bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐speed micellar electrokinetic capillary chromatography of the common phosphorylated nucleosides
Authors: Liu Jinping , Banks J. Fred , Novotny Milos
Published: May 2005

A high‐speed separation of the mono‐, di‐, and triphosphorylated common ribonucleosides has been explored using micellar electrokinetic capillary chromatography (MECC). Retention behavior in terms of electroosmotic flow, peak capacity (to/tmc) and resolution can be manipulated by the choice of surfactant type and the concentration in the buffer phase. The relative effects of an anionic surfactant, SDS, and two cationic surfactants, DTAB and HTAB, were explored and optimized to produce an effective separation of the solutes.
Splitless injection method with mixing chamber in capillary supercritical fluid chromatography
Authors: Hirata Y. , Inomata K.
Published: May 2005

Mixing, hence dilution, of organic sample solvents with a carbon dioxide mobile phase was an effective method for solute focusing. Mixing was affected by the density differences between sample solvents and mobile phase as well as the orientation of the injector assembly. The use of two mixing chambers connected in series improved mixing and allowed a 1‐μL injection.
Analytical separation of polystyrene nanospheres by capillary electrophoresis
Authors: VanOman Barbara B. , McIntire Gregory L.
Published: May 2005

The analytical capillary electrophoretic separation of polystyrene nanospheres is reported. Although these particles are negatively charged and possess intrinsic mobilities, their Separations are based upon particle size with the smallest particles having the highest velocity through the capillary. Pretreatment of the capillary with a cationic surfactant is necessary to observe these Separations. Interestingly, particles larger than about 700 nm in diameter cannot be observed to move through a 50‐μm‐ i.d. capillary, whereas particles as small as 39 nm in diameter can be resolved in this system. In contrast to normal electrophoretic Separations, the mechanism of this process appears to be that of particlexapillary wall interaction as mediated by the adsorbed surfactant.
Separation of polyamines in rat tissues by capillary electrophoresis
Authors: Tsuda Takao , Kobayashi Yasufumi , Hori Akihiro , Matsumoto Takatoshi , Suzuki Osamu
Published: May 2005

Free polyamines in rat tissues were determined by high performance capillary electrophoresis using fluorescence detection. After precipitation of proteins with perchloric acid, the sample solution was derivatized with fluorescamine using a microscale procedure. Ethylenediamine was added to the medium to avoid adsorption of polyamines onto the capillary wall. An internal standard of 6‐amino‐n‐caproic acid a was used. To improve detector sensitivity, the fluorescence signal was collected with a cylindrical lens. The minimum detectable amount and concentration of the sample for the present method were around 200 fmol and 10 nmol mL−1, respectively.
Extended path length UV absorbance detector for capillary zone electrophoresis
Authors: Grant Iain H. , Steuer Wolfgang
Published: May 2005

A method of UV absorbance detection for use in capillaries using axial as opposed to transcolumn illumination is described in which laser‐induced fluorescence acts as a tool for determining, indirectly, the absorbance within a given length of the capillary. The length of the optical path can be chosen arbitrarily, regardless of the capillary diameter. The technique is demonstrated by means of capillary zone electrophoresis (CZE), in which path lengths of up to a few millimeters can be tolerated without serious loss of separation efficiency. Results for 50‐μm‐diameter capillaries show that optical densities consistent with an optical path of 3 mm can be obtained. This leads to a considerable increase in absorbance signal, compared with the usual transcolumn UV absorption technique. It is concluded that further exploitation of the technique requires the use of a more stable light source.
Characterization of low molecular weight poly(acrylic acid) samples by capillary supercritical fluid chromatography and capillary supercritical fluid chromatography–mass spectrometry
Authors: Pinkston J. David , Delaney Thomas E. , Bowling Donald J.
Published: May 2005

Low molecular weight poly(acrylic acid) (PAA) samples were derivatized to increase their solubilities in the supercritical mobile phase, CO2. tert‐Butyldimethylsilyl ester derivatives provided better chromatographic performance and molecular weight range than did trimethylsilyl or methyl esters. Individual oligomers were resolved through approximately n = 28. Higher oligomers, up to approximately n = 45 (corresponding to an underivatized molecular weight of more than 3300), were eluted from the column but were not resolved. Ammonia chemical ionization and electron ionization supercritical fluid chromatography–mass spectrometry data revealed that the PAA terminal groups of the samples studied were sulfonate and hydrogen.
On‐line isotachophoretic sample preconcentration for enhancement of zone detectability in capillary zone electrophoresis
Authors: Foret Frantisek , Sustacek Vladimir , Bocek Petr
Published: May 2005

A simple isotachophoretic (ITP) preconcentration column for subsequent online capillary zone electrophoresis is described, and its use for enhancing detectability in capillary zone electrophoresis (CZE) is evaluated. Sample preconcentration using ITP is shown to enhance detectability in CZE by several orders of magnitude. Experimental verification of the detectability gain is demonstrated for cationic and anionic separations; an increase in detectability of more than 200‐fold was achieved. The practical applicability of this method is demonstrated using a direct analysis of thiamine in human blood.
Detection and sequence analysis of tryptic peptides by microcolumn liquid chromatography‐tandem mass spectrometry using an electrospray interface
Authors: Hail Mark , Lewis Sydell , Jardine Ian , Liu Jinping , Novotny Milos
Published: May 2005

