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At least 883 records · Page 49Linked to original sources

PubMed2006

Can the theory of gradient liquid chromatography be useful in solving practical problems?

Advances in the theory of gradient liquid chromatography and their practical impacts are reviewed. Theoretical models describing retention in reversed-phase, normal-phase and ion-exchange modes are compared. Main attention is focused on practically useful models described by two- or three-parameter equations fitting the experimental data in the range of mobile phase composition utilized for sample migration during gradient elution. The applications of theory for gradient method development, optimization and transfer are addressed. The origins and possibilities for overcoming possible pitfalls are discussed, including the effects of the instrumental dwell volume, uptake of mobile phase components on the column and size of the sample molecules. Special attention is focused on gradient separations of large molecules.

Biopolymers↗

PubMed1989

Effects of mobile phase composition on the chromatographic and electrochemical behaviour of catecholamines and selected metabolites. Reversed-phase ion-paired high-performance liquid chromatography using multiple-electrode detection.

The effects of pH, ionic strength, organic modifier, heptanesulphonic acid and citric acid content of a high-performance liquid chromatography mobile phase on the chromatographic and electrochemical behaviour of norepinephrine, epinephrine, dopamine, 3,4-dihydroxybenzylamine, 3,4-dihydroxyphenylethylene glycol, 3,4-dihydroxyphenylalanine and 3,4-dihydroxyphenylacetic acid in a reversed-phase system have been systematically studied. Optimal mobile phase conditions have been derived allowing the separation and reductive-mode detection of these compounds, applicable to both alumina and ion-paired solvent extracts of plasma. It is demonstrated that mobile phase composition significantly affects the sensitivity of a triple-electrode electrochemical detection system, in reductive and oxidative modes, and that electrochemical pre-treatment of mobile phase is required to attain maximum detector sensitivity in the reductive mode.

Catecholamines↗

PubMed1998

Studying neuronal peptide release and secretory granule dynamics with green fluorescent protein.

Neurons and endocrine cells release peptides stored in a limited pool of secretory granules. Although it has been possible to measure secretion or exocytosis, studying events within cells that influence the size and speed of secretory responses has been difficult. Here we describe how green fluorescent protein (GFP)-tagged hormones can be used to measure release and granule mobility. Epifluorescence allows one to measure total peptide content and granule trajectories within a plane of focus. Confocal microscopy facilitates measurements within a better defined optical section. Granule mobility can also be measured with fluorescence recovery after photobleaching (FRAP). Application of these optical approaches to the study of neuronal peptide secretion has revealed that the releasable pool is not spatially defined and that sustained peptide release is limited by the availability of mobile secretory granules.

Biological Transport↗

PubMed2005

The branching gene RAMOSUS1 mediates interactions among two novel signals and auxin in pea.

In Pisum sativum, the RAMOSUS genes RMS1, RMS2, and RMS5 regulate shoot branching via physiologically defined mobile signals. RMS1 is most likely a carotenoid cleavage enzyme and acts with RMS5 to control levels of an as yet unidentified mobile branching inhibitor required for auxin inhibition of branching. Our work provides molecular, genetic, and physiological evidence that RMS1 plays a central role in a shoot-to-root-to-shoot feedback system that regulates shoot branching in pea. Indole-3-acetic acid (IAA) positively regulates RMS1 transcript level, a potentially important mechanism for regulation of shoot branching by IAA. In addition, RMS1 transcript levels are dramatically elevated in rms3, rms4, and rms5 plants, which do not contain elevated IAA levels. This degree of upregulation of RMS1 expression cannot be achieved in wild-type plants by exogenous IAA application. Grafting studies indicate that an IAA-independent mobile feedback signal contributes to the elevated RMS1 transcript levels in rms4 plants. Therefore, the long-distance signaling network controlling branching in pea involves IAA, the RMS1 inhibitor, and an IAA-independent feedback signal. Consistent with physiological studies that predict an interaction between RMS2 and RMS1, rms2 mutations appear to disrupt this IAA-independent regulation of RMS1 expression.

Alleles↗

PubMedDate not supplied

[Results of radiosynoviorthesis with yttrium 90 in chronic synovitis: a long-term prospective study. I. Total results and effect of local factors].

