Showing papers in "Journal of Chromatographic Science in 1989"

Chromatographic Characterization of Silica C18 Packing Materials. Correlation between a Preparation Method and Retention Behavior of Stationary Phase

Abstract: Differentes phases stationnaires greffees C 18 sont preparees selon diverses conditions et leurs proprietes chromatographiques sont etudiees

Fundamentals and Applications of Supercritical Fluid Extraction in Chromatographic Science

Abstract: [/ The unique properties of supercritical fluids have prompted their use for a variety of applications in the field of analyticai chemistry. Perhaps the most widely cited use of these compressed fluids has been in the field of chromatography, either as mobile phase eluents or as extraction solvents. This study examines the various modes in which supercritical fluid extraction (SFE) can be employed by the chromatographer. Extraction, solubilization, and fractionation conditions are predicted by the application of well-known solution thermodynamic principles. Experimental results are reported for the removal of lipid phases from natural products and the coextraction of pe,sticide moieties. Finally, a method of predicting the required mobile phase pressures for solubilizing and fractionating oligomeric mixtures in supercritical fluid chromatography is compared with literature data.

Inductively Coupled Plasma Mass Spectrometry and Atomic Emission Spectrometry Coupled to High-Performance Liquid Chromatography for Speciation and Detection of Organotin Compounds

Abstract: Inductively coupled plasma mass spectrometry (ICP/MS) is utilized as a detector for several organotin species separated by high-performance liquid chromatography. Detection limits obtained by ICP/MS are 3 orders of magnitude lower than those obtained with inductively coupled plasma atomic emission spectrometry (ICP/AES) detection under the same chromatographic conditions. Chromatographic detection limits are higher than conventional solution nebulization for the same compound by a factor of 20. Ion-exchange chromatography yields linear response over 3 orders of magnitude, while ion pair chromatography gives a linear response of only 2 orders of magnitude as a result of poor resolution. The relative standard deviation for the injection of 20 ng of tin compounds is less than 10%.

Enrichment of tocopherols in wheat germ by directly coupled supercritical fluid extraction with semipreparative supercritical fluid chromatography.

Abstract: Enrichment of tocopherol by coupled supercritical fluid extraction/preparative supercritical fluid chromatography is described. Wheat germ powder is used as the starting material and is subjected to supercritical fluid extraction with carbon dioxide. The extracted oil containing tocopherols is concentrated and trapped on a silica gel column by reducing the pressure of carbon dioxide. The trapped oil is then eluted and separated on a silica gel column of 20 mm i.d. x 20 mm length. The column effluent is fractionated by monitoring UV absorption at 290 nm. With this method, tocopherol content of the wheat germ is enriched 100-fold.

The Application of Porous Graphitic Carbon as an HPLC Stationary Phase

Abstract: Etude de la phase stationnaire pour la separation des isomeres du cresol, des analogues des steroides, des antibiotiques et des isomeres de produits naturels

Direct determination of chromium (III) and chromium (VI) with ion chromatography using direct current plasma emission as element-selective detector

Abstract: A method is described that utilizes direct current plasma atomic emission spectrometry as an element-selective method of detection for ion chromatographic determination of chromium(III) and chromium(VI) species. The eluting chromium-containing species are detected on the basis of the atomic emission of chromium without any species conversion. Both anion and cation separator columns give similar results when used with varying sample matrices. By employing an on-column preconcentration procedure, the detectable concentrations of the chromium species are reduced to less than 1.0 ppb. This method is applied to the determination of chromium species in human serum, natural water, and industrial process stream samples.

Gradient separation of PTH-amino acids employing supercritical CO2 and modifiers.

Abstract: Twenty-four PTH-amino acids are rapidly and efficiently separated on a packed cyanopropyl Zorbax column by gradient elution of supercritical CO2 and tetramethylammonium hydroxide-modified methanol. Complete or partial resolution of 22 derivatives is observed with only valine coeluting with norleucine and lysine coeluting with asparagine. A wide variety of stationary phases and modifiers are investigated with supercritical CO2 in attempting to achieve the separation in less than 15 min. Critical to achieving a rapid and efficient separation is the control of modifier flow into the CO2. No modifier is required for elution of neutral PTH-amino acids. The addition of base plays a major role in the elution of acidic and basic PTH-amino acids. Peak tailing is minimized and the elution order of several peaks is altered upon incorporation of reagent into the mobile phase.