Fused‐silica packed LC capillaries were interfaced with a triple quadrupole mass spectrometer through the electrospray ionization device. The coupling of these powerful techniques is suitable for structural characterization of constituents of peptide maps generated at high sensitivity. Sequence determinations appear possible at the femtomole level following this approach.
Microanalysis of explosives and propellants by on‐line supercritical fluid extraction/chromatography with triple detection
Authors: Munder Albrecht , Christensen Richard G. , Wise Stephen A.
Published: May 2005

A compact analytical instrument is described which allows microsamples to be extracted with supercritical fluids, and the extract preconcentrated and analyzed by capillary supercritical fluid chromatography in a single coupled unit. Thus, no off‐line sample pretreatment is required, and the possibility of extraneous contamination is reduced. To achieve greater selectivity and sensitivity for selected species, three different detectors (UV absorption, flame ionization and electron capture) were all connected on‐line. This analytical instrument configuration was established by upgrading a commercial capillary supercritical fluid chromatograph using regular chromatographic supplies. To illustrate the analytical utility of this hyphenated technique, an assortment of compounds that are not easily determined by traditional gas chromatographic or liquid chromatographic methods was selected: explosives, propellants, and related species. The instrumental design, as well as selected analytical conditions (sample pretreatment, extraction, preconcentration, separation, and detection) were investigated to improve selectivity and/or sensitivity. The determination of explosive residues on soil is described as an environmental analysis application of the system. Detection limits for some compounds are estimated to be as low as 100 pg. The firearm propellants were characterized through their extractable organic constituents, and the usefulness of such characterization in forensic investigations is discussed. Closely related to this issue is the analysis of the residue in expended cartridge cases. A chromatographic fingerprint was obtained from the propellant used in the ammunition. This fingerprint can be used under certain circumstances to correlate a specific batch of propellant with the residue left in a fired cartridge case.
Preparation of polyacrylamide gel‐filled capillaries for capillary electrophoresis
Authors: Dolnik Vladislav , Cobb Kelly A. , Novotny Milos
Published: May 2005

A procedure for preparing polyacrylamide gel‐filled capillaries, for use in capillary gel electrophoresis, is decribed. The method involves the principle of isotachophoretic polymerization, in which the polymerization initiator is introduced by electromigration to promote gradual polymerization of the acrylamide in a sequential manner along the length of the capillary. This procedure has been found to be superior to other methods for polymerizing gels inside of small‐bore (i.e., 50‐μm i.d.) capillaries, because of the reduced formation of bubbles in the gels during polymerization. The method described is simple, reproducible, and several capillaries can be prepared simultaneously. A preliminary result showing the use of 50‐μm i. d. gel‐filled capillaries for SDS‐polyacrylamide gel electrophoresis of proteins is shown.
Diffusion and thermodynamic measurements by supercritical fluid chromatography
Authors: Roth Michal
Published: May 2005

Applications of supercritical fluid chromatography (SFC) to physicochemical measurements are reviewed. Emphasis is laid on the determination of binary diffusion coefficients at infinite dilution of solutes in supercritical solvents, and on actual or potential applications of SFC to the measurements of thermodynamic quantities in dilute, binary, supercritical mixtures. Physicochemical measurements emerge as a specific application field of SFC with many links to transport phenomena and to molecular thermodynamics of fluid‐phase equilibria.
Application of sample stacking to gravity injection in capillary electrophoresis
Authors: Burgi Dean S. , Chien Ring‐Ling
Published: May 2005

Sample stacking can be used to increase the amount of analyte loaded onto a capillary column without loss in resolution. After the sample is loaded onto the column, the analytes are then separated by conventional capillary zone electrophoresis. When using gravity injection, over an order of magnitude improvement in detection limit is achieved. There is an optimal point for the amount of material which can be injected onto the column based on the resolution desired for the separation.
Diffusion coefficients of oligonucleotides in capillary gel electrophoresis
Authors: Yin Hong‐Feng , Kleemiß Maria Helen , Lux Jürgen Alfred , Schomburg Gerhard
Published: May 2005

Diffusion coefficients of oligonucleotides have been measured in polyacrylamide gel capillaries without application of an electrical field. A relationship between such diffusion coefficients and molecular size of the oligonucleotides could be achieved. The slower diffusion of larger oligonucleotides cannot explain the high separation efficiencies of capillary gel electrophoretic separations alone. By theoretical considerations it became obvious that diffusion coefficients of oligonucleotide molecules and also their intermolecular interaction with the polyacrylamide gel may be considerably changed by application of electrical fields.
Predictability and effect of phase behavior of CO2/propylene carbonate in supercritical fluid chromatography
Authors: Page Steven H. , Raynie Douglas E. , Goates Steven R. , Lee Milton L. , Dixon David J. , Johnston Keith P.
Published: May 2005

The phase behavior (P‐T‐x) of propylene carbonate was studied using a variable volume view cell for the regions applicable to supercritical fluid chromatography (SFC) and extraction (SFE). Type 5 phase behavior was observed. Phase separation was shown to significantly alter retention and selectivity in the analysis of coal extracts by capillary SFC. Propylene carbonate was found to have limited use as a modifier in capillary SFC. With 5.1 mol% propylene carbonate at 60°C, a single phase is maintained only at pressures above 250 atm.

