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At least 667 records · Page 37Linked to original sources
PubMed2001

Evaluation of the leucocyte contamination of plateletpheresis concentrates collected on Trima separators: a review of three years of use at fixed sites and mobile units.

The Trima separator, manufactured by the Gambro, was introduced at the end of 1997 and the first separators were tested in France in early 1998. They are now routinely used on our Grenoble site for the collection of platelets and plasma. The aim of this paper is to evaluate the residual contamination of leucocytes of platelet products routinely collected on the Trima separator in a French blood transfusion center (ETS). Two separators are used at the fixed site and two separators are used for mobile collection (500 km/week). After a preliminary period of validation on site, 3237 plateletpheresis concentrates were collected by four separators qualified for fixed site or mobile unit use. An analysis taking into account the separator site (fixed or mobile) fails to reveal any significant difference for means or non-conformity percentages (data available).

Equipment Design↗
PubMed2002

Capillary electrochromatographic separation of aromatic amino acids possessing peptides using porphyrin derivatives as the inner wall modifiers.

Two different porphyrin derivatives (H2TPP(m-OPh)4 and Rh(III)TPP(m-OPh)4) were investigated with respect to their capability to help resolution of five model aromatic peptides in capillary electrophoresis/open tubular capillary electrochromatography. Though the main separation mechanism was preferentially based on the ionic properties of the separated analytes, involvement of particularly H2TTPP(m-OPh)4-peptide interactions at alkaline pH (8.0) was clearly demonstrated. In combination with Tris-phosphate buffer, a speed up of the separation was observed at pH 2.25 (particularly if Rh(III)TPP(m-OPh)4 was used as capillary coating); in spite of the speed up of the separation the selectivity of the system was sufficient and resulted in a complete separation of the five model peptides. It can be expected that Rh(III)TPP(m-OPh)4 capillary coating in combination with Tris-phosphate buffer can be generally used for a considerable speeding up of lengthy separations of peptides in acidic media with some decrease in the separation power of the system.

Amino Acids, Aromatic↗
PubMed2001

Objective data alignment and chemometric analysis of comprehensive two-dimensional separations with run-to-run peak shifting on both dimensions.

Data from comprehensive two-dimensional (2-D) separation techniques, such as comprehensive 2-D gas chromatography (GC x GC), liquid chromatography/liquid chromatography (LC x LC) and liquid chromatography/ capillary electrophoresis (LC x CE) can be readily analyzed by various chemometric methods to increase chemical analysis capabilities. A retention time alignment, preprocessing method is presented that objectively corrects for run-to-run retention time variations on both separation dimensions of comprehensive 2-D separations prior to application of chemometric data analysis algorithms. The 2-D alignment method corrects for run-to-run shifting of a sample data matrix relative to a standard data matrix on both separation time axes in an independent, stepwise fashion. After 2-D alignment, the generalized rank annihilation method (GRAM) is successfully applied, substantiating the performance of the alignment method. The alignment method should have important implications, because most 2-D separation techniques exhibit, in the context of chemometric data analysis, considerable run-to-run retention time shifting on both dimensions. Even when there are only three to four points/peak, that is, with three to four separations on the second dimension (column 2) per peak width from the first dimension (column 1), the 2-D alignment coupled with GRAM provides dependable analyte peak identification capabilities and adequate quantitative precision for unresolved analyte peaks. Thus, the 2-D alignment algorithm is applicable to lower data density conditions, which broadens the scope of chemometric analysis to high-speed 2-D separations.

Journal Article↗
PubMed2002

Electrochromatography in microchips: reversed-phase separation of peptides and amino acids using photopatterned rigid polymer monoliths.

