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 1,567 records · Page 87Linked to original sources
PubMed1999

Separation of the glucuronides of entacapone and its (Z)-isomer in urine by micellar electrokinetic capillary chromatography.

A micellar electrokinetic capillary chromatography (MECC) method was developed for the separation of the 3-O-glucuronides of entacapone and its (Z)-isomer, the two main urinary metabolites of entacapone in humans. Entacapone is a novel, potent inhibitor of catechol-O-methyltransferase (COMT) intended for use as an adjunct in the treatment of Parkinson's disease. Urine samples spiked with synthetic 3-O-glucuronides were used to study the effects of running buffer pH, composition and applied voltage on separation of the closely migrating glucuronides. The 3-O-glucuronide of nitecapone, was used as internal standard. The greatest improvement in separation was achieved by increasing the running buffer ionic concentration. Changes in pH had little effect on the separation, whereas increase in sodium dodecyl sulfate (SDS) concentration slightly improved resolution. Baseline separation and good selectivity relative to urine components were achieved by using a phosphate (25 mM)-borate (50 mM)-SDS (20 mM) running buffer, pH 7.0, in a 75 microm x 60/67 cm fused-silica capillary at 15 kV and a 335 nm cut-off filter in the UV detector. The limits of detection (LOD) at a signal-to-noise ratio of 3 were about 0.25 microg/ml (5.2 x 10(-7) M) (injection 0.5 p.s.i./8 s). The linear detection range was 2-100 microg/ml (r2>0.999). Good repeatability of injection and relative migration times were obtained.

Buffers↗
PubMed1999

Complete two-dimensional separation for analysis of acidic compounds in plasma using column-switching reversed-phase liquid chromatography.

A complete two-dimensional separation technique for the determination of acidic compounds in plasma was developed by using column-switching reversed-phase liquid chromatography. This technique was based on solute peak enrichment at the top of the second column during heart-cutting and an ion-pair chromatographic separation in the second column using tetrabutylammonium ion, where different separation modes in the first and second columns and solute peak enrichment at the top of the second column during heart-cutting were achieved coincidentally. Retention behaviors of two solutes, zidovudine-beta-D-glucuronide (AZT-beta-D-Gluc) and probenecid, in the first and second column and solute peak enrichment at the top of the second column were investigated for establishment of the system. Different retention behaviors of the solutes in the first and second column, which were evaluated by changes in capacity factor versus acetonitrile concentration in the mobile phases, and peak enrichment could be accomplished by using ion-pair chromatography in the second column. System suitability was confirmed by assessing the number of theoretical plates (N) of the second column for the solutes after heart-cutting. The N values in the second column after column switching were almost same as those in the case that the solutes were directly injected onto the second column. These results indicate that complete two-dimensional separation should be achieved by using this system. Furthermore, this technique was applied to method development for the determination of AZT-beta-D-Gluc and probenecid in rat plasma. The peaks of each analyte in the plasma extract obtained by deproteinization were well separated from those of endogenous substances, and easy determination of the analytes could be accomplished at the ng/ml level only by changing the acetonitrile concentration in the mobile phases.

Acids↗
PubMed1999

Separation and identification of neuropeptide Y, two of its fragments and their degradation products using capillary electrophoresis-mass spectrometry.

This paper describes the development of an analytical method for the separation and identification of neuropeptide Y (NPY) and two important NPY fragments by capillary electrophoresis (CE) and mass spectrometry (MS). A satisfactory separation and the highest sensitivity were obtained with formic acid at high concentrations (250 mM, pH 2.75). The addition of 25 or 50 mM triethylamine (TEA) improved the separation. When applying full scan CE-MS, the separated peptides could be detected and identified using the spectra of each peak. The use of TEA as an additive to the formic acid slightly decreased the sensitivity but was compensated by the improved efficiency. The best compromise for optimal separation and MS detection was found to be 50 mM formic acid to which 50 mM TEA was added. CE-MS could be used for identification of the decomposition products of NPY. Decomposition products with one amino acid difference, which could not be distinguished with CE-UV, could be distinguished with CE-MS.

Amino Acid Sequence↗
PubMed1999

Non-aqueous capillary electrophoresis chiral separations with sulfated beta-cyclodextrin.