Twenty‐two methods used to estimate critical pressure (Pc), twenty‐seven methods used to estimate critical temperature (Tc), and thirty methods used to estimate critical volume (Vc) were evaluated for various modifiers employed in supercritical fluid chromatography (SFC). None of the methods could predict Pc, Tc, or Vc to within a 5% relative error for all of the modifiers tested. However, several of the methods were successful in predicting Pc, Tc, or Vc to within 5% for select chemical classes of compounds.

Four methods used to estimate the vapor‐liquid critical loci of binary mixtures not only failed to accurately predict vapor‐liquid separation, but failed to predict the type of phase separation occurring. None of the above methods could reliably estimate the critrical parameters of propylene carbonate or the critical parameters of the mixture.
Determination of toluene diisocyanate in air using micro liquid chromatography with UV‐detection
Authors: Brunmark Per , Dalene Marianne , Sangö Carsten , Skarping Gunnar , Erlandsson Per , Dewaele Chris
Published: May 2005

A routine method using micro‐LC for the determination of toluene diisocyanate (TDI) in air is presented. Air is sampled in impingers containing a toluene solution of 9‐(N‐methylaminomethyl)anthracene as derivatization reagent. The samples are evaporated to complete the reaction, dissolved in toluene, and shaken with buffer to remove access reagent. They are finally evaporated again, dissolved in acetonitrile/aqueous triethylamine phosphate solution and analyzed with micro‐LC. The LC‐system, except for the column and detector, consisted of conventional LC components. The concentration range investigated, 10–50 ng mL−1, gave correlation coefficients of 0.995 for the 2,6‐TDI isomer and 0.998 for the 2,4‐TDI isomer. The relative standard deviation for the method was 3.3% for 2,6‐TDI and 1.5% for 2,4‐TDI when analyzing solutions containing 10 ng mL−1 2,6‐TDI and 20 ng mL−1 2,4‐TDI (n = 15). Injection volumes of up to 200 μL gave a linear peak area response. The detection limits calculated for three times the chromatographic noise were 0.15 ng mL−1 for both TDI isomers when injecting 100 μL from a 1‐mL sample. This corresponds to 0.03 μg m−3 with 1 L min−1 air flow through the impinger for 5 min. The detection limits were found to be better than a factor of ten lower compared to conventional LC.
Influence of derivatization on the chiral selectivity of cyclodextrins: Alkylated/acylated cyclodextrins and γ‐/δ‐lactones as an example
Authors: Schmarr Hans‐George , Mosandl Armin , Kaunzinger Astrid
Published: May 2005

Selectively alkylated and acylated cyclodextrin derivatives are suitable stationary phases for capillary GC. To obtain a closer insight into the separation mechanism, an inverse substituted cyclodextrin derivative was synthesized and characterized, and its chiral selectivity was compared with a traditionally substituted and characterized cyclodextrin. The influence of a polar group in the cyclodextrin molecule on the enantioselectivity for γ‐/δ‐lactones is shown with a new, diacylated, cyclodextrin derivative.
Boiling range distribution of petroleum and coal‐derived heavy ends by supercritical fluid chromatography
Authors: Raynie Douglas E. , Markides Karin E. , Lee Milton L.
Published: May 2005

Alternatives to conventional gas chromatographic simulated distillation methods for high boiling materials are reviewed. Operational parameters for the use of supercritical fluid chromatography for simulated distillation are explored and examples for the analysis of both petroleum and coal‐derived samples are compared to conventional gas chromatographic methods and thermogravimetric analysis. Extension of the boiling range determined by simulated distillation to over 800°C is demonstrated. An n‐ octylpolysiloxane stationary phase minimized the aliphatic versus aromatic boiling point discrepancy common to other chromatographic methods.
Influence of pressure on solute retention in liquid chromatography
Authors: McGuffin Victoria L. , Evans Christine E.
Published: May 2005

Although the mobile phase is generally considered to be incompressible in liquid chromatography, the local pressure appears to have a significant effect upon solute retention. In this investigation, laser fluorescence detection was utilized to measure solute retention directly along a reversed‐phase packed capillary column with a methanol mobile phase. For derivatized fatty acids, n‐C10:0 to n‐C20:0, the capacity factors increased systematically by +9.3% to + 24.4% under normal operating pressure conditions (1,500 to 5,000 psi). Whereas the magnitude of this increase in solute retention seems surprising, it appears to correlate well with the unified theoretical model developed by Martire.
Volatile oil analysis of Thymus vulgaris L. by directly coupled SFE/GC
Authors: Hartonen Kari , Jussila Matti , Manninen Pekka , Riekkola Marja‐Liisa
Published: May 2005

Dynamic supercritical fluid extraction (SFE) with CO2 as the supercritical fluid was coupled to capillary gas chromatography (GC). A cryotrap/thermal desorption unit external to the GC was used to collect the extracted compounds and introduce them into the GC column. The reproducibility of the SFE/GC system was tested through replicate analyses of thyme, and the recoveries of thyme components were compared with those obtained from hydrodistilled oil of thyme by GC. Excellent agreement was achieved, but the results showed that chromatographic valves and valve materials may be critical in obtaining good results.
Indirect UV photometric detection in capillary zone electrophoresis for the determination of phytate in soybeans
Authors: Nardi Annalisa , Cristalli Michele , Desiderio Claudia , Ossicini Luigia , Shukla Shyama Kant , Fanali Salvatore
Published: May 2005

