bluuebunny/crossref_metadata_2025_split huggingface dataset:
Group separation of crude oil by supercritical fluid chromatography using packed narrow bore columns, column switching, and backflushing
Authors: Skaar H. , Norli H. R. , Lundanes E. , Greibrokk T. 
Published: May 2005

AbstractDetermination of saturates, aromatics, and resins and asphaltenes in crude oil has been made using supercritical fluid chromatography (SFC) with a carbon dioxide mobile phase and flame ionization detection. The separation system consists of three columns. The first column separates resins and asphaltenes from saturates plus aromatics, and the other two columns separate the saturates from the aromatics. The saturates are eluted directly through the three columns, the aromatics are backflushed from the last two columns in the sequence, and the resins and asphaltenes are backflushed from the first column. The properties of three different systems — which respectively employ packed 0.25‐mm‐i.d. fused silica, 0.7‐mm‐i.d. glass‐lined steel, and 1‐mm‐i.d. steel columns — have been investigated. Column diameters of 0.5–0.7 mm are recommended to obtain the best flow rate compatibility with the detector. Good class separations were obtained on all three systems, but, due to practical considerations, the more rugged all‐steel columns were found to be more convenient. In order to improve column reproducibility and stability and increase column lifetime as compared to earlier SFC group separations, changes were made to the column packings. The current system consists of two cyano columns and one silver‐loaded cation exchanger. With standard mixtures and crude oils, close to 100% recoveries were obtained. The analysis time was approximately 15 min. Weight percents of aliphatics and aromatics were determined with response factors of 1.0 and those of the asphaltenes and resins with response factors of 0.7–0.8.
Development of a model for predicting retention times in solvent‐gradient micellar electrokinetic capillary chromatography
Authors: Powell A. Craig , Sepaniak Michael J. 
Published: May 2005

AbstractInstrumentation and a computational method are described that are capable of predicting retention times of solutes separated by solvent‐gradient micellar electrokinetic capillary chromatography (MECC). Theoretical predictions are based on capacity factor, electroosmotic flow rate, and micellar flow rate data obtained by the separation (under isocratic conditions) of a test mixture of fluorescently labeled alkylamines with the use of differing concentrations of organic modifier in the mobile phase. Separations are performed using continuous concave, linear, and convex gradients, and the resultant solute retention times are shown to correlate reasonably well with values obtained from the theoretical model. Thus, a computational method for optimization of solvent‐gradient MECC is made possible.
A comparison of tryptic digests of bovine and equine cytochrome C by comprehensive reversed‐phase HPLC–CE
Authors: Bushey Michelle M. , Jorgenson James W. 
Published: May 2005

AbstractComprehensive two‐dimensional reversed‐phase HPLC–capillary electrophoresis (RP HPLC–CE) was used to compare the tryptic digest fingerprints of horse heart cytochrome C and bovine heart cytochrome C. The peptide fragments were labeled with fluorescamine and detected with a fluorescence detector. The two‐dimensional separation system proved to be reproducible enough to identify some species differences in the tryptic digest fingerprints. Improvements in instrumentation and daily procedures yielding faster analysis times and better reproducibility compared to a previous system are described. Improvements in software yielding gray‐scale images of the two‐dimensional data are described. Identification of selected tryptic fragments was achieved.
Rapid separation of proteins and peptides by reversed‐phase microcolumn liquid chromatography
Authors: Nagae Norikazu , Itoh Hiroko , Nimura Noriyuki , Kinoshita Toshio , Takeuchi Toyohide 
Published: May 2005

AbstractProteins and peptides were separated in the reversed‐phase mode on microcolumns packed with nonporous octadecyl‐group bonded silica gel with an average particle diameter of 4.5 or 20 μm. Separation columns were prepared from glass‐lined stainless steel tubing of 39 or 56‐mm × 0.5‐mm i.d. An artificial mixture of several proteins could be separated within 1 min by split‐flow gradient elution. The system was applied to the separation of a triptic digest of mouse amyloid A. On‐column sample enrichment allowed direct injection of 2‐5 μL of sample solution, leading to improved detectability. The limits of detection were ≤ 1 μg mL−1.
On‐line supercritical fluid extraction/chromatography system for trace analysis of pesticides in soybean oil and rendered fats
Authors: Murugaverl Balasingam , Voorhees Kent J. 
Published: May 2005