The purpose of the presented study was to investigate, whether the results of radiosynovectomy were dependent on different characteristics of the chronic synovitis. In our unit, from October 1978 to April 1981 193 joints--174 knee joints and 19 shoulder joints--of 107 patients underwent radiosynoviorthesis. 93 patients (169 joints) suffered from rheumatoid arthritis of different ARA-stages (I = 16, II = 31, III = 27, IV = 19; 67 seropositive, 26 seronegative), 14 patients with 24 treated joints had chronic synovitis other than rheumatoid arthritis. Only joints with chronic synovitis in the local stages I and II were treated if they did not respond to medical therapy and intraarticular applications of corticosteroids, respectively. Joints with local stage III and IV, respectively, with instability or with a secondary osteoarthrosis were excluded from radiosynovectomy. Every six months the patients were reinvestigated, and pain, swelling, mobility, stability of the joint, frequency of effusions and intraarticular steroid applications were assessed as well as the overall activity of the disease, SR, hemoglobin and effectivity of medical treatment. The overall result was good in 60% of cases after 6 and 12 months, respectively, in 54% of cases after 2 years and in 50% of cases after 3 years, it was fair in about 35% of cases. The results of 20 repeated radiosynovectomies were comparable. The frequency of joint effusions and of necessary intraarticular corticosteroid injections was significantly reduced even in patients showing a "poor" result of synoviorthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex Hormones↗

PubMed2006

Safety of adenosine stress magnetic resonance imaging using a mobile cardiac magnetic resonance system.

BACKGROUND: Contrast-enhanced magnetic resonance imaging (ceMRI) allows for the detection of ischemic heart disease. Aim of this prospective study was to show feasibility, practicability and safety of adenosine stress ceMRI in routine outpatients with a mobile scanner. METHODS: Consecutive patients were scanned in six different cardiac outpatient centers with a 1.5 T mobile ceMRI scanner. First-pass wash-in patterns of gadolinium chelate were evaluated after three minutes of adenosine infusion. After a second bolus of gadolinium chelate myocardial late enhancement (MLE) images of the left ventricle were acquired to visualize myocardial necrosis. RESULTS: Five hundred seventy-four patients were enrolled to the study. No major complications during examination and adenosine infusion were observed. One hundred seventy-three minor complications as temporary atrio-ventriculare blockade, mild chest pain or dyspnea and nausea were noticed. None of the complications led to further special treatment CONCLUSION: This ceMRI protocol is suitable for application in outpatient settings. CeMRI stress testing using a mobile scanner in an outpatient setting is feasible and safe.

Adenosine↗

PubMed2004

Sensitive determination of erdosteine in human plasma by use of automated 96-well solid-phase extraction and LC-MS/MS.

A sensitive and selective method for quantitation of erdosteine in human plasma was established by use of 96-well solid-phase extraction (SPE) and liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI/MS/MS). Plasma samples were transferred into 96-well OASIS HLB extraction plate using an automated sample handling system and the drugs were eluted with methanol. The eluents were then evaporated and reconstituted with mobile phase. All sample transfer and SPE was automated through the application of both the Perkin-Elmer MultiPROBE II HT and TOMTEC Quadra 96 workstation. Compounds were separated on a C18 column with 1 mM ammonium acetate-acetonitrile (80:20, pH 3.2), as mobile phase at a flow rate of 0.3 ml/min. The limit of quantitation (LOQ) was 0.2 ng/ml, using a sample volume of 0.2 ml for the analysis. The reproducibility of the method was evaluated by analyzing three at 14 quality control (QC) levels over the nominal concentration range from 0.2 to 5000 ng/ml. The intraday accuracy was found to range from 99.6 to 105.0% with precision (% RSD) of less than 4.76% at five QC levels. The interday accuracy was found to range from 95.0 to 100.5% with precision of less than 5.26% at five QC levels. Erdosteine produced a protonated precursor ion ([M+H]+) at m/z 250, and a corresponding product ion at m/z 204. Internal standard (letosteine) produced a protonated precursor ion ([M+H]+) at m/z 280 and a corresponding product ion at m/z 160. The high sample throughput of the method has been successfully applied to a pharmacokinetic study of erdosteine in human plasma.

Adult↗

PubMed2004

Isokinetic performance at diagonal pattern and shoulder mobility in elite overhead athletes.