This paper reports the application of an anionic cyclodextrin (CD), sulfated beta-cyclodextrin with a degree of substitution of four (beta-CD-(SO4-)4, in chiral separations of pharmaceutical enantiomers by non-aqueous capillary electrophoresis (NACE). Upon complexation with the anionic CD, electrophoretic mobilities of the basic enantiomers decreased, however, both separation selectivity and resolution were enhanced. The advantage of NACE chiral separations over the aqueous CE with the charged CD is that higher electric field strength and higher ionic strength could be applied due to the characteristics of the solvent formamide. The higher ionic strength leads to stacking of peaks and reduces the electrodispersion caused by the mobility mismatch between beta-CD-(SO4-)4-analyte complexes and the co-ions in the running buffer. As a result, better peak shapes and higher separation efficiency were obtained. Comparing with NACE chiral separations with neutral CDs, lower concentration of beta-CD-(SO4-)4 was needed due to the fact that the electrostatic attraction caused stronger binding between beta-CD-(SO4-)4 and the enantiomers. The effects of the experimental parameters, such as concentration of the CD, apparent pH (pH*), degree of substitutions of the CDs, percentage of water in mixed solvent systems, and type of solvents were also studied.

Cyclodextrins↗
PubMed2000

Suppression of tone burst evoked otoacoustic emissions in relation to frequency separation.

Tone burst evoked otoacoustic emissions (TBEOAEs) were measured for two tone bursts presented separately and as a two-tone burst complex to examine the linearity of TBEOAE generators for different frequency separations of the stimuli. The stimuli were: (a) tone bursts of 5-ms duration and center frequencies of 1, 1.5, 2 and 3 kHz; (b) complex stimuli with the 1-kHz tone burst combined digitally with each of the other specified tone bursts. Signals were delivered at 70 dB SPL using a non-linear processing method and at 60 dB SPL using a linear method to 21 ears of normally hearing adults. Spectra of TBEOAEs obtained with single-tone bursts were superimposed (composite) and compared to those of the two-tone burst complex. A close correspondence between the composite and complex spectra was present in all ears. However, the components on the higher-frequency slope of the 1-kHz spectral peak were reduced in the complex spectra obtained with a frequency separation of 0.5 kHz when compared to the corresponding composite spectra. The reduction was greater at a stimulus level of 70 dB SPL than with 60 dB SPL. The effect was smaller for a frequency separation of 1 kHz, and almost absent for the tone burst separation of 2 kHz. Thus, suppression leads to weak non-linear frequency superposition for higher-level, closely spaced stimuli.

Acoustic Stimulation↗
PubMed2001

Screening for the presence of drugs in serum and urine using different separation modes of capillary electrophoresis.

Capillary electrophoresis (CE) is a modern separation technique that has some distinct advantages for toxicological analysis, such as a high efficiency, fast analysis, flexibility, and complementary separation mechanisms to chromatographic methods. CE can be applied in various modes, which each have a different separation mechanism or selectivity. The most common mode is capillary zone electrophoresis (CZE), in which charged analytes migrate in a buffer under the influence of an electric field. In micellar electrokinetic chromatography (MEKC), micelles are added to the buffer which interact with the analytes. MEKC can also be used for the separation of neutral compounds. In non-aqueous CE (NACE), the aqueous buffer is replaced by a background of electrolytes in organic solvents. A sample that needs to be screened can easily be analyzed subsequently by these CE modes using the same instrumentation. The aim of the study was to develop procedures for the analysis of basic and acidic drugs in serum and urine using CZE, MEKC, and NACE. A test mixture that consisted of six basic and six acidic compounds was used to study the separation behavior of five CE methods. The results showed that three methods (based on CZE, MEKC, and NACE) were suitable for the analysis of basic compounds and three methods (based on CZE and MEKC) for the analysis of acidic compounds. For the extraction of analytes from serum and urine, a solid-phase extraction (SPE) and a liquid-liquid extraction (LLE) method were compared. Both SPE and LLE methods provided clean extracts after extraction of the basic compounds from serum and urine. The extracts of acidic compounds contained more matrix interferences, especially for urine. The SPE method had some advantages compared to LLE, as it lead to cleaner extracts and higher peaks, and as it elutes basic and acidic compounds in one fraction. The potentials and pitfalls of the various methods for screening purposes in analytical toxicology are discussed.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2002

Chiral separation of pemoline enantiomers by cyclodextrin-modified micellar capillary chromatography.

