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 613 records · Page 34Linked to original sources
PubMed1992

Separation of dideoxyribonucleosides in trace amounts by automated liquid chromatography and capillary electrophoresis.

No satisfactory high-performance liquid chromatographic (HPLC) method is currently available for the separation of the major dideoxyribonucleosides (ddNs) and their derivatives. A method involving HPLC has been developed for the separation of five major ddNs [ddA, ddC, ddI, azT and 2',3'-dideoxy-2',3'-didehydrothymidine (d4T)]. Elution of the common and modified components of DNA was also examined under the selected separation conditions of HPLC. The elution characteristics of these compounds were studied using serum plasma samples spiked with ddN derivatives. In addition, capillary electrophoresis (CE) was investigated for the separation of ddNs and their derivatives. Picomolar amounts of the five major ddNs and the metabolic product of azT [5'-O-glucuronide-3'-azido-3'-deoxythymidine (Glo-azT)] were satisfactorily resolved in 10 min by using a modification of CE. The spectral properties of the ddNs were characterized under different pH conditions and compared with those of their parent deoxyribonucleosides (dNs) because these compounds are commonly measured in HPLC by their spectral properties. The spectra of ddC and ddT derivatives resemble very closely those of dC and dT, but those of ddA and ddI differ to some extent from their parent dNs. The HPLC method was extensively examined for satisfactory resolutions of these compounds. For example, an isocratic elution method, although simple, failed to resolve these compounds and ion-pair chromatography did not offer any advantage. Gradient elution involving buffered solutions and increasing amounts of an organic modifier yielded satisfactory results. Methanol appeared to be the organic modifier of choice. A reversed-phase matrix with smaller than octadecyl alkyl chains did not produce the necessary interactions. Uniform spherical beads of smaller diameter produced superior resolutions. The separation of these compounds on three commercially available columns is discussed. The separation of human plasma samples spiked with dideoxynucleoside derivatives by HPLC was accomplished in ca. 16 min. The presence of the dNs did not interfere in their separations.

Capillary Action↗
PubMed1993

Use of glucomannan for the separation of DNA fragments by capillary electrophoresis.

Glucomannan, a natural polysaccharide extracted from Amorphophallus konjac, was employed as a sieving additive for the separation of restriction DNA fragments in capillary electrophoresis. A stable solution of entangled glucomannan was successfully prepared under mild conditions. The separation capillary filled with 0.25% glucomannan exhibited excellent resolution and reproducibility on separation of DNA fragments over the range of ca. 1400 base pairs. The separation was dependent on the size of the fragments, which allowed the determination of the size of separated DNAs directly from the migration time. In addition to these separation characteristics, glucomannan has practical advantages in its chemical stability, non-toxicity and ease of handling. Because the method is applicable to the separation and characterization of the DNA fragments generated by digestion with restriction enzymes or produced by polymerase chain reactions, it is concluded that glucomannan is a good alternative to the conventional sieving additives for capillary electrophoresis, such as polyacrylamide and hydroxymethylcellulose.

Bacteriophage phi X 174↗
PubMed1996

Separation parameters via virtual migration distances in high-performance liquid chromatography, capillary zone electrophoresis and electrokinetic chromatography.

Among the various differential migration processes of separation, high-performance liquid chromatography (HPLC) and capillary zone electrophoresis (CZE) have emerged as the two major high-performance analytical techniques for separation of complex biological substances. In both HPLC and CZE with electroendoosmotic flow, the differential migration process can be divided into a separative component, which involves selective interactions with the stationary phase or differences in the electrophoretic migration velocities, and a non-separative component representing migration by convection that does not contribute directly to separation. The introduction of virtual migration distances leads to an additivity relationship for the two components that is applicable to both of the above techniques and facilitates the recognition of the underlying similarities as well as the expression and comparison of the various separation parameters. Examination of the key migration parameters led to the characterization and the classification of the various modes of CZE with electroendoosmotic flow. The treatment was extended to the analysis of capillary electrochromatography and micellar electrokinetic chromatography; two hybrid processes which exhibit features borrowed from HPLC and CZE. The use of virtual migration distances also led to a consistent and unified description of the characteristic parameters of these separation systems.

Chromatography, High Pressure Liquid↗
PubMed1989

Both separation and eccentricity can limit precise position judgements: a reply to Morgan and Watt.