A microfabricated glass chip containing fluidic channels filled with polymer monolith has been developed for reversed-phase electrochromatography. Acrylate-based porous polymer monoliths were cast in the channels by photopolymerization to serve as a robust and uniform stationary phase. UV light-initiated polymerization allows for patterning of polymer stationary phase in the microchip, analogous to photolithography, using a mask and a UV lamp for optimal design of injection, separation, and detection manifolds. The monoliths are cast in situ in less than 10 min, are very reproducible with respect to separation characteristics, and allow easy manipulation of separation parameters such as charge, hydrophobicity, and pore size. Moreover, the solvent used to cast the polymer enables electroosmotic flow, allowing the separation channel to be conditioned without need for high-pressure pumps. The microchip was used for separation of bioactive peptides and amino acids labeled with a fluorogenic dye (naphthalene-2,3-dicarboxaldehyde) followed by laser-induced fluorescence detection using a Kr+ ion laser. The microchip-based separations were fast (six peptides in 45 s), efficient (up to 600,000 plates/m), and outperformed the capillary-based separations in both speed and efficiency. We have also developed a method for complete removal of polymer from the channels by thermal incineration to regenerate the glass chips.

Amino Acids↗
PubMed2002

Entropic recoil separation of long DNA molecules.

A novel technique that can rapidly separate long-strand polymers according to length is presented. The separation mechanism is mediated by a confinement-induced entropic force at the abrupt interface between regions of vastly different configuration entropy. To demonstrate this technique, DNA molecules were partially inserted into a dense array of nanopillars (an entropically unfavorable region) using a pulsed electric field and allowed to relax to their natural state by removal of the field. Molecules of dissimilar lengths (T2 and T7 coliphage DNA) were inserted into this region in such a way that shorter molecules were fully inserted in this region, while longer molecules remained partially across the interface. The longer T2 molecules were observed to recoil entirely out of the pillar array, leaving the shorter T7 molecules inserted, and effecting separation of the two species in a single step. To show how this method can be used for separation of unknown samples, the inserting electric field was pulsed for progressively longer times, allowing passage of progressively longer molecules and producing the equivalent of a conventional electropherogram. The effects limiting resolution in this device are discussed, and the expected separating power of a multistage device is reported. The extracted resolution and running separation time compare favorably with current conventional separation techniques.

Algorithms↗
PubMed2004

Integration of isoelectric focusing with parallel sodium dodecyl sulfate gel electrophoresis for multidimensional protein separations in a plastic microfluidic [correction of microfludic] network.

An integrated protein concentration/separation system, combining non-native isoelectric focusing (IEF) with sodium dodecyl sulfate (SDS) gel electrophoresis on a polymer microfluidic chip, is reported. The system provides significant analyte concentration and extremely high resolving power for separated protein mixtures. The ability to introduce and isolate multiple separation media in a plastic microfluidic network is one of two key requirements for achieving multidimensional protein separations. The second requirement lies in the quantitative transfer of focused proteins from the first to second separation dimensions without significant loss in the resolution acquired from the first dimension. Rather than sequentially sampling protein analytes eluted from IEF, focused proteins are electrokinetically transferred into an array of orthogonal microchannels and further resolved by SDS gel electrophoresis in a parallel and high-throughput format. Resolved protein analytes are monitored using noncovalent, environment-sensitive, fluorescent probes such as Sypro Red. In comparison with covalently labeling proteins, the use of Sypro staining during electrophoretic separations not only presents a generic detection approach for the analysis of complex protein mixtures such as cell lysates but also avoids additional introduction of protein microheterogeneity as the result of labeling reaction. A comprehensive 2-D protein separation is completed in less than 10 min with an overall peak capacity of approximately 1700 using a chip with planar dimensions of as small as 2 cm x 3 cm. Significant enhancement in the peak capacity can be realized by simply raising the density of microchannels in the array, thereby increasing the number of IEF fractions further analyzed in the size-based separation dimension.

Electrophoresis, Gel, Two-Dimensional↗
PubMed2004

Simultaneous concentration and separation of enantiomers with chiral temperature gradient focusing.