A rapid and simple analytical method was developed to determine phytate anion in soybeans. The analysis was performed by capillary zone electrophoresis with indirect UV photometric detection. The determination of phytate was carried out with a background electrolyte in which benzoate was the absorbing ion at 254 nm.
Influence of coiling on performance in capillary electrophoresis using open tubular and polymer network columns
Authors: Wicar Stanislav , Vilenchik Masha , Belenkii Alexii , Cohen Aharon S. , Karger Barry L.
Published: May 2005

The influence of coiling on column efficiency in capillary electrophoresis (CE) has been examined. In open tubular columns of 75‐μm i.d., no significant effect of column coiling on efficiency was observed, even at plate counts of 2 × 106 m−1. The small column internal diameter and radial diffusion in free solution was able to minimize the potential deleterious effect of coiling. With gel‐filled columns of very high efficiency (˜107 plates m−1), the influence of coiling on column efficiency was, however, significant, e.g., a factor of 3 or more loss in plate count per coil. For relatively rigid gels (e.g., 9% T linear polyacrylamide with 7 M urea), this observed loss of column efficiency was attributed mainly to the inability of the polymer network to permit diffusional relaxation of the coiling effects. A significant influence of coiling on column efficiency was also found with medium concentration polymer networks (e.g., 3‐6% T linear polyacrylamide with no urea). The polymer network structure was assumed to change under the influence of mechanical stress caused by coiling, resulting in anisotropy across the column. Furthermore, the changes in structure and in efficiency were found to be time dependent and, in general, reversible. The effect appears to be caused by the shear force imposed on a polymer network structure, since changes are only observed when the column shape is altered after the polymer has been loaded into the capillary.
Packed capillary liquid chromatography/electrospray ionization/mass spectrometry in the pharmaceutical sciences: Characterization of protein mixtures
Authors: Moseley M. Arthur , Unger Steve E.
Published: May 2005

The coupling of packed capillary liquid chromatography with electrospray ionization mass spectrometry has yielded an instrument capable of generating molecular weight information from very complex natural protein mixtures. The use of the packed capillary liquid chromatography columns offers two principle advantages over conventional liquid chromatography columns: high separation efficiencies and very low mobile phase flow rates (100 nL min−1). The low mobile phase flow rates permit the use of a relatively high ionic strength buffer (0.1% trifluoroacetic acid), While delivering a very low mass flux of the buffer to the mass spectrometer.
Syntheses of isomeric cyanobiphenyl‐substituted polysiloxanes for stationary phases in gas chromatography
Authors: Rossiter Bryant E. , Reese Shawn L. , Morgan Sarah , Malik Abdul , Bradshaw Jerald S. , Lee Milton L.
Published: May 2005

Nine isomeric cyanobiphenyl‐substituted polysiloxanes were synthesized using a four‐step procedure and tested as stationary phases in open tubular column gas chromatography.
Novel cyanobiphenylpolysiloxane stationary phases for gas and supercritical fluid chromatography
Authors: Malik Abdul , Ostrovsky Ivan , Sumpter Sheldon R. , Reese Shawn L. , Morgan Sarah , Rossiter Bryant E. , Bradshaw Jerald S. , Lee Milton L.
Published: May 2005

Nine different 25% cyanobiphenyl‐substituted polysiloxane (CBP) stationary phases were evaluated for use in gas and supercritical fluid chromatography. They were easily coated and cross‐linked on fused silica capillaries to produce highly efficient columns. For a 200 μm i.d. column, an efficiency of as high as 5,100 plates m−1 was obtained. For most of the new phases, the upper temperature limit was 300°C. A comparative study of the chromatographic behaviors of the cyanobiphenyl and commercial reference phases was made. Some of the cyanobiphenyl stationary phases showed polarities higher than those for carbowax 20M or 50% cyanopropyl. All six positional isomers of dodecylxylene and the five isomers of four‐ring polycyclic aromatic hydrocarbons were baseline resolved on GC capillary columns with certain of the cyanobiphenyl phases, demonstrating higher selectivity over SE‐54 or Carbowax 20M phases. In SFC, a cyanobiphenyl column provided better separation of a standard coal tar sample than columns with biphenyl or cyanopropyl phases. The retention behavior of fatty acid methyl esters and a mixture of polar solutes was investigated on the cyanobiphenyl and references phases. With respect to certain solute pairs, the selectivities of the new stationary phases were found to increase with temperature. The new cyanobiphenyl phases were found to be useful for GC and SFC separations of various classes of complex mixtures including essential oils, explosives, and polycyclic aromatic hydrocarbons.
Direct examination of separation processes in liquid chromatography: Effect of temperature and pressure on solute retention
Authors: McGuffin Victoria L. , Evans Christine E. , Chen Shu‐Hui
Published: May 2005

In this study, retention processes in reversed‐phase liquid chromatography were examined in situ along an optically transparent column by means of laser‐induced fluorescence. Using a homologous series of derivatized fatty acids as model solutes, the capacity factors were systematically measured as a function of temperature in the range from 10 to 60°C and pressure in the range from 980 to 4,430 psi. A phase transition was observed for the octadecylsilica stationary phase as temperature was decreased and as pressure was increased. From evaluation of its thermodynamic properties during this phase transition, the stationary phase appears to be more similar to a randomly oriented alkane solvent than a highly ordered system such as a phospholipid membrane. Because this phase transition occurs within the range of routine operating conditions in liquid chromatography, it has important implications for both fundamental and practical applications.
Solventless injection technique for microcolumn separations
Authors: Arthur Catherine L. , Chai Meng , Pawliszyn Janusz
Published: May 2005