Weber's law is ubiquitous in position judgements. In a variety of position acuity tasks, the position threshold is proportional to the separation of the reference features. Recently, we (Klein & Levi, 1987; Levi, Klein & Yap, 1988) suggested that two sensory processes may serve to limit position acuity, and thus contribute to Weber's law for position. One is the target separation, and the other is the target eccentricity. In order to test this idea, we pitted separation against eccentricity by measuring spatial interval discrimination thresholds on an iso-eccentric arc (Levi et al., 1988). Over a 5-fold range of separations, we found that thresholds were independent of separation, and concluded that at large separations, eccentricity can limit precise position judgements. In the preceding article, Morgan and Watt (1989) have questioned this conclusion, and have shown that the effects of eccentricity are small in an arc length discrimination task. In the present article, we: (i) address the objections raised by Morgan and Watt; (ii) show that our data and 2-mechanism model are consistent with many previous studies; and (iii) show that Morgan and Watt's task is inherently difficult, so that rather than tapping the sensory limits imposed by the target eccentricity, performance on the arc length task is constrained by the cognitive demands of the task, or by the difficulty of reconstruction. In contrast, the measurement of chord length (spatial interval discrimination on an iso-eccentric arc) can be simply done by calculating the distance between the endpoints. Thus, at large separations, thresholds for the chord length judgements are much lower than those of Morgan and Watt, and are proportional to the eccentricity of the targets.

Humans↗
PubMed1990

Spatial interval discrimination with blurred lines: black and white are separate but not equal at multiple spatial scales.

We used Gaussian blurred lines of same- and opposite-polarity to measure the effects of blur on 3-line spatial interval discrimination (bisection). The results of our experiments can be summarized as follows. Spatial interval discrimination (3-line bisection) thresholds are proportional to the separation of the lines (i.e. Weber's law). At the optimal separation, spatial interval discrimination thresholds for same-polarity lines represent a "hyperacuity" as small as 2 sec arc. For same-polarity Gaussian blurred lines, over a wide range of the blur standard deviations (sigma), the optimal threshold occurs when the separation is approx. 2 sigma, and the optimal threshold is about 0.02 sigma, or a Weber fraction (delta s/s) of 0.01. For opposite-polarity lines, under conditions where same-polarity stimuli yield the best thresholds (at a separation approximately 2 sigma), spatial interval thresholds are an order of magnitude worse than that for same-polarity lines, suggesting that the localization of stimili of opposite-polarity is much worse than that of same-polarity stimuli over a wide range of spatial scales. At large separations, greater than about 5 sigma, spatial interval discrimination thresholds are more or less independent of both contrast and polarity. While hyperacuity is generally thought of in terms of the tiny spatial thresholds which are obtained at small separations with stimuli comprised of thin lines, the present results, and those of others, suggest that for same-polarity stimuli, hyperacuity thresholds are a general property of the visual system, occurring at many spatial scales. The present results also suggest that the poor localization of opposite-polarity lines occurs at multiple spatial scales, when the line separation is less than about five times the stimulus spread. We consider several models which can account for particular features of our data.

Contrast Sensitivity↗
PubMed1992

The effects of common movement and spatial separation on position- and motion-based judgements of relative movement.

When common movement is superimposed on relative movement (changes in separation between two dots), relative movement thresholds increase nonlinearly as a function of initial dot separation. For large separation (greater than 2.0 deg), thresholds increase gradually with increased separation. It is shown that this reflects judgments based on perceived relative motion. For small separations (less than 2.0 deg), thresholds increase sharply with increased separation. It is shown that this reflects judgments based on perceived changes in relative position. Evidence is presented that superimposed common movement reduces sensitivity to relative movement by reducing sensitivity to relative motion. This provides a "window", in the range of small dot separations, for relative movement judgements to be based on the perception of changes in relative position, even though motion is perceived for individual dots.

Humans↗
PubMed1993

Visibility and vernier acuity for separated targets.

The purpose of this study was to investigate the roles of the putative "spatial filter" and "local sign" mechanisms in determining line vernier thresholds for a range of target separations, using stimulus contrast or visibility as a tool. In Expt 1, the effects of varying target contrast and exposure duration on vernier thresholds for lines separated by 90 min arc, where the reference line was fixated, were measured. Contrast thresholds for the nonfixated test line were also measured, so that the role of its visibility in limiting vernier thresholds could be assessed. Vernier thresholds decreased almost proportionally with increasing contrast only until the visibility of the test line reached about 3 times the contrast detection threshold, regardless of exposure duration. At higher visibility levels, vernier thresholds were virtually independent of target contrast. In Expt 2, the effects of varying target contrast on vernier thresholds for a range of target separations (2-90 min arc) were measured using a 250 msec exposure duration. Vernier thresholds for abutting lines and for those separated by 2 min arc, decreased with target contrast until about 30 times the test line's contrast detection threshold. However for lines separated by 4 min arc or more, they were only weakly dependent on target contrast at much lower visibility levels. We propose that for very close separations vernier thresholds are limited by the contrast response properties of spatial filters. For separations of 4 min arc or more, thresholds appear to be limited by the positional uncertainty of the test line, which increases with eccentricity.

