It has been found that the selectivity of the mixed phases can be predicted at any temperature if the properties of the single phases are known. At the melting temperature the selectivity of the mixed phases is usually higher than that of the single phases. The efficiencies of columns with mixed phases are usually higher than expected from the additivity principle. Separations of mixtures of disubstituted benzene derivatives obtained on the mixed phases are comparable to those obtained using capillary columns with liquid-crystalline stationary phases.

Properties of single and mixed liquid-crystalline stationary phases : I. Single liquid-crystalline stationary phases

The polarities and selectivities of twelve liquid-crystalline stationary phases have been tested as well as their column efficiencies. The effect of these properties on the separating ability of the liquid-crystalline stationary phases with respect to di-substituted benzene isomers is discussed. The separating properties of the individual stationary phases have been predicted, and experimentally confirmed by carrying out separations of mixtures of isomers of disubstituted benzene derivatives.

Improved gas-chromatographic columns of liquid crystals supported on glass beads for analysis of polycyclic aromatic hydrocarbons

Glass microbead columns withN, N′-bis-(p-butoxybenzilidene) α, α′-bi-p-toluidine (BBBT) a high-temperature smectic-nematic liquid crystalline stationary phase have been prepared. The best efficiency was obtained with BBBT from 0.025% w/w (ca. 1800 theoretical plates m−1) to 0.1% w/w (ca. 2100 theoretical plates m−1). Capacity ratios and separation efficiencies of columns packed with glass microbeads treated and untreated with a surfaceactive agent were studied as a function of analysis time. A separation of five methylchrysene isomers is shown.

Investigations of the properties of liquid–crystalline stationary phases containing naphthalene fragments in their molecules

Six new liquid–crystalline stationary phases have been produced containing naphthalene fragments in their molecules. The mesophase range lies between 45 and 132°C, the highest clearing temperature being 295°C and the lowest melting point 126°C. The physicochemical properties of these stationary phases have been tested, and the usefulness of the phases for the analysis of polycyclic aromatic hydrocarbons, naphthylamines, naphthols and methylnaphthalene isomers has been demonstrated.

Liquid crystals : III. application of laterally substituted liquid crystals for the separation of alkylbenzenes compared with conventional stationary phases in gas chromatography

The retention behaviours of 26 alkylbenzenes on a laterally substituted liquid crystalline stationary phase and on conventional stationary phases in gas chromatography have been compared. Elution of alkylbenzenes in the nematic state of liquid crystalline substrates is dependent on the linearity and planarity of the probe molecules, whereas on conventional stationary phases they elute on the basis of their boiling points. The relative retention values (α) for close-boiling positional isomers on conventional stationary phases are near unity, but their separation can be achieved on liquid crystalline substrates. The variation of the relative retention value with respect to the chain length of the alkyl substituents is discussed.

Ligand-exchange gas chromatography of lower aliphatic amines on solid and liquid crystalline stationary phases

Ligand-exchange gas chromatography of lower aliphatic amines on solid and liquid crystalline stationary phases

Determination of contaminants in anthracene by gas chromatography using a liquid crystalline stationary phase

The separation of contaminants in anthracene and the determination of phenanthrene, carbazole, and fluoranthene with triphenylmethane as an internal standard are described. These compounds and others that occur in the mixture in various amounts can be determined with the application of a new high-temperature liquid crystalline stationary phase. The precision of the method has been calculated.

Effect of the amount of liquid crystal and type of support on some properties of the liquid crystalline stationary phase-support system

The effects of the amount of liquid crystalline stationary phase (from about 0.2 to about 10%) and of the type of the support on the properties of the system being formed were studied. Chromosorb P NAW, PAW, PAW DMCS and GAW DMCS were used as supports. The dependences of V g , V s , k′ and HETP on the temperature of the column and the moment of the stationary phase on the support were studied and it was found that the interaction of the Chromosorb with the stationary phase decreases in order NAW > AW > DMCS.

New ester phase with nematic working range for GLC

A new nematic liquid crystalline GC stationary phase is introduced. The systematic name is: ethylen-4,4′ diphenyl bis (4-methoxybenzoate): EPMB. It has a nematic range 168°C to 302°C. Coated on a support (Chromosorb W AW DMCS 100/120 mesh) it can be supercooled to 65°C and used for temperature programmed GC from 65°C to 260°C. The selectivity, bleeding, supercooling and temperature dependence of the capacity ratio are reported. In comparison with nematic phases with similar working range, EPMB shows equal separating power, but less bleeding and an extended temperature range. The main point of this work is the use of EPMB as an example of a liquid crystalline compound as a stationary phase for the gas chromatographic separation of certain compounds.