Thermal desorption of analytes from a solid phase microextraction (SPME) device is the ideal techniques for sample introduction into microcolumns because the solvent is entirely eliminated. SPME is compatible with various injector designs, is independent of the instrument manufacturer, and can be completely automated. It can be used to concentrate the analytes from liquid, gaseous, or headspace samples with equal success. The location of the fiber in the injector for programmable direct and splitsplitless injectors are described since fiber positioning varies with injector design. An SPME injection consists of two parts: desorption in the injector followed by cryofocusing in the gas chromatographic column. The factors affecting desorption and cryofocusing, and the thickness of the column stationary phase. Example of fiber injections of liquid and gaseous samples are discussed.
Reduced elution speed detection for capillary electrophoresis/mass spectrometry
Authors: Goodlett David R. , Wahl Jon H. , Udseth Harold R. , Smith Richard D.
Published: May 2005

A combined capillary electrophoresis/mass spectrometry (CE/MS) method is described that provides an increase in the efficiency of analysis by decreasing the analyte elution rate into an electrospray ionization (ESI) interface. The method is readily implemented by instituting a step change in the CE electric field strength for desired periods of time during a separation. As a result, the m/z range or the number of times an m/z range can be scanned while a solute elutes is increased by a factor proportional to the decrease in CE electric field strength. In addition, the method is shown not to cause any significant loss in separation quality as demonstrated for mixtures of proteins and peptides, while providing an effective gain in sensitivity. This allows an enhancement in the quality of mass spectra recorded while scanning wide m/z ranges. Mass spectra for a set of standard proteins were obtained for injections of 60 femtomole/protein, while analysis of an albumin tryptic digest was obtained for injections corresponding to 40 femtomoles of protein.
Separation of nucleosides and nucleotide‐3′‐monophosphates by micellar electrokinetic capillary chromatography
Authors: Lecoq Anna‐Francesca , Montanarella Luca , Biase Sebastiano Di
Published: May 2005

Simultaneous separation of ionic and neutral compounds in micellar electrokinetic capillary chromatography (MECC) is a consequence of a combination of charge/mass ratios, hydrophobicity and charge interactions at the surface of the micelles. The type of resolution can be chosen mainly by modification of the buffer composition and pH. Reproducibility depends on the capillary tubing characteristics, operating conditions, and temperature effects. We report here on the different buffer compositions, pH, temperature, operating conditions, and capillary tubing treatments for the optimal separation and best reproducibility of deoxynucleosides and deoxynucleotide‐3′‐monophosphates. The effects of different buffer compositions were tested when operating in a constant current mode at 38 μAmps. Lithium phosphate buffer improved the separation speed with little loss in resolution. The best concentration was found to be 20 mM. A concentration of 5% acetonitrile substantially improved the efficiency of the nucleoside peaks and therefore their resolution. The optimum SDS concentration was found to be at 100 mM. The pH has a significant influence on retention time and resolution, and was adjusted for maximum resolution at pH 9.6. Capillary surface treatments were also investigated. Effective heat dissipation occurred below an operating voltage of 15kV, and a temperature of 35°C was found to give a good compromise between efficiency, resolution, and time of analysis. Time of analysis can be decreased by using higher operating voltages without compromising the resolution. Efficiencies were 350,000 and 235,000 plates m−1 for the nucleosides and nucleotides, respectively. The reproducibility of retention times was good with coefficients of variation below 1%, which allows the possibility for automatic fraction collection.
tert‐Butyldimethylsilyl‐substituted cyclodextrin derivatives as versatile chiral stationary phases in capillary GC
Authors: Maas Birgit , Dietrich Armin , Karl Volker , Kaunzinger Astrid , Lehmann Detmar , Köpke Thomas , Mosandl Armin
Published: May 2005

tert‐Butyldimethylsilylated cyclodextrin derivatives dissolved in polysiloxanes were shown to be versatile chiral stationary phases for the differentiation of important chiral food and flavor ingredients and chiral acids of biochemical and pharmaceutical interest.
Introduction of large volumes of methylene chloride in capillary GC with electron capture detection
Authors: Staniewski Jacek , Janssen Hans‐Gerd , Rijks Jacques A. , Cramers Carel A.
Published: May 2005

In this paper, a system is presented that allows direct introduction of large volumes of methylene chloride in capillary gas chromatography (GC) using the electron capture detector (ECD). The system is based on a two‐dimensional (one‐oven) GC instrument equipped with a programmed temperature injector. During sample introduction, the solvent is eliminated via the split line. Residual traces of methylene chloride that enter the precolumn are eliminated via a column‐switching device located between the precolumn and the analytical column. The system is used for the analysis of pesticides and polychlorinated biphenyls (PCBs) in methylene chloride at ultra low concentrations. The introduction of large sample volumes significantly improved the detection limits. Using the system described here, the solvent exchange step, normally necessary when the ECD is used to analyze samples containing methylene chloride as the solvent, is no longer required.
Determination of 5‐hydroxymethyl‐2‐furaldehyde in honey by micellar electrokinetic capillary chromatography
Authors: Corradini Claudio , Corradini Danilo
Published: May 2005