A new technique is demonstrated for the simultaneous concentration and high-resolution separation of chiral compounds. With temperature gradient focusing, a combination of a temperature gradient, an applied electric field, and a buffer with a temperature-dependent ionic strength is used to cause analytes to move to equilibrium, zero-velocity points along a microchannel or capillary. Different analytes are thus separated spatially and concentrated in a manner that resembles isoelectric focusing but that is applicable to a greater variety of analytes including small chiral drug molecules. Chiral separations are accomplished by the addition of a chiral selector, which causes the different enantiomers of an analyte to focus at different positions along a microchannel or capillary. This new technique is demonstrated to provide high performance in a number of areas desirable for chiral separations including rapid separation optimization and method development, facile reversal of peak order (desirable for analysis of trace enantiomeric impurities), and high resolving power (comparable to capillary electrophoresis) in combination with greater than 1000-fold concentration enhancement enabling improved detection limits. In addition, chiral temperature gradient focusing allows for real-time monitoring of the interaction of chiral analyte molecules with chiral selectors that could potentially be applied to the study of other molecular interactions. Finally, unlike CE, which requires long channels or capillaries for high-resolution separations, separations of equivalent resolution can be performed with TGF in very short microchannels (mm); thus, TGF is inherently much more suited to miniaturization and integration into lab-on-a-chip-devices.

Buffers↗
PubMed2004

Pinched flow fractionation: continuous size separation of particles utilizing a laminar flow profile in a pinched microchannel.

A concept of "pinched flow fractionation" for the continuous size separation and analysis of particles in microfabricated devices has been proposed and demonstrated. In this method, particles suspended in liquid were continuously introduced into a microchannel having a pinched segment and were aligned to one sidewall in the pinched segment by another liquid flow without particles. The particles were then separated perpendicularly to the flow direction according to their sizes by the spreading flow profile inside the microchannel. Polymer microbeads were successfully separated, and the effects of the flow rate and channel shapes on the separation performance were examined. Also, separated particles were collected independently by making branches at the end of the pinched segment. Since this method utilizes only the laminar flow profile inside a microchannel, complicated outer field control could be eliminated, which is usually required for other kinds of particle separation methods such as field flow fractionation. Also, this method can be applied both for particle size analysis and for preparation of monodispersed particles, since separation can be rapidly and continuously performed.

Journal Article↗
PubMed1996

Molded monolithic rod of macroporous poly(styrene-co-divinylbenzene) as a separation medium for HPLC of synthetic polymers: on-column precipitation--redissolution chromatography as an alternative to size exclusion chromatography of styrene oligomers and polymers.

A process for the separation of styrene oligomers and polymers by size and composition using a novel separation medium has been demonstrated. The process involves precipitation of the macromolecules on the molded macroporous rod columns, followed by progressive elution utilizing a simple gradient of the mobile phase. Molded macroporous rod columns are ideally suited for this technique because convection through the large pores of the rod enhances the mass transport of large analyte molecules and accelerates the separation process. Styrene oligomers and polymers are separated in a 50-mm x 8-mm-i.d. column using a solvent gradient composed of a poor solvent such as water, methanol, or acetonitrile and increasing amounts of a good solvent, tetrahydrofuran. Excellent separations are obtained, demonstrating that precipitation-redissolution can be a suitable alternate to size exclusion chromatography (SEC) of some polymers. Compared to SEC, the gradient elution separation can be achieved at higher flow rates in a much shorter time. Precipitation-redissolution with gradient elution can also be used for the separation of copolymers, for which the process is controlled not only by molecular weight but also by the composition of the copolymers.

Chromatography, Gel↗
PubMed1998

Separation of tryptic digests using a modified buffer in pressurized capillary. Electrochromatography with an ion trap storage/reflectron time-of-flight mass spectrometer.

A rapid and efficient separation method using pressurized capillary electrochromatography (pCEC) has been developed to separate protein digests. The effects of mobile-phase ion conductivity, pH, and column size on separation speed and column efficiency were studied and optimized. The pCEC method was demonstrated to provide enhanced speed with more efficient and selective separation than HPLC by performing separations of a bovine beta-lactoglobulin A digest. A human hemoglobin digest was separated by pCEC under optimized conditions, and more than 20 peaks were separated in less than 20 min. Using an ion trap storage/reflectron time-of-flight mass spectrometer, coeluting components were clearly identified, and the resolving power of the pCEC method was further enhanced.