Micellar electrokinetic chromatography (MEKC) was successfully applied to the chiral separation with the addition of cyclodextrins (CDs) as chiral selector to running buffer. Chiral separation depended on the type of CDs. Mono-3-O-phenylcarbamoyl-beta-CD was effective for the chiral separation of pemoline. We investigated the type and concentration of CD and other parameters such as buffer pH, the concentration of SDS and the effect of organic modifier. The conditions for enantiomeric separation of pemoline were as follows: 40 mmol/l borate buffer at pH 9.0 with 40 mmol/l SDS, 20 mmol/l mono-3-O-phenylcarbamoyl-beta-CD and 10% 2-propanol. Baseline separation (Rs=2.21) of pemoline can be achieved.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2003

Micro-HPLC and standard-size HPLC for the separation of peptide stereoisomers employing an ion-exchange principle.

Standard-size (4 mm ID) and micro-HPLC columns (0.5 mm ID) packed with a quinine-based ion-exchange type chiral stationary phase are comparatively evaluated for the separation of peptide enantiomers with up to six amino acid residues. The results show that downscaling the separation system in order to gain the advantages of miniaturized HPLC is possible without sacrificing separation power. Further, five different N-terminal protections (3,5-dinitrobenzoyl, 2,4-dinitrophenyl, 3,5-dinitrobenzyloxycarbonyl, carbazole-9-carbonyl, and 9-fluorenylmethoxycarbonyl) of the analytes are investigated regarding their effect on enantioselectivity. A comparison between a hydro-organic and a polar-organic mobile phase is also reported. The enantiomers of the peptides containing one to four amino acid residues were baseline resolved, while for the penta- and hexamers only partial separations were possible. In addition, all four stereoisomers of alanylalanine could be baseline separated.

Chromatography, High Pressure Liquid↗
PubMed2003

Optimisation for the separation of the oligosaccharide, sodium Pentosan Polysulfate by reverse polarity capillary zone electrophoresis using a central composite design.

The separation by reverse polarity capillary zone electrophoresis of the therapeutically developed sodium salt of Pentosan Polysulfate was optimised through the analysis of response surface methodologies, modeled using a central composite design. The optimisation investigated injection pressure, injection time and voltage and the effect of the conditions on retention times, peak areas, separation efficiency and the method sensitivity. The overall goal was to develop the most sensitive results with no decrease in separation efficiency. The following results were obtained: (1) retention times generally decreased as injection pressure, injection time and voltage increased, injection time having the least effect; (2) as expected peak areas increased as injection pressure and injection time increased but decreased as voltage increased; (3) separation efficiencies generally increased as injection pressure and injection time decreased, with voltage having almost no effect. For the optimum condition, the sample was introduced at the inlet vial at the cathode hydrodynamically, at optimal setting of 44 s at 35 mbar. The optimal voltage was -20 kV. In comparison with other methods, the optimum showed increased sensitivity, resolution and separation efficiency. Repeatability studies were performed on the optimum parameter conditions. Relative standard deviation values obtained were between 0.9 and 5.4%.

Carbohydrate Sequence↗
PubMed1997

Selectivity optimization for the separation of chlorophenols in an irregularly shaped experimental region in capillary electrophoresis.

The separation of seventeen chlorophenol congeners and phenol was studied as a function of several variables. The pH and the concentration of sodium dodecylsulphate (SDS) were found to be important. During the implementation of a central composite design for the optimization of the separation it appeared that a part of the domain was not feasible as it resulted in very long migration times and extremely deformed peaks. Therefore, a D-optimal design was selected within the boundaries of the feasible region. The optimization of the selectivity did not result in selective regions for a simultaneous separation. It was, however, possible to find a region for the simultaneous separation of 15 compounds. Further optimization at these optimal conditions resulted in a separation where 17 peaks could be observed.

Chlorophenols↗
PubMed1998

Separation of the four stereoisomers of a potent inhibitor (L-694,458) of human leukocyte elastase and its determination in human plasma using achiral/chiral chromatography with column switching.