Contrast Sensitivity↗
PubMed1990

Magnetic aqueous two-phase separation in preparative applications.

Magnetic aqueous two-phase separation is a new technique to speed up the separation of aqueous two-phase systems (Anal. Biochem. 1987, 167, 331-339). It is based on the addition of magnetically susceptible material (e.g. 1-micron iron oxide particles) which induces rapid phase separation when a mixed system is placed in a magnetic field. The technique has been applied to a number of two-phase systems. The time for phase separation was decreased by a factor of 5-240,000, with the largest improvement for systems containing high concentrations of protein and for systems with viscous or nearly isopycnic phases. An apparatus for preparative multistage extraction with magnetic separation was constructed and tested on glycolytic enzymes present in a yeast extract using a dextran/Cibacron blue-polyethylene glycol system. The presence of iron oxide particles did not adversely affect the extracted enzymes. An electromagnet-based apparatus for continuous phase separation on a larger scale was also designed. A phase system containing crude dextran and unpurified cell homogenate was effectively processed. The apparatus also allowed effective separation when the phase containing iron oxide particles was only a small fraction (4%) of the total phase system.

Alcohol Dehydrogenase↗
PubMed1986

Isoelectric focusing using non-amphoteric buffers in free solution: III. Separation of amino acids.

Separation of proteins or amino acids by isoelectric focusing in multicompartment devices has been proposed for large-scale purifications of biological mixtures. In the perspective of industrial applications, the present authors built a multicompartment apparatus and studied the pH profiles stabilized by simple non-amphoteric buffers (acetic acid and sodium acetate). Mixtures of two amino acids were separated to test this device. A theoretical model comprising one dimensionless separation parameter is proposed to characterize these separations. This model allows one to calculate the purity of the recovered amino acids, the yield of a separation at steady-state or the time necessary to obtain a given concentration of an amino acid in one of the compartments of the isoelectric focusing cell. The separation parameter contains the physical parameters which intervene in the electric migration and in the diffusion. Values of this separation parameter have been experimentally determined for three amino acids under various experimental conditions. The results confirm the usefulness of this model in designing a multicompartment isoelectric focusing apparatus.

Amino Acids↗
PubMed1986

The separation of 99mTc(Sn)EHDP complexes by HPLC and GPC.

For the characterization of the multi-component bone-scan agent 99mTc(Sn)EHDP we have analysed the complex mixture with reversed phase ion pair chromatography (IPC) and soft gel permeation chromatography (GPC). With IPC five major complexes were found within a separation-time of 40 min. To avoid decomposition of the complexes during separation, the concentrations of EHDP and the reductant Sn(II) in the eluent had to be identical to the EHDP and Sn(II) concentrations used for the preparation of the complexes. To investigate the stability of the complexes we applied separation by IPC, followed by re-analysis of the fractions within 1 h and after 21-25 h. It appears that there is a state of equilibrium between the five complexes. Within 1 h after isolation the separated complexes were still more than 90% in their original form while after 20 h considerable amounts of the other complexes are found. The two complexes with the largest retention time with IPC are the most stable ones. When the total mixture was re-analysed after 26 h all five components appeared to be still present, but the relative amount of the most stable component had increased. Using GPC for the separation of the complex mixture, we found four major peaks within a separation time of 14 h. The elution orders of the complexes with the two separation methods are opposite.

Bone and Bones↗
PubMed2005

Workload of window cleaners using ladders differing in rung separation.

The objective of the present study was to compare energetic workload, perceived exertion, perceived discomfort, safety, and mechanical load at lower limb joints among window cleaners during usage of extension ladders with 30 and 35 cm rung separation. Eleven healthy male professional window cleaners of short and tall stature participated in this study. No significant differences between 30 and 35 cm rung separation were observed for the energetic workload. Results concerning the perceived exertion, discomfort, and safety indicate that 35 cm rung separation is preferred. Based on the mechanical load at the hip, knee, and ankle during ascending and descending the ladder, 30 cm rung separation is preferable to 35 cm rung separation. It is advised to climb ladders with the knees inside the side rails of the ladder, but this seems only possible with 35 cm rung separation. Findings of the presents study suggest that overall, a 35 cm rung separation is marginally favourable while using extension ladders.