AbstractA method for trace analysis incorporating solid phase extraction (extraction and clean‐up) with supercritical fluid chromatography (SFC) for analytes in fats and oils has been developed. Direct coupling (on‐line) of supercritical fluid solid phase extraction with supercritical fluid chromatography (SESPE/SFC) allows analysis of solutes in fats and oils for which on‐line SFE/SFC is unsuitable. The main feature of SFSPE/SFC is that extraction and clean‐up are accomplished in one step using unmodified supercritical carbon dioxide. Extraction/clean‐up is monitored by a photodiode array detector which allows fractionation. The operational set‐up and potential usefulness of the SFSPE/SFC system and applications for pesticide analysis of lipid sample matrices are described.
Capillary supercritical fluid chromatography and microwave‐induced plasma detection of cyclic boronate esters of hydroxy compounds
Authors: Luffer Debra R. , Novotny Milos V. 
Published: May 2005

AbstractA Surfatron microwave‐induced plasma was used for selective detection after capillary supercritical fluid chromatography of various biologically important compounds. Cyclic boronates were formed by esterifying catechols, monosaccharides, and cortisone, with an alkyl‐ or aryl‐substituted boronic acid. An available spectroscopic system was modified so that the third‐order boron emission line at 749.4 nm was utilized. Sensitivity for boron in catechol boronate was 25 pg s−1, and the molar selectivity was >5,000 for both carbon dioxide and nitrous oxide mobile phase. Some comparisons were made with flame ionization detection.
Formic acid modified carbon dioxide as a mobile phase in capillary supercritical fluid chromatography
Authors: Crow Jeffrey A. , Foley Joe P. 
Published: May 2005

AbstractA small percentage (0.3% w/w) of formic acid was added to supercritical carbon dioxide to increase mobile phase polarity and improve separation of polar solutes on three different commercially available capillary columns. Formic acid reduced retention and altered selectivity for several polar compounds. Thermodynamic studies revealed that the enthalpy of solvation was as much as 27 kcal mol−1 more negative when formic acid was added due to increased solute‐solvent interactions. Entropy measurements show that formic acid modified mobile phase is more ordered than a pure carbon dioxide mobile phase, apparently as a result of modifier clustering around polar solutes. Van't Hoff plots for some very polar solutes showed a region of retrograde behavior at low temperatures and pressures, indicating an increase in modifier clustering. Comparisons between pure and modified mobile phases were also made by examining practical separations obtained with each, revealing differences in retention, selectivity and peak shape.
Crown ether substituted polysiloxanes as stationary phases for open tubular column gas chromatography
Authors: Ge Jilong , Fu Ruonong , Zhang Aiqin , Zhu Rongping , Deng Jinghui , Gu Junling , Zhu Jiya , Huang Zaifu , Zhang Bin 
Published: May 2005

AbstractTwo new crown ether substituted polysiloxanes, 4‐propylbenzo‐15‐crown‐5polysiloxane(PSO‐B‐15C5) and propyloxydibenzo‐14‐crown‐4polysiloxane (PSO‐DB‐14C4), were prepared and used as stationary phases coated on fused‐silica open tubular columns. The chromatographic characteristics, including column efficiency, polarity, phase transition temperature, allowable operating temperature range and selectivity, were studied. A unique selectivity of these columns was found for the separation of all six dimethylphenol isomers. The separation mechanism is discussed.
Copper wire amperometric detector for capillary electrophoresis
Authors: Engstrom‐Silverman Charlotte E. , Ewing Andrew G. 
Published: May 2005

AbstractThe use of a copper wire amperometric detector for capillary electrophoresis is reported. Detection is accomplished by use of a porous glass joint, which allows amperometric detection at a copper wire electrode inserted in the end of the capillary. An anodic current is produced by a change in the copper oxide film solubility, resulting from complexation of copper ions with certain analytes at the electrode surface. This copper/copper oxide electrode has been used to detect nonelectroactive native amino acids and dipeptides. Subfemtomole detection limits in picoliter injection volumes have been obtained without solute derivatization. In addition, simultaneous analysis of nonelectroactive amino acids and electroactive catecholamines has been demonstrated.
Optimization of internal valve injection in open tubular column supercritical fluid chromatography
Authors: Tuominen Jari P. , Markides Karin E. , Lee Milton L. 
Published: May 2005

