bluuebunny/crossref_metadata_2025_split huggingface dataset:
Retention and peak shape of acidic substances in capillary supercritical fluid chromatography with binary and ternary mobile phases
Authors: Karlsson Lars , Buttler Torbjörn , Mathiasson Lennart 
Published: May 2005

AbstractAcidic model compounds were chromatographed on a cyanopropyl capillary column using binary and ternary mobile phases with supercritical carbon dioxide as the primary mobile phase component. When a binary mobile phase was used, large amounts (> 15%) of methanol in carbon dioxide were needed to elute the most polar analytes. Formic and citric acid were tested as modifier additives. The addition of formic acid to the eluent resulted in virtually no positive effects on the chromatographic behavior of the acidic substances. Addition of small amounts of citric acid to the modifier did, on the other hand, significantly improve peak shapes of all acidic compounds tested. Retention could then be adjusted by changing the concentration ratio between carbon dioxide and the methanol‐citric acid solution. The effect of the ternary citric acid additive is probably caused by deactivation of stationary phase active sites and possibly also facilitation of solute mass transfer across the boundary between the chromatographic phases. Finally, methanol could be replaced by less toxic ethanol as a modifier in binary and ternary mobile phases, without noticeable effects on the chromatographic behavior.
Analysis of cations and anions in small volumes using micro‐LC and CE
Authors: Bächmann Knut , Steeg Karl‐Heinz , Groh Thomas , Haumann Ingo , Boden Jana , Holthues Heike 
Published: May 2005

AbstractInorganic ions can be analyzed in small volumes using micro‐liquid chromatography (micro‐LC) and capillary zone electrophoresis (CE). Results for the analysis of alkali, alkaline earth, and ammonium cations as well as the main organic and inorganic anions are given and discussed. For the determination of the cations in micro‐LC and CE, cerium(III) was chosen as eluent and electrolyte, respectively. Micro‐LC anion analysis was carried out with hexacyanoferrate(II) and ‐(III) and indirect photometric detection. In CE 2,5‐dihydroxybenzoic acid was used as the fluorescent electrolyte for indirect detection. For CE sample introduction an injection port was developed to handle volumes smaller than 1 μL.
Separation of DNA sequencing fragments at 53 bases/minute by capillary gel electrophoresis
Authors: Rocheleau Marie‐Josée , Dovichi Norman J. 
Published: May 2005

AbstractPolyacrylamide gels are unstable in 50‐μm internal diameter capillaries at electric fields greater than about 500 V cm−1 due to the formation of bubbles, which destroy the separation. We describe the use of a modified polyacrylamide capillary gel that is stable at electric fields of at least 800 V cm−1. This capillary gel produces sequencing rates of 3,200 bases h−1 for fragments up to 250 bases in length; a total of 7 min are required to separate fragments of 250 bases in length. Longer fragments tend to coelute and do not generate useful sequencing information. This sequencing rate is a factor of 40 times higher than that produced by conventional sequencing gels and a factor of 3 faster than previous reports in the literature.
Hydrogel polymer coating for capillary electrophoretic separation of proteins
Authors: Huang Mingxian , Lee Milton L. 
Published: May 2005

AbstractThree hydrogel polymers, poly(2‐hydroxypropylmethacrylate), poly(2‐hydroxyethylmethacrylate), and hydroxypropylcellulose, were coated and immobilized on fused silica capillary surfaces using three different methods, all involving modification of the surfaces before polymeriszation and/or cross‐linking. Since the hydrogel polymers swelled in aqueous solution and allowed permeation of low‐molecular‐weight compounds, an equilibrated state was attained between the hydrogel polymer layers and the buffer solution, which eliminated the interactions between proteins and the capillary surface, and allowed highly efficient and reproducible capillary electrophoretic separations of both basic and acidic proteins. The experimental results indicated that silanol groups on the capillary surface were covered and phosphate anions were trapped in the coating layers, which produced defined, but reduced, electroosmotic flows when compared to uncoated capillaries. High resolution separations of ribonuclease B variants and cytochrome c proteins from different sources were obtained.
Novel pseudostationary phase for micellar electrokinetic capillary chromatography
Authors: Palmer Christopher P. , McNair Harold M. 
Published: May 2005