Animals↗
PubMed1999

End-column amperometric detection in capillary electrophoresis: influence of separation-related parameters on the observed half-wave potential for dopamine and catechol.

Capillary electrophoresis (CE) was coupled to a micro-electrode-based end-column amperometric detector. The influences of separation voltage, CE buffer concentration, and capillary-to-electrode distance on the observed hydrodynamic voltammetry of dopamine and catechol were studied using a separation capillary with an i.d. of 25 microns. It was found that an increased CE voltage, increased buffer concentration, or decreased capillary-to-electrode distance resulted in a positive shift of the observed half-wave potentials for both dopamine and catechol. At a constant separation current of 1.6 microA, the observed half-wave potential was found to increase with applied separation voltage. Furthermore, when experiments were carried out with a platinum quasi-reference electrode instead of a Ag/AgCl reference electrode, similar shifts in half-wave potential were observed. These results indicate that the observed shifts are an effect of the separation voltage rather than the separation current or a change in the reference potential. The characteristics of end-column detection with and without a fracture decoupler were compared. It was found that the effects of separation voltage, CE buffer concentration, and capillary-to-electrode distance were minimized by the use of a decoupling device. The observed half-wave potentials for dopamine and catechol were more positive when a CE capillary without a decoupler was employed compared to when a decoupler was used. Additionally, using the fracture decoupler, the observed half-wave potentials for both dopamine and catechol were approximately the same as when no CE voltage was applied (i.e., when the hydrodynamic voltammograms were recorded under flow injection conditions).

Catechols↗
PubMed1982

Role of lipid phase separations and membrane hydration in phospholipid vesicle fusion.

The relationship between lipid phase separation and fusion of small unilamellar phosphatidylserine-containing vesicles was investigated. The kinetics of phase separation were monitored by following the increase of self-quenching of the fluorescent phospholipid analogue N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine, which occurs when the local concentration of the probe increases upon Ca2+-induced phase separation in phosphatidylserine (PS) bilayers [Hoekstra, D. (1982) Biochemistry 21, 1055-1061]. Fusion was determined by using the resonance energy transfer fusion assay [Struck, D. K., Hoekstra, D., & Pagano, R. E. (1981) Biochemistry 20, 4093-4099], which monitors the mixing of fluorescent lipid donor and acceptor molecules, resulting in an increase in energy transfer efficiency. The results show that in the presence of Ca2+, fusion proceeds much more rapidly (t 1/2 less than 5 s) than the process of phase separation (T 1/2 congruent to 1 min). Mg2+ also induced fusion, albeit at higher concentrations than Ca2+. Mg2+-induced phase separation were not detected, however. Subthreshold concentrations of Ca2+ (0.5 mM) or Mg2+ (2 mM) induced extensive fusion of PS-containing vesicles in poly(ethylene glycol) containing media. This effect did not appear to be a poly(ethylene glycol)-facilitated enhancement of cation binding to the bilayer, and consequently Ca2+-induced phase separation was not observed. The results suggest that macroscopic phase separation may facilitate but does not induced the fusion process and is therefore, not directly involved in the actual fusion mechanism. The fusion experiments performed in the presence of poly(ethylene glycol) suggest that the degree of bilayer dehydration and the creation of "point defects" in the bilayer without rigorous structural rearrangements in the membrane are dominant factors in the initial fusion events.

Calcium↗
PubMed2006

Rapid purification and size separation of gold nanoparticles via diafiltration.