The purpose of this study was to measure isokinetically glenohumeral joint movement peak torque and work in professional basketball, volleyball, handball and baseball players and determine whether significant differences exist between the dominant and non-dominant extremity in athletes and controls. Eighty healthy professional overhead athletes (basketball, volleyball, handball and baseball players) and 20 controls were tested bilaterally on a CYBEX 6000 isokinetic dynamometer at 60 degrees and 180 degrees s(-1) for diagonal pattern of the glenohumeral joint. A standardized protocol and testing guidelines were strictly followed. The range of motion of internal rotation (IR) on the dominant side of baseball players was significantly smaller than those on the dominant side of basketball, handball and volleyball players, and controls (P<0.01). Flexion/abduction/external rotation were consistently higher on the dominant arm (8.5%) for peak torque at 60 degrees s(-1) in baseball players, and bilateral ratios were lower on the dominant arm (14.8%) for peak torque at 180 degrees s(-1) in basketball players. The results of this study are important for the application and interpretation of isokinetic data and flexibility and mobility characteristics on unilaterally dominant overhead athletes. Functional weakness in external rotators, mobility impairments in IR and muscle imbalance have been shown in the dominant arm of these overhead athletes.

Adult↗

PubMed2006

Development and application of a specially designed heating system for temperature-programmed high-performance liquid chromatography using subcritical water as the mobile phase.

A specially designed heating system for temperature-programmed HPLC was developed based on experimental measurements of eluent temperature inside a stainless steel capillary using a very thin thermocouple. The heating system can be operated at temperatures up to 225 degrees C and consists of a preheating, a column heating and a cooling unit. Fast cycle times after a temperature gradient can be realized by an internal silicone oil bath which cools down the preheating and column heating unit. Long-term thermal stability of a polybutadiene-coated zirconium dioxide column has been evaluated using a tubular oven in which the column was placed. The packing material was stable after 50h of operation at 185 degrees C. A mixture containing four steroids was separated at ambient conditions using a mobile phase of 25% acetonitrile:75% deionized water and a mobile phase of pure deionized water at 185 degrees C using the specially designed heating system and the PBD column. Analysis time could be drastically reduced from 17 min at ambient conditions and a flow rate of 1 mL/min to only 1.2 min at 185 degrees C and a flow rate of 5 mL/min. At these extreme conditions, no thermal mismatch was observed and peaks were not distorted, thus underlining the performance of the developed heating system. Temperature programming was performed by separating cytostatic and antibiotic drugs with a temperature gradient using only water as the mobile phase. In contrast to an isocratic elution of this mixture at room temperature, overall analysis time could be reduced two-fold from 20 to 10 min.

Chromatography, High Pressure Liquid↗

PubMed2001

Isolation of the components of a complex mixture by means of column switching for their enhanced detection by mass spectrometry.

Mass spectral characterization of low-level impurities in drug substances and formulations may be challenging when using a validated HPLC method developed for optimal chromatographic performance. In many cases, either the mobile phase contains non-volatile additives that are deleterious to the operation of the mass spectrometer, or some of the related substances fail to ionize effectively under electrospray ionization or atmospheric pressure chemical ionization conditions. This paper describes a way to capture these low-level compounds from an analytical HPLC column using a small trapping column. Mixture components are retained on the trapping column by means of reducing the solvent strength of the eluent. Subsequent elution of trapped compounds using mobile phases more amenable to mass spectral analysis yields improved detection and characterization of low-level compounds of interest. Possible applications of peak trapping and elution include: (1) analysis of compounds separated using a mobile phase containing high concentrations of non-volatile additives, (2) analysis of organic acids separated using a low-pH mobile phase (containing trifluoroacetic acid), and (3) improving the detection limit of a low-level compound of interest through multiple collections. The peak trapping apparatus and optimization experiments are described.

Chromatography, High Pressure Liquid↗

PubMed1992

Patient discomfort levels at the time of debonding: a pilot study.

Several investigations have evaluated the degree of discomfort that patients experience during orthodontic treatment, but most of the research centered on tactile sensory (touch) threshold, reaction to spacers used to separate the teeth or reaction to the initial leveling wires, and the periodic adjustment of the appliances. The purpose of this investigation is to determine the discomfort threshold for patients undergoing orthodontic treatment at the time immediately before appliance removal. Such information will be useful in determining the force levels that patients can tolerate during debonding. From the findings in this study the following can be concluded: (1) The threshold of patient discomfort, at the time of debonding, is significantly influenced by two factors: the mobility of the tooth and the direction of force application. Sex and tooth type differences also influence the discomfort threshold but to a lesser degree. (2) At the time of debonding, patients can withstand intrusive forces significantly more than forces applied in a mesial, distal, facial, lingual, or an extrusive direction. The clinical implications of these findings are discussed.