AbstractAs in the case of all chromatographic methods, the ideal sample introduction method for supercritical fluid chromatography (SFC) would provide a narrow and sharp solvent peak (or no solvent peak), quantitative transfer of the sample into the column, and high reproducibility. Elimination of the solvent before the solutes enter the column would be preferred; however, this practice is always associated with the risk of partial solute elimination. In open tubular column SFC, samples are normally introduced using a smallvolume internal loop valve. These valves can be operated such that none, some, or all of the solvent is eliminated. Several approaches were quantitatively evaluted, and optimized conditions were determined. Particular attention was given to trace analysis. The minimum detectable levels (S/N >4) achievable using a flame ionization detector were determined to be approximately 30 ng (150 ppm) for split injection, 4 ng (20 ppm) for delayed split injection, and 1 ng (5 ppm) for direct injection.
Free solution capillary electrophoresis of basic proteins in uncoated fused silica capillary tubing
Authors: Bullock John A. , Yuan Lung‐Chi 
Published: May 2005

AbstractA series of buffer systems encompassing the pH range from 3.5 to 9.0 have been developed for free solution capillary electrophoretic (CE) analysis of basic proteins in uncoated fused silica capillaries. Separations of model proteins possessing isolectric points between 9.1–11.0 have been achieved with efficiencies in the range of 95,000–690,000 theoretical plates. In each case the modifier 1,3‐diaminopropane is incorporated in the operating buffers at concentrations of 30–60 mM along with moderate levels of alkali metal salts to suppress protein‐capillary wall interactions normally encountered with basic proteins. The combination of these buffer additives allows the analyses to be conducted at pHs below the protein isoelectric points. No special capillary pretreatment is required. The advantages of this approach to analyzing basic proteins include its simplicity, the ability to perform the analyses in the pH range where proteins are stable and the greater flexibility available in the choice of pH as a means of affecting selectivity changes.
High pressure microbore packed column gas chromatography using common liquid chromatography stationary phases
Authors: Liu Yan , Yang Frank J. 
Published: May 2005

AbstractHigh pressure gas chromatography (GC) using microbore packed columns was investigated. The microbore columns were packed with common microparticulate liquid chromatography (LC) stationary phases such as 5‐μm alky‐modified silicas and a 5‐μm macroporous polymer beads. The effects of the stationary and mobile phases, the mobile phase linear velocity and the column temperature were studied. The LC stationary phases were found to retain the expected selectivity and efficiency under high pressure GC conditions using either helium or CO2 gas as the mobile phase. The results indicate that microbore columns packed with common LC microparticulate stationary phases can be used in high pressure GC to provide rapid and efficient separation of volatile polar and nonpolar compounds. The results also suggest that the same instrument components such as the pump, injector, column, restrictor, and detector can be used for both high pressure GC and supercritical fluid chromatography (SFC) separations.
High temperature stable OH‐terminated poly(3,3,3‐trifluoropropylmethylsiloxane/silphenylene) copolymer stationary phases for capillary gas chromatography
Authors: Blum Wolfgang , Aichholz Reiner 
Published: May 2005

AbstractThe unexpectedly good thermal stability of OH‐terminated 3, 3, 3‐trifluoropropylmethylsiloxane/silarylene copolymers can be attributed to both the inclusion of bulky aromatic units in the polysiloxane backbone and to an autocrosslinking process taking place at temperatures above 370°C, being specific for trifluoropropyl substituted polysiloxanes. The crosslinking mechanism is discussed. Both new OH‐terminated phases, sildiphenylene/trifluoropropylmethyl and sildiphenylene ether/trifluoropropylmethyl‐polysiloxane (SA‐TF and SDPE‐TF) were characterized, and their performance at high temperatures (>400°C) is demonstrated.
Xenon as a mobile phase in supercritical fluid chromatography
Authors: Raynor Mark W. , Shilstone Gavin F. , Clifford Anthony A. , Bartle Keith D. , Cleary Michael , Cook Bernard W. 
Published: May 2005