Purification and size-based separation of nanoparticles remain significant challenges in the preparation of well-defined materials for fundamental studies and applications. Diafiltration shows considerable potential for the efficient and convenient purification and size separation of water-soluble nanoparticles, allowing for the removal of small-molecule impurities and for the isolation of small nanoparticles from larger nanostructures in a single process. Herein, we report studies aimed at assessing the suitability of diafiltration for (i) the purification of water-soluble thiol-stabilized 3-nm gold nanoparticles, (ii) the separation of a bimodal distribution of nanoparticles into the corresponding fractions, and (iii) the separation of a polydisperse sample into fractions of differing mean core diameter. NMR, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) measurements demonstrate that diafiltration produces nanoparticles with a much higher degree of purity than is possible by dialysis or a combination of solvent washes, chromatography, and ultracentrifugation. UV-visible spectroscopic and transmission electron microscopic (TEM) analyses show that diafiltration offers the ability to separate nanoparticles of disparate core size. These results demonstrate the applicability of diafiltration for the rapid and green preparation of high-purity gold nanoparticle samples and the size separation of heterogeneous nanoparticle samples. They also suggest the development of novel diafiltration membranes specifically suited to high-resolution nanoparticle size separation.

Journal Article↗
PubMed2003

Identification of phase separation in solid dispersions of itraconazole and Eudragit E100 using microthermal analysis.

PURPOSE: To evaluate the phase separation in itraconazole/Eudragit E100 solid dispersions prepared by hot-stage extrusion. METHODS: Extrudates were prepared using a corotating twin-screw extruder at 180 degrees C. Micro-TA was used to evaluate the phase separation, where the AFM mode is used to visualize the different phases and local thermal analysis (LTA) to characterize the different phases RESULTS: Itraconazole formed a homogeneous mixture with Eudragit E100 with drug concentrations up to approximately 20%. Above this concentration, phase separation was observed. MTDSC revealed two Tgs and the mesophase of free glassy itraconazole. Performing micro-TA on the surface of these dispersions indicated an increase in sample roughness in the z-axis piezo signal, which could be an indication of free glassy itraconazole. However, thermal conductivity did not reveal differences between separate phases. Performing LTA, where only a small area (20 x 20 microm) is heated, showed two separate and mixed phases of itraconazole and Eudragit E100. Tip penetration in itraconazole and Eudragit E100 occurred at 332K and 383K respectively. The difference in tip penetration was explained in terms of the difference in fragility. CONCLUSION: Micro-TA makes it possible to characterize separate phases of itraconazole and Eudragit E100, thereby confirming the MTDSC results on phase separation.

Differential Thermal Analysis↗
PubMed1979

Accessing similarity and dimensional relations: effects of integrality and separability on the discovery of complex concepts.

A series of studies investigated how stimulus integrality and separability impact the cognitive accessibility of similarity and dimensional relations. A good deal of previous work has established that stimulus integrality and separability differentially determine perception; here, the question is whether they also have differential effects on conception. Are the principles that govern perception also principles that can be readily discovered in concept learning tasks? Is a similarity-based rule especially easy to abstract from integral stimuli and a dimensionally-based rule especially easy to abstract from separable stimuli? In Experiments 1 and 2, we measured the relative ease with which the two types of rules (similarity and dimensional) are discovered by adults with the two types of stimuli (integral and separable). In experiment 1, the two rules were made redundant and we asked which rule the subjects learned. In Experiment 2, one rule was made relevant and the other irrelevant, and we compared relative speeds of learning. The results from the studies led us to conclude (a) that dimensionally based rules are more accessible from separable than from integral stimuli; (b) that similarity-based rules are more accessible from integral than from separable stimul; and (c) that, in general, subjects have a bias to access dimensional relations in this type of task. Experiment 3 pursued an additional suggestion from Experiments 1 and 2 that the dimensional relations within integral stimuli are sometimes accessible, more so when larger interstimulus differences are encountered. In confirmation, Experiment 3 demonstrated that adult subjects are more successful in applying a dimensional rule to pairs of integral stimuli that differ by a small amount if they also have exposure to pairs of integral stimuli that differ by a large amount. In a later discussion, it was argued that such a finding is consistent with the notion that the "dimensions" of integral stimuli are merely arbitrary directions in the integral stimulus space, and some relevant pilot data to that effect were presented. Finally, Experiment 4 took up a developmental issue. Young children have sometimes produced perceptual responses governed by similarity relations when presented with stimuli that are separable for adults. Will they more readily access similarity-based or dimensionally-based relations from such stimuli in the concept learning tasks here? The results showed that both kindergarteners and fifth graders more readily access the dimensional relations. A final discussion integrated the findings from the several experiments, taking up the following issues: (a) the relation between the perception and the conception of stimulus relations and (b) the nonprimacy of the dimensional axes in the integral stimulus space.

