Gas chromatographic properties of two thermotropic Poly(L-glutamates) with long alkyl side chains

Summary Comparative gas chromatographic properties of two thermotropic Poly(L-glutamates) with long alkyl side chains (10 and 16 carbons called Poly 10 and Poly 16 respectively) are studied.Their thermal properties were established with differential scanning calorimetry (DSC) and gas chromatography. They present a cholesteric liquid crystal in a large temperature range.The chromatographic separation abilities of the two polymers in the liquid crystal state were studied using capillary glass columns. Interesting analytical performances were obtained in different fields: isomeric separation of alkanes, aromatics, polyaromatics, volatile aroma compounds and cis and trans isomers. Some differences were noticed in their behaviours; 2 and 3-methyloctane and xylene isomers are separated only on Poly 10 while limonene and eucalyptol are separated only on Poly 16.     

Simplified Solid-Phase Extraction Procedure and Liquid Chromatographic Determination of Celecoxib in Rat Serum

A simplified solid phase extraction method, eliminating a preliminary protein precipitation has been developed for the determination of celecoxib in rat plasma. The technique included a solid phase extraction of the serum samples on a [poly (divinylbenzene-co-N-vinylpyrrolidone)] sorbent. After conditioning, the cartridge was loaded with 0.5 mL of acidified serum containing internal standard. Elution was made with 1 mL of a mixture of acetonitrile and methanol (1/1, v/v). After evaporation of the eluate to dryness and reconstitution with methanol, the samples were analyzed on an octadecyl bonded phase with several mobile phases containing acetonitrile and a phosphate buffer. Detection was carried out using a Photodiode Array Detector. Full validation of the proposed method was provided (linearity range: 0.01–2 mg. L^–1, average extraction efficiency: 92.4%; average intra-day variability: 4.6% with an accuracy of 94.8%; average interday variability: 5% with an accuracy of 95.3%, limit of detection: 0.005 mg. L^–1, limit of quantification: 0.002 mg. L^–1). The proposed method was successfully utilised to quantify celecoxib in rat plasma for a pharmacokinetic study.Revised: 26 January and 23 April 2004     

Nematogens incorporating a lateral flexible ring

A lateral flexible ring can be introduced on a mesogenic core containing four rings. Lateral aliphatic rings containing up to 12 atoms have been synthesized. Despite this large lateral protruding substituent, a large nematic range is obtained. A compound with a benzo15-crown-5 lateral ring has been successfully obtained and shows the possibility of designing nematic liquid crystals with a crown ether moiety at a lateral position.     

Microemulsion high performance liquid chromatography method for the determination of ibuprofen in the presence of preservatives and impurities in oral pediatric suspension

A simple and rapid isocratic oil-in-water microemulsion HPLC method (MELC) has been developed for the analysis of ibuprofen in oral suspension formulation. The method was optimized for simultaneous separation and determination of Ibuprofen and its related compound C (Imp C), sodium benzoate, methylparaben, propylparaben and their related compound A (Imp A). The optimum conditions were achieved by testing several columns and mobile phase compositions, while the chromatographic parameters (retention time, plate number, tailing factor and resolution) were measured. The six compounds were successfully separated within a run time of 14 min, using Eurospher II C18 (150 mm × 4.6 mm i.d., 5 µm) at ambient temperature, a mobile phase made of 5.0 g SDS, 6.6 g butan-1-ol, 0.8 g n-heptane in 100 mL of 0.05% TFA. Flow rate was fixed to 1 mL min^?1 and wavelength detection to 254 nm. The same phase was used in UHPLC and monolithic columns. A rapid comparison of system suitability between the three methods was made. The HPLC method was validated following ICH guidelines in terms of selectivity, linearity, accuracy and precision. The developed method was successfully applied to a commercial pharmaceutical formulation which shows that it can be used for routine analysis.     

Evaluation of the Effect of Citronellol Group on Functionalized Mesogenic Materials by Capillary GC

In this paper, the effects of functionalization with terpenes on two new liquid-crystalline stationary phases for gas chromatography (GC) are described. Citronellol was used as the terminal group in the first material, and tetrahydrogeraniol was used with a second material. Inverse GC showed that the new materials have wide liquid-crystalline ranges (mesophases), 371–500 and 395–501 K, respectively. Moreover, they show good thermal stability up to 523 K and good potential as stationary phases for capillary GC. To clarify the effects of the liquid crystal structures and functional groups on retention and separation, the chromatographic behaviors of the two stationary phases were compared by eluting alkylbenzenes, polycyclic aromatic hydrocarbons, aromatic compounds, and terpenoids. The selectivities for a wide range of analytes achieved using the citronellol column were significantly better than those obtained using the tetrahydrogeraniol column. The columns showed different retention behaviors and fine resolutions for some of the main constituents of essential oils. Introduction of the double bond of citronellol greatly improved the polarization interactions involved in the shape recognition of the liquid-crystalline state for isomers. The new citronellol liquid-crystalline stationary phase, therefore, has a high affinity for natural compounds.

     

Phase Transition Behavior of a New Monotropic Liquid Crystal by Inverse GC

A new monotropic liquid crystal with crown ether substituent called Substance M was synthetized and characterized by several methods: ¹H NMR, hot stage polarizing microscopy, differential scanning calorimetry and inverse gas chromatography. Annealing experiments with inverse gas chromatography confirmed the monotropic behavior of the compound. Isothermally in the nematic state, solute probes chosen were chromatographed after different heating times. The changes of the corresponding retention times were studied.     

Influence of structure and polarity of polysiloxanes on retention of N-TFA butyl esters of amino acids

In this work, we have investigated the influence of the polarities and structures of 13 polysiloxanes on the retention of some N-TFA N-butyl esters of amino acids. Gehrke [1] was the first to examine the possible relationship between polarity and retention data of amino acid derivatives for 9 stationary liquid phases. He concluded that the molecular structure of the stationary liquid phase is an important factor determining retention.     

Influence of the lateral alkoxy chain length on the gas chromatographic properties of five liquid crystals

The gas Chromatographic properties of five laterally substituted liquid crystals are the subject of a comparative study. These liquid crystals belong to the homologous series: 2-alkoxy-3-methyl-4-(4-ethoxybenzoyl-oxy)-4′-(4-trans-n-pentyclcyclohexanecarboxyloxy) azobenzene, referred to as ALn, where n, the carbon number in the lateral alkoxy chain, is equal to 4, 6, 8, 10, or 12 carbon atoms. Their thermal properties were established by differential scanning calorimetry (DSC). It appears that the introduction of a lateral alkoxy chain affects the nematic temperature range which decreases when the carbon number increases. The chromatographic separation abilities of AL4, AL6, AL8, AL10, and AL12 were studied using capillary glass columns. The five liquid cystals are efficient before and after solid-nematic or nematic-liquid transitions; however, the plate numbers are higher in the nematic state. Interesting analytical properties were noted in various fields: iisomeric separation of alkanes, aromatics, polyaromatics, volatile aroma compounds, and cis and trans isomers. However, the chain length does not exert any great influence on the separation abilities.