bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of the dodecyl sulfate counter ion on selectivity and resolution in micellar electrokinetic capillary chromatography: SDS vs. Mg(DS)2
Authors: Nielsen Kurt R. , Foley Joe P. 
Published: May 2005

AbstractIn micellar electrokinetic capillary chromatography (MECC) the most widely used surfactant for the pseudostationary phase is sodium dodecyl sulfate (SDS), although other types of surfactants have been investigated. We have synthesized the magnesium salt of dodecyl sulfate (Mg(DS)2) in order to investigate how changes in the counter ion identity affect resolution via changes in selectivity (α) and retention. Buffer solutions containing Mg(DS)2 exhibited operating currents and electroosmotic velocities one third to one half that of a comparable SDS buffer solution, and significantly larger methylene and functional group selectivities for the compounds studied. In addition, capacity factors, K', for netral solutes were between 1.5 and 2.5 times larger for the Mg(DS)2. The elution range, tmc/to, for the Mg(DS)2 was independent of the percentage of organic modifier in the buffer solution while the elution range for SDS increased as the percentage of organic modifier increased. Improvements in α and increased retention resulted in increased Rs for neutral solutes in Mg(DS)2. The relatively constant elution range for Mg(DS)2 also aided in the retention‐mediated optimization of Rs and Rs per unit time.
Large particle micropacked columns in supercritical fluid chromatography
Authors: Ibáñez Elena , Alvarez Pedro J. Martin , Reglero Guillermo , Herraiz Marta 
Published: May 2005

AbstractThe advantages of using micropacked columns with low packing density and liquid stationary phases, which are currently used in gas chromatography, in supercritical fluid chromatography (SFC) have been studied. An equation fitted to 199 experimental data is proposed to describe the relationship between the plate height and the linear mobile phase velocity of the mobile phase in a micropacked column. A comparison of the performances of micropacked, open capillary, and standard packed columns in SFC is presented. The pressure drop at the optimal linear velocity per unit column length and per theoretical plate were evaluated and considered comparatively. Chromatographic efficiency, resolution, speed of analysis, and separation impedance achievable with each column were also evaluated. Preliminary results with column pressure drops similar to those of open tubular columns look promising. Data obtained lead to the conclusion that the use of large particle micropacked columns in SFC could be a suitable approach for the analysis of samples of medium complexity, where trace compound detection may require the use of columns having high sample capacities as well as high specific efficiencies.
Comprehensive two‐dimensional gas chromatography applied to the analysis of complex mixtures
Authors: Venkatramani Cadapakam J. , Phillips John B. 
Published: May 2005

AbstractComprehensive two‐dimensional gas chromatography is applicable to the analysis of complex petroleum mixtures. A kerosene sample analyzed by this method generates over six thousand chromatographic peaks. The chromatogram is orthogonal such that the second dimension separation is independent of the first. Aliphatics, aromatics, and naphthalene derivatives form distinct bands of peaks on the chromatographic plane with further subdivisions within each band based on chemical structure. With a nonpolar first column and a moderately polar second column, the first dimension separation is based largely on substance volatility while the second dimension separation is based on polarity. Each chromatographic peak has a pair of characteristic retention times, providing a more reliable identification. Peak capacity is much greater than that obtainable from any one‐dimensional separation.
Trapping efficiency and solute focusing in on‐line supercritical fluid extraction/capillary supercritical fluid chromatography
Authors: Daimon Hiroyuki , Hirata Yukio 
Published: May 2005

AbstractAn on‐line supercritical fluid extraction/capillary supercritical fluid chromatography system was developed using a capillary trap with stationary phase and a linear restrictor. With the system, samples can be injected into either the supercritical fluid chromatography (SFC) column or the trapping tube with the same injector, allowing rapid and accurate measurements of trapping efficiency. The self‐cooling effect due to fluid expansion drastically improved the trapping efficiency. External cooling allowed quantitative collection of n‐decane, provided that condensing of CO2 in the trap was avoided. Volatile solutes were more favorably refocused onto the SFC column at the lower column temperature. This system can also be used as a sample introduction method for volatile solutes.
On‐column atomic emission detection in capillary gas chromatography using a radio frequency plasma
Authors: Pedersen‐Bjergaard Stig , Greibrokk Tyge 
Published: May 2005