Adult↗
PubMed2004

Maternal separation affects male rat copulatory behaviour and hypothalamic corticotropin releasing factor in concert.

Maternal separation (MS) is an animal model of early adverse experience, which is known to affect hypothalamic-pituitary-adrenal (HPA) axis function and various aspects of emotional behaviour. Sexual dysfunction is a prominent symptom in depression and in the present study we investigated the effects of maternal separation on copulatory behaviour and partner preference in adult male rats and paced mating in adult female rats. It has been suggested that corticotropin releasing factor (CRF) inhibits copulatory behaviour in male rats and we therefore examined if changes in male sexual behaviour were accompanied by changes in hypothalamic corticotropin releasing factor protein content. We found changed copulatory behaviour reflected in decreased mount latency, intromission latency, and post-ejaculatory interval in rats subjected to 180 min daily separation compared to handled rats, separated for 15 min daily on postnatal days (PNDs) 2-14. Ejaculation latency was not affected and there were no changes in partner preference in male rats. Paced mating behaviour of adult maternally separated female rats was unaffected. The concentration of corticotropin releasing factor-like immunoreactivity was lower in the hypothalamus of male rats separated for 180 min compared to male handled rats. We therefore suggest that 180 min of maternal separation generates a male phenotype with increased sexual motivation possibly due to inadequate levels of corticotropin releasing factor in the hypothalamus.

Animals↗
PubMed2004

Maternal separation affects cocaine-induced locomotion and response to novelty in adolescent, but not in adult rats.

Maternal separation is known to exert long-term effects on both behavior and the neuroendocrine system. We investigated cocaine-induced locomotor activation as well as the locomotor and corticosterone response to forced novelty in maternally separated adolescent and adult rats. Maternal separation consisted of separating litters from their dams daily during 5 h from postnatal days 2 to 6. Control animals were subjected only to regular cage changes. Cocaine- (10 mg/kg, i.p.) and novelty-induced locomotion were recorded in an activity cage. After the animals were tested for behavioral response to novelty, trunk blood samples were collected and plasma corticosterone levels were determined by radioimmunoassay. Adolescent rats exposed to maternal separation exhibited an increased locomotor response to novelty and cocaine; corticosterone levels were lower in these adolescent animals, after exposure to the novel environment. These effects of maternal separation were not observed in rats that were tested as adults. Thus the maternal separation protocol produced enduring but transient changes in the behavioral response to cocaine and in the stress response to novelty.

Age Factors↗
PubMed2004

Separation of oligostyrene isomers in a complex mixture using two-dimensional heart-cutting reversed-phased liquid chromatography.

The development of a two-dimensional liquid chromatographic system requires a process of assessment that can yield an optimum performing system with minimal experimental evaluation. Information Theory and a geometric approach to Factor Analysis are two techniques that when used in combination, provide important information on the expected two-dimensional performance. In the present study, we compare the predicted separation performance of two-dimensional systems that have been subjected to analysis by Information Theory and Factor Analysis to that of actual chromatographic separation performance. Our test separation comprised a mixture of 32 oligostyrene structural isomers and stereoisomers. The optimal combination as determined by Information Theory and Factor Analysis consisted of a C18 column with a methanol mobile phase in the first dimension and a carbon clad zirconia column with an acetonitrile mobile phase in the second dimension. This system was also shown to be the most successful practical system when a heart-cutting approach was employed. The practical results were in total agreement with the results from Information Theory and Factor Analysis. The number of isomers resolved using this system was 27. A second system, namely one comprising of a C18 column and methanol mobile phase in the first dimension and a carbon clad zirconia column with a methanol mobile phase in the second dimension was also predicted to be a system with high separation potential. However, practical assessment of this system did not realise the theoretical predictions, largely due to the long separation times required in the second dimension. Furthermore, all combinations that employed a C18 column with an acetonitrile mobile phase in the first dimension failed to realise the theoretical separation potential due to high solute crowding, low orthogonality and a disordered arrangement of bands along the first separation axis. This was also predicted by the theoretical assessment.

Chromatography, High Pressure Liquid↗
PubMed2004

Separation of phosphatidylcholine and phosphatidylethanolamine by using high-performance displacement chromatography.