A stereoselective method based on high-performance liquid chromatography (HPLC) and ultraviolet detection at 235 nm for the separation of the four possible stereoisomers of compound 1 ((S-(R*,S*))-2-(4-((4-methylpiperazin-1-yl)carbonyl)phenoxy)-3,3-d iethyl-N-(1-(3,4-(methylenedioxy)phenyl)butyl)-4-oxo-1-azetidinecarbo xamide, L-694,458), a potent, selective, and orally active human leukocyte elastase (HLE) inhibitor, in human and monkey plasma has been developed. The molecule of 1 contains two chiral centers and is being developed as a single stereoisomer with the absolute configuration S and R in positions 'a' and 'b', respectively. Although the baseline separation of each of the two pairs of enantiomers (SS/RR and SR/RS) was achieved on a single chiral column (Chiralcel OD-H) using hexane methyl-t-butyl ether (MTBE)-methanol 80/10/10, (v/v/v) as a mobile phase (alpha(RS,SR) = 2.03, alpha(RR,SS) = 4.97), only partial separation of RS from RR was observed under these conditions (k'RS = 3.32, k'RR = 3.08). Baseline separation of all four stereoisomers from each other and from endogenous plasma components required the initial chromatography of the two diastereomeric racemates (SS/RR and SR/RS) on the achiral silica column (50 x 4.6 mm, 5 microm), followed by column switching and further separation of the stereoisomers on a Chiralcel OD-H column (250 x 4.6 mm, 5 microm) using isopropanol (IPA)-hexane diethylamine (DEA), 65/35/0.3, (v/v/v) on both columns as a mobile phase. The drug was extracted from basified (pH 11) plasma (1 ml) using liquid liquid extraction with MTBE. After evaporation of the extract to dryness, the residue was reconstituted in the mobile phase (200 microl) and part of the extract (125 microl) was injected into the HPLC system. Using this method, it was demonstrated that after oral dosing of monkeys at 40 mg kg(-1) with 1 the only stereoisomer detected in the post-dose plasma samples was the starting material 1, and no inversion of the configuration at positions 'a' and 'b' of 1 had occurred in vivo. Based on this observation, a non-chiral assay for 1 in human plasma was also developed. The method was validated in the concentration range 10-500 ng ml(-1) with the assay precision (expressed as the coefficient of variation, CV) better than 9% and assay accuracy in the range of 95-107% of the nominal concentrations at all concentrations within the standard curve range. The total run time in the non-chiral assay was 12 min. The details of both chiral and non-chiral methods are provided.

Animals↗
PubMed2002

An experiment of mailing physician surveys on two different issues in joint or separate mail.

High response rates from physicians play an important role in obtaining valid data on practice patterns. We wanted to know whether two questionnaires (one on hernia surgery and one on perioperative pain management) should better be sent out in one letter or two separate letters. We randomized 2,393 surgeons who received the two questionnaires either in one letter or by separate mail, in two letters, at a time interval of 4 weeks. The response rate for the separate mailout was not significantly higher when compared to the joint mailout. The differences were 3.3% (95%-CI -0,4% to 7.1%) and 2.2% (95%-CI -1,4% to 5.9%) for the two surveys. Due mainly to higher postage costs, the costs per response were doubled in the separate mailout group (5.85 Euro versus 2.93 Euro). Sending out two surveys separately seems to have only little effect on the response rates.

Data Collection↗
PubMed1997

[Psychological effects of parental separation on children].

A study on the psychological consequences of parental separation on children was performed among 3,098 pupils of first year secondary school during the 1995-1996 academic year in the department of Isère. The children family situation was compared with the results of personality test of Coopersmith (SEI). The main characteristics of the children, in particular family condition such as parental death or parental separation are in agreement with the French national data. Among the children with separated parents, 29% were less than 3 years old when their parents broke up. In 85% of the cases the child lived mainly with his/her mother, in 9% of the cases with his/her father, in 4% of cases in a joint-custody arrangement, in 1% of the cases in an other person's home. The overall SEI scores were good. There was a significant overrepresentation of girls with extreme scores. Compared with the scores of the children of unseparated parents, the average SEI scores were low for children with separated parents and for children with one dead parent, but differences were observed between girls end boys. The age of children at the time of the separation did not influence the SEI score and there was little influence of the father-child regular contacts.

Child↗
PubMed2003

Microfluidic separation of DNA.

DNA separation is important for numerous applications in biotechnology and medicine. Efforts to improve DNA separation in microdevices have led to advances in capillary electrophoresis and the development of novel separation strategies. Current research on microcapillary electrophoresis materials is focused on the development of separation matrices with low injection viscosities and wall-coating capabilities. Microcapillary injector geometries are being designed to allow increased control of sample plug volumes. Novel separation strategies using entropic traps, arrays of pillars and Brownian ratchets are also being developed.

