Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Separation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,585 records · Page 88Linked to original sources
PubMedDate not supplied

Effects of light intensity and pattern contrast on the ability of the land crab, Cardisoma guanhumi, to separate optic flow-field components.

Using a novel suite of computer-generated visual stimuli that mimicked components of optic flow, the visual responses of the tropical land crab, Cardisoma guanhumi, were investigated. We show that crabs are normally successful in distinguishing the rotational and translational components of the optic flow field, showing strong optokinetic responses to the former but not the latter. This ability was not dependent on the orientation of the crab, occurring both in "forwards-walking" and "sideways-walking" configurations. However, under conditions of low overall light intensity and/or low object/background contrast, the separation mechanism shows partial failure causing the crab to generate compensatory eye movements to translation, particularly in response to low-frequency (low-velocity) stimuli. Using this discovery, we then tested the ability of crabs to separate rotational and translational components in a combined rotation/translation flow field under different conditions. We demonstrate that, while crabs can successfully separate such a combined flow field under normal circumstances, showing compensatory eye movements only to the rotational component, they are unable to make this separation under conditions of low overall light intensity and low object/background contrast. Here, the responses to both flow-field components show summation when they are in phase, but, surprisingly, there is little reduction in the amplitude of responses to rotation when the translational component is in antiphase. Our results demonstrate that the crab's visual system finds separation of flow-field components a harder task than detection of movement, since the former shows partial failure at light intensities and/or object/background contrasts at which movement of the world around the crab is still generating high-gain optokinetic responses.

Adaptation, Physiological↗
PubMed1993

Electrical field-flow fractionation in particle separation. 1. Monodisperse standards.

In its original implementation, electrical field-flow fractionation (EFFF) was carried out in membrane-walled channels with the electrodes placed externally to the flow channel. The poor separation efficiency of this system left the technique largely unattended for about two decades. In the present study, we describe a new and simple approach to EFFF, which demonstrates the technique's ability to carry out rapid, high-resolution separations of colloidal samples in aqueous suspensions. The present channels are bounded by the smooth and rigid graphite electrodes which allow for the application of small voltages, typically less than 2 V, across the thin (178 microns) separation space defined by a Mylar spacer. Although this arrangement generates nominal fields of the order of 100 V/cm, polarization of the electrodes considerably reduces the effective field across the bulk of the channel to less than 1% of the nominal value. Nevertheless, under conditions of low ionic strength the system is shown to retain and separate polystyrene (PS) latex standards with sizes ranging from 60 to 10,000 nm. For small particles of comparable zeta-potential, separating in the "normal" mode of EFFF, the size selectivity Sd, is approximately 0.7. As with other FFF techniques, EFFF displays a transition from "normal" to "steric" behavior; the critical diameter for this transition is highly dependent on ionic strength, with values ranging from approximately 500 nm in deionized water to approximately 1200 nm in 133 microM aqueous NaCl under an applied voltage of 1.37 V and a flow of 1 mL/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Fractionation↗
PubMed1993

Continuous electrophoretic separations in narrow channels coupled to small-bore capillaries.

Continuous zone electrophoretic separations in channels have been demonstrated. This new technique has the potential to continuously sample and separate analytes from volume-limited microenvironments. A small-bore capillary is used to electrophoretically sample, but not separate, a mixture of dansylated amino acids. The capillary is coupled to a quartz channel structure in a manner which allows continuous injection of the sampled material into the channel. The channel functions to continuously separate the sampled material via electrophoresis. A laser-induced fluorescence detection scheme, which involves two fiber optic arrays situated at the channel exit, monitors eluting analytes. A continuous separation of dansylated amino acids on the time scale of a few minutes demonstrates the utility of the technique. Sampling has been performed continuously up to 400 s, and initial detection limits are approximately 30 microM.

Dansyl Compounds↗
PubMed1994

Chiral separations in capillary electrophoresis using human serum albumin as a buffer additive.

This study examined the theory and mechanisms of chiral separations in capillary electrophoresis based on the use of proteins as buffer additives. Human serum albumin (HSA) was used as the model ligand; D,L-tryptophan and (R,S)-warfarin were used as the test analytes to be separated by this protein. Items examined in this work included the amount of HSA adsorbed to the capillary wall and the stability of this adsorbed protein layer. These were investigated by performing frontal analysis on the capillary with HSA and by injecting neutral markers through the capillary at different applied voltages before and after HSA treatment. The role of adsorbed HSA vs HSA in the buffer in determining the stereoselectivity of the CE system was also examined. Adsorbed HSA was the predominant agent involved in the separation of (R,S)-warfarin, while HSA in the buffer had the most significant effect in the resolution of D,L-tryptophan. Two distinct separation mechanisms were proposed to explain these differences. Good agreement was obtained between the results predicted by these mechanisms and the experimental data. Under optimized conditions, both pairs of enantiomers were separated with baseline resolution in less than 12 min.