Postcolumn Techniques: A Critical Perspective for Ion Chromatography

Abstract: Part I. General overview and systems with suppressors. Postcolumn techniques represent a particularly fast-growing area in ion chromatography (IC). The developments since 1985 are surveyed in this paper. A general overview of reagent introduction means, including membrane devices and reaction conduit designs - especially various geometrically deformed open tubular designs - is provided. Part II. Determination of metals, various ionic and ionizable species. This review discusses the direct and indirect absorptiometric, fluorometric, and electrochemical detection of metal species, including rare earth elements, alkyltin, and alkyllead compounds. Part III. New methods on the horizon. The final part of this three-part review discusses chemiluminescence detection. Photolytic methods for derivatization before electrochemical detection is suggested as an important avenue for exploration. The use of postcolumn reactors built of metal tubes, wires and powder for selective reductions, electrochemical generation of reagents, fluorescence enhancement by inclusion complex formation by cyclodextrins, the coupling of reversed-phase liquid chromatography to electron capture detectors, and post separation zone compression to sharpen otherwise broad chromatographic peaks are critically reviewed.

Packed-column supercritical fluid chromatography/mass spectrometry via a two-stage momentum separator.

Abstract: The practical utility of a two-stage momentum separator for combining packed-column supercritical fluid chromatography (SFC) with mass spectrometry (MS) is described. A Hewlett-Packard model 1084B liquid chromatograph modified for packed-column SFC is connected to a linear fused-silica capillary restrictor housed in a heated probe held at 60 degrees at the terminus. A makeup of coaxial helium gas (1.5 L/min) or dissolved solvent (0.2-0.4 mL/min) can be introduced at the point of supercritical fluid expansion. The latter SFC effluent (0.3-2.0 mL/min) is expanded into a heated (44 degrees) desolvation chamber and directed through a nozzle positioned at the entrance of a two-stage momentum separator. Enrichment of the analyte relative to the volatile gases allows the transfer of sample particles to the MS ion source to produce electron ionization of flash-volatilized eluates. On-line SFC/MS separation and detection of low microgram levels of involatile, thermally labile analytes in synthetic mixtures is accomplished. Identification of an unknown compound in a drug tampering incident and the identification of an unknown metabolite isolated from horse urine is also accomplished.

Unified Fluid Chromatography

Abstract: Des separations chromatographiques avec des modes differents peuvent s'effectuer avec un systeme chromatographique unique en changeant la temperature et la pression dans la colonne. Separations des hydrocarbures en chromatographie en phase gazeuse et des oligomeres du styrene en chromatographie SFC

A Sequential Analysis for Volatile Organics in Water by Purge-and-Trap Capillary Column Gas Chromatography with Photoionization and Electrolytic Conductivity Detectors in Series

Abstract: Systeme pour analyser 58 composes organiques halogenes et aromatiques dans de l'eau potable

Comparison of Thermodynamic Retention Behaviors on Various C18 Columns Different in Their Hydrophobicity

Abstract: Afin de caracteriser les materiaux de garnissage, un parametre de solubilite apparente de la phase stationnaire est estime en prenant compte differents materiaux C 18 avec un eluant donne. La relation entre la polarite de la phase stationnaire et les comportements de retention thermodynamique des bases de la purine est etudiee

CP-MAS13C Nuclear Magnetic Resonance Spectra for Identification of Functionality of Octadecylsilica Bonded Phases

Abstract: La methode RMN a polarisation croisee, a rotation de l'angle magique est comparee a la methode de la retention pour l'identification de la fonctionnalite des phases stationnaires greffees

Cleanup of environmental sample extracts using Florisil solid-phase extraction cartridges.

Abstract: Disposable cartridges containing 1 g of Florisil are investigated for cleanup of extracts obtained from various environmental matrices. Elution patterns and recoveries are determined for 22 chlorinated hydrocarbons and 16 phthalate esters in the presence of interferents such as corn oil, diesel hydrocarbons, organochlorine pesticides, and chlorinated phenols. Hexane, hexane/diethyl ether (1:1), hexane/acetone (9:1), and various combinations of hexane/methylene chloride are used as eluants.

Calculation of chromatographic dead times and retention indices with the aid of a computer program in BASIC

Abstract: A computer program is presented for calculating chromatographic dead time from the observed retention times of an homologous series of standards using the iterative approximation procedure of Guardino et al. The program is written in BASIC and is readily adaptable to most microcomputers capable of using BASIC. Corrected retention times and capacity factors of standards and of samples are also calculated by the program. Examples of applications in gas chromatography and reversed-phase high-pressure liquid chromatography are presented. A listing of the BASIC program is given.

Zwitterionic Stationary Phases in HPLC

Abstract: Etude des echangeurs d'ions amphoteres sur silice. Caracterisation de ces nouvelles classes d'echangeurs a l'aide de la spectrometrie IR a transformee de Fourier par reflexion diffuse