DNA↗
PubMed2002

Separation efficiency and particle size distribution in relation to manure type and storage conditions.

Mechanical separation of liquid animal manure can be an effective technique for production of a liquid and a nutrient-rich solid fraction. The efficiency of separators depends on the physical and chemical composition of the animal manure. Therefore, the particle size composition was measured for different types of manure before treatment with a decanting centrifuge and a screw press. Storage of pig manure reduces the total dry matter content, and the content of small particles (< 0.0016 mm) is reduced more than the content of large particles. In consequence, the proportion of large particles will increase, while the portion of small particles will decrease. The separation efficiency of the screw press was found to be low, as this separator only retains particles > 1 mm. The decanter centrifuge retained all the particles > 0.02 mm and was therefore much more efficient than the screw press. Separation efficiency was also found to be highly dependent on the type of manure used.

Agriculture↗
PubMed2002

The performance and potential of faecal separation and urine diversion to recycle plant nutrients in household wastewater.

In household wastewater and biodegradable solid waste, the main proportion of the plant nutrients are found in the toilet water (i.e. in urine and faeces). In order to recover most of these nutrients, with the purpose of decreasing the emission of eutrophicating agents and of increasing their recycling, present waste and wastewater systems have to be changed. If the urine and the faeces are collected, up to 91%, 83%, and 59% for N, P and K, respectively, can be recovered and recycled from the household wastewater. The urine was collected separately in a double flushed urine-diverting toilet and the faeces were separated from the flushwater using two parallel Aquatrons. The Aquatron separates by a combination of a whirlpool effect, gravitation and surface tension. In this study, nitrogen and phosphorus from the faeces were separated to 73% and 58%, respectively, to the dryer fraction. The combination of faecal separation and urine diversion in the house Ekoporten made it possible to collect 60% of N, 46% of P and 43% of K from the wastewater, indicating that this method is an alternative when aiming to recover plant nutrients while still wanting to use water-flushed, urine-diverting toilets, though the potential to collect the nutrients is much higher.

Agriculture↗
PubMed2002

Chelator, metal ion and buffer studies for protein C separation.

Protein C (PC) is the pivotal anticoagulant and antithrombotic in the human coagulation cascade. PC deficiency can result in major medical problems such as deep vein thrombosis (DVT), leading to tissue oxygen deprivation. PC treatment has no bleeding or skin necrosis problems because it circulates in the blood as a zymogen and is only activated when and where it is needed. One source of PC is transgenic animal milk. The major components in the milk, such as alpha-casein, beta-casein, kappa-casein, alpha-lactalbumin and beta-lactoglobulin, are proteins that must be separated from PC. Immobilized metal affinity chromatography (IMAC) is an inexpensive separation technology with relatively high specificity, and it has great potential for difficult protein separations. After systematic studies of different chelator, metal ion and buffers, the combination of iminodiacetic acid (IDA) and Fe was found to be effective to separate PC from major milk components. alpha-Lactalbumin and beta-lactoglobulin fell through the column in the starting buffer. PC was eluted. alpha-Casein, beta-casein, kappa-casein remained bound in the column after PC elution. This technology might be applied for PC separation from transgenic animal milk. It is very important for PC production in large quantities and at low cost to treat PC-deficient patients.

Animals↗
PubMed2007

Parental separation, loss and psychosis in different ethnic groups: a case-control study.

BACKGROUND: Numerous studies have reported high rates of psychosis in the Black Caribbean and Black African populations in the UK. However, few studies have investigated the role of specific risk factors in different ethnic groups. We sought to investigate the relationship between long-term separation from, and death of, a parent before the age of 16 and risk of adult psychosis in different ethnic groups. METHOD: All patients with a first episode of psychosis who made contact with psychiatric services in defined catchment areas in London and Nottingham, UK and a series of community controls were included in the AESOP (Aetiology and Ethnicity in Schizophrenia and Other Psychoses) study. Data relating to clinical and social variables, including parental separation and loss, were collected from patients and controls. RESULTS: Separation from, and death of, a parent before the age of 16 were both strongly associated with a two- to threefold increased risk of psychosis. The strength of these associations were similar for White British and Black Caribbean (but not Black African) subjects. Separation from (but not death of) a parent was more common among Black Caribbean controls than White British controls. CONCLUSIONS: Early separation may have a greater impact in the Black Caribbean population, because it is more common, and may contribute to the excess of psychosis in this population.

Adolescent↗