Development of a stability-indicating HPLC method of etifoxine with characterization of degradation products by LC-MS/TOF, 1H and 13C NMR.

This paper describes a new LC-MS/TOF method for the degradation products determination when Etifoxine (ETI) is submitted to different stress conditions. Chromatography is performed by using Kromasil C18 column (250mm×4.6mm, 5μm particle size).

Effect of the chain length on the thermal and analytical properties of laterally biforked nematogens.

Three laterally substituted liquid crystals were synthesized in order to investigate the effect of a lateral biforked chain on the thermal and analytical properties. The mesogenic molecules have the same core containing four aromatic rings connected by two ester and one diazo linkages, they differ by the length of one chain within the lateral biforked substituent. The phase transition temperatures were obtained by polarized light microscopy and differential scanning calorimetry (DSC).

General contribution of nonspecific interactions to fluorescence intensity.

Many chemical compounds, including nonfluorescent ones, induce changes in the fluorescence spectra of certain probes, such as berberine cation and Reichardt's betaine, both in the absence and the presence of solvent, that affect almost exclusively emission intensity. In this work, the application of fluorescence detection by intensity changes (FDIC) to HPLC and TLC chromatographic systems with fluorescence detectors has been studied. FDIC detection is of special interest in detecting nonfluorescent analytes, either in HPLC or in TLC mode.

Solid phase extraction and liquid chromatographic determination of sildenafil and N-demethylsildenafil in rat serum with basic mobile phase.

HPLC method for the determination of sildenafil and its metabolite (N-demethylsildenafil) in rat serum has been developed. The technique included a solid phase extraction of the serum samples on a [poly(divinylbenzene-co-N-vinylpyrrolidone)] solid phase extraction sorbent. After conditioning, the cartridge was loaded with 0.

Analytical performances of two liquid crystals and their mixture as stationary phases in capillary gas chromatography.

Comparative gas chromatographic applications of two new liquid crystals called LCa and LCb and their equimolar mixture LC(a+b) were investigated. The thermal properties of LCa, LCb and LC(a+b) were established with differential scanning calorimetry (DSC) and polarizing microscopy. Differential scanning calorimetry of LC(a+b) showed that the melting or clearing temperature was intermediate between the corresponding temperatures of the pure compounds.

Organization of four thermotropic liquid crystals of different polarities on model liquid and solid surfaces.

The thermodynamic and surface properties of four structurally related thermotropic liquid crystals (LC) were investigated to understand their organization at gas-liquid and gas-solid interfaces. In this study, LC with a benzoyloxy azobenzene mesogenic core substituted with heptyloxy and/or dioxyethylene ether groups were used. The propensity of the LC to form self-assembled multilayers was demonstrated in the films spread at the air/aqueous interface using the Langmuir technique and Brewster angle microscopy and on the solid surfaces of Chromosorb WHP and silica, using differential scanning calorimetry.

Solid-phase extraction and HPTLC determination of isoniazid and acetylisoniazid in serum. Comparison with HPLC.

A new solid-phase extraction (SPE) and quantitative determination of isoniazid (INH) and its acetyl metabolite (AcINH) in serum by high-performance thin-layer chromatography (HPTLC) is presented. Alkalized serum samples with nicotinamide as an internal standard are applied to an SPE cartridge containing a new SPE sorbent, [poly (divinylbenzene-co-N-vinylpyrrolidone )]. A simple procedure of conditioning, washing, and eluting steps is described.

Synthesis, characterization and liquid chromatographic behaviours of a new chemically bonded liquid crystal.

A new bonded liquid crystal stationary phase (2OC12) for high-performance liquid chromatography was studied. It resulted from coupling of LiChrospher Si 100 NH2 and a mesogenic carboxylic acid, 4-(4-(4-(3,4-didoceyloxystyrenyl)phenyl-diazenyl)phenyloxy-methylene) benzoic acid (ILC). ILC was characterized with proton NMR and differential scanning calorimetry, while 2OC12 was characterized by solid state 13C NMR and elemental analysis.

Assay of naproxen in rat serum by high-performance thin-layer chromatography/densitometry.

A simple, sensitive, and reproducible high-performance thin-layer chromatographic method using densitometry is presented for the determination of naproxen in rat serum. Only 0.1 mL serum was used for extraction.

Synthesis and properties of two new liquid crystals: an analytical and thermodynamic study.

Synthesis, analytical performances, thermodynamic and surface properties of two new liquid crystals substituted with poly(ethylene oxide) chains are described. The first of them is N,N'-diphenyl-[4-[2,3,4-tri[2-(2-metoxyethoxy)ethoxy]benzylidene]i mine]piperidine (LC1) and the second is 2-hydroxy-3-methyl-4-[4-[2-(2-butoxyethoxy)ethoxy]] 4'-[4-[2-(2-butoxyethoxy)ethoxy]styryl]azobenzene (LC2). The nematic ranges of the two liquid crystals, determined by differential scanning calorimetry do not interfere.

Assay of tinidazole in human serum by high-performance thin-layer chromatography--comparison with high-performance liquid chromatography.

Determination of tinidazole in human serum by high-performance thin-layer chromatography (HPTLC) is presented. It includes use of 10 x 10 cm plates coated with silica gel 60 and chloroform-acetonitrile-acetic acid (60 + 40 + 2) as mobile phase. Quantitation was performed by densitometry at 320 nm.

Direct assay of tinidazole in human serum by micellar liquid chromatography.

A liquid chromatographic procedure for the direct determination of tinidazole in human serum is presented. It includes the use of a micellar mobile phase consisting of SDS (5.10(-2) M): propan-1-ol; (94:6, v/v) and a mu Bondapak CN column with UV detection at 320 nm.

Direct determination of theophylline in human serum by high-performance liquid chromatography using zwitterionic micellar mobile phase. Comparison with an enzyme multiplied immunoassay technique.

A liquid chromatographic procedure is reported for the direct determination of theophylline in human serum. It includes the use of a micellar zwitterionic mobile phase [10(-3) mol l-1 3-(dimethyldodecylammonio) propanesulfonate (also known as C12 DAPS)-propanol (97 + 3, v/v) and a muBondapak phenyl column. Detection is based on ultraviolet absorption at a wavelength of 273 nm.

Determination of furosemide in rat plasma using HPLC and liquid scintillation.

A rapid and convenient HPLC method for the determination of furosemide in plasma is described. The method uses a buffered mobile phase containing 22% (v/v) acetonitrile. The precision, detection limit and the correlation between the HPLC method and a liquid scintillation determination of furosemide are satisfactory.