Adsorption↗
PubMed2001

A tandem column ensemble with an atmospheric pressure junction-point vent for high-speed GC with selective control of peak-pair separation.

A series-coupled (tandem) ensemble of two capillary GC columns using different stationary phases and a pneumatically actuated low-volume valve connecting the column junction point to an atmospheric-pressure vent line is used to adjust the ensemble separation of selected pairs of target compounds. The valve is normally closed, and the pressure at the column junction point assumes the value that would occur in the absence of any other connections. The valve can be opened for brief periods of time, thus producing pulses of atmospheric pressure at the column junction point. If a component pair is separated by the first column but coelutes from the column ensemble, the ensemble separation can be increased if a pulse occurs when one of the components has migrated across the column junction but the second component is still on the first column. All of the mixture components that are on the same column during the time that the valve is open (pulse duration) will be shifted to either larger or smaller retention times, but the pattern of peaks (elution order) for these components from the column ensemble will be relatively unaffected by the pressure pulse. Multiple pulses can be used to enhance the separation of different component pairs, which sequentially reach the column junction point. Performance of the valve-operated system is described. Time-of-flight mass spectrometry with time-array detection is used to examine the effects of pulse duration on the separation achieved for different component pairs.

Journal Article↗
PubMed2001

An extraction chromatography method for Hf separation prior to isotopic analysis using multiple collection ICP-mass spectrometry.

A novel method for the single-step separation of Zr + Hf from all matrix elements of geological samples has been developed for Hf isotopic measurements using multiple collector-ICP-mass spectrometry. The method combines an effective sample decomposition by LiBO2 fusion with a selective separation of Hf + Zr by a solid-phase extraction material based on dipentyl pentyl phosphonate, commercially available as U-TEVA.Spec. Using this simple and rapid procedure, Hf and Zr can be isolated in a single separation step with good recoveries (>90%) and satisfactory blank levels (approximately 55 pg of Hf), so that a subsequent isotopic measurement with ICPMS is possible. An excellent separation from rock-forming constituents is achieved, including those elements (Al, P, Ti, Cr, Fe, Mo, etc.) known to interfere in conventional separation methods based on ion-exchange techniques. The potential of this new method for Hf isotopic analysis is demonstrated by replicate MC-ICPMS measurements of 176Hf/177Hf ratios in seven international reference materials of silicate rocks, spanning a range of Hf contents and bulk compositions.

Journal Article↗
PubMed2001

Electrophoresis separation in open microchannels. A method for coupling electrophoresis with MALDI-MS.

The separation of biological mixtures in open micro-channels using electrophoresis with rapid and simple coupling to mass spectrometry is introduced. Rapid open-access channel electrophoresis employs microchannels that are manufactured on microchips. Separation is performed in the open channels, and the chips are transferred to a matrix-assisted laser desorption/ionization (MALDI) source after the solvent is evaporated. The matrix (2,5-dihydroxybenzoic acid) is placed in the solution with the run buffer before the separation of the analyte components. After separation, the solvent is evaporated and the microchip is ready for MALDI-MS analysis. The microchip is placed directly into a specially designed ion source of an external source Fourier transform mass spectrometry instrument. Separation of simple mixtures containing oligosaccharides and peptides is shown.

Animals↗
PubMed2001

Separation of selected basic pharmaceuticals by reversed-phase and ion-exchange chromatography using thermally tuned tandem columns.