Analysis of Variance↗

PubMed2002

Self-organization of supramolecular helical dendrimers into complex electronic materials.

The discovery of electrically conducting organic crystals and polymers has widened the range of potential optoelectronic materials, provided these exhibit sufficiently high charge carrier mobilities and are easy to make and process. Organic single crystals have high charge carrier mobilities but are usually impractical, whereas polymers have good processability but low mobilities. Liquid crystals exhibit mobilities approaching those of single crystals and are suitable for applications, but demanding fabrication and processing methods limit their use. Here we show that the self-assembly of fluorinated tapered dendrons can drive the formation of supramolecular liquid crystals with promising optoelectronic properties from a wide range of organic materials. We find that attaching conducting organic donor or acceptor groups to the apex of the dendrons leads to supramolecular nanometre-scale columns that contain in their cores pi-stacks of donors, acceptors or donor-acceptor complexes exhibiting high charge carrier mobilities. When we use functionalized dendrons and amorphous polymers carrying compatible side groups, these co-assemble so that the polymer is incorporated in the centre of the columns through donor-acceptor interactions and exhibits enhanced charge carrier mobilities. We anticipate that this simple and versatile strategy for producing conductive pi-stacks of aromatic groups, surrounded by helical dendrons, will lead to a new class of supramolecular materials suitable for electronic and optoelectronic applications.

Journal Article↗

PubMed1978

Sensitive fluorimetric method for the determination of putrescine, spermidine and spermine by high-performance liquid chromatography and its application to human blood.

A fast and sensitive method for the determination of putrescine, spermidine and spermine by high-performance liquid chromatography is described. These compounds are converted to their fluorescent dansyl derivatives and are separated by a reversed-phase chromatographic system (Micropak CH-10) with water and acetonitrile as mobile phase. The sensitivity of the method is 30 pmoles. The application of the method to the determination of polyamines in blood is described. It was found that most of the polyamines circulating in blood are localized in the erythrocytes, their content in normal human blood being spermidine 14.1 +/- 3.1, and spermine 8.4 +/- 2.8 nmoles/ml packed erythrocytes. The polyamine level in serum is less than 0.1 nmole/ml. The polyamine content of the erythrocytes from patients with malignant neoplasms was significantly elevated.

Chromatography, High Pressure Liquid↗

PubMed2005

Porous monoliths: stationary phases of choice for high performance liquid chromatography in various formats.

Modern porous monoliths have been conceived as a new class of stationary phases for high performance liquid chromatography (HPLC) in classical columns in the early 1990s and later extended to the capillary format. These monolithic materials are prepared using simple processes carried out in an external mold (inorganic monoliths) or within the confines of the column (organic monoliths and all capillary columns). These methods afford macroporous materials with large through-pores that enable applications in a rapid flow-through mode. Since all the mobile phase must flow through the monolith, the convection considerably accelerates mass transport within the monolithic separation medium and improves the separations. As a result, the monolithic columns perform well even at very high flow rates. The applications of monolithic capillary columns are demonstrated on numerous separations in the HPLC mode.

Acrylic Resins↗

PubMed2004

MET system: a new approach to m-health in emergency triage.

The MET (Mobile Emergency Triage) system is an m-health application that supports emergency triage of various types of acute pain at the point of care. The system is designed for use in the Emergency Department (ED) of a hospital and to aid physicians in disposition decisions. Given patient's condition, MET recommends a triage by consulting decision rules stored in the system's knowledge base. The rules have been created using a data mining method (based on rough set methodology) applied to data collected during a retrospective chart study and verified by the clinicians. MET is designed following the extended client-server architecture, suited for weak-connectivity conditions, where stable connection between clients and a server cannot be provided. The MET server interacts with the hospital's patient information system in order to retrieve information about patients admitted to the ED. It also stores current patients' demographic and clinical data to be exchanged with mobile clients. The MET mobile client, running on a Personal Digital Assistant (PDA), is used for collecting clinical data and supporting triage decisions. The support function runs solely on the client side, thus it can be invoked anytime and anywhere, even if there is no communication link with the server (e.g., there is no wireless network available in the ED). Due to implementation on PDAs and working in weak-connectivity conditions, the MET system is very well suited for use in the ED and fits seamlessly into the regular clinical workflow without introducing any hindrances or disruptions that are often reported when using stationary (i.e., working on desktop computers) clinical systems. The system facilitates patient-centered service and timely, high quality patient management. It provides recommendations using a limited amount of clinical data, normally available at the point of care. Furthermore, it provides a possibility for the structured evaluation of this data by an attending physician.