AbstractDetection limits of heteroatoms and carbon were improved by eliminating the make‐up gas and sustaining a 350 kHz radio frequency plasma inside the end of a fused silica gas chromatography (GC) column (0.32 mm i.d.) for capillary GC with atomic emission detection. Due to the small internal diameter of the plasma cell, a stable plasma was maintained in only 1.5–3 mL min−1 of helium used as the GC carrier gas. The optical system consisted of a single low resolution monochromator for the near‐infrared region in order to develop a simple and low‐cost system. For on‐coloumn detection of C, H, S, Cl, Br, and I, the plasma was doped with traces of oxygen. The oxygen dopant served to suppress peak tailing and to maintain high selectivity and repeatability. Detection limits for C, H, S, Cl, Br, and I ranged from 0.9 to 11.8 pg s−1, and selectivities between 4 × 102 and 4 × 103 were obtained. On‐column F‐selective detection required a plasma doped with a mixture of hydrogen and oxygen. The detection limit for F was 13.0 pg s−1; however, the selectivity was poor (10) due to the low resolution of the spectrometer.
Multichannel restrictor for supercritical fluid chromatography
Authors: Verjrosta Jiří , Mikešová Milena , Ansorgová Alena , Zátorský Jan , Hajer Miloš , Janda Václav 
Published: May 2005

AbstractA new multichannel restrictor for supercritical fluid chromatography has been developed. Four construction parameters (number, length and inner diameter of channels, and their geometrical arrangement) can be varied so that restrictors with different flow characteristics can be designed. The effective ratio, L/d, in which L is the length of a channel and d is the inner diameter, is about two orders lower than values assumed for porous frit restrictors.
Packed capillary supercritical fluid chromatography of organophorus pesticides: Selective detection and applications
Authors: Zegers Bart N. , Hogenboom Ariadne C. , Dekkers Silvio E. G. , Lingeman Henk , Th. Brinkman Udo A. 
Published: May 2005

AbstractPacked capillary supercritical fluid chromatography coupled with thermionic detection was used for the selective determination of nineteen organophosphorus pesticides in vegetable extracts. The chromatographic behavior of some pesticides was studied using seven different stationary phases. Addition of an organic modifier to carbon dioxide was needed to improve peak shape and reduce retention. Quantitation of organophosphorus pesticides in vegetable extracts showed good linearity. Extraction was performed in a one‐step extraction procedure using a water‐miscible solvent (acetone) and an organic solvent with limited water capacity (dichloromethane). Under these conditions a wide range of both polar and apolar pesticides can be recovered from vegetable extracts down to the 3–25 μg kg−1 level. The recoveries found ranged from 35 to 95% depending on the polarity of the pesticides.
Effect of the dodecyl sulfate counterion on selectivity and resolution in micellar electrokinetic chromatography: II. Organic counterions
Authors: Nielsen Kurt R. , Foley Joe P. 
Published: May 2005

AbstractVarious tetraalkylammonium ions, such as tetramethyl‐, tetrapropyl‐, tetrapentyl‐, and cetyltrimethylammonium, can be added to sodium dodecyl sulfate (SDS) micellar solutions to achieve unique selectivities in micellar electrokinetic chromatography (MEKC). The cetyltrimethylammonium/SDS buffer system showed the greatest increase in methylene selectivity, while both tetrapropylammonium/SDS and cetyltrimethylammonium/SDS buffer systems had the greatest selectivities for the solutes studied. In addition, the buffer systems that used symmetrical tetraalkylammonium ions showed reductions in retention specific for the carbonyl functional group. The tetramethylammonium/SDS buffer system had the best resolution due to both improved selectivity and an elution range that was 2.5 times that of a comparable SDS buffer system.
Automated LC‐GC: A powerful method for essential oils analysis. Part IV. Coupled LC‐GC‐MS (ITD) for bergamot oil analysis
Authors: Mondello Luigi , Bartle Keith D. , Dugo Paola , Gans Peter , Dugo Giovanni 
Published: May 2005