The separation of basic pharmaceuticals is usually performed on C8 or C18 bonded silica supports. Silanolphilic interactions between basic analytes and surface silanol groups often lead to tailed peaks, poor efficiency, and irreproducible retention times. To solve these problems, many new types of silica-, zirconia-, and polymer-based columns, which provide unique selectivities, improved stability at high pH, or both, have been developed for the analysis of basic compounds. The essence of method development for the chromatographic analysis of basic compounds is to choose a system in which the band spacing can be varied dramatically, quickly, and conveniently while minimizing the tailing due to silanolphilic interactions. The thermally tuned tandem column (T3C) approach has been shown to provide an effective way to adjust stationary-phase selectivity for nonionic compounds. In this study, a tandem combination of an octadecylsilane (ODS) and a polybutadiene-coated zirconia (PBD-ZrO2) phase was used to separate nine antihistamines. Selectivity is tuned by independently adjusting the isothermal temperatures of the two columns. We found dramatic differences in the retention factors, elution sequences, and band spacing for the above set of basic drugs on the two types of columns. The T3C model has been used successfully to locate the optimal temperatures based on only four exploratory runs. The nine antihistamines were baseline separated on the tandem column combination even though they could not be separated on the individual phases. The effect of the buffer concentration on retention of the basic antihistamines was also studied. We conclude that cation-exchange interactions predominate on the PBD-ZrO2 phase, while reversed-phase interactions are more important on the ODS phase. Interestingly, an increase in column temperature causes a significant increase in the retention on the ODS column and a decrease of retention on the PBD-ZrO2 column. This can be explained by the change in the analyte's degree of ionization with temperature. The T3C combination of silica- and zirconia-based RPLC columns is demonstrated to be a powerful approach for the separation of this mixture of basic analytes.

Buffers↗
PubMed2002

Liquid core waveguide for full imaging of electrophoretic separations.

We employed a liquid core waveguide to image both DNA electrophoresis separations and isoelectric focusing of proteins. The utility of the system is demonstrated for DNA fragment sizing and protein separations. The system utilizes the liquid-core waveguide as an efficient window for both the excitation of separated samples and the collection of light through total internal reflectance, with an ability to detect target molecules in the zeptomolar range. Scanning the excitation laser along the length of the electrophoresis capillary excites individually separated analyte bands, while the fluorescence is collected end-on by an optical fiber coupled to a photomultiplier, thus, creating an image of the separation along the length of the capillary.

DNA↗
PubMed2003

Hydroxypropyl cellulose as an adsorptive coating sieving matrix for DNA separations: artificial neural network optimization for microchip analysis.

Effective DNA separations in microelectrophoretic systems are complicated by the need to passivate the surface dynamically or covalently. We describe the optimization and utilization of a novel buffer system for fast DNA separations by capillary and microchip electrophoresis without the need for any surface modification or conditioning prior to separation. At concentrations as high as 5%, hydroxypropyl cellulose (HPC) has a relatively low viscosity, allowing for microchip channel filling to be performed with ease. A MES/TRIS buffer system at pH 6.1 eliminates the need for surface preconditioning procedures due to the promotion of hydrogen bonding of HPC with the wall. An additional benefit with this buffer system is the low current observed at high fields when compared to other common DNA separation buffers. An artificial neural network (ANN) was used to model the data and to predict the optimum conditions. Utility of the ANN-optimized system for molecular diagnostic testing was demonstrated by performing microchip separations on DNA samples from patients suspected of having genetic mutations associated with Duchenne muscular dystrophy (DMD). Microchip analysis easily allowed for the patient samples positive for DMD mutations to be distinguished from patient samples negative for the disease.

Adsorption↗
PubMed2003

Nonaqueous electrophoresis microchip separations: conductivity detection in UV-absorbing solvents.

The use of organic solvents in microfabricated capillary electrophoresis (CE) devices is demonstrated in connection with the separation of aliphatic amines in pure dimethylformamide, dimethylacetamide, dimethyl sulfoxide, or propylene carbonate media. Contactless conductivity detection is employed for monitoring the separated solutes in these UV-absorbing solvents. The effect of the physicochemical properties of the organic solvent upon the migration behavior is investigated. The apparent mobility increases nearly linearly with the reciprocal of the solvent viscosity, while the electroosmotic mobility increases in a linear fashion with the dielectric constant/ viscosity ratio. Some deviation from theoretical predictions is observed using propylene carbonate. The nonaqueous CE microchip offers high separation efficiency, reflected in plate numbers ranging from 93,680 to 127,680, using a separation voltage of +3,000 V, a dimethylformamide medium, and a contactless conductivity detection. Experimental parameters affecting the analytical performance of the nonaqueous CE/conductivity microchip are examined. Calibration and precision experiments indicate a linear and reproducible response. Such use of organic solvents can benefit microchip separations through extended scope (toward nonpolar solutes) and tunable selectivity.

Journal Article↗
PubMed2002

A chip system for size separation of macromolecules and particles by hydrodynamic chromatography.