Acute Disease↗

PubMed1999

Role of proximal His93 in nitric oxide binding to metmyoglobin. Application of continuum solvation in Monte Carlo protein simulations.

Monte Carlo protein simulations with continuum solvation were used to explore the conformational mobility of NO within the active site of metmyoglobin. To the best of our knowledge this is the first application of a continuum solvation model for exploring protein binding sites. The usefulness of the Monte Carlo conformational analysis was demonstrated in comparative molecular dynamics simulations. Analysis of conformer populations revealed that Monte Carlo conformational analysis is more effective in mapping the relevant region of the potential surface. Distribution of low-energy conformers obtained for the metmyoglobin-NO complex was found to depend on the orientation of proximal His93. Different charge distributions corresponding to the two experimentally verified possible torsions of this proximal residue result in strong binding of NO or its release to a nearby hydrophobic trap. Conformer populations obtained by Monte Carlo conformational analysis were grouped into three main families: one, with the NO directly bound to the iron, appears when the CA-CB-CG-CD2 torsion of His93 is at its ligand binding value (-113 degrees); and two conformers exist where NO is trapped in a nearby hydrophobic pocket, the same cavity that was determined to be the geminate trap of CO in ferrous Mb as a result of the torsional flip of His93 to its ligand releasing state (-125 degrees). Based on this analysis, we suggest that the electrostatic rearrangement coupled to the conformational fluctuation of the proximal His leads to the geminate trapping of the ligand. Conformational rearrangement of the proximal side would provide the possibility of rebinding of the ligand to Fe.

Animals↗

PubMed1988

[Peridural analgesia with fentanyl--an alternative to control of labor pain].

Modern obstetrics should include not only an optimal labour monitoring but also an adequate pain relief during delivery. Due to the discovery of specific opiate receptors, for example in the substantia gelatinosa of the posterior horn in the spinal cord and the proof of direct pain-modifying effects on spinal level, new ways of the therapy of pain have been developed. The analysis was made with 40 parturients, who had decided for an epidural analgesia. They were given 0.1 mg fentanyl epidurally at a cervical dilatation of 3 to 5 cm and regular uterine contractions. The registrated onset time of fentanyl was between 6 and 15 minutes. A fentanyl dose of 0.1 mg applied epidurally proved to be sufficient for all parturients for the alleviation of pain in the period of dilatation. The interval without pain amounted to 130 mins. The motoricity was not impaired by the peridural application of fentanyl, because the parturient was able to be mobilized under continuous telemetric monitoring including telemetric management of the profile of the uterine activity. The period of the active and latent phases as well as the total delivery time was within the desirable ranges. An impairment of the general condition, e.g. vomiting, nausea or pruritus, was not noticed. There were no circulatory disturbances either. After the application of fentanyl the cardiotocograms remained uninfluenced in all parameters. All parturients declared that they had a positive birth experience under this kind of obstetric analgesia and that they would decide for this method again in case of a further delivery.

Anesthesia, Epidural↗

PubMed1986

Clinical assessment of manipulation and mobilization of the lumbar spine. A critical review of the literature.

The widespread use of manual therapy techniques suggests some degree of success in their application. In this article, I review the applied clinical research on the effectiveness of using manipulation or mobilization of the lumbar spine. The literature reviewed indicates highly equivocal results when the goal of therapy was to decrease pain and increase motion. Because of a high incidence of spontaneous recovery from low back syndromes, performance measures may appear to improve significantly when proper controls are not used. Evaluation of the therapeutic effects of manual therapy is complicated by potentially confounding variables when used with other physical therapy procedures. I discuss the need for further, well-designed studies.

Back Pain↗