AbstractSupercritical xenon and CO2 are compared as solvents by means of solubilities (calculated by means of the Peng‐Robinson equation of state) and chromatographic behavior for some polynuclear aromatic hydrocarbons; reasons for the apparent superiority of xenon are discussed. The advantages of the use of xenon as a mobile phase in coupled supercritical fluid chromatography‐Fourier transform infrared spectrometry are evaluated from analyses of monomer and oligomer mixtures.
Effects of ionic strength of eluent on retention behavior and on the peak broadening process in hollow fiber flow field‐flow fractionation
Authors: Carlshaf Alf , Jönsson Jan Åke 
Published: May 2005

AbstractThe influence of forces on the particles other than the applied cross flow is studied in hollow fiber flow field‐flow fractionation (HF5). Such forces can be of either attractive or repelling in nature. It is shown by injecting polystyrene latex beads (0.091 μm in diameter) at different cross flows and by using eluents with different ionic strengths, that there will be disturbances in the concentration profile of the sample irrespective of the type of interacting forces. The retention time and peak broadening were either increased or decreased compared to the theoretical value, depending on the nature of the dominating interaction force. It is, nevertheless, possible to minimize the total interaction energy between particles and between the particles and the channel wall by choosing a suitable ionic strength.
Molecular shape recognition of polycyclic aromatic hydrocarbons with a liquid‐crystal bonded phase in supercritical fluid chromatography
Authors: Jinno Kiyokatsu , Mae Hideo , Saito Yoshihiro , Pesek Joseph J. , Fetzer John C. , Biggs Wilt R. 
Published: May 2005

AbstractThe chromatographic characteristics of a liquid crystal bonded phase have been evaluated for the separation of polycyclic aromatic hydrocarbons (PAHs), especially focusing on its shape recognition capability in supercritical fluid chromatography (SFC). The results clearly indicate that the phase has a stronger molecular planarity and shape recognition capability than typical polymeric and monomeric octadecylsilica (ODS) phases because of the very ordered bonded phase structure. The recognition capability was slightly dependent on SFC conditions such as column pressure, column temperature, and mobile phase density. Modifier addition did not make a large difference on the recognition capability. The phase seems to be a very promising stationary phase in SFC because the recognition capability is slightly influenced by the SFC conditions. Selectivity enhancement for molecular shape and planarity recognition has been found in SFC compared to reversed‐phase LC separations with the same stationary phase.
Sample introduction in capillary supercritical fluid chromatography using sequential density gradient focussing and solvent venting
Authors: Liu Zaiyou , Farnsworth Paul B. , Lee Milton L. 
Published: May 2005

AbstractA technique was developed for large volume sample introduction in capillary supercritical fluid chromatography. A 20‐cm length of 200‐μm i.d. capillary tubing was used as precolumn. The precolumn temperature could be easily controlled by passing an electrical current through an electrically conductive paint coated on its outer surface. During injection, the sample solvent was vented from the precolumn with CO2 (gas) at 32 atm, while the precolumn was kept at room temperature. Solutes were transferred onto the head of the analytical column as a narrow band by density gradient focussing, which was established with (a) a temperature gradient along the precolumn, (b) a rapid expansion of CO2 from supercritical fluid to gas, and (c) a temperature difference between the precolumn and the analytical column. This injection approach minimized solute mass discrimination and could be easily performed.
Fused silica microcolumn LC‐MS and MS/MS using an aeronebulized interface
Authors: Karlsson Karl‐Erik 
Published: May 2005