For the first time, a miniaturized hydrodynamic chromatography chip system has been developed and tested on separation of fluorescent nanospheres and macromolecules. The device can be applied to size characterization of synthetic polymers, biopolymers, and particles, as an attractive alternative to the classical separation methods such as size exclusion chromatography or field-flow fractionation. The main advantages are fast analysis, high separation efficiency, negligible solvent consumption, and easy temperature control. The prototype chip contains a rectangular flat separation channel with dimensions of 1 microm deep and 1000 microm wide, integrated with a 300-pL injector on a silicon substrate. The silicon microtechnology provides precisely defined geometry, high rigidity, and compatibility with organic solvents or high temperature. All flows are pressure driven, and a specific injection system is employed to avoid excessive sample loading times, demonstrating an alternative way of lab-on-a-chip design. Separations obtained in 3 min show the high performance of the device and are also the first demonstration of flat channel hydrodynamic chromatography in practice.

Chromatography, Liquid↗
PubMed2003

Separation and quantitation of short-chain coenzyme A's in biological samples by capillary electrophoresis.

Because of the importance of coenzyme A's (CoA's or CoASH) in many metabolic processes and the biosynthesis of some carbohydrates and lipids, many methods have been developed to separate and determine their levels in various tissues for metabolism studies, including enzymatic assays, paper chromatography, and high-performance liquid chromatography (HPLC). However, inadequate separation of coexisting CoA's in biological samples was often encountered due to the similarity of their structures. In this paper, we demonstrated for the first time the separation and quantitation of 12 different CoA's by using capillary electrophoresis with UV detection at 254 nm. All 12 CoA's (CoASH, HMG CoA, methylmalonyl CoA, succinyl CoA, methylcrotonyl CoA, isobutyryl CoA, oxidized CoA, acetyl CoA, crotonoyl CoA, n-propzoyl CoA, acetoacetyl CoA, malonyl CoA) were completely separated at -30 kV in a 100 mM NaH2PO4 running buffer containing 0.1% beta-cyclodextrin at pH 6.0. The total separation time was less than 30 min. The signal response was linear over 2 orders of magnitudes (from 1 to 100 nmol), and the detection limits were in the picomole range. The effects of pH, buffer concentration, additives, and operation voltages on sensitivity and resolution were also discussed. This technique, described here, is much more sensitive, faster, and simpler than the published HPLC methods and can potentially be used for mechanistic study in biological systems involving CoA metabolism.

Animals↗
PubMed2003

High-efficiency, two-dimensional separations of protein digests on microfluidic devices.

High-efficiency, two-dimensional separations of tryptic digests were achieved using glass microfluidic devices. Following micellar electrokinetic chromatography (MEKC) separations in a 19.6-cm-long serpentine channel, the peptides were rapidly sampled into a 1.3-cm-long second-dimension channel, where they were separated by capillary electrophoresis (CE). The turns in the serpentine channel were asymmetrically tapered to minimize geometrical contributions to band broadening and to provide ample channel length for high-efficiency chromatographic separations. Analysis of rhodamine B injections routinely produced plate numbers of 230000 and 40000 in the first (MEKC) and second (CE) dimensions, respectively, corresponding to plate heights of 0.9 and 0.3 microm. The electric field strengths were 200 V/cm for MEKC and 2400 V/cm for CE. In analysis times less than 15 min, two-dimensional separation of bovine serum albumin tryptic digest produced a peak capacity of 4200 (110 in the first dimension and 38 in the second dimension). The system was used to identify a peptide from a tryptic digest of ovalbumin using standard addition and to distinguish between tryptic digests of human and bovine hemoglobin.

Animals↗
PubMed2003

Separation of recombinant human erythropoietin glycoforms by capillary electrophoresis using volatile electrolytes. Assessment of mass spectrometry for the characterization of erythropoietin glycoforms.