AbstractA novel, highly stable pseudostationary phase for use in micellar electrokinetic capillary chromatography has been synthesized and evaluated. Sodium‐10‐undecylenate has been oligomerized to form a micelle‐like structure following the procedure of Durairaj et al. [1]. The effective critial micelle concentration of this new pseudostationary phase is zero, permitting electrokinetic chromatography to be performed at lower ionic strength than is possible with the corresponding free surfactant. The structural stability of this pseudostationary phase permits its use with relatively high percentages of organic modifiers in the buffer medium, allowing the separation and detection of hydrophobic analytes such as alkyl phthalates which are difficult to analyze by conventional micellar electrokinetic chromatography.
Capillary electrophoresis of DNA fragments in entangled polymer solutions: A study of separation variables
Authors: Dolník Vladislav , Novotny Milos 
Published: May 2005

AbstractCapillary electrophoresis (CE) in entangled polymer solutions was studied using pBR322 DNA Hae III digest as a model sample. The influences of polymer nature, monomer chain length, and polymer concentration were investigated. The use of a novel polymer, galactomannan, as the entangled matrix for the separation of DNA fragments has been demonstrated.
Enantiomeric separation by GC on chirasil‐dex: Systematic study of cyclodextrin concentration, polarity, immobilization, and column stability
Authors: Jung Martin , Schurig Volker 
Published: May 2005

AbstractPolysiloxane‐anchored permethylated β‐cyclodextrin (Chirasil‐Dex) was used for enantiomeric separation by GC. Four types of Chirasil‐Dex, containing up to 36% permethylated β‐cyclodextrin by weight, were synthesized and compared with 10% permethylated β‐cyclodextrin dissolved in OV–1701. The influence of the cyclodextrin weight percentage on the chiral separation factor α and on polarity, as expressed by the Kovats indices, was studied. The chiral separation factors α did not increase significantly above a threshold of ˜30% permethylated β‐cyclodextrin by weight. The plots of α vs. weight percentage depend on the complexation strength of the chiral solutes, as do the Kovats indices; for weakly complexing solutes, changes in the cyclodextrin concentration result in larger changes in α, but in less pronounced changes in the Kovats indices, as compared to strongly complexing solutes. Column performances were investigated for immobilized and nonimmobilized stationary phases. As expected, immobilization properties were found to depend on the content of Si‐H groups in the polysiloxane backbone. Immobilized columns exhibited a much better long‐term stability of all chromatographic variables investigated.
Thermionic ionization detection of halogenated compounds using supercritical fluid chromatography
Authors: Jew Raymond K. , Richter Bruce E. 
Published: May 2005

AbstractA thermionic ionization detector utilizing the TID‐1‐N2 mode for the analysis of chlorinated compounds was evaluated for use with supercritical fluid chromatography (SFC). A nitrogen atmosphere was employed in the detection zone to give electron capture detector (ECD)‐like responses. Optimum conditions allowed detection of halogenated compounds in the low picogram range with good base line stability during density programming. Selectivity over aliphatics and aromatics ranged between 104 to 105.
Separation of ethoxylated alcohol sulfates by capillary electrophoresis using indirect UV detection
Authors: Goebel Lisa K. , McNair Harold M. , Rasmussen Henrik T. , McPherson Bruce P. 
Published: May 2005

AbstractEthoxylated alcohol sulfates were analyzed without derivatization by capillary electrophoresis (CE) using a borate buffer with 1 mM potassium dichromate and 30% (v/v) acetonitrile. The feasibility of using the technique for separation of raw materials (Neodol 23–2A) and commercial products (dishwashing detergent) is demonstrated.
Effect of surface modification and mobile phase velocity on the performance of parallel current open tubular liquid chromatography
Authors: Šlais Karel , Horká Marie 
Published: May 2005