AbstractAn aeronebulized interface has been developed for use with 0.15–0.25‐mm i.d. slurry‐packed fused silica columns. The interface was built in a removable probe that uses tha direct inlet on a triple quadrupole mass spectrometer for easy switching between LC, GC, or the solids probe. The probe is indirectly heated by the ion source, and premature evaporation of the mobile phase, acetonitrile/water, is prevented by controlled water cooling. A standard EI/CI ion source was used in the chemical ionization mode using methane to control the pressure in the source. Several variables that influence the performance of the interface were evaluated using various drugs as model compounds. Typically, 50,000 to 70,000 theoretical plates could be generated. The minimum detectable quantities were generally in the low picogram range. The best result was 3 pg using negative ion SIM, corresponding to a concentration of 8 × 10−8 M in the injected sample.
Analysis of chemical warfare agents in soil samples by off‐line supercritical fluid extraction and capillary gas chromatography
Authors: Kuitunen Marja‐Leena , Hartonen Kari , Riekkola Marja‐Liisa 
Published: May 2005

AbstractNerve agents and two other chemical warfare agents were extracted from spiked soil with supercritical CO2. Supercritical fluid extraction (SFE) was used as an off‐line technique. The extracts were analyzed with a two‐channel capillary gas chromatograph, equipped with an autosampler and flame ionization and nitrogen‐phosphorus detectors. Compounds were identified and quantified automatically with the help of retention index monitoring (RIM). Recoveries were equal to or better than those obtained with solvent extraction by sonication.
Comparative study of “on‐column focusing” applied to micro‐LC and conventional LC
Authors: Ling Betty Lin , Baeyens Willy , Dewaele Chris 
Published: May 2005

AbstractThe technique of „on‐column focusing”︁ allows the injection of high sample volumes onto a conventional LC or micro‐LC column for improved sensitivity without severe peak broadening effects. For early eluting compounds, the application of this technique provided better results for micro‐LC studies than for LC assays. An increase in sensitivity of more than two times was obtained with injection volumes of up to 50 μL onto a capillary column. Therefore, the main drawback of reduced detectability in miniaturized systems could be overcome. For the late eluting compounds, this technique could be similarly applied to both types of chromatographic systems.
Use of SFC/MS for the confirmation of peak identities in the SFC/FID chromatogram of olestra
Authors: Pinkston J. David , Bowling Donald J. 
Published: May 2005

AbstractOpen tubular supercritical fluid chromatography (SFC) with flame ionization detection (FID) has been used for characterizing olestra, a mixture of fatty acid sucrose esters. In this publication, we describe SFC/mass spectrometry (SFC/MS) of olestra using the direct fluid introduction interface. Chemical ionization spectra were used in confirming SFC/FID peak identities. Electron ionization SFC/MS of olestra was also investigated. Both major and minor component peaks in the SFC chromatogram of olestra were characterized. A slight modification of the interface‐probe tip was necessary for operation at higher temperature. A procedure was developed for tuning and calibrating the instrument in the 10‐4000‐u mass range, chemical ionization mode using Ultramark 3200, a perfluorinated polyether. The use of additional pumping in the form of liquid nitrogen cooled cryopumps was key in providing good signal‐to‐noise ratios for the latereluting (i.e., eluting at higher mobile phase pressures and flow rates) olestra components.
Reproducibility of migration times and propagation of error in micellar electrokinetic chromatography
Authors: Vindevogel John , Szücs Roman , Sandra Pat 
Published: May 2005

AbstractThe contributions of several factors (electroosmosis, capacity factor, and elution range) to migration time reproducibility have been evaluated using the theory of error propagation. Experimentally obtained values confirm that a single factor, electroosmosis, can explain most of the observed variability.
Separations of proteins and proteolytic digests of proteins by capillary electrophoresis on superox‐coated open tubular columns
Authors: Zhao Zhongxi , Malik Abdul , Lee Milton L. 
Published: May 2005

AbstractFused silica open tubular columns treated with Superox 0.6 and 4 for capillary electrophoresis were evaluated. Excellent separations of proteins were obtained. Column effeiciencies of over 700,000 theoretical plates were achieved for basic proteins. The relative standard deviations (RSDs) in migration times for these proteins were below 1%. Comparisons were made of the electropherograms of α‐, β‐, γ‐, and δ‐chymotrypsins. Three different protein digestion reagents were used to produce complex peptide mixtures for analysis: trypsin, chymotrypsin, and pepsin. Each reagent produced a unique mixture of peptides. Capillary electrophoresis was used to elute the peptides, yielding highly efficient and reproducible separations.