Methodology using micellar electrokinetic capillary chromatography (MECC) to determine 5‐hydroxymethyl‐2‐furaldehyde (HMF) as a degradation product of carbohydrates in aged and thermal treated honey is described. Sodium dodecyl sulfate was employed as the anion surfactant in a phosphate buffer, pH 7.5. The sample preparation was limited to dissolution of honey in water and addition of an internal standard solution (2‐furylmethylketone). The method was highly selective and exhibited high reporducibility, accuracy, and short analysis time.
Dual chiral recognition system involving cyclodextrin derivatives in capillary electrophoresis
Authors: Mayer Sabine , Schleimer Michael , Schurig Volker
Published: May 2005

An immobilized chiral stationary phase, Chirasil‐Dex, coated onto the inner surface of a 50 μm i.d. capillary and cyclodextrin derivatives added to the running buffer were simultaneously used for the study of enantiomer separations by capillary electrophoresis. Dependent on the cyclodextrin concentration in the mobile phase, a reversal of the elution order of enantiomers due to dual chiral recognition mechanisms was observed.
Analysis of intracellular ribonucleotide pools in a drug‐treated human cancer cell line using capillary zone electrophoresis
Authors: Liu Shaofan , North James A. , Murray Byron K. , Huang Mingxian , Lee Milton L.
Published: May 2005

Capillary zone electrophoresis was used to separate and identify intracellular ribonucleotides and nucleotide analogues from ribavirin‐ and guanine‐treated HeLa cells, a human cervical carcinoma cell line. Nine ribonucleotides in HeLa cell extracts were identified and quantitated. In cell extracts, the average ATP/ADP ratio was 6.5 and the average energy charge of the HeLa cells was 0.92. In HeLa cells treated with guanine, the GTP pool increased to 309% of control values. When cells were treated with ribavirin, the GTP pool was reduced to 33% of nondrug treated controls. Ribavirin triphosphate reached levels of 113.25 nmols/107 cells, while ribavirin diphosphate reached levels of 4.96 nmols/107 cells.
Capillary zone electrophoresis of pathological metabolites in phenylketonuria
Authors: Dolník Vladislav
Published: May 2005

The pathological metabolites (phenylpyruvate, 2‐hydroxyphenylacetate, phenyllactate, and phenylacetate) from urine of phenylketonuric individuals were separated by capillary zone electrophoresis within 12 minutes. Significant differences in the content of these metabolites in urine can be found if a healthy man, a phenylketonuric newborn, and a phenylketonuric individual on a low‐phenylalanine diet are compared.
Quantitative determination of ionized calcium and total calcium in human serum by capillary zone electrophoresis with indirect photometric detection
Authors: Zhang Rulin , Shi Honlan , Ma Yinfa
Published: May 2005

We have developed a new method to quantitatively determine ionized calcium and total calcium by using high performance capillary electrophoresis (HPCE) with indirect photometric detection. Other cations such as Na+, K+, and Mg+ can also be quantitatively determined. A 70 cm × 50 μm i.d. fused silica capillary was used for the separation. The detection window was located 25 cm from the cathodic end, and the detection wavelength was set at 214 nm. A 100 mM imidazole solution at pH 7.4 (adjusted with 5% H2SO4) containing 0.1% hydroxypropylmethylcellulose (HMC, 4000 centipoise) was used as background electrolyte. Whole serum was injected for 5 s at 15 kV for the determination of ionized calcium. The total calcium levels in a number of human serum samples were determined by HPCE and compared with the NIST reference method (atomic absorption), and the results agree with each other within 95% confidence. Two NIST standards were analyzed by HPCE, and the results fit each other perfectly. The ionized calcium levels in sera by this HPCE method have been compared with those obtained with ion‐selective electrode (ISE) method, and the results were lower than those of ISE, which was what we anticipated. The effects of sample temperature and buffer pH were studied.
Sensitivity and detection limit enhancement of gas chromatographic detection by thermal modulation
Authors: Liu Zaiyou , Phillips John B.
Published: May 2005

A thermal desorption modulator placed between the outlet of a column and the inlet of a detector enhances chromatographic sensitivity, signal‐to‐noise ratio and detection limit. The modulator operates at a selectable frequency up to 10 Hz, chopping the effluent from the chromatographic column into a series of concentration pulses whose envelope follows the form of the chromatogram. Measuring the difference between the top of each concentration pulse and the following valley demodulates the detector output signal. Thermal modulation increases the recorded signal amplitude because the modulator concentrates substances emerging from the column over a relatively long time into concentration pulses of much shorter duration. Thermal modulation also attenuates low frequency drift. Using this technique enhanced the signal amplitude of a flame ionization detector by a factor of 15 and the signal‐to‐noise ratio by a factor of 5.
Automated on‐line solid phase adsorption/supercritical fluid extraction/supercritical fluid chromatography of analytes from polar solvents
Authors: Ullsten Ulrika , Markides Karin E.
Published: May 2005

An automated setup for on‐line solid phase adsorption (SPA)/supercritical fluid extraction (SFE)/supercritical fluid chromatography (SFC) was evaluated. Low nanogram amounts of analytes dissolved in ethanol were delivered in the form of injections (≥ 10 μL) to the solid phase adsorbent consisting of deactivated glass beads, and the analytes were then extracted with supercritical carbon dioxide. The analytes were applied to the adsorbent by an autosampler, which also controlled rinsing and adsorption times. During the chromatographic run, the adsorbent was automatically cleaned with high density supercritical carbon dioxide to be ready for the subsequent injection. Memory effects were between 0 and 4% depending on the analyte, and the reproducibilities were between 6 and 17% of the relative peak areas.
Modifier addition in microcolumn supercritical fluid chromatography with a high pressure pulsed valve
Authors: Francis Eric S. , Lee Milton L. , Richter Bruce E.
Published: May 2005