Adult↗
PubMed1984

Predictability and coping with separation in infant squirrel monkeys.

Twelve infant squirrel monkeys were separated from their mothers once every 48 hr for a total of 20 separations. Half of the infants experienced separations for a fixed interval (FI) of 30 min. The remaining 6 infants experienced separations for a variable interval (VI) which averaged 30 min. During the separation periods, movement and vocalizations were recorded. Blood was sampled for later cortisol assay after the 1st, 5th, 10th, 15th, and final separation. The FI group showed increased levels of movement and vocalization over repeated separations when compared with the VI group. Cortisol showed significant increases over basal levels and remained elevated throughout the entire period in both groups. These findings suggest that predictability may be more stressful than unpredictability when organisms cannot control the predicted event.

Adaptation, Psychological↗
PubMed2002

Long-lasting changes in morphine-induced locomotor sensitization and tolerance in Long-Evans mother rats as a result of periodic postpartum separation from the litter: a novel model of increased vulnerability to drug abuse?

Daily postpartum separations from the litter produce enduring changes in anxiety and sensitivity to the antinociceptive effects of morphine in Long-Evans dams. We tested whether postpartum experience alters sensitivity to the effects of morphine on locomotor activity. Dams were tested 4-6 weeks after their pups were weaned, and had one of the following backgrounds: daily separation from the litter on postpartum days 2-14 for either 3 h (prolonged separation-LS) or 15 min (brief separation-BS), or no separation (nonhandled control-NH). After 2 consecutive days (B1-2) of baseline activity measurements, subjects were tested daily after s.c. injections of either morphine (10 mg/kg) or saline for 7 days and again on day 10. Beginning 5 days later, saline and 1.0-10 mg/kg of morphine were tested in all dams. On B1, LS and BS dams habituated slower than NH controls, yielding higher horizontal counts. LS dams failed to habituate across baseline days and were more active than other dams on B2. Sensitization, a progressive increase in horizontal activity, was more rapid and robust in LS and BS dams compared to NH animals. LS was the only group that developed tolerance to morphine-induced decreases in vertical activity. In LS dams with the history of morphine treatment, injection of saline resulted in higher horizontal activity and center time compared to saline-treated counterparts, indicative of conditioning. Among animals with a history of saline treatment, LS dams were more sensitive to morphine challenges than BS and NH dams. As a result of the robust and long-lasting increases in the ability of morphine to induce behavioral sensitization in litter-separated dams, periodic postpartum separation may represent a new animal model of increased vulnerability to substance abuse.

Animals↗
PubMed2002

Simultaneous separation of inorganic anions and cations using capillary electrophoresis with a movable contactless conductivity detector.

A number of small inorganic anions and cations were separated after injection of the sample into both ends of a separation capillary. The ions were detected using a capacitively coupled contactless conductivity detector (CCCCD) which could be placed at various positions along the capillary length. Counter-directional migration of anions and cations occurs towards the detector, which is placed at an appropriate position along the capillary so that the migration order is determined by the respective effective separation capillary lengths for both anions and cations. As the CCCCD detector can be easily moved to any position along the capillary, virtually any effective separation length can be attained. Depending on the number of analytes in the sample, one can choose to obtain either electropherograms with inter-migrating zones of cations and anions or separations with distinct regions of anion and cation zones, respectively. A new term 'apparent separation selectivity' is introduced to describe the manner in which the position of the detector can be varied in order to determine the final separation.

Journal Article↗