AbstractA fully automatic on‐line LC‐GC‐MS system for the analysis of bergamot essential oil has been used. The system allows the pre‐separation by LC of the oil into compound classes by gradient elution followed by the transfer of these fractions into a capillary GC column and detection by MS (ITD) and FID. Combining LC‐GC‐MS produces data which are considerably more informative than data from GC‐MS of the whole essential oil.
Solid phase techniques in the extraction of pesticides and related compounds from foods and soils
Authors: Picó Yolanda , Moltó Juan C. , Mañes Jordi , Font Guillermina 
Published: May 2005

AbstractThe application of SPE technology to the isolation of pesticides and related compounds from food and soils has grown enormously in the last decade. Much of this growth has been due to the relative ease of sample handling and the wide range of solid supports currently available for a variety of applications. The aim of this review is to present the methods for solid phase extraction (SPE) of pesticide residues from soils and foods. There are three main areas according to the type of approach used to handle the sample: solid phase extraction, solid phase clean‐up (SPC), and matrix solid phase dispersion (MSPD). This review covers milk products, fatty foods, fruits, vegetables, and soils. Solid phase materials are discussed in each case in terms of reversed bonded‐phase silica sorbents (C18, C8, C2, etc.) and polar sorbents (alumina, Florisil, and silica).
Preparation of small diameter thick film capillary columns for microcolumn separations
Authors: Steenackers Dirk , Sandra Pat 
Published: May 2005

AbstractOpen tubular columns of 25 and 50 μm i.d. have been coated with up to 2 μm thick layers of SE‐54 (lowest β‐value = 6.25). Filling of the columns and evaporation of the solvent were studied as a function of column length and time. Since the viscosity of the stationary phase solution increases exponentially with concentration, the filling process becomes time consuming and high filling pressures are required. The evaporation or coating speed is shown to be controlled by the resistance to mass transfer of the solvent vapor through the coated sections of the column. For 25 and 50 μm i.d. columns, experimental evaporation times deviate little from theoretical predictions. Almost no influence of the stationary phase on the coating speed was observed. The transition from mass transfer limited coating speed to heat transfer limited coating speed is illustrated using literature data.
Effect of ammonia on the response of the nitrogen phosphorus detector (NPD)
Authors: Abdel‐Rehim Mohamed , Hassan Moustapha 
Published: May 2005

AbstractThe effect of ammonia as a carrier gas and as a make‐up gas on the response of the nitrogen phosphorus detector (NPD) was investigated. This study showed that the response of the NPD increased 2.2 to 10.3 fold for all studied aliphatic amines when 5% ammonia in nitrogen was used as a make‐up gas. This increase was about 5.3 to 22.8 fold when ammonia was used as a carrier gas. The response of the NPD for nitro‐aromatic compounds increased 1.8 to 3.1 fold using 5% ammonia as a make‐up gas and 4.2 fold when ammonia was used as a carrier gas. The higher response obtained using ammonia as the carrier gas is related to improvements in the chromatographic performance (reduced tailing). The response of the NPD to phosphorus compounds was about 1.5 times higher using ammonia either as a carrier gas or as a make‐up gas compared to nitrogen. Although the noise of the NPD increased, the signal‐to‐noise ratios for both amines and phosphorus compounds improved with the use of ammonia.
Post‐column derivatization in narrow‐bore capillaries for the analysis of amino acids and proteins by capillary electrophoresis with fluorescence detection
Authors: Gilman S. Douglass , Pietron Jeremy J. , Ewing Andrew G. 
Published: May 2005

AbstractThe construction and performance of a post‐column reactor for capillary electrophoresis with laser‐induced fluorescence detection in 10 μm i.d. capillaries is described. The post‐column reactor is based on a gap design and relies primarily on diffusion for addition and mixing of derivatizing reagents. Reactors with gaps of 4 to 160 μm are easily built with minimal micromanipulation between two 10 μm i.d. capillaries. Optimal separation efficiencies and sensitivities are obtained with gaps of less than 10 μm. Separations of amino acids and proteins with o‐phthaldialdehyde/2‐mercaptoethanol post‐column derivatization and laser‐induced fluorescence detection are shown. Linear detector response is found for amino acids and proteins, and peak efficiencies as high as 230,000 theoretical plates are obtained for some analytes. The use of relatively small columns for capillary electrophoresis results in a separation and detection system that produces very low mass detection limits for biological molecules from picoliter sample injections. Mass detection limits of 130 and 5.2 attomoles are obtained for glycine and human transferrin, respectively.
Fiber optic‐based UV‐absorption detector cell for high temperature open tubular column liquid chromatography
Authors: Svensson Lena M. , Markides Karin E. 
Published: May 2005

AbstractA new UV‐absorption detector cell for on‐column detection in open tubular column liquid chromatography was evaluated. Optical fibers and quick‐fit connections were employed for flexibility and ease in alignment and mounting in an oven for high temperature detection. Different optical fiber diameters were evaluated for 50 μm i.d. capillary columns. The best combination of optical fibers (200 μm source and collector) resulted in a detection limit of 2 × 10−6 M for acetophenone. No dramatic change in the signal‐to‐noise ratio was found when the temperature was raised to 150°C.
Tandem supercritical fluid extraction/chromatographic studies of the desert botanical species, Dalea spinosa
Authors: Taylor Scott L. , King Jerry W. , Snyder Janet M. 
Published: May 2005

AbstractOff‐line and on‐line supercritical fluid extraction (SFE) coupled with gas chromatography (GC), supercritical fluid chromatography (SFC), and mass spectrometry (MS) have been used to characterize the composition of extracts from the desert botanical species, Dalea spinosa. Off‐line SFE conducted at pressures as high as 680 atm yielded odoriferous extracts similar in composition to an isopropyl alcohol‐derived extract when the two extracts were characterized by SFC and GC/MS. SFC of the extracts revealed the presence of up to 18 components, GC/MS indicated six major compounds, and headspace GC/MS showed over 20 components. On‐line micro‐SFE/SFC was performed on single seeds of D. spinosa as well as dissected single seeds over the pressure range of 100‐400 atm at 45°C. SFE/SFC on portions of a single seed, such as the calyx or incised resin sac, indicated subtle differences in molecular composition. These results suggest that the resin sac is particularly enriched in many odoriferous compounds.
High‐resolution separation of oligonucleotides and DNA sequencing reaction products by capillary electrophoresis with linear polyacrylamide and laser‐induced fluorescence detection
Authors: Chen Nong , Manabe Takashi , Terabe Shigeru , Yohda Masafumi , Endo Isao 
Published: May 2005

AbstractBy employing linear polyacrylamide (LPA) as a sieving matrix, oligonucleotides and DNA sequencing fragments have been separated by capillary electrophoresis. A commercially available apparatus equipped with a laser‐induced fluorescence (LIF) detection system has been utilized, but the capillary cartridge has been modified in order to set the capillaries without coiling. Single‐base resolution was achieved for a mixture of FITC‐labeled oligonucleotides [FITC‐p(dT)] up to 500 base‐long chains. Because of high resolution, minor components of FITC‐p(dT) have also been separated. The mobility differences between single‐base adjacent peaks of FITC‐labeled DNA sequencing fragments have been detected up to 520 base‐long fragments. These results confirmed that linear polyacrylamide is an excellent sieving matrix in DNA sequencing by capillary electrophoresis.
Investigation of acridinium labelling for chemiluminescence detection of peptides separated by capillary electrophoresis
Authors: Ruberto Michael A. , Grayeski Mary Lynn 
Published: May 2005

AbstractAn acridinium ester has been used to tag mixtures of peptides followed by separation by capillary electrophoresis with chemiluminescence detection. The labelling of the peptides was performed at the picomole level. The chemiluminescence reaction conditions were optimized for the acridinium tag resulting in CE separations performed on attomole amounts of tagged peptides. Baseline resolution was obtained for a separation of standard peptides. The detection sensitivity was found to improve when multiple acridinium labels were attached to the peptides. The effect of acridinium tagging on the migration rate of the peptides was also studied. The increased weight of the acridinium tagged analyte increased the run time and resolution of a separated tryptic digest without resulting in excessive band broadening.
Hydrofluorocarbon and perfluorocarbon mobile phases for capillary supercritical fluid chromatography
Authors: Blackwell John A. , Schallinger Luke E. 
Published: May 2005

AbstractThe eluotropic strength of several hydrofluorocarbon and perfluorocarbon supercritical fluids is examined using capillary supercritical fluid chromatography. The results obtained are compared with carbon dioxide, fluoroform, and carbon dioxide modified with 5% methanol. Various naphthalene derivatives are used to determine differences in functional group selectivity between these fluids. Specific hydrogen bonding interactions are observed between hydrogen bond donating hydrofluorocarbon fluids and naphthalene derivatives with hydrogen bond accepting functional groups. Unexpectedly, perfluorocarbon fluids are much stronger in eluotropic strength than carbon dioxide, fluoroform, or methanol‐modified carbon dioxide.
Gas chromatographic analysis of methadone in urine samples after solid phase microextraction
Authors: Chiarotti Marcello , Marsili Remo 
Published: May 2005

AbstractThe use of solid phase microextraction for quantitative analysis of methadone in urine is reported. The proposed procedure allows the extraction of methadone from a urine matrix, avoiding sample handling and saving evaporation of solvents and concentration steps. A fiber coated with polymethylsiloxane was employed for the extraction of methadone from urine and subsequently directly injected into the GUMS apparatus. Specific and reproducible results were obtained with high sensitivity.
Enantiomer separation of DNP‐amino acids by capillary electrophoresis using chiral buffer additives
Authors: Wistuba Dorothee , Diebold Heike , Schurig Volker 
Published: May 2005

AbstractThe direct enantiomeric analysis of six DNP‐amino acids by capillary electrophoresis is reported. This study describes a comparison of several chiral buffer additives. Both the natural proteins BSA, AGP, ovomucoid and casein, and the cyclic oligosaccharides α‐, β‐, and γ‐cyclodextrin were used as chiral selectors. For the first time, casein from goat milk was successfully applied for chiral discrimination. The influence of the modifier n‐propanol on chiral discrimination is demonstrated with BSA as a buffer additive.
Supercritical fluid extraction/gas chromatography with thermal desorption modulator interface and nitro‐specific detection for the analysis of explosives
Authors: Francis Eric S. , Wu Mingin , Farnsworth Paul B. , Lee Milton L. 
Published: May 2005

AbstractSupercritical fluid extraction (SFE) can greatly reduce the sample preparation time of analytes in solid matrices. The on‐line coupling of SFE with high‐speed gas chromatography (GC) can further reduce the total analysis time. SFE has been coupled to GC with a thermal desorption modulator (TDM) interface. A thermal energy analyzer (TEA), a chemiluminescence detector which is specific for nitro and nitroso compounds, has been coupled to the system to analyze explosives in soil samples.The use of organic modifiers to increase the solvation power of carbon dioxide was necessary for the extraction of various explosives, and did not adversely affect the performance of the system. Thermally labile compounds, however, such as the nitrate esters, were shown to decompose in the modulator before the chromatographic separation.This method allows for the rapid analysis of relatively volatile and thermally stable nitro compounds from solid matrices. The system can be used for screening small samples in short periods of time. Total analysis can be completed in less than 10 minutes and requires only 200 mg of soil. The minimum detectable quantity for the analysis of 2,4‐DNT was found to be 2.6 ppb in an actual soil sample.
Separation of fullerenes with liquid crystal bonded silica phases in microcolumn high performance liquid chromatography
Authors: Saito Yoshihiro , Ohta Hatsuichi , Nagashima Hideo , Itoh Kenji , Jinno Kyokatsu , Pesek Joseph J. 
Published: May 2005

AbstractThe liquid chromatographic separation of C60 and C70 fullerenes with liquid crystal bonded silica phases was carried out and the separation performance was evaluated with various mobile phase compositions and column temperatures. The results clearly indicate that one liquid crystal bonded phase possesses better retention capability and separation power for these fullerene molecules than commercially available octadecylsilica (ODS) phases. The capacity factors of C60 and C70 were 2.82 and 8.46, respectively, with n‐hexane as the mobile phase.In contrast to the normal temperature dependency of the retention of some polycyclic aromatic hydrocarbons (PAHs) versus column temperature, unusual behaviors for C60 and C70 have been observed with the liquid crystal phase.
Di‐tert‐butyldimethylsilylated cyclodextrins as chiral stationary phases: Thermodynamic investigations
Authors: Maas Birgit , Dietrich Armin , Beck Thomas , Börner Susanne , Mosandl Armin 
Published: May 2005

AbstractThermodynamic data, which are derived from measurements of separation factors at different temperatures for various chiral compounds, show some expected, but also some surprising effects concerning the mechanism of chiral recognition for the cyclodextrin derivatives investigated.