bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractIn 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

AbstractMethodology 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

AbstractAn 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

AbstractCapillary 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

AbstractThe 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

AbstractWe 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

AbstractA 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

AbstractAn 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

AbstractThe 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

AbstractSupercritical 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

AbstractCapillary 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

AbstractCapillary 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

AbstractA 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

AbstractThe 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

AbstractThree 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

AbstractSpherically 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

AbstractThe 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

AbstractHigh 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

AbstractA 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.
A new method for the preparation of polymeric porous layer open tubular columns for GC application
Authors: Shen Thomas C. , Wang Mei‐Ling 
Published: May 2005

AbstractA new method to prepare polymeric PLOT columns by using in situ polymerization technology is described. The method involves a straightforward in situ polymerization of the monomer. The polymer produced is directly coated on the metal tubing. This eliminates many of the steps needed in conventional polymeric PLOT column preparation. Our method is easy to operate and produces very reproducible columns, as shown previously (T. C. Shen, J. Chromatogr. Sci. 30, 239, 1992). The effects of solvents, tubing pretreatments, initiators and reaction temperatures in the preparation of PLOT columns are studied. Several columns have been developed to separate (1) highly polar compounds, such as water and ammonia or water and HCN, and (2) hydrocarbons and inert gases. A recent improvement has allowed us to produce bonded polymeric PLOT columns. These were studied, and the results are included also. © 1995 John Wiley & Sons, Inc.
Applications of reversed‐phase high performance liquid chromatography using enhanced‐fluidity liquid mobile phases
Authors: Lee Stephen T. , Olesik Susan V. , Fields Steven M. 
Published: May 2005

AbstractEnhanced‐fluidity liquid mobile phases (methanol/H2O/CO2) were used as eluents in reversed‐phase HPLC. The low pressure drop across the column allowed serial connection of micro‐scale columns to achieve the efficient separation of a coal tar sample. Other applications such as the separation of fat soluble vitamins and probucol and related compounds are shown. © 1995 John Wiley & Sons, Inc.
Enantiomer separations using chloroacyl pentyl cyclodextrins as chiral GC stationary phases
Authors: Shitangkoon Aroonsiri , Vigh Gyula 
Published: May 2005

AbstractChloroacyl pentyl β‐cyclodextrin derivatives were synthesized for use as gas chromatographic stationary phases. Capillary columns of identical phase ratios were prepared with the liquid undiluted monochloro‐, dichloro‐, and trichloroactyl phases and the respective column efficiency, capacity factor, and separation selectivity values were determined. For most of the enantiomeric pairs studied, monochloroacetyl pentyl β‐cyclodextrin (M) offers the highest selectivity values, though at the expense of large capacity factors (long analysis times) and low column efficiencies. Dichloroacetyl pentyl β–cyclodextrin (D) provides a good compromise between sufficiently high chiral selectivities and acceptable column efficiencies. Trichloroacetyl pentyl β‐cyclodextrin (T) permits the preparation of very efficient columns, but offers lower chiral selectivities than the other two chloroacyl derivatives. © 1995 John Wiley & Sons, Inc.
Variation of selectivity among the poly(siloxane) stationary phases for gas chromatography
Authors: Poole Salwa K. , Miller Kenneth G. , Poole Colin F. 
Published: May 2005

AbstractThe solvation parameter model is used to characterize the solvent properties of 12 poly(siloxane) stationary phases of varied structure. Selectivity differences are explained in terms of differences in the cohesive energy of the solvents and their capacity for dispersion, dipole‐type, hydrogen bonding, and electron pair complexation interactions. None of the poly(siloxane) stationary phases exhibited significant hydrogen‐bond acid character. Principal component analysis indicates that replacing a methyl group by a phenyl group in the poly(siloxane) backbone predominantly produces incremental increases in the capacity of the stationary phase for dipole‐type interactions (up to about 50 mol% phenyl groups with only small changes at higher phenyl composition). The poly(methylphenylsiloxanes), however, only span a small sector of the selectivity space and provide limited opportunities for selectivity optimization. OV—275 and QF‐1 are identified as important phases with unique characteristics—OV‐275 because of its high cohesive energy and great capacity for dipole‐type and solvent hydrogen‐bond base interactions and QF‐1 because of its unusually small hydrogen‐bond basicity for a phase with an intermediate capacity for dipole‐type interactions as well as a low capacity for n‐ and π‐electron complexation interactions. From these studies it is possible to speculate on the needs for new phases to explore the full selectivity potential of gas chromatography and to address the issue of temperature and its relationship to selectivity. © 1995 John Wiley & Sons, Inc.