AbstractThe role of the mobile phase velocity in the stability of the flowing retentive film in parallel current open tubular liquid chromatography (PC‐OTLC) is shown. Criteria for optimization of the solvent pair indicates that, from the solvents examined, cyclohexanol represents the best choice for the retentive liquid when an aqueous mobile phase and revesed phase PC‐OTLC (RP PC‐OTLC) are considered.Several procedures for capillary internal surface modification were compared with the aim to optimize the performance of RP PC‐OTLC using the cyclohexanol/water system. From the examined methods of modification, persilylation with octadecylcyclotetrasiloxane (D4 reagent) gives the optimum which enables retention close to theory.
Miniaturized light scattering detector for packed capillary supercritical fluid chromatography
Authors: Demirbuker M. , Anderson P. E. , Blomberg L. G. 
Published: May 2005

AbstractPacked capillary columns provide excellent separation of neutral lipids by supercritical fluid chromatography. For these separations, it is necessary to add a polar modifier to the mobile phase; hitherto, a detector suitable for quantitative analysis has been lacking. For this purpose, a miniaturized evaporative light scattering detector for combination with packed microcolumns in supercritical fluid chromatography has been developed. Since the detector response is dependent on the mobile phase flow rate, a drop in response was found at flow rates above 16 mL min−1 of expanded mobile phase. However, below this flow rate, there was a region of relatively constant response. In this region, quantitative analysis could also be successfully performed when the pressure and/or the temperature of the separation were programmed. The detection limit was lower than 6 ng. With pressure programming, the relative standard deviation in peak area was less then 4%. Minor peaks gave higher RSD values.Further, it is demonstrated that argentation SFC of triacylglycerols provides separation according to chain length as well as to the degree of unsaturation.
Charged surface coatings for capillary electrophoresis
Authors: Huang Mingxian , Yi Guoliang , Bradshaw Jerald S. , Lee Milton L. 
Published: May 2005

AbstractFused‐silica capillaries with specially designed charged surface coatings were developed for the control of electroosmotic flow and for the separation of peptides and proteins in capillary electrophoresis. Cryptand moieties were immobilized onto the capillary surface through a crosslinking reaction of a cryptand‐containing polymer and copolymerization of a cryptand‐containing monomer. The resultant coatings provided switchable electroosmotic flow from low to high pH due to the complexing ability of the cryptand moieties with the metal ions from the buffer solution. A positively charged quaternary amine surface‐coated column was found to be very effective in reversing the electroosmotic flow compared to an untreated fused silica capillary, and to be suitable for separation of proteins whose pI values are greater than the buffer pH. Also, a negatively charged sulfonic acid surface‐coated column could be used to stabilize the electroosmotic flow from pH 3 to 9, and the magnitude of the electroosmotic flow could be controlled by varying the concentration of sulfonic acid groups in the coating solution. This negatively charged surface coating gave excellent reproducibility for the separation of a tryptic digest of β‐casein.
Capillary electrophoresis separation of sulphonamides and dihydrofolate reductase inhibitors
Authors: Ricci Maria C. , Cross Reginald F. 
Published: May 2005

AbstractTwenty‐two sulphonamides and three dihydrofolate reductase inhibitors (DHFR) were included in this study. At pH 7.5, eighteen drugs were resolved in 22 min. Above pH 7.5 the DHFR are not resolved and the pH range of 7‐7.5 was found to be optimal. Around pH 7, where the degree of ionization of the SFA is highly variable, pKa and migration time are strongly correlated. Increasing phosphate buffer concentration from 25‐100 mM generally improves resolution but increases analysis times. A good correlation between analyte mobility and the ratio of net charge to molecular weight indicates that this ratio may be used as a quick guide to the possibility of separation of related compounds. Our secondary objective was to compare the lead time and effectiveness of CZE with LC. It is clear that method development is much more rapid in CZE but with a sufficiently diverse group of compounds, CZE can be incapable of providing a full analysis without gradient control. Nonionized compounds are not separated at one extreme, and excessively mobile species may not emerge in a reasonable time, or, may migrate to the wrong electrode.
Diode laser‐based concentration gradient detector for capillary isotachophoresis
Authors: Wu Jiaqi , Pawliszyn Janusz 
Published: May 2005