The separation of the glycoforms of erythropoietin (EPO) by capillary electrophoresis (CE) was recently published as a monograph by the European Pharmacopoeia (European Pharmacopoeia 4 2002, 1316, 1123-1128). Although the experimental CE conditions employed a background electrolyte containing additives suitable for on-line UV-absorption detection, they were not appropriate for on-line mass spectrometry (MS) detection. In this work, an attempt was made to investigate experimental conditions employing volatile electrolyte systems to achieve the separation and characterization of EPO glycoforms using CE and ESI-MS methodologies. The influence of several operating conditions, such as the coating of the internal walls of the capillary as well as the composition, concentration, and the pH of the separation buffer were investigated. The results demonstrated that when the internal walls of the capillaries were permanently coated with Polybrene and a buffer electrolyte containing 400 mM of HAc-NH4Ac (acetic acid-ammonium acetate), pH 4.75, was used, a significantly reproducible separation was achieved for EPO glycoforms. Intact EPO was characterized by two mass spectrometry techniques: electrospray ionization (ESI-MS) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF-MS). The data demonstrated that MALDI-TOF-MS provided a good approximation to an average molecular mass of the EPO molecule. However, it was still necessary to carry out further separation of the intact EPO glycoforms in order to obtain molecular mass information when ESI-MS was used.

Electrolytes↗
PubMed2004

Separation of long DNA molecules by quartz nanopillar chips under a direct current electric field.

We have established the nanofabrication technique for constructing nanopillars with high aspect ratio (100-500 nm diameter and 500-5000 nm tall) inside a microchannel on a quartz chip. The size of pillars and the spacing between pillars are designed as a DNA sieving matrix for optimal analysis of large DNA fragments over a few kilobase pairs (kbp). A chip with nanopillar channel and simple cross injector was developed based on the optimal design and applied to the separation of DNA fragments (1-38 kbp) and large DNA fragments (lambda DNA, 48.5 kbp; T4 DNA, 165.6 kbp) that are difficult to separate on conventional gel electrophoresis and capillary electrophoresis without a pulsed-field technique. DNA fragments ranging from 1 to 38 kbp were separated as clear bands, and furthermore, the mixture of lambda DNA and T4 DNA was successfully separated by a 380-microm-long nanopillar channel within only 10 s even under a direct current (dc) electric field. Theoretical plate number N of the channel (380-1450 microm long) was 1000-3000 (0.7 x 10(6)-2.1 x 10(6) plates/m). A single DNA molecule observation during electrophoresis in a nanopillar channel revealed that the optimal nanopillars induced T4 DNA to form a narrow U-shaped conformation during electrophoresis whereas lambda DNA kept a rather spherical conformation. We demonstrated that, even under a dc electric field, the optimal nanopillar dimensions depend on a gyration radius of DNA molecule that made it possible to separate large DNA fragments in a short time.

DNA↗
PubMed2004

Optimization of two-dimensional off-line LC/MS separations to improve resolution of complex proteomic samples.

In off-line 2D-HPLC a continuous salt gradient is applied in the first separation dimension. This increases the number of identified proteins from complex samples significantly due to higher chromatographic resolution compared to stepwise elution. Achievement of optimal resolution requires the optimization of the two separation dimensions. The influence of LC elution gradients in the first and second dimensions, of analysis time, of stationary-phase material, and of column dimensions was systematically investigated in order to obtain information on the overall peak capacity of the separation system. Provided data indicate that for complex samples such as an E. coli cell extract, a shallow LC SCX gradient with a high number of collected fractions significantly increases the overall peak capacity while for lower complexity samples short gradients with few fractions were sufficient to obtain a maximum of identified peptides. In addition, column dimensions and materials exhibited a strong effect on the overall efficiency of the 2D HPLC separation. The outcome of these experiments could hence serve as a guideline for investigators to adapt their method for the separation of their specific proteome sample to achieve a maximum of peptide sequence information by 2D LC MS/MS analysis.

Cell Extracts↗
PubMed2004

Recycling size exclusion chromatography for the analysis and separation of nanocrystalline gold.

Recycling size exclusion chromatography (RSEC) provides a high-resolution technique for the analysis and separation of materials based on size. We show here the application of this method to gold nanocrystals stabilized by thiols. Alternate recycling is more effective at separating nanomaterials as compared to closed-loop recycling because of its improved efficiency and high resolution. With the use of this technique, we find the resolution ratio of nanocrystal separation increases with the square root of the cycle number, in good agreement with theory. The increased resolution of the size exclusion chromatograms permits the use of RSEC in the baseline separation of nanocrystals which differ by only 6 A in size. In addition to separations, RSEC is valuable as an analytical tool. For example, after recycling processes an initially broad and chromatographic feature from a gold nanocrystal solution resolves into three distinct peaks. Transmission electron microscopy of collected fractions reveals that these peaks correspond to distinct populations of gold nanoparticles with narrowly defined sizes.

Chromatography, Gel↗