High performance liquid chromatography of terpenoids

HPLC-separation using a reversed-phase system is described for phytosterols, pentacyclic triterpenoid acids, -diols and –ketones.     

Determination of flurazepam and its hydroxyethyl and dealkyl metabolites by some packed and capillary ECD-GLC methods: Application to pharmacokinetic studies

A sensitive gas-liquid chromatographic assay was developed for plasma determinations of flurazepam (F), N1-desalkylflurazepam (DF), and N1-hydroxyethylflurazepam (HF). The internal standards used were delorazepam for F and DF and 1 ã-hydroxymidazolam for HF. Following extraction and derivatization for HF, these compounds were analyzed by ECD-GLC, using either glass packed columns (poly A 103 for F and DF, OV 225 for HF) or CP-Sil 5 capillary columns for DF and HF. The detection limit of the packed-column assay was approximately 3ng/ml for HF and DF, and 5ng/ml for F; with capillary GLC analysis, the sensitivity limit for HF and DF was lower than 1 ng/ml. These methods were used for pharmacokinetic investigations after i. v. administration of these compunds.     

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Analysis of gases containing inorganic and organic compounds using a combination of a thick-film capillary column and a packed adsorption column

A gas chromatographic system consisting of one multiport valve, two (hot-wire and flame-ionization) detectors and two analytical columns (one thick-film capillary and one packed adsorption column) is used for the analysis of gas samples containing a number of inorganic compounds (hydrogen, argon, oxygen, nitrogen, carbon monoxide, and carbon dioxide) and organic compounds. Examples include samples containing hydrocarbons up to n-nonane and benzene and toluene. The system also permits the analysis of more complicated samples containing, for example, alcohols, in addition to hydrocarbons.     

The effects of modifiers in supercritical fluid chromatography

Investigations have been initiated to examine the basic elements of resolution and how they vary individually and collectively in terms of modifiers used in supercritical fluid chromatography (SFC). Capacity factors (k′) have been determined for a mixture of polynuclear aromatic hydrocarbons from SFC experiments as function of modifier identity and concentration using different stationary phases. Using carbon dioxide as the primary mobile phase, the modifiers investigated included methanol, 2-methoxy ethanol, 1-propanol, tetrahydrofuran, dimethyl sulfoxide, acetonitrile, sulfur hexafluoride, and freon 11.     

Some practical experiences in the use of a solventless injection system for packed column supercritical fluid chromatography

The operating characteristics of a solventless injector for packed column supercritical fluid chromatography are described. Successful operation depends on the difference between the volatilities of the analytes and the solvent or matrix being sufficient for their separation by gas purging in a thermostatted precolumn, and also on the existence of an effective re-focusing mechanism at the head of the analytical column for the sample dissolved in liquid or supercritical fluid carbon dioxide. The latter is easily achieved in density programmed operation by stationary phase trapping at low fluid densities or phase ratio trapping by changing the temperature at low to moderate fluid densities. The solventless injector can easily accommodate sample volumes from 1–100 μl and is easily adapted for in-line derivatization using reagents which can, after reaction, be eliminated by gas purging. For general purposes the solventless injector can be used to overcome most of the problems encountered when rotary valve loop injectors are used with small bore packed columns, and will probably replace this type of injector as the injector of choice for supercritical fluid chromatography with mobile phases of low polarity.     

Mathematical simulation of radial heat transfer in packed beds by pseudohomogeneous modeling

Uniform flow regime and constant effective thermal conductivity inside packed beds are commonly accepted in the evaluation of the fluid dynamics and heat transfer in such systems.However,several authors have confirmed the presence of an oscillatory velocity profile caused by the effective contribution of porosity profile in the fluid dynamic behavior of packed beds,which directly influences the heat transfer inside the beds.This paper describes the application of a pseudo-homogeneous mathematical ...     

Modeling the reactive processes within a catalytic porous medium

A one-dimensional modelling approach to the reactive processes within a heated homogeneously premixed fuel–air mixture in its passage through a non-adiabatic catalytically reactive porous medium is described. The main focus of this contribution was comparison of the results obtained while using different modeling approaches that include mass diffusion to solid pores versus neglecting it; single step reaction versus detailed kinetic simulation; adiabatic versus non-adiabatic reactor operation; two different approaches accounting for radiation heat transfer. This model was tailored to our experimental results so as to obtain original kinetic data for corresponding global reactions for different types of catalysts and validate at the same time the predictive approaches.     

Separation of unsaturated and aromatic hydrocarbons on capillary columns packed with barium sulphate

Summary Isomeric hydrocarbons with molecules having similar geometry but differing in the electron density distribution were separated on capillary columns packed with barium sulphate, a non-porous ionic adsorbent. Samples of BaSO₄ were washed free of foreign ions and modified by solutions of alkaline metal halides. The selectivity of the separation of unsaturated and aromatic hydrocarbons can be controlled by varying the conditions of the BaSO₄ treatment. Capillary columns packed with the ionic adsorbent were successfully used to separate all xylene and butene isomers, as well as isomers of cis and trans octene-2.     

High efficiency packed column supercritical fluid chromatography of sulfonylurea herbicides and metabolites from large water samples

Summary Five sulfonylurea herbicides were separated by SFC on both a 25 cm and a 1.6 meter packed column. The former produced rapid analysis, the latter allowed high resolution of a complex mixture containing the solutes of interest. The solutes were simultaneously detected with UV, nitrogen-phosphorus (NPD), and electron capture (ECD) detectors. Peaks of breakdown products of sulfonylureas were characterized by their UV spectra and the presence or absence of nitrogen and chlorine from their NPD and ECD response. Both parent and breakdown products of sulfonylureas were on-line extracted from large water samples with detection limits as low as 50 parts per trillion.