The need for mixed mobile phases at low flow rates suitable for capillary and packed capillary supercritical fluid chromatography (SFC) has led to the use of an air actuated high pressure prime/purge valve for on‐line modifier introduction. This valve can consistently deliver small amounts of modifier into the mobile phase, and allows rapid changes of modifier concentrations. Methanol modified carbon dioxide (CO2), from 0.5 to 15 mole percent, has been generated using this valve at a flow rate compatible with a packed capillary column without the need for flow splitting. Two instrumental configurations were used to evaluate the valve. One configuration used separate pumps for the mobile phase and the modifier. The other configuration used only one pump with a pneumatic amplifier as the modifier reservoir. The valve provides reproducible modifier concentrations, percent relative standard deviation (%RSD) for retention times less than 2%, and dependable use, leak free after > 250,000 pulses. The use of this valve, with both the 2‐pump and 1‐pump/pneumatic amplifier configuration is demonstrated. The effects of modifier addition on the retention times of components in several samples are shown.
Supercritical fluid extraction and clean‐up with temperature fractionation: Application to determination of polychlorinated dibenzo‐ρ‐dioxins
Authors: Miao Zhuang , Zhang Zhouyao , Pawliszyn Janusz
Published: May 2005

Supercritical fluid extraction (SFE) and clean‐up with neat carbon dioxide (CO2), selective sorbents and high extraction temperature was developed as a sample preparation method. The effects of temperature and pressure on SFE efficiencies were investigated by spiking a polychlorinated dibenzo‐ρ‐dioxin (PCDD)/polychlorinated biphenyl (PCB) standard mixture onto a Florisil™ adsorbent and extracting these compounds at different temperatures and pressures with neat CO2. High extraction temperatures and pressures were found to increase the extraction rate and efficiency. PCDDs were quantitatively extracted from Florisil™ only when the temperature was raised to 200°C and the pressure was 9000 psi. PCBs were efficiently extracted at low temperature and pressure, such as 50°C and 2000 psi. Fractionation of PCBs from PCDDs with Florisil™ using CO2 was accomplished by first quantitatively recovering all of the PCBs at 3500 psi and 80°C and then the dioxins at 9000 psi and 250°C.

The determination of PCDDs in fly ash was carried out by spiking the fly ash extract (obtained after 80 min extraction at 250°C and 9400 psi using neat CO2) onto FlorislTM, followed by the clean‐up step outlined above. This step produced much cleaner chromatograms compared to direct extraction. The modifier‐free high temperature SFE method produced comparable results to 20 h Soxhlet extraction of fly ash, but it was shorter by an order of magnitude.
Separation of homologous fatty acids by capillary electrophoresis
Authors: Gutnikov George , Beck Wolfgang , Engelhardt Heinz
Published: May 2005

Capillary electrophoretic methods with normal and reversed electroosmotic flows (EOF) and indirect UV detection were developed for the separation of fatty acids. Rapid separation of acids up to C12 was achieved via reversed EOF using 30% acetone, a cationic surfactant and 3,5‐dinitrobenzoic acid as carrier electrolyte. Analysis of acids up to C18 was feasible by normal EOF with 60% acetonitrile and trinitrobenzenesulfonic acid as carrier. Also investigated was the influence of the concentration of various organic solvents on the magnitude and direction of the EOF and on the solubility of the fatty acid solutes. The reversed EOF method was applied to the analysis of acids in fat hydrolysates.
Determination of the electrophoretic mobility of polystyrene particles by capillary electrophoresis
Authors: Huff Barbara VanOrman , McIntire Gregory L.
Published: May 2005

Capillary electrophoresis (CE) can be used to determine the electrophoretic mobilities of polystyrene particles from the migration times of these particles assuming that (1) the particles do not interact with the capillary wall, (2) the particles can be detected, and (3) the colloidal suspension of particles is physically stable over the time course of the CE experiment (i.e., > 5 min). CE offers advantages of small sample size, automation, and ease of analysis. CE determined mobility data are used to qualitatively assess the adsorption of polymeric surfactants onto polystyrene particles.
Microwave‐assisted process (MAP™): Application to the headspace analysis of VOCs in water
Authors: Paré J. R. Jocelyn , Bélanger Jacqueline M. R. , Li Ken , Stafford Sally S.
Published: May 2005

A method combining the techniques of microwave‐assisted process (MAP) and gas chromatography (GC) has been developed for the determination of volatile organic compounds in water. For comparison purposes, MAP and conventional gas‐phase extractions using static headspace methods were performed on laboratory‐spiked water samples. The analytes used as models in this preliminary investigation were benzene, toluene, ethylbenzene, chlorobenzene, o‐, m‐, and p‐xylenes, and 1,2‐, 1,3‐, and 1,4‐dichlorobenzenes. MAP uses microwaves to very rapidly heat the bulk of the matrix and achieve a selective vaporization of the analytes that are then transferred onto the gas chromatographic apparatus via identical sampling conditions. The method was tested over a 10–5000 ppb range and proved capable of yielding excellent linearity (R2 > 0.99999) and precision (RSD 1.4%). Compared to the conventional static headspace extraction method, the MAP extraction method offered enhanced sensitivity as evidenced by a response in signal greater by 35% for aliquots from the same aqueous solutions. This level of performance is achieved within one minute of overall sample preparation time for the MAP method, whereas the conventional static headspace method used for comparison purposes required 30 minutes of equilibration time. Similar performance was observed with actual samples.
Charcoal porous layer open tubular column gas chromatography for permanent gas analysis
Authors: Yun Hao , Lee Milton L. , Markides Karin E.
Published: May 2005