A binary mixture of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was successfully separated by high-performance displacement chromatography (HPDC) on an 150 mm x 4.6 mm analytical silica column (3-5 microm packing), using dichloromethane-methanol (9:1, v/v) as carrier and ethanolamine as displacer. The effects of displacer concentration, flow-rate, loading amount and the composition of the sample on separation efficiency were studied. Eighty-four milligrams sample (PE:PC 1:1.16) was separated perfectly by using 83 mM ethanolamine (in carrier) as displacer at the flow-rate of 0.1 ml/min. The yields of the pure PE and PC (100% purity) were 94.8% and 87.9%, respectively and the cycle time for a single separation was about 195 min. It was valuable that the optimum loading amount (the allowed maximum of sample loading) was investigated only by using the sample to be simulated the composition of the separated actual one, because the separation efficiency was significantly affected by the composition of the sample. For the same loading amount of 175 mg, the yields of the pure PE and PC were improved greatly from 31.4 and 16.9 to 56.0 and 77.6%, respectively, when the proportion of PE to PC was adjusted from 1:1.16 to 1:4. Furthermore, the separation of PE and PC in an actual sample (soybean phospholipids) was achieved using the proposed HPDC method.

Chromatography, Thin Layer↗
PubMed2005

Electrophoretic separations of twelve phenothiazines and N-demethyl derivatives by using capillary zone electrophoresis and micellar electrokinetic chromatography with non ionic surfactant.

We focused our work on the separation of phenothiazines that are important drugs used for the treatment of psychic diseases. For a better understanding of the metabolism of these solutes, we wanted to separate not only a mixture of 12 phenothiazines but also a mixture containing phenothiazines and their N-demethyl metabolites by capillary electrophoresis. Separations in capillary zone electrophoresis were performed using 3 x 10(-2) mol/L H3PO4 (pH 2.5) but the obtained resolutions were not entirely satisfactory especially with regard to phenothiazine -N-demethyl derivative pairs. To improve the obtained results, we have performed separations by using micellar electrokinetic chromatography. In this approach, we used a running electrolyte containing 3 x 10(-2) mol/L H3PO4 electrolyte (pH 2.5) and octaethylene glycol monododecyl ether (C12E8) as neutral surfactant. By introducing 2 x 10(-3) mol/L C12E8 in the electrolyte, 11 out of 12 phenothiazines have been baseline separated. With respect to the separation of a mixture containing 3 phenothiazines and their 3 demethyl derivatives, we obtained an excellent separation by using a running electrolyte prepared with 7.5 x 10(-4) mol/L C12E8 and 3 x 10(-2) mol/L H3PO4.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2006

Two-dimensional capillary liquid chromatography: pH gradient ion exchange and reversed phase chromatography for rapid separation of proteins.

In the present work, an orthogonal two-dimensional (2D) capillary liquid chromatography (LC) method for fractionation and separation of proteins using wide range pH gradient ion exchange chromatography (IEC) in the first dimension and reversed phase (RP) in the second dimension, is demonstrated. In the first dimension a strong anion exchange (SAX) column subjected to a wide range (10.5-3.5) descending pH gradient was employed, while in the second dimension, a large pore (4,000 A) polystyrene-divinylbenzene (PS-DVB) RP analytical column was used for separation of the protein pH-fractions from the first dimension. The separation power of the off-line 2D method was demonstrated by fractionation and separation of human plasma proteins. Seventeen pH-fractions were manually collected and immediately separated in the second dimension using a column switching capillary RP-LC system. Totally, more than 200 protein peaks were observed in the RP chromatograms of the pH-fractions. On-line 2D analysis was performed for fractionation and separation of ten standard proteins. Two pH-fractions (basic and acidic) from the first dimension were trapped on PS-DVB RP trap columns prior to back-flushed elution onto the analytical RP column for fast separation of the proteins with UV/MS detection.

Animals↗
PubMed2006

Separation of hydrophobic solutes by organic-solvent-based micellar electrokinetic chromatography using cation surfactants.

In this study, the separation of 13 homologous stick-like hydrophobic solutes, i.e., biphenyl nitrile derivatives, by organic-solvent-based micellar electrokinetic chromatography (MEKC) was investigated in terms of separation medium composition, species and concentration of surfactant, other additives, separation voltage and temperature. The results showed that the 13 strong hydrophobic compounds were baseline separated in 25 min with a repeatability of less than 1.3% (RSD) for migration time. The separation medium was a mixture of methanol, 2-propanol and water (58.5:10:31.5), containing 150 mM cetyltrimethylammonium bromide (CTAB) and 20 mM sodium borate. Variety of solvent composition, temperature and applied voltage all showed remarkable effect on the separation. The organic-solvent-based MEKC method proved to be superior to the aqueous MEKC and microemulsion electrokinetic chromatography (MEEKC) methods for the separation of strongly hydrophobic compounds.

Cations↗