AbstractA diode laser‐based, universal concentration gradient detector was applied to capillary isotachophoresis (CITP). The inexpensive CITP instrument also included a 30 cm long, 300 μm i.d. capillary, a 5 cm focal length lens and a photodiode light beam position sensor. Factors affecting the sensitivity and performance of the detector, i.e., separation conditions, spatial resolution of the detector, and the concentration of leading electrolyte, were discussed theoretically and experimentally. The diode laser‐based concentration gradient detector appears to be one of the best detectors for CITP due to its high resolution, derivative nature, and low cost. The experimental detection limit reached 4 × 10−6 M for small cations, which was near the theoretical value. The detection limit can be further reduced by at least one order of magnitude if a longer capillary is used. The CITP‐concentration gradient detector instrument has high efficiency, and was applied to detect impurities in antidepressant drugs.
UV Longitudinal cell design with enhanced sensitivity for capillary electrophoresis
Authors: Onuska Francis I. , Terry Ken A. 
Published: May 2005

AbstractA UV‐absorbance cell assembly for use in capillary zone electrophoresis, or in micellar electrokinetic chromatography, employing a perpendicular variable path length U‐shaped cell of nl volume instead of conventional on‐column detection is described. The length of the optical path can be chosen arbitrarily, regardless of capillary diameter. The extracolumn variance has been overcome through the elimination of connectors between the capillary and the detection system. The technique is demonstrated by means of micellar electrokinetic chromatography for phenols, in which path lengths of up to 4 mm can be tolerated without serious loss of separation efficiency. An efficiency of approximately 130,000 plates m−1 for a mixture of phenols using a cell of 50 μm in diameter and an optical path of 4 mm was obtained. This leads to a considerable increase in absorbance signal as compared with the usual on‐column UV‐absorption cell. Construction details are provided.
Dynamic film formation and the use of retention gaps with direct injection in open‐tubular supercritical fluid chromatography
Authors: Chester Thomas L. , Innis David P. 
Published: May 2005

AbstractOpen‐tubular supercritical fluid chromatography (SFC) is a useful technique for many analyses, but is somewhat limited, in current practice, with respect to trace analysis of liquid samples. Direct injection of the volumes required for trace analysis with ordinary detectors creates a meter or more length of flooded zone and may lead to unacceptable band broadening. We studied solvent mass transfer on short, uncoated columns for several solvents forming Type I binary mixtures with CO2, and found evidence in the solvent peak shapes of distinct liquid and vapor phases, with the liquid present as a dynamically formed film. This study suggests that selecting an injection temperature and pressure to reduce, but not eliminate, the surface tension of the liquidvapor interface, and increasing the mobile phase velocity during injection increase the liquid film thickness and reduce the length of the resulting flooded zone. When a separate uncoated inlet tube (that is, a retention gap) is used to connect the injector with the column, decreasing the inlet tube radius improves the ratio of maximum effective injection volume to inlet tube volume.Just as in GC, dynamically formed films function as pseudo‐stationary phases during injection. Without a liquid film, solutes can be transported by injection‐solvent‐modified mobile phase well beyond the length of a typical film, increasing the difficulty of refocusing the solutes before separation. Refocusing solutes from film‐coated flooded zones is easily accomplished using either a solvent effect (specifically, solvent trapping) or phase‐ratio focusing.We recommend the use of solvents with phase behavior like toluene and carbon tetrachloride, both of which form films at convenient temperatures and pressures. We discourage the use of solvents with phase behavior like n‐pentane which tend to make single‐phase, supercritical mixtures with CO2 under typical SFC injection conditions.
Evaluation of on‐column labeling with intercalating dyes for fluorescence detection of DNA fragments separated by capillary electrophoresis
Authors: Clark Brian K. , Sepaniak Michael J. 
Published: May 2005