The preparation of charcoal porous layer open tabular (PLOT) columns, and their application to the separation of permanent gases and light hydrocarbons are reported. Two types of charcoal, coconut and darco charcoal, were used to prepare columns from fused silica capillaries. The performance of these columns was compared to that of a commercially available carbon molecular sieve PLOT column. The coconut charcoal PLOT column produced good retention and resolution for both permanent gases and light hydrocarbons; all separations were achieved in less than eight minutes under isothermal conditions. © 1995 John Wiley & Sons, Inc.
Micropreparative focusing of proteins in carrier‐ampholyte‐free solution with electrically controlled compositions of electrolytes
Authors: Pospíchal Jan , Chmelík Josef , Deml Mirko
Published: May 2005

Three proteins (myoglobin, ribonuclease, and cytochrome C) were concentrated, separated, and isolated from a dilute mixture by electrically controlled focusing in carrier‐ampholyte‐free solution. Electrolytes were modified at both sides of the capillary. The described method is suitable for the micropreparation of hundred‐μg quantities of proteins in times comparable to other capillary techniques (tens of minutes). © 1995 John Wiley & Sons, Inc.
Comparison of spherically and irregularly shaped stationary phase packings in microcolumn liquid chromatography
Authors: Vissers Johannes P. C. , Van Den Hoef Edgar C. J. , Claessens Henk A. , Laven Jozua , Cramers Carel A.
Published: May 2005

Spherically and irregularly shaped reversed phase packings were used to slurry pack capillary fused silica columns. The selection of the packing solvents was based on the colloidal properties of the stationary phase particles and investigated by sedimentation experiments. The chromatographic performance of the microcolumns was measured with conventional parameters from plate and rate theories, and the column resistance parameter and separation impedance. Also studied was the time of analysis. The performance of spherical and irregular packings was comparable with a light preference for spherically shaped materials when time of analysis is concerned. © 1995 John Wiley & Sons, Inc.
Theoretical studies of the preparation of packed capillary columns for chromatography
Authors: Tong Daixin , Bartle Keith D. , Clifford Anthony A. , Edge Anthony M.
Published: May 2005

The theoretical aspects of the preparation of packed capillary columns for chromatography have been studied. The variation of the mean bulk density of the columns prepared with carbon dioxide fluids in different physical states and under different supercritical fluid conditions has been investigated. A new concept of the packing formation during the preparation of packed capillary columns with supercritical CO2 as packing fluid is described. A mathematical model for column preparation is derived that indicates the importance of the sonication effect in packing process. This studies indicate that the column performances (density and efficiency) can be controlled by varying the packing conditions. The wall effect in packed capillary columns (the effect of the packing densities on the column efficiencies) and the explanation for the production of very long columns are also discussed. © 1995 John Wiley & Sons, Inc.
Silver‐complexed dicyanobiphenyl‐substituted polymethylsiloxane encapsulated particles for packed capillary column supercritical fluid chromatography
Authors: Shen Yufeng , Reese Shawn L. , Rossiter Bryant E. , Lee Milton L.
Published: May 2005

High nitrile content cyano‐substituted polymethylsiloxane encapsulated particles were prepared for double bond selectivity in packed capillary column supercritical fluid chromatography (SFC). Silica particles were deactivated with 50% cyanopropyl‐substituted polymethylhydrosiloxane, and coated with 25% o,p‐dicyano‐p‐biphenyl‐substituted polymethylsiloxane (o,p,p‐DCBP), and 25% m,m‐dicyano‐p‐phenyl‐substituted polymethylsiloxane (m,m,p‐DCBP) stationary phases. Argentation of the particles was carried out by complex formation between silver ions and the cyano groups on the particles. Unsaturated fatty acid methylesters (FAMEs) were used to investigate the selectivity of these packing materials to double bonds using packed capillary column SFC. Separations were performed according to the degree, position, and geometrical configuration of the double bonds. The effect of temperature on selectivity was also investigated. The stability of the packing materials was evaluated by monitoring the loss in selectivity of the oleate/elaidate isomers after washing the column with supercritical CO2 at 300 atm and 85°C. The separation of FAMEs in a commercial fish oil was compared using capillary columns packed with DCBP coated and silver‐complexed particles.
Field‐programmed flow field‐flow fractionation
Authors: Botana Ana M. , Ratanathanawongs S. Kim , Giddings J. Calvin
Published: May 2005

A flow field‐flow fractionation (FIFFF) system capable of accurate and reproducible flowrate programming has been assembled and tested. This modified system consists of three computer‐controllable pumps, two that regulate the incoming and outgoing cross flowrates and one that controls the channel flowrate. The system also has a computer‐linked balance that allows for instantaneous measurement of the cross flowrate. Programming of the field strength (or cross flowrate) was used to decrease the analysis time and improve detectability of late eluting peaks in FIFFF analysis. A six component latex mixture, with microspheres ranging from 20 to 426 nm in size, was used as a test material. With programming, this mixture can be separated in 8 min. © 1995 John Wiley & Sons, Inc.