AbstractThe analytical figures of merit of laser‐excited fluorescence detection of DNA restriction fragments, based on the enhanced fluorescence of selected dyes upon intercalation, are presented. The fragments present in a ϕX174 Hae III digest are efficiently separated by capillary electrophoresis employing methyl cellulose as a sizesieving reagent. On‐column DNA labeling is accomplished by adding either ethidium bromide (EB) or POPO‐3 iodide (POPO‐3) to the electrophoretic running buffer. Experimental parameters that are evaluated include type of laser (helium‐cadmium at 325 nm or helium‐neon at 543 nm) and laser power, dye type and concentration, pre‐injection labeling procedure, and applied field. Calibration plots are linear over two orders of magnitude in DNA concentration. Limits of detection are in the low‐to‐mid femtogram injected range for the individual fragments, with the POPO‐3 providing slightly lower values. Both dyes exhibit large increases in fluorescence quantum efficiency upon intercalation and contribute little or nothing to the observed optical background. Detectability with the dyes is enhanced by a spectral shift upon intercalation. Signal intensities increase with DNA fragment size in approximately a linear fashion. Intercalation by the dyes also influences mobility and the resolution of the fragments studied.
High temperature stable CH3O‐terminated poly(diphenyl/dimethyl)‐ and poly(diphenyl/3,3,3‐trifluoropropylmethyl)siloxane copolymer stationary phases for capillary gas chromatography
Authors: Blum Wolfgang , Aichholz Reiner 
Published: May 2005

AbstractThe preparation of two new medium polar CH3O‐terminated 50% diphenyl substituted polysiloxane phases by means of a one step condensation of bis(dimethylamino)alkylsilanes and diphenysilanediol is reported. Both phases can be used up to temperatures of 420°C. The unusual route of synthesis offers an easy and reliable way to prepare a variety of tailor‐made high temperature stable polysiloxane phases.
Fully automated water analyzer based on on‐line solid phase extraction‐gas chromatography
Authors: Louter Arjan J. H. , Brinkman Udo A. Th. , Ghijsen Rudy T. 
Published: May 2005

AbstractAn automated procedure for the analysis of aqueous samples by membrane disk extraction coupled on‐line to capillary gas chromatography (GC) is presented. Organophosphorus pesticides are preconcentrated from aqueous samples on three 0.5 mm thick, 4.0 mm diameter XAD‐2 membrane extraction disks which are mounted in a polymer holder for use in a PROSPEKT sample processor. The layers are dried by a stream of nitrogen (30 min at ambient temperature). Desorption of the analytes is carried out with ethyl acetate which is directly introduced into a retention gap under partially concurrent solvent evaporation conditions, using an early solvent vapor exit. The method is a fully software‐controlled automated system, and includes sample preparation, sample transfer and GC analysis. The final analysis is carried out by GC with nitrogen‐phosphorus (NPD) or mass‐selective detection. The technique is applied to the determination of a series of organophosphorus pesticides in tap water and water from European rivers. With a sample volume of only 2.5 mL, the detection limits achieved with the NPD were 20–50 ng L−1 in tap water and 20–100 ng L−1 in river water.
On‐line solid‐phase extraction/thermal desorption for introduction of large volumes of aqueous samples into a capillary gas chromatograph: Part 2
Authors: Vreuls Jolan J. , De Jong Gerhardus J. , Ghijsen Rudy T. , Brinkman Udo A. Th. 
Published: May 2005

AbstractA module for combined solid‐phase extraction and thermal desorption (SPETD) was incorporated into a system for automated GC analysis. Solid‐phase extraction of analytes from water could be carried out after injection of an aqueous sample of 100 μL either by a loop using the carrier gas for sample introduction or manually with a syringe. After drying of the stationary phase by the carrier gas at a high flow rate, thermal desorption could be carried out at temperatures up to 300–350°C. Suitable packing materials for the liner in the SPETD module, i.e., materials which efficiently trap the organic compounds from an aqueous solution and are sufficiently thermostable, include Tenax and carbon‐based phases, as well as a silylated alkylmodified silica. With the latter, however, the problem of efficient drying after sorption still must be solved. Each phase has its own application range which, from among the analytes which are trapped during sorption, is determined at the volatile end by losses occurring during drying by helium purging, and at the nonvolatile end by losses due to incomplete release during thermal desorption. From this study (using n‐alkanes, chlorobenzenes, and chlorophenols as test solutes), it appears that the Tenax phases, Tenax‐TA and Tenax‐GR, have the widest application range; essentially quantitative recoveries were obtained for C10 through C26 n‐alkanes. The carbon‐based phases appear to be useful for relatively volatile compounds, i.e., up to C19 n‐alkanes. Each phase gave good recoveries for two test mixtures containing chlorobenzenes and chlorophenols dissolved in 100 μL of water